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PAGE 1 (p. 112) - IMMUNOLOGIC BLOOD TRANSFUSION REACTIONS

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1. ALLERGIC / ANAPHYLACTIC REACTION

• What is Type I hypersensitivity? Think of it like an extreme allergy. The body already has antibodies called IgE sitting on the surface of special cells called mast cells (imagine mast cells as loaded guns). When a foreign protein from donor blood comes in, it pulls the trigger - the mast cell explodes and releases chemicals (histamine etc.) that cause the allergic reaction.
• "Plasma proteins in transfused blood" - Blood is not just red cells. It also contains a liquid called plasma that carries hundreds of proteins. The patient's immune system attacks these donor proteins.

• Some people are born without IgA (a type of antibody - think of it as a security guard that patrols mucosal surfaces like your gut and nose). If such a person receives blood containing IgA, their body sees that IgA as completely foreign and mounts a massive allergic reaction. So doctors must give them IgA-free blood products to be safe.

• Preformed = already made and stored inside the mast cell before the reaction starts.
• Degranulating = the mast cell bursting open and spilling its contents (de = releasing, granules = the storage packets inside the cell). Since these chemicals are already made, the reaction happens FAST - within minutes.

• Urticaria = hives - itchy, raised welts on skin. (Like mosquito bites everywhere)
• Pruritus = itching
• Wheezing = difficulty breathing because airways are constricting
• Hypotension = low blood pressure (the blood vessels are dilating because of histamine)
• Respiratory arrest, shock = the most severe form - anaphylaxis - where you stop breathing and blood pressure crashes. This can kill.

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2. ACUTE HEMOLYTIC TRANSFUSION REACTION

• What is Type II hypersensitivity? Here, antibodies attack things directly stuck ON cells (unlike Type I where free proteins are attacked). In this case, antibodies attack antigens sitting on the surface of donor red blood cells.

• Hemolysis = destruction of red blood cells (hemo = blood, lysis = breaking apart)
• Intravascular = happening INSIDE blood vessels (the red cells burst while they are still in the bloodstream, releasing their contents - mainly hemoglobin - directly into the blood)
• ABO incompatibility = you gave the wrong blood type. Imagine giving Type A blood to a Type B patient. The patient already has pre-made antibodies against Type A. They immediately attack the donor red cells.

• Again, because the antibodies are already made (preformed), the reaction is fast. This can start THE MOMENT you begin the transfusion.

• Tachypnea = fast breathing (tachy = fast, pnea = breathing)
• Tachycardia = fast heart rate (cardia = heart)
• Flank pain = pain in the sides of your lower back - because the kidneys are getting clogged with free hemoglobin from the burst red cells
• Hemoglobinuria = hemoglobin spilling into urine - your urine turns dark red/brown like Coca-Cola. This is because burst red cells release hemoglobin directly into plasma, which spills into urine.
• Jaundice = yellow skin - when red cells are destroyed outside vessels (extravascular), their contents are broken down into bilirubin, which turns skin yellow.

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3. FEBRILE NONHEMOLYTIC TRANSFUSION REACTION

• Cytokines = chemical messengers of the immune system. Think of them as tiny text messages that immune cells send to each other saying "come here, there is an emergency!"
• WBC = White Blood Cells = immune cells
• When blood sits in a blood bank, donor white cells inside that blood keep making cytokines. These cytokines accumulate over time. When this blood is transfused, the patient receives a large dose of these pro-inflammatory cytokines.

• Leukoreduction = filtering out the white blood cells (leuko = white cells, reduction = removing) from donated blood before storage. No WBCs = no cytokine accumulation = no febrile reaction. This is now done routinely in most countries.

• Same concept - already made beforehand, so reaction happens quickly.

• Notice: the name says "NONhemolytic" - that means red blood cells are NOT being destroyed here. You feel sick (fever, chills), but your blood cells are intact. This is a milder reaction compared to the hemolytic ones.

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4. TRANSFUSION-RELATED ACUTE LUNG INJURY (TRALI)

• Neutrophils = the most common white blood cells; first responders of your immune system (like ambulances)
• Sequestered = trapped/stuck in one place
• Primed = put on high alert, ready to explode (like a grenade with the pin slightly pulled)
• Pulmonary vasculature = the tiny blood vessels inside the lungs
• The patient's own underlying condition (e.g., sepsis, surgery) causes neutrophils to get stuck in the lung vessels and become primed. This is Hit 1 - the patient is already vulnerable.

• Antileukocyte antibodies = antibodies in the donor blood that are directed against white blood cells
• When these donor antibodies arrive, they deliver Hit 2 - they activate the already-primed neutrophils stuck in the lungs
• Inflammatory mediators = chemicals that cause damage and inflammation
• Capillary permeability = how leaky the tiny blood vessels (capillaries) are. Normally capillaries keep fluid inside. When permeability increases, fluid leaks out into the surrounding lung tissue.
• Pulmonary edema = fluid in the lungs (pulmonary = lung, edema = swelling/fluid). Imagine the lungs filling with water - the patient cannot breathe.

• Noncardiogenic = NOT caused by the heart. This is key! Normal pulmonary edema is from heart failure. TRALI edema is from immune damage to vessels. This distinction is medically important.

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5. DELAYED HEMOLYTIC TRANSFUSION REACTION

• Anamnestic = "memory response" (anamnesis = to remember). The patient encountered this antigen before - maybe from a previous transfusion or pregnancy - and their immune system formed a memory. When they get blood again with the same antigen, the memory B cells wake up and make LOTS of antibodies.
• Rh[D] = the Rhesus D antigen - a protein on red blood cells. This is what the "+" and "-" means in blood type (like A+, O-). Rh- patients who receive Rh+ blood will sensitize.
• Minor blood group antigens = there are many blood group systems beyond ABO and Rh. Antibodies against these minor antigens cause delayed reactions.

• Extravascular = red cells are destroyed OUTSIDE blood vessels, in organs like the spleen and liver (the reticuloendothelial system eats the coated red cells).

• Reticuloendothelial system = a network of immune cells in the liver, spleen, bone marrow and lymph nodes that clean up old/damaged/antibody-coated cells slowly over days to weeks.

• Self-limited = it resolves on its own
• Clinically silent = the patient may not even notice (mild symptoms)
• Hyperbilirubinemia = elevated bilirubin in blood (remember, extravascular hemolysis → red cells broken down → bilirubin released → mild jaundice)

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PAGE 2 (p. 113) - AUTOANTIBODIES

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• ACh receptor = Acetylcholine receptor. Acetylcholine is a chemical that nerve cells release to tell muscles to contract. It sits at the junction between nerve and muscle.
• Postsynaptic = on the muscle side (post = after the synapse)
• In Myasthenia Gravis, your body makes antibodies that block or destroy these receptors. The muscle never gets the signal to contract properly. Result: muscle weakness, especially with use (drooping eyelids, double vision, difficulty swallowing).

• Presynaptic = on the NERVE side
• Voltage-gated Ca²+ channel = a gate in the nerve ending that opens when electricity passes through, letting calcium in, which triggers acetylcholine release
• Antibodies block this gate → less ACh released → weak muscles. Unlike Myasthenia (weakness WORSENS with use), Lambert-Eaton IMPROVES with repeated use (because repeated stimulation compensates).

• β2-glycoprotein I = a protein that binds to phospholipids (fats in cell membranes). These antibodies cause CLOTTING (paradoxically, despite being called "lupus anticoagulant" in the lab, they cause clots in real life). Features: recurrent blood clots, miscarriages.

• ANA = antibodies against the NUCLEUS of cells (the control center). A positive ANA just means autoimmunity is likely present - it is not specific to one disease. It is like a smoke alarm - it tells you fire is possible but not which room it is in.
• SLE = Systemic Lupus Erythematosus - a disease where the immune system attacks multiple organs.

• Cardiolipin = a phospholipid found in mitochondrial membranes. Antibodies against it are seen in lupus and antiphospholipid syndrome.

• Anti-dsDNA = antibodies against double-stranded DNA (your actual genetic material). Highly specific for SLE. Levels fluctuate with disease activity - if dsDNA antibodies go up, the patient is flaring.
• Anti-Smith = antibodies against spliceosomes (protein complexes involved in processing RNA). Very specific for SLE but less sensitive (not found in everyone with SLE).

• Histones = proteins that DNA wraps around (like thread on a spool). When someone develops lupus-like symptoms FROM A DRUG (common culprits: hydralazine, procainamide, isoniazid, minocycline - remembered as HPIM), they have antihistone antibodies. Stops when the drug is stopped.

• U1 RNP = a type of ribonucleoprotein (a complex of protein and RNA involved in gene processing)
• Mixed connective tissue disease = a condition with overlapping features of lupus, rheumatoid arthritis, scleroderma, and myositis all at once.

• Rheumatoid Factor = an antibody (specifically IgM type) that attacks OTHER antibodies (specifically the bottom portion - Fc region - of IgG antibodies). Bizarre right? Your immune system attacking its own weapons.
• Anti-CCP = anti-cyclic citrullinated peptide. This is MORE SPECIFIC for RA. Citrullinated peptides are normal proteins modified in a certain way that the RA immune system attacks. Anti-CCP appears even before symptoms start.
• Rheumatoid Arthritis = chronic inflammation and destruction of joints, especially small joints of hands and feet.

• The SS highlights that these antibodies are seen in Sjogren's Syndrome - a disease where immune cells destroy moisture-producing glands (tear glands → dry eyes, salivary glands → dry mouth).

• Scl = Scleroderma. Anti-Scl-70 = antibody against topoisomerase I (an enzyme that unwinds DNA).
• Scleroderma (Diffuse) = widespread skin hardening AND involvement of internal organs (kidney, lung, heart). The scl in the antibody name literally tells you the disease name.

• Centromere = the middle part of a chromosome
• CREST = Calcinosis (calcium deposits in skin), Raynaud phenomenon (fingers turn white/blue/red in cold), Esophageal dysmotility (swallowing difficulty), Sclerodactyly (skin tightening on fingers), Telangiectasias (dilated small blood vessels visible on skin). Limited scleroderma mainly affects skin.

• These are muscle diseases. Polymyositis = muscle inflammation only. Dermatomyositis = muscle inflammation + skin findings (purple rash around eyes called heliotrope rash, Gottron papules over knuckles).

• Mitochondria = energy factories in cells
• Primary biliary cholangitis (1° BC) = immune attack on the bile ducts in the liver (bile ducts drain bile from liver to intestine). Leads to progressive liver damage, jaundice, itching.

• The immune system attacks the liver cells themselves.

• ANCA = Anti-Neutrophil Cytoplasmic Antibodies - antibodies targeting the insides of neutrophils
• MPO = Myeloperoxidase - an enzyme inside neutrophil granules
• p-ANCA = perinuclear pattern (the staining appears around the nucleus of the neutrophil when seen in the lab)
• These diseases involve inflammation of blood vessels (vasculitis = vas + itis = vessel inflammation)

• PR3 = Proteinase 3, another neutrophil enzyme
• c-ANCA = cytoplasmic pattern (staining spreads through the whole neutrophil cytoplasm)
• Granulomatosis with Polyangiitis = destroys upper airway (nose, sinuses, ears), lower airway (lungs), and kidneys. Classic triad.

• Attacks the filtering membrane in kidneys → protein leaks into urine → nephrotic syndrome

• Hemidesmosomes = anchoring structures that attach the outer skin layer (epidermis) to the deeper layer (dermis)
• Antibodies attack these anchors → fluid collects between layers → large, tense (hard to pop) blisters on skin. Mainly in elderly people.

• Desmoglein = a protein that glues skin cells together within the epidermis
• Antibodies attack this glue → cells separate from each other WITHIN the epidermis → flaccid (easily popped, fragile) blisters. Mucosal involvement (mouth blisters). More serious than pemphigoid.

• Thyroglobulin = the storage form of thyroid hormone in the thyroid gland
• Thyroid peroxidase (TPO) = enzyme that makes thyroid hormone
• Immune attack destroys the thyroid gland → hypothyroidism (low thyroid function → fatigue, cold intolerance, weight gain, constipation)

• TSH receptor = the receptor on thyroid cells that responds to TSH (Thyroid Stimulating Hormone from the brain)
• In Graves, the antibody STIMULATES this receptor (acts like TSH) → thyroid is constantly being told "make more hormone" → hyperthyroidism (high thyroid function → weight loss, heat intolerance, fast heart rate, bulging eyes)

• Gluten (found in wheat, barley, rye) is broken down into gliadin in the gut. In celiac disease, the immune system attacks gliadin AND attacks the enzyme (transglutaminase) that modifies gliadin AND attacks the inner lining of the small bowel (endomysium).
• Result: destruction of small intestinal villi (tiny finger-like projections that absorb nutrients) → malabsorption, diarrhea, bloating

• Islet cells = clusters of cells in the pancreas that make insulin (beta cells), glucagon (alpha cells), etc.
• GAD = enzyme inside these cells. Immune system attacks and destroys the insulin-producing beta cells → no insulin → Type 1 diabetes

• Parietal cells = cells in the stomach that produce intrinsic factor (a protein needed to absorb Vitamin B12)
• Antibodies destroy parietal cells AND/OR block intrinsic factor → no B12 absorption → Vitamin B12 deficiency → megaloblastic anemia (large, immature red cells) and nerve damage

• Glomerular basement membrane = a filtering layer in the kidney's tiny filtration units (glomeruli)
• This antibody also attacks alveolar basement membrane in the lungs. Classic presentation: pulmonary hemorrhage + rapidly progressive glomerulonephritis (blood in urine, kidney failure)

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PAGE 3 (p. 114) - IMMUNODEFICIENCIES (B-CELL AND T-CELL DISORDERS)

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B-CELL DISORDERS

X-Linked (Bruton) Agammaglobulinemia (XLA)

• BTK = Bruton Tyrosine Kinase - a signaling molecule (like an "on switch") inside B cell precursors. Without it, B cells cannot mature past a certain stage.
• B cells = the immune cells that make antibodies (think of them as antibody factories)
• X-linked recessive = the gene is on the X chromosome. Boys have only one X (XY), so one defective copy = disease. Girls have two X chromosomes (XX), so one bad copy is backed up by the good one - girls are carriers but not affected.
• No B-cell maturation = no B cells → no antibodies of any kind (agamma = no, globulinemia = antibodies in blood)

• Newborns are protected for the first 6 months by maternal IgG that crossed the placenta during pregnancy. After this wears off, the baby has nothing to fight bacteria.
• Enteroviral infections = viruses that enter through the gut (like echovirus, coxsackievirus). Normally controlled by antibodies. Without them, patients get severe enteroviral meningitis and encephalitis.

• No B cells = no lymph nodes that can grow large (you have never seen tonsils or palpable lymph nodes in these patients)
• 1° follicles = areas in lymph nodes where naive B cells live; germinal centers = areas where B cells learn to make better antibodies
• Live vaccines contraindicated = live vaccines (MMR, polio oral, varicella) contain weakened LIVE organisms. Since the patient has no immune defense, even the weakened organisms can cause disease.

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Selective IgA Deficiency

• Primary immunodeficiency = born with it (not acquired like HIV)

• Familial = runs in families; Sporadic = happens randomly with no family history
• 2° = secondary - caused by something else

• Most people never know they have it!
• IgA is the antibody that patrols mucosal surfaces (airways, gut). Without it, bacteria/parasites can gain a foothold at these surfaces.
• Atopy = allergic tendency (asthma, eczema, food allergies)
• Anaphylaxis to IgA in blood products = same as described on page 1 - must receive IgA-free blood

• Giardia = a gut parasite normally controlled by IgA in the intestine
• False-negative celiac test = celiac tests rely on IgA antibodies (anti-endomysial IgA, anti-TTG IgA). If IgA is absent, these tests will be negative even if the patient HAS celiac disease - classic trap!
• False-positive pregnancy test = rare but documented - the serum hCG test can cross-react

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Common Variable Immunodeficiency (CVID)

• B cells exist but cannot fully mature into plasma cells (the antibody-producing factories). Unlike Bruton's where B cells are absent, here B cells are present but dysfunctional.

• This is a key distinguisher. XLA presents at 6 months; CVID presents in young adults (teens/20s). The late onset catches many doctors off guard.

• Bronchiectasis = permanent widening and scarring of airways due to repeated infections (the airways are damaged and dilated permanently - like a worn-out rubber tube). Patients cough up large amounts of sputum chronically.

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T-CELL DISORDERS

Thymic Aplasia (DiGeorge Syndrome)

• 22q11 = a tiny piece of chromosome 22 is deleted
• Pharyngeal pouches = during embryo development, the throat/neck area forms from pouches. The 3rd and 4th pouches give rise to the THYMUS (where T cells learn) and PARATHYROID GLANDS (which control calcium levels).
• Without these pouches: no thymus = no T cells; no parathyroids = no PTH = low calcium

• C = Cardiac defects (conotruncal abnormalities = defects in the main blood vessels coming out of the heart, e.g., Tetralogy of Fallot)
• A = Abnormal facies (face looks different - low-set ears, small chin, wide-set eyes)
• T = Thymic hypoplasia → T-cell deficiency → recurrent viral and fungal infections
• C = Cleft palate (roof of mouth has a gap)
• H = Hypocalcemia secondary to parathyroid aplasia → TETANY (painful muscle spasms because calcium is needed for normal muscle function)
• 22 = chromosome 22 deletion

• These are both caused by the same 22q11 deletion but emphasize different features. DiGeorge = immunological emphasis. Velocardiofacial = structural emphasis.

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IL-12 Receptor Deficiency

• IL-12 = Interleukin-12 = a cytokine made by macrophages that tells T cells to become Th1 cells (the type that fight bacteria inside cells - intracellular pathogens)
• If you cannot receive IL-12's message (receptor is broken), you cannot make Th1 cells properly
• Autosomal recessive = need two bad copies (one from each parent) for the disease to appear

• Mycobacteria = bacteria that live INSIDE cells (like TB bacteria - Mycobacterium tuberculosis, Mycobacterium avium). Th1 cells are specifically needed to kill these.
• BCG vaccine = a live weakened mycobacterial vaccine given to protect against TB. In an immunocompetent child, it is harmless. In this patient, even the weakened vaccine bacteria spread throughout the body = disseminated BCG disease.
• IFN-γ decreased = Interferon-gamma is the main cytokine that Th1 cells produce. If you cannot make Th1 cells, IFN-γ will be low.

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Autosomal Dominant Hyper-IgE Syndrome (Job Syndrome)

• Th17 cells = a type of T helper cell whose job is to coordinate neutrophil responses at infection sites (especially skin and lung)
• STAT3 = a signaling protein. When mutated, Th17 cells cannot develop properly.
• Without Th17, neutrophils never get the memo to come to infections in the skin.

• Abscesses - Cold (noninflamed!) staphylococcal abscesses in skin, lungs, lymph nodes. They are "cold" because neutrophils never arrived - so no redness, no warmth, no pus. The body just forms a walled-off pocket. This is paradoxical and classic.
• Baby teeth retained - Normally baby teeth fall out because the bone around them resorbs. In Job syndrome this resorption is defective → baby teeth persist → adult teeth grow in the wrong places
• Coarse facies - rough/asymmetric facial features
• Dermatologic problems - eczema-like rash
• E - IgE elevated (very high! The hallmark lab finding)
• Fractures from minor trauma - bone abnormalities

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Chronic Mucocutaneous Candidiasis

• Candida = a yeast/fungus that normally lives harmlessly on our skin and in our gut, kept in check by T cells
• Cell-mediated immunity = immunity that uses T cells directly (as opposed to antibody-mediated)
• AIRE (Autoimmune Regulator) = a gene that teaches T cells to recognize "self" in the thymus. If AIRE is defective, T cells never learn to fight Candida specifically.

• Noninvasive = Candida stays on the surface (skin, mouth, vagina, nails). It does NOT go into the blood and organs (that would be invasive). The immune defect is specific to surface T-cell responses.

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PAGE 4 (p. 115) - IMMUNODEFICIENCIES CONTINUED

SEVERE COMBINED IMMUNODEFICIENCY (SCID)

• IL-2R gamma chain = part of the receptor for IL-2 (a cytokine needed for T-cell growth and survival). Without this receptor, T cells cannot grow. And without T cells, B cells also cannot function properly (B cells need T cell help). Most common form.
• Adenosine deaminase (ADA) deficiency = ADA is an enzyme that breaks down toxic metabolites. Without it, toxic products (deoxyadenosine) accumulate and kill lymphocytes (T and B cells). This was the first disease treated with gene therapy.
• RAG mutation → V(D)J recombination defect = RAG enzymes are scissors that cut and rejoin DNA segments to create diverse antibodies and T cell receptors. Without RAG, you cannot make any functioning T cells or B cells.

• These babies get EVERYTHING because they have NO immune defense. They often die within the first year of life without treatment.
• Thrush = white patches in the mouth from Candida - a sign of immune deficiency

• TRECs = when T cells mature in the thymus, they cut out DNA circles like punching holes in paper. These circles are detectable in a blood test. Low TRECs = fewer T cells being made = suggests SCID. This is now tested on the newborn heel prick screening in many countries.

• CXR = chest X-ray. The thymus is visible as a shadow on chest X-ray in infants. No thymic shadow = no thymus = SCID clue.

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Ataxia-Telangiectasia

• ATM gene = encodes a protein that is essentially the DNA damage sensor. When DNA breaks (from radiation, free radicals, etc.), ATM sounds the alarm and stops cell division until repairs are made.
• Without ATM: broken DNA = not detected = cell keeps dividing WITH broken DNA = mutations pile up = cancer predisposition + immune cell death

• Ataxia = loss of balance and coordination. The cerebellum (balance center of the brain) degenerates because its cells cannot repair DNA damage from normal metabolism.
• Telangiectasia = spider-vein like dilated blood vessels visible on the whites of the eyes and skin (especially face and ears). Caused by vascular damage from unrepaired DNA damage.
• IgA deficiency = because lymphocytes also have defective DNA repair, they die off → low IgA (and IgG, IgE)

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Hyper-IgM Syndrome

• CD40L = a molecule on the surface of T helper cells that binds to CD40 on B cells. This interaction is the SIGNAL for B cells to switch from making IgM (the first antibody made) to making other types like IgG, IgA, IgE.
• If CD40L is broken (on T cells): B cells keep making IgM only, and never switch. Result: lots of IgM, but virtually no IgG, IgA, IgE.

• Pyogenic = pus-forming infections caused by bacteria
• Pneumocystis jirovecii = a fungus that causes pneumonia in immunocompromised patients. Normally controlled by T cell-mediated immunity. Its presence here makes sense because IgM alone provides poor protection against intracellular organisms.
• Cryptosporidium = a parasite that causes severe diarrhea. Normally controlled by IgA. No IgA here.

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Wiskott-Aldrich Syndrome

• WAS gene = encodes the Wiskott-Aldrich Syndrome Protein (WASP), which controls actin reorganization inside immune cells
• Actin cytoskeleton = the internal scaffolding of cells made of actin filaments (like the cell's muscles/skeleton). Immune cells need to rearrange this scaffolding to present antigens to T cells and to migrate.
• Without WASP: lymphocytes and platelets cannot form the right structures → poor immune response → defective platelet function

• Wiskott-Aldrich
• Thrombocytopenia (low platelet count → bleeding - these patients bleed easily with tiny, dysfunctional platelets)
• Eczema (allergic skin inflammation)
• Recurrent (pyogenic) infections
• Also increased risk of autoimmune disease and malignancy (lymphoma)

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Leukocyte Adhesion Deficiency (LAD) Type 1

• LFA-1 integrin (CD18) = an adhesion molecule on the surface of neutrophils that acts like velcro, allowing neutrophils to stick to blood vessel walls and then climb out of vessels to reach infection sites
• Without this integrin: neutrophils cannot leave the bloodstream to go to infection sites
• Chemotaxis = the process of cells following chemical signals toward a destination (like following a smell trail). C5a, IL-8, leukotriene B4 are chemoattractants - normal attractants that guide neutrophils. They cannot respond because they cannot even stick to vessel walls.

• Normally the umbilical cord stump falls off in 1-2 weeks because neutrophils arrive to help separate it. In LAD, neutrophils cannot get there → delayed separation. This is a CLASSIC clue in exams.

• Because neutrophils cannot leave vessels, they pile up in blood (high count on CBC) but infection sites have no neutrophils. You get infected, no pus forms, wounds do not heal.

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Chédiak-Higashi Syndrome

• Lysosomes = the digestive chambers inside cells (like stomach-acid filled bags). Neutrophils engulf bacteria into phagosomes (pockets). Normally these phagosomes fuse with lysosomes to KILL the bacteria.
• LYST = the gene that controls how lysosomes are transported and fused. When defective, lysosomes are GIANT and cannot fuse properly with phagosomes.
• Result: bacteria are engulfed but not killed.

• Progressive neurodegeneration
• Lymphohistiocytosis (abnormal lymphocyte and macrophage accumulation)
• Albinism (partial) - melanosomes (pigment granules in skin cells) are also lysosomes in behavior. Giant lysosomes cannot distribute pigment properly → pale skin, silver hair, light eyes
• Infections - recurrent pyogenic bacterial infections
• Neuropathy - peripheral nerve damage

• The giant lysosomes are visible under the microscope as giant purple granules inside neutrophils. This is pathognomonic (classic diagnostic finding).
• Pancytopenia = low red cells, white cells, AND platelets (because the bone marrow is affected too)

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Chronic Granulomatous Disease (CGD)

• NADPH oxidase = an enzyme in neutrophils that generates toxic oxygen molecules (reactive oxygen species - ROS) to kill bacteria
• Respiratory burst = when a neutrophil engulfs bacteria, it suddenly ramps up oxygen consumption to make ROS - it literally "bursts" with oxygen activity to kill the bug
• Without NADPH oxidase: neutrophils engulf bacteria normally but cannot generate the killing oxygen blast. They eat the bacteria but cannot digest them.

• Catalase-positive organisms = bacteria that make their own enzyme (catalase) to neutralize hydrogen peroxide (the very weapon that even FAULTY neutrophils can make a little of from other sources).
• Normal bacteria that LACK catalase: even the small amount of H2O2 produced by backup pathways kills them. Catalase-positive bugs neutralize even that small amount → they survive completely.
• Mnemonic organisms: Staphylococci, Burkholderia cepacia, Pseudomonas, Nocardia, Serratia, Aspergillus, Candida

• Granulomas = collections of immune cells (macrophages) that wall off bacteria they cannot kill. Think of a granuloma as the body's last-ditch effort - it cannot kill the bug so it walls it off in a little prison. In CGD, bacteria hide inside macrophages too (because macrophages also use NADPH oxidase to kill) → body keeps making granulomas everywhere.

• These are the tests for CGD.
• Dihydrorhodamine (DHR) test = a modern test. Normal neutrophils (which make ROS) oxidize DHR → it turns green/fluoresces. CGD neutrophils cannot make ROS → DHR stays dim.
• Nitroblue tetrazolium (NBT) test = old test. NBT is yellow. Normal neutrophils (making ROS) turn it BLUE. CGD neutrophils cannot → stays yellow.

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PAGE 5 (p. 116) - INFECTIONS IN IMMUNODEFICIENCY

• T cells fight viruses and fungi (intracellular threats). Without T cells, you get the classic AIDS-defining infections.
• CMV = Cytomegalovirus (causes retinitis, pneumonia, colitis in immunocompromised)
• JC virus = causes Progressive Multifocal Leukoencephalopathy (PML) - destroys the white matter of brain
• PCP = Pneumocystis jirovecii Pneumonia - classic AIDS-defining pneumonia

• B cells make antibodies, especially against bacteria that have a polysaccharide capsule (a sugar coat that helps them evade phagocytosis without opsonization). Antibodies are the key weapon against encapsulated bacteria.
• Without antibodies → encapsulated bacteria run wild → sepsis, meningitis, pneumonia
• Enteroviral encephalitis, poliovirus (live vaccine contraindicated) - B cells also defend against enteroviruses. Without them, even live vaccines can cause disease.
• GI giardiasis (no IgA) - reminder for selective IgA deficiency

• Without neutrophils: catalase-positive organisms (same list as CGD) and invasive fungi can cause fatal systemic infections

• Complement system = a cascade of blood proteins that punch holes in bacteria (the Membrane Attack Complex - MAC). The terminal complement components (C5-C9) form the MAC.
• Without C5-C9: you cannot form the MAC → you specifically cannot kill Neisseria (both meningitidis and gonorrhoeae have thin cell walls that the MAC normally destroys efficiently)
• KEY NOTE from text: "B-cell deficiencies tend to produce recurrent BACTERIAL infections, whereas T-cell deficiencies produce more FUNGAL/VIRAL infections."

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PAGE 6 (p. 117) - TRANSPLANT REJECTION & GRAFT-VERSUS-HOST DISEASE

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HYPERACUTE REJECTION

• The recipient already had antibodies against the donor's tissue (from previous transfusions, pregnancies, or prior transplants). The moment the transplanted organ's blood supply is opened, these antibodies immediately attack the blood vessels of the new organ and activate complement.

• Thrombosis = clot formation in blood vessels
• Ischemia = lack of blood supply to tissue (no blood = no oxygen = tissue death)
• Fibrinoid necrosis = the blood vessel wall itself dies and looks like fibrin under the microscope
• The organ turns dark and dies almost immediately. There is NO treatment - the transplanted organ MUST be surgically removed.

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ACUTE REJECTION

• MHC = Major Histocompatibility Complex = the protein identity tags on ALL your cells. Each person has unique MHC proteins (like a fingerprint). Donor MHC is "foreign" to the recipient's T cells.
• CD8+ T cells = cytotoxic T cells = the killers. They recognize foreign MHC on donor cells and destroy them.
• Type IV hypersensitivity = cell-mediated (not antibody-mediated). Takes days to develop.

• After transplant, the recipient's immune system makes NEW antibodies against donor tissue
• C4d = a breakdown product of complement. It deposits in the blood vessels of the rejected organ and is a histologic marker for antibody-mediated (humoral) rejection.

• Interstitial = in the spaces between structures
• Lymphocytic infiltrate = T lymphocytes invading the organ tissue
• Can be treated/reversed with immunosuppressants.

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CHRONIC REJECTION

• Arteriosclerosis = hardening and narrowing of blood vessels (like accelerated aging of vessels)
• Parenchymal atrophy = the functional cells of the organ shrink and die (parenchyma = the working cells)
• Interstitial fibrosis = replacement of normal tissue with scar tissue
• This is slow and cannot be reversed. The organ slowly chokes off.

• Chronic allograft nephropathy (kidney)
• Bronchiolitis obliterans (lung - airways scar over)
• Accelerated atherosclerosis (heart)
• Vanishing bile duct syndrome (liver)

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GRAFT-VERSUS-HOST DISEASE (GVHD)

• The transplanted bone marrow contains T cells from the DONOR. The recipient is immunocompromised (cannot fight back). Donor T cells see all of the recipient's cells as foreign and attack them.
• HLA mismatches increase the risk for GVHD
• Type IV hypersensitivity reaction (cell-mediated)

• Maculopapular rash = red flat spots and raised bumps on skin - classic skin GVHD
• Jaundice = liver damage from GVHD attacking bile ducts
• Diarrhea = GI tract damage
• Hepatosplenomegaly = liver and spleen enlargement

• Here is the silver lining: the same donor T cells that cause GVHD can also attack any remaining leukemia cells in the recipient. This is called the graft-versus-leukemia (GVL) effect. Doctors sometimes deliberately allow mild GVHD to take advantage of this anti-tumor activity.

• Irradiating blood destroys the donor WBCs in blood products before they can be transfused into immunocompromised patients, preventing GVHD from transfused T cells.

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PAGES 7-8 (pp. 118-119) - IMMUNOSUPPRESSANTS

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CYCLOSPORINE

• How T cells normally get activated: When a T cell recognizes its target (antigen), it triggers a cascade inside the cell → an enzyme called calcineurin is activated → calcineurin activates a transcription factor called NFAT → NFAT goes to the nucleus and turns ON the IL-2 gene → IL-2 (Interleukin-2) is made → IL-2 drives T cell proliferation (think of IL-2 as the gas pedal for T cells).
• Cyclosporine binds to cyclophilin (a protein inside T cells) → the Cyclosporine+Cyclophilin complex jams calcineurin → calcineurin cannot activate NFAT → no NFAT in nucleus → no IL-2 gene turned on → T cells cannot multiply → immunosuppression.

• Nephrotoxicity = kidney damage (most important side effect - the kidneys are very sensitive to cyclosporine)
• Gingival hyperplasia = gum overgrowth (gums grow large and cover the teeth - classic side effect)
• Hirsutism = excessive body/facial hair growth

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TACROLIMUS (FK506)

• Same mechanism as cyclosporine (inhibits calcineurin/IL-2) but binds a DIFFERENT protein (FKBP instead of cyclophilin). Result is identical - no IL-2 → no T cell proliferation.

• Tacrolimus DOES NOT cause gum overgrowth or hair growth - this distinguishes it from cyclosporine on exams
• But it carries MORE risk of causing diabetes than cyclosporine

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SIROLIMUS (RAPAMYCIN)

• Wait - Sirolimus also binds FKBP (same protein as tacrolimus) BUT the Sirolimus+FKBP complex targets a DIFFERENT enzyme: mTOR (mammalian Target Of Rapamycin).
• mTOR = the master switch for cell growth and protein synthesis. When IL-2 tells a T cell to grow and divide, it signals THROUGH mTOR. Sirolimus blocks mTOR → the cell cannot respond to IL-2's signal → no T cell proliferation. (Tacrolimus prevents IL-2 from being MADE; Sirolimus prevents cells from RESPONDING to IL-2.)

• Key exam point: Sirolimus is NOT nephrotoxic - it is sometimes used INSTEAD of calcineurin inhibitors in patients with kidney problems!
• Hyperlipidemia = elevated blood fats (cholesterol, triglycerides)

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BASILIXIMAB

• Monoclonal antibody = an engineered single antibody type
• IL-2R = the IL-2 Receptor on T cells. Basiliximab is an antibody that sticks to IL-2R and blocks it → T cells cannot receive the IL-2 signal → cannot proliferate.
• Used specifically for kidney transplant rejection prophylaxis (especially in combination with other agents)

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AZATHIOPRINE

• Antimetabolite = a drug that interferes with normal cell metabolism
• 6-MP is the active form. It gets incorporated into DNA synthesis pathways and blocks the production of purine nucleotides (the building blocks of DNA/RNA). Without new DNA, cells cannot divide.

• Xanthine oxidase = an enzyme that breaks down 6-MP (and also uric acid). Allopurinol blocks xanthine oxidase. If a patient takes both azathioprine AND allopurinol, 6-MP cannot be broken down → it accumulates to toxic levels → severe bone marrow suppression. Dangerous drug interaction!

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MYCOPHENOLATE MOFETIL

• IMP dehydrogenase = an enzyme in the de novo (from scratch) purine synthesis pathway
• Lymphocytes (T and B cells) are UNIQUELY dependent on this de novo pathway for purines (unlike most cells which have a salvage pathway as backup). So mycophenolate specifically suppresses lymphocytes more than other cells.

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GLUCOCORTICOIDS (Steroids)

• NF-kB = Nuclear Factor kappa B = a master transcription factor (a protein that turns on many inflammatory and immune genes). Think of NF-kB as the commander in chief of inflammation.
• Glucocorticoids block NF-kB → most inflammatory genes shut down → massive anti-inflammatory effect
• Also directly kill T cells (apoptosis = programmed cell death)

• Cushing syndrome = moon face, buffalo hump, central obesity, stretch marks (all from too much cortisol)
• Osteoporosis = weak bones (steroids inhibit bone-building osteoblasts)
• Hyperglycemia = raised blood sugar (steroids raise glucose - this is "steroid-induced diabetes")
• Diabetes amenorrhea = menstrual irregularities
• Adrenocortical atrophy = if you give steroids long-term, the adrenal glands stop making their own cortisol. If you SUDDENLY stop the drug, the adrenals cannot make cortisol fast enough → adrenal crisis. This is why steroids must be TAPERED (gradually reduced) not stopped abruptly.
• Psychosis = mood changes, paranoia, frank psychosis
• Peptic ulcers = stomach ulcer formation
• Cataracts = lens clouding
• Avascular necrosis (femoral head) = the head of the thigh bone loses its blood supply and dies. Classic complication.

• Demargination = normally many neutrophils cling to blood vessel walls (marginated). Steroids cause them to release into blood → WBC count looks artificially high on blood test even though you haven't actually made more cells.

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RECOMBINANT CYTOKINES AND CLINICAL USES

• EPO = a hormone naturally made by kidneys to stimulate red blood cell production in bone marrow
• Used in: anemias (especially in chronic kidney disease where the kidneys cannot make enough EPO)
• "Associated with ↑ risk of hypertension, thromboembolic events" - Too many red cells → blood too thick → clots and high blood pressure

• G-CSF = Granulocyte Colony Stimulating Factor = tells bone marrow to make more neutrophils (granulocytes)
• GM-CSF = Granulocyte-Macrophage CSF = tells bone marrow to make more neutrophils AND monocytes/macrophages
• Used in: leukopenia (low WBCs), recovery of granulocyte/monocyte counts after chemotherapy

• TPO = Thrombopoietin = hormone that stimulates platelet production
• Used in: autoimmune thrombocytopenia (low platelets from immune destruction)
• Memory: "Romiplostim = Platelet stimulator"

• A recombinant form of IL-2 used to treat renal cell carcinoma and metastatic melanoma
• Stimulates T-cell (immune) attack on cancer cells

• Used in: Chronic hepatitis B and C, renal cell carcinoma, multiple myeloma, certain leukemias
• Interferons = proteins naturally made by virus-infected cells to warn neighboring cells and activate immune responses

• Used in: Multiple sclerosis - reduces frequency of relapses

• Used in: Chronic granulomatous disease (CGD!)
• Boosts macrophage activity - helps partially compensate for the NADPH oxidase deficiency
• Multiple granulomatous disease listed as use as well

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1. Blood transfusion reactions differ by which antibody type and which mechanism - timing helps you tell them apart (minutes = allergic/acute hemolytic; hours = FNHTR/TRALI; days-weeks = delayed hemolytic).
2. Autoantibodies are fingerprints - each disease has a specific one; memorize the pairs.
3. Immunodeficiencies follow a pattern: B-cell defects = bacterial infections (especially encapsulated bacteria); T-cell defects = viral/fungal infections; phagocyte defects = catalase-positive and fungal infections; complement defects = Neisseria.
4. Transplant rejection: Hyperacute = minutes (pre-formed antibodies); Acute = weeks-months (T cells + new antibodies); Chronic = months-years (fibrosis/atherosclerosis). GVHD is the reverse - donor T cells attacking the recipient.
5. Immunosuppressants: Cyclosporine and Tacrolimus block IL-2 PRODUCTION (via calcineurin). Sirolimus blocks IL-2 RESPONSE (via mTOR). Azathioprine and Mycophenolate block DNA/nucleotide synthesis. Steroids block everything via NF-kB.