Important points for mcqs
Reading File
Based on the image (from First Aid — Hematology & Oncology, immune cells section), here are the high-yield MCQ points:
Dendritic Cells (APCs)
- Highly phagocytic antigen-presenting cells
- Bridge between innate and adaptive immunity
- Express MHC class II and Fc receptors on surface
- Can present exogenous antigens on MHC class I → called cross-presentation
- Activate T cells (T-cell stimulation)
Eosinophils
- Bilobate nucleus (key identifier)
- Highly phagocytic for antigen-antibody complexes
- Packed with large eosinophilic granules of uniform size
- Defend against helminthic infections (major basic protein = helminthotoxin)
- Produce: MBP (major basic protein), eosinophil cationic protein, eosinophil-derived neurotoxin, IL-5 → promotes eosinophilic activation
Causes of Eosinophilia — PACMAN E:
| Letter | Cause |
|---|---|
| P | Parasites |
| A | Asthma |
| C | Chronic adrenal insufficiency |
| M | Myeloproliferative disorders |
| A | Allergic processes |
| N | Neoplasia (eg, Hodgkin lymphoma) |
| E | Eosinophilic granulomatosis with polyangiitis |
Basophils
- Densely basophilic granules (stain with basic stains)
- Granules contain: heparin (anticoagulant) + histamine (vasodilator)
- Leukotrienes synthesized and released on demand
- Mediate allergic reactions
- Basophilia → sign of myeloproliferative disorders (especially CML)
Mast Cells
- Mediate local tissue allergic reactions (type I hypersensitivity)
- Originate from same precursor as basophils — NOT the same cell type
- Can bind Fc portion of IgE to membrane
- Activated by: tissue trauma, C3a, C5a, surface IgE cross-linking → degranulation
- Degranulation releases: histamine, heparin, tryptase, eosinophil chemotactic factors
- Cromolyn sodium prevents mast cell degranulation (used for asthma prophylaxis)
- Vancomycin, opioids, radiocontrast dye → IgE-independent mast cell degranulation
Mastocytosis:
- Rare proliferation of mast cells in skin ± extracutaneous organs
- Associated with c-KIT mutations + ↑ serum tryptase
- Symptoms: flushing, pruritus, hypotension, abdominal pain, diarrhea, peptic ulcer disease
Quick MCQ Tips:
- Bilobate nucleus + large granules = Eosinophil
- Helminth defense = Eosinophils (MBP is the key weapon)
- IL-5 = key cytokine for eosinophil activation/proliferation
- Heparin + histamine in granules = Basophil
- IgE bound to surface = Mast cells (not basophils in tissue)
- Cross-presentation on MHC I = Dendritic cells
- c-KIT mutation + ↑ tryptase = Mastocytosis
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