Rheumatoid arthritis which type of hypersensitivity
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Rheumatoid Arthritis - Type of Hypersensitivity
Rheumatoid arthritis (RA) primarily involves Type III (Immune Complex-Mediated) and Type IV (T Cell-Mediated) hypersensitivity. For most exam purposes, Type III is cited as the classic answer, but the full picture is more nuanced.
Type III Hypersensitivity (Immune Complex-Mediated) - the classic answer
As stated in K.J. Lee's Essential Otolaryngology: "Type III (immune complex) reactions...include Rheumatoid arthritis, serum sickness, and lupus."
The mechanism in RA:
- Rheumatoid factors (RF): Auto-antibodies (usually IgM) directed against the Fc portion of the patient's own IgG molecules. These form IgM-IgG immune complexes that deposit in synovial tissue.
- Anti-citrullinated protein antibodies (ACPAs): Found in 60-80% of patients (seropositive RA), these form immune complexes with citrullinated proteins (vimentin, fibrinogen, etc.).
- Immune complex deposition activates complement (C3a, C5a), recruiting neutrophils and macrophages into the synovium, causing chronic inflammatory joint destruction.
Type IV Hypersensitivity (T Cell-Mediated) - equally important
From Cellular and Molecular Immunology (Abbas), RA is explicitly listed in the T Cell-Mediated Diseases table (Table 19.4):
| Disease | Pathogenic T cells | Mechanism |
|---|---|---|
| Rheumatoid arthritis | Against collagen? Citrullinated self proteins? | Inflammation mediated by Th1 and Th17 cytokines; role of antibodies and immune complexes |
The T cell-driven mechanism:
- CD4+ Th1 cells produce IFN-γ, activating macrophages in the synovium
- Th17 cells secrete IL-17, recruiting neutrophils and inducing synovial cells to release collagenases
- Net result: progressive cartilage and bone destruction
- Susceptibility is linked to HLA-DR4 (shared epitope), reinforcing the T cell-antigen presentation axis
Gell & Coombs Classification - Summary
| Type | Name | Mechanism | Role in RA |
|---|---|---|---|
| Type I | IgE-mediated | Mast cell degranulation | Not involved |
| Type II | Antibody vs. cell surface Ag | Complement/ADCC lysis | Minor (anti-RF targeting Fc) |
| Type III | Immune complex | IgG/IgM complexes + complement | Classic - synovial deposition of RF & ACPA complexes |
| Type IV | T cell-mediated | Th1/Th17 cytokines, macrophage activation | Major driver of chronic joint destruction |
Key Points for Exams
- Short answer: Type III hypersensitivity (immune complex-mediated)
- Complete answer: Type III + Type IV
- Rheumatoid factor = IgM antibody against Fc of IgG = hallmark immune complex in RA
- HLA association: HLA-DR4 (shared epitope) - links to Type IV T cell response
- Seropositive RA (RF+ and/or ACPA+) = more severe, stronger Type III component
Sources: - Cellular and Molecular Immunology (Abbas), Table 19.4 & pp. 1279-1282 | - K.J. Lee's Essential Otolaryngology, Immunology and Allergy chapter | - Robbins & Kumar Basic Pathology, Chapter 5
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