Regarding the immunopathological mechanisms in rheumatoid arthritis, all of the following are true EXCEPT:

Question

Accepted Answer

C. Immune complexes in RA are primarily composed of IgA-dominant deposits that activate complement exclusively through the alternative pathway. ## Immunopathological Mechanisms in Rheumatoid Arthritis

### Key Autoimmune Features

**Key Point:** The immunopathology of RA involves multiple layers of adaptive and innate immune activation, centered on loss of tolerance to self-antigens and formation of pathogenic immune complexes.

### Autoantibodies in RA

| Autoantibody | Target | Clinical Significance |
|---|---|---|
| Rheumatoid Factor (RF) | Fc portion of IgG | Present in ~80% of RA; can be IgM, IgG, or IgA |
| Anti-CCP | Citrullinated proteins | ~95% specific for RA; predicts erosive disease and poor prognosis |
| Anti-dsDNA | Double-stranded DNA | More specific for SLE; NOT typical of RA |

**High-Yield:** Anti-CCP antibodies are superior to RF for early diagnosis and prognostication in RA because they appear earlier in disease course and correlate with radiographic progression.

### Th17 Cell Axis in RA

**Key Point:** IL-17-producing T helper cells (Th17) are a critical driver of synovial inflammation in RA:
- Th17 cells are differentiated from naïve T cells by IL-6 and TGF-β
- IL-17 recruits neutrophils and activates synovial fibroblasts
- IL-17 also promotes osteoclast differentiation via RANKL upregulation, leading to bone erosion

### Immune Complex Composition — The Distractor

**Warning:** The incorrect option claims immune complexes are "IgA-dominant" and activate complement "exclusively through the alternative pathway." This is FALSE:

1. **Dominant Immunoglobulin Class:** Immune complexes in RA are predominantly **IgG and IgM**, not IgA. IgA-dominant immune complexes are characteristic of IgA nephropathy (in the kidney) and IgA vasculitis, NOT RA.

2. **Complement Activation Pathway:** RA immune complexes activate complement through **both classical and alternative pathways**:
   - Classical pathway: IgG and IgM in immune complexes bind C1q directly
   - Alternative pathway: Amplification loop is activated secondarily
   - NOT exclusively alternative pathway

3. **Clinical Consequence:** Complement activation (especially C3a, C5a) drives recruitment of neutrophils and macrophages into the synovium, perpetuating inflammation.

**Clinical Pearl:** Low serum complement (C3, C4) in RA indicates active immune complex disease and correlates with systemic manifestations (vasculitis, pericarditis).

### Summary of Correct Statements

- **Option 1 (TRUE):** RF is indeed an IgM autoantibody against IgG Fc region—classic definition.
- **Option 2 (TRUE):** Anti-CCP is more specific (~95%) than RF (~80%) and is the best predictor of erosive RA.
- **Option 3 (TRUE):** Th17 cells and IL-17 are central to synovial inflammation and osteoclast activation via RANKL.
- **Option 4 (FALSE):** Immune complexes are IgG/IgM-dominant (not IgA) and activate complement via classical pathway (not exclusively alternative).

Answer

A. T helper 17 (Th17) cells and their cytokine IL-17 play a central role in synovial inflammation and osteoclast activation

Answer

B. Rheumatoid factor (RF) is an IgM autoantibody directed against the Fc portion of IgG

Answer

D. Anti-CCP (cyclic citrullinated peptide) antibodies are more specific for RA than rheumatoid factor and predict erosive disease

Regarding the immunopathological mechanisms in rheumatoid arthritis, all of the following are true EXCEPT:

Explanation

Immunopathological Mechanisms in Rheumatoid Arthritis

Key Autoimmune Features

Autoantibodies in RA

Th17 Cell Axis in RA

Immune Complex Composition — The Distractor

Summary of Correct Statements

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Autoantibody	Target	Clinical Significance
Rheumatoid Factor (RF)	Fc portion of IgG	Present in ~80% of RA; can be IgM, IgG, or IgA
Anti-CCP	Citrullinated proteins	~95% specific for RA; predicts erosive disease and poor prognosis
Anti-dsDNA	Double-stranded DNA	More specific for SLE; NOT typical of RA