Which of the following is most specific antibody detected in patients with Rheumatoid arthritis?
First, I remember that rheumatoid arthritis (RA) is associated with certain autoantibodies. The main ones are rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies. RF is an antibody against the Fc portion of IgG, but it's not very specific because it can be present in other conditions like Sjögren's syndrome or even in healthy elderly people.
Anti-CCP antibodies are more specific for RA. They target citrullinated proteins, which are modified during the disease process. Citrullination is a post-translational modification where arginine residues become citrulline. In RA, the immune system mistakenly attacks these citrullinated proteins. This makes anti-CCP antibodies a better diagnostic marker compared to RF.
Looking at the options provided, I need to identify which one corresponds to anti-CCP. The other options might include RF, anti-nuclear antibodies (ANA), or others. Since the question is about specificity, anti-CCP is the answer. Let me make sure about the other options. ANA is more associated with lupus, so that's not correct here. Anti-dsDNA is specific for SLE. So the correct answer is anti-CCP.
**Core Concept**
Rheumatoid arthritis (RA) is an autoimmune disorder characterized by synovial inflammation and joint destruction. The most specific serological marker is anti-cyclic citrullinated peptide (anti-CCP) antibody, which detects autoantibodies against citrullinated proteins. This distinguishes RA from other arthritides.
**Why the Correct Answer is Right**
Anti-CCP antibodies are highly specific for RA (specificity >95%) and are produced in response to citrullinated antigens. Citrullination, a post-translational modification of arginine residues, occurs in RA synovial tissues, triggering an autoimmune response. Anti-CCP antibodies predict disease severity and response to treatment, making them a cornerstone of RA diagnosis.
**Why Each Wrong Option is Incorrect**
**Option A:** *Rheumatoid factor (RF)* is less specific, present in 60–70% of RA patients but also in other autoimmune diseases (e.g., Sjögren’s syndrome) and 5% of healthy individuals.
**Option B:** *Anti-nuclear antibodies (ANA)* are hallmark of systemic lupus erythematosus (SLE), not RA.
**Option C:** *Anti-dsDNA antibodies* are specific for SLE, targeting double-stranded DNA.
**Option D:** *Anti-Sm antibodies* are unique to SLE, recognizing Smith nuclear antigen.
**Clinical Pearl / High-Yield Fact**
Anti-CCP antibodies are more specific than RF for RA and are often used to confirm early RA even when RF is negative. Remember: *CCP = Citrullinated Cyclic Peptide = RA*.
**Correct Answer: C. Anti-cyclic citrullinated peptide antibody**