**Question:** Immune complex deposition is-

A. Deposition of antibodies and antigens in tissues
B. Enhancement of antigen presentation
C. Activation of complement system
D. Inhibition of antigen presentation

**Core Concept:** Immune complex deposition is a key event in the pathogenesis of various autoimmune and inflammatory diseases. Immune complexes (IC) are formed when antibodies (IgG, IgM, IgA) bind to antigens, resulting in the formation of immune complexes that can be deposited in tissues. These deposits can lead to tissue damage, inflammation, and organ dysfunction.

**Why the Correct Answer is Right:** Immune complex deposition leads to the deposition of antibodies and antigens in tissues, which can cause inflammation and tissue damage. This process is a key feature of several diseases, such as systemic lupus erythematosus (SLE), systemic vasculitis, and cryoglobulinemia.

**Why Each Wrong Option is Incorrect:**

A. Deposition of antibodies and antigens in tissues is incorrect because the correct answer describes the deposition of immune complexes, not just antibodies and antigens.
B. Enhancement of antigen presentation is unrelated to immune complex deposition and is a different aspect of the immune response.
C. Activation of the complement system is a consequence of immune complex deposition, not a description of immune complex deposition itself.
D. Inhibition of antigen presentation is also unrelated to immune complex deposition and describes a different aspect of the immune response.

**Clinical Pearl:** Understanding immune complex deposition and its consequences is essential for diagnosing and treating patients with autoimmune and inflammatory diseases. A thorough clinical examination, coupled with appropriate laboratory tests and imaging studies, can help identify these conditions and guide treatment strategies.

**Correct Answer:** A. Deposition of antibodies and antigens in tissues