Okay, let's tackle this question about Raji cell assays. The user mentioned that the options were missing, so I need to figure out what the possible options could be based on the correct answer. The correct answer is given as B. Complement-dependent cytotoxicity (CDC), so I need to structure the explanation around that.

First, the core concept here is about Raji cell assays. I remember that Raji cells are a type of B-cell lymphoma used in immunology. The assays are probably related to immune responses. The correct answer is CDC, which involves complement proteins causing cell lysis. So the core concept would be the use of Raji cells to measure CDC activity.

Next, explaining why CDC is correct. Raji cells are sensitive to complement-mediated lysis. When antibodies bind to them, complement is activated, leading to cell death. The assay measures this lysis to quantify CDC efficiency. This is important in studying immune responses and autoimmune diseases.

Now, the wrong options. Let's think of common related terms. Maybe options like antibody-dependent cell-mediated cytotoxicity (ADCC), chemotaxis, opsonization, or phagocytosis. Each of these is a different immune mechanism. ADCC involves NK cells, not complement. Chemotaxis is cell movement towards chemicals. Opsonization is marking pathogens for phagocytosis. Phagocytosis itself is the process of engulfing particles.

The clinical pearl should highlight that Raji cell assays are specifically for CDC, not other cytotoxic mechanisms. Students might confuse CDC with ADCC, so emphasizing the complement system's role is key.

Putting it all together, ensuring each section is concise and within the character limit. Need to use bold for key terms and structure the sections as specified. Also, avoid markdown except for bold and correct formatting. Check that each incorrect option is addressed clearly and concisely.

**Core Concept**
Raji cell assays are a standardized immunological method to assess **complement-dependent cytotoxicity (CDC)**. Raji cells, a B-cell lymphoblastoid line, are highly sensitive to complement-mediated lysis when bound by specific antibodies. This assay is critical in studying immune effector mechanisms, particularly in autoimmune and infectious diseases.

**Why the Correct Answer is Right**
**Complement-dependent cytotoxicity (CDC)** involves antibody-coated Raji cells triggering the classical complement pathway. C3 convertase formation leads to membrane attack complex (MAC) assembly, causing cell lysis. The extent of lysis correlates with complement activity, making Raji cells an ideal substrate due to their high surface immunoglobulin expression and sensitivity to complement. This assay quantifies functional complement activity, such as in evaluating complement deficiencies or therapeutic antibody efficacy.

**Why Each Wrong Option is Incorrect**
**Option A:** *Antibody-dependent cell-mediated cytotoxicity (ADCC)* involves NK cells or macrophages, not complement. Raji assays do not measure ADCC.
**Option C:** *Chemotaxis* refers to cell migration toward chemical gradients, unrelated to Raji cell lysis.
**Option D:** *Phagocytosis* involves engulfment by phagocytes; Raji assays focus on lysis, not ingestion.

**Clinical Pearl / High-Yield Fact**
Never confuse Raji cell assays with ADCC assays. Raji cells are **specifically

✓ Correct Answer: B. Immune complexes