Question

Which is NOT antibody-mediated effector function?

• A. Opsonization
• B. Activation of complement system
• C. Antibody- dependent cell mediated cytotoxicity
• D. Phagocytosis

Hint:

Antibody effector mechanisms require the Fc region:
1. Opsonization (FcR binding)
2. Complement Activation (C1q binding)
3. ADCC (Fc$\gamma$R binding on NK cells)
Phagocytosis itself is a cellular process carried out by inte immune cells.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify the process that is an intrinsic cellular mechanism performed directly by phagocytic immune cells rather than a specialized effector mechanism mediated by antibody molecules.

Step 2: Key Formula or Approach:
Antibodies (immunoglobulins) act as molecular adaptors that bind antigens via their Fab regions and trigger specific effector functions by interacting with Fc receptors or complement proteins via their Fc regions:

• Opsonization: Coating of pathogens with antibodies to enhance recognition by Fc receptors on phagocytes.

• Complement Activation: Classical complement pathway initiated by C1q binding to antigen-bound IgM or IgG.

• ADCC: NK cells and granulocytes destroying antibody-coated target cells via Fc$\gamma$RIII interaction.

• Direct Phagocytosis: Engulfment of microbes by macrophages/neutrophils mediated by direct binding of Pattern Recognition Receptors (PRRs) to Pathogen-Associated Molecular Patterns (PAMPs) without requiring antibodies.

Step 3: Detailed Explation:

• Antibody-Mediated Effector Functions: Opsonization, complement activation, and antibody-dependent cell-mediated cytotoxicity (ADCC) strictly require the presence and binding of specific antibodies to function.

• Phagocytosis as an Intrinsic Cellular Function: Phagocytosis itself is a fundamental cellular process executed by phagocytes (such as macrophages, neutrophils, and dendritic cells).

• Inte Phagocytosis Mechanism: Phagocytes can directly recognize, engulf, and interlize foreign particles or microorganisms via inte surface receptors (e.g., scavenger receptors, mannose receptors, and Toll-like co-receptors) independently of antibodies.

• Enhancement vs. Effector Function: While antibodies facilitate phagocytosis through opsonization, the primary mechanism of phagocytosis is a cellular engulfment process rather than an antibody-driven effector cascade.

Step 4: Fil Answer:
Direct phagocytosis is an intrinsic cellular uptake mechanism that can occur independently of antibody mediation.