Question

Which of the statement is incorrect?

• A. Phagocytes are involved in innate immunity
• B. Antibodies are produced by cells of adaptive immunity
• C. Fab fragment of antibody binds to antigen
• D. Fc fragment of antibody binds to antigen

Hint:

Antibody Domains:
Fab (Fragment antigen-binding) $\rightarrow$ Binds Antigen.
Fc (Fragment crystallizable) $\rightarrow$ Binds Fc-Receptors Fixes Complement (Effector function).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Antibody functional anatomy segregates antigen-binding activity ($V_H/V_L$ within Fab) from effector mediation ($C_H2/C_H3$ within Fc).

Step 2: Detailed Explanation:
Evaluating the immunological statements:
1. Option 1 (Correct): Macrophages, neutrophils, and dendritic cells are phagocytic cells of innate immunity.
2. Option 2 (Correct): Plasma B cells of the adaptive immune system synthesize antibodies.
3. Option 3 (Correct): The Fab (Fragment antigen-binding) contains the hypervariable CDR loops that bind specific epitopes on antigens.
4. Option 4 (INCORRECT): The Fc (Fragment crystallizable) region binds to Fc receptors ($Fc\gamma R$) on phagocytes, NK cells, and fixes complement (C1q); it does NOT bind antigen.

Step 3: Final Answer:
Hence, the incorrect statement is 'Fc fragment of antibody binds to antigen', corresponding to option (D).