Answer: Coating of pathogens with antibodies or complement, enhancing their recognition and phagocytosis.
- A The direct killing of bacteria carried out exclusively by circulating natural killer (NK) cells
- B Coating of pathogens with antibodies or complement, enhancing their recognition and phagocytosis
- C Formation of the complement membrane attack complex (MAC) pore within a cell membrane
- D Activation of a resting B lymphocyte immediately upon its first contact with a matching antigen
Correct answer: B. Coating of pathogens with antibodies or complement, enhancing their recognition and phagocytosis
Explanation: Opsonization is the coating of pathogens with opsonins (IgG antibodies, complement fragments C3b). Phagocytes have receptors for these opsonins (Fc receptors for IgG; CR1 for C3b), greatly enhancing phagocytosis of opsonized pathogens.
An antibody is Y-shaped, with two identical antigen-binding sites at the tips of the variable regions - each shaped to recognise one specific antigen - while the constant (Fc) region at the base is recognised by immune cells to trigger further responses.
Concept context
Innate and adaptive immunity, B cells, T cells, antibodies, vaccines, and immune disorders. Critical for NEET.