Answer: Pattern recognition (opsonizing bacteria/viruses by binding their surface patterns) to enhance phagocytosis by alveolar macrophages.
- A Reducing alveolar surface tension alone, with no other contributing immune function, a role actually performed by the lipid component of surfactant, not the SP-A protein
- B Pattern recognition (opsonizing bacteria/viruses by binding their surface patterns) to enhance phagocytosis by alveolar macrophages
- C Directly stimulating B cells to increase circulating antibody production, despite SP-A acting locally on macrophages rather than systemically on B lymphocytes
- D Actively inhibiting the complement cascade within the alveolar space, despite SP-A enhancing rather than suppressing local innate defence mechanisms
Correct answer: B. Pattern recognition (opsonizing bacteria/viruses by binding their surface patterns) to enhance phagocytosis by alveolar macrophages
Explanation: Surfactant proteins A and D (SP-A, SP-D) are collectins that function as opsonins -- binding pathogen surface patterns (PAMPS), enhancing alveolar macrophage phagocytosis and innate defense.
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.