Answer: Classical (antibody-bound antigen), lectin (mannose on pathogens), or alternative (directly on pathogen surfaces) pathways, leading to MAC pore formation.
- A Activation occurring through hormonal signaling pathways alone, without any antigen involvement, bypassing the classical, lectin, and alternative pathways
- B Classical (antibody-bound antigen), lectin (mannose on pathogens), or alternative (directly on pathogen surfaces) pathways, leading to MAC pore formation
- C Activation that is mediated mainly by circulating T lymphocytes, despite T cells playing no direct role in triggering any complement pathway
- D A process that results mainly in the direct killing of pathogens, with little contribution toward opsonization or inflammatory signaling
Correct answer: B. Classical (antibody-bound antigen), lectin (mannose on pathogens), or alternative (directly on pathogen surfaces) pathways, leading to MAC pore formation
Explanation: Complement: 3 activation pathways converge at C<sub>3</sub> convertase. Downstream C5b-9 forms membrane attack complex (MAC). Also produces opsonins (C3b), and chemotactic factors (C5a).
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.