- A MAC is a protein that attracts phagocytes to the site of infection rather than forming any pore in a pathogen's membrane directly according to conventional understanding
- B MAC is formed by polymerization of C5b, C6, C7, C8, and multiple C9 proteins into a pore in the bacterial membrane, causing osmotic lysis
- C MAC is an antibody complex generated by plasma cells rather than assembled from complement components C5b through C9 specifically in routine practice
- D MAC activates T cells directly, bypassing any membrane-damaging or pore-forming activity altogether in the process overall in most cases
Correct answer: B. MAC is formed by polymerization of C5b, C6, C7, C8, and multiple C9 proteins into a pore in the bacterial membrane, causing osmotic lysis
Explanation: MAC forms at the end of the complement cascade: C5b recruits C6, C7, C8, then multiple C9 molecules polymerize to create a transmembrane pore (~10nm). This allows uncontrolled ion/water flow across the bacterial membrane, causing osmotic lysis. Gram-negative bacteria are more susceptible (thin peptidoglycan layer).
Concept context
Innate and adaptive immunity, B cells, T cells, antibodies, vaccines, and immune disorders. Critical for NEET.