A 25-year-old presents with recurrent Neisseria infections (meningococcemia twice, disseminated gonococcal infection once). The most likely immunological defect is:

• A C3 deficiency
• B Terminal complement component deficiency (C5–C9) ✓
• C Mannose-binding lectin deficiency
• D Properdin deficiency

Explanation

Deficiency of terminal complement components C5 through C9 (the membrane attack complex) specifically predisposes to recurrent and disseminated Neisseria infections including meningococcemia and gonorrhea. C3 deficiency causes susceptibility to encapsulated bacteria broadly. Properdin (X-linked) also predisposes to meningococcal disease but primarily affects the alternative pathway amplification loop. MBL deficiency causes mild susceptibility to encapsulated bacteria in early childhood.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.