Meningococcal meningitis is seen with which of the following complement deficiency?

**Core Concept**
Meningococcal meningitis is a severe infection caused by the bacterium Neisseria meningitidis. The disease is more common in individuals with complement system deficiencies, particularly those involving the late components of the complement pathway.

**Why the Correct Answer is Right**
The correct answer involves a deficiency in the late component of the complement system, specifically C5-C9. This deficiency impairs the formation of the membrane attack complex (MAC), which is essential for bacterial lysis and clearance. Without an intact MAC, individuals are more susceptible to infections, including meningococcal meningitis. The late components of the complement pathway, including C5-C9, work together to form the MAC, which inserts into the bacterial membrane, ultimately leading to cell lysis and death.

**Why Each Wrong Option is Incorrect**
**Option A:** Deficiency of C1q is incorrect because C1q is a component of the classical pathway, which is not directly involved in the clearance of meningococci.
**Option B:** Deficiency of C4 is incorrect because C4 is also a component of the classical pathway and is not directly involved in the clearance of meningococci.
**Option C:** Deficiency of C3 is incorrect because, although C3 is a critical component of the complement system, its deficiency is associated with increased susceptibility to infections, including Neisseria species, but not specifically meningococcal meningitis.

**Clinical Pearl / High-Yield Fact**
A deficiency in the late components of the complement system, particularly C5-C9, increases the risk of meningococcal meningitis. This is an important consideration for individuals with a family history of complement deficiencies or previous episodes of recurrent infections.

**Correct Answer: C. Deficiency of C5-C9.**