Meningococcal (Neisseria meningitidis) infection is predisposed by deficiency of –
**Core Concept**
The question is testing the understanding of the underlying pathophysiology of meningococcal infections, specifically the role of genetic deficiencies in predisposing individuals to such infections. Neisseria meningitidis is a Gram-negative bacterium that causes meningococcal disease, which can range from asymptomatic colonization to severe meningitis and sepsis.
**Why the Correct Answer is Right**
Meningococcal infections are indeed predisposed by deficiencies in certain genes that encode for proteins involved in the immune response. The most notable deficiency is the lack of proper functioning of the late component of the complement system, specifically C5b-9 (also known as the Membrane Attack Complex). This complex is crucial for forming pores in the bacterial cell wall, ultimately leading to bacterial lysis. Deficiencies in the genes encoding for the C5b-9 complex, such as C5, C6, C7, C8, or C9, increase the susceptibility to meningococcal infections.
**Why Each Wrong Option is Incorrect**
* **Option A:** Deficiency of IgA is associated with increased susceptibility to infections, particularly those caused by Gram-negative bacteria. However, it is not directly linked to meningococcal infections.
* **Option B:** Deficiency of C1q is a part of the classical pathway of the complement system and is associated with increased susceptibility to infections. However, it is not specifically linked to meningococcal infections.
* **Option C:** Deficiency of CD4+ T cells is associated with increased susceptibility to viral infections, particularly HIV. It is not directly linked to meningococcal infections.
**Clinical Pearl / High-Yield Fact**
Meningococcal infections are more common in areas with poor sanitation and crowded living conditions, which facilitate the spread of the bacterium. Individuals with deficiencies in the late component of the complement system should be aware of their increased risk and take preventive measures, such as receiving meningococcal conjugate vaccines.
**Correct Answer: C. Deficiency of C5, C6, C7, C8, or C9.**