American Board of Internal Medicine (ABIM) Certification Practice Exam

Patients with late complement component deficiencies are primarily susceptible to which type of infections?

1. Viral infections

2. Pneumococcal infections

3. Meningococcal or gonococcal infections

4. Fungal infections

The correct answer is: Meningococcal or gonococcal infections

Patients with late complement component deficiencies, specifically those affecting complement components C5 through C9, face a heightened risk of developing certain types of infections due to their impaired ability to form the membrane attack complex (MAC). This complex plays a crucial role in the immune system's defense against encapsulated bacteria, particularly Neisseria species, which includes Neisseria meningitidis (the causative agent of meningococcal infections) and Neisseria gonorrhoeae (responsible for gonococcal infections). The inability to effectively form the MAC compromises the body’s ability to lyse these Gram-negative bacteria, thereby increasing susceptibility to infections like meningitis and gonorrhea. This specific immune deficiency illustrates why these patients are particularly vulnerable to infections caused by organisms such as meningococcus and gonococcus, rather than other pathogens. In contrast, infections such as pneumococcal infections, while associated with complement deficiencies, are more typically linked to deficiencies in the early complement components (like C1 through C4) that affect opsonization and clearance of encapsulated bacteria. Similarly, viral infections and fungal infections are not primarily tied to late complement component deficiencies; they often involve different immune pathways, such as cellular immunity or the action of neutrophils and