This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology and Rheumatology, Subject name: Medicine
A 30-year-old man has developed fever, chills, and neck stiffness. Cerebrospinal fluid shows gram-negative diplococci. He has had a past episode of sepsis with meningococcemia. Select the most likely immunologic deficiency. 
Select and explain. 
A. Complement deficiency C5-C9, B. Post-splenectomy, C. Drug-induced agranulocytosis, D. Interleukin-12 receptor deficit
A: Complement deficiency C5-C9
Answer: A: Complement deficiency C5-C9 
Explanation: Patients who have a deficiency of one of the terminal components of complement have a remarkable susceptibility to disseminated Neisseria infection, particularly meningococcal disease. This association with meningococcal disease is related to the host inability to assemble the membrane attack complex-a single molecule of complement components that creates a discontinuity in the bacteria's membrane lipid bilayer. The complement deficiency results in inability to express complement-dependent bactericidal activity.