This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (E.N.T.), Subject name: ENT
Human immunodeficiency virus (HIV) affects the immune response. The primary change brought about is: 
Select and explain. 
A. A gammaglobulinemia, B. Defect in cell-mediated immunity, C. Defect in complement system, D. Defect in natural killer cells
B: Defect in cell-mediated immunity
Answer: B: Defect in cell-mediated immunity 
Explanation: HIV infects CD4 (helper) T-lymphocytes, macrophages and monocytes and leads to cell-mediated immune deficiency which predisposes to opportunistic infections and malignancies.