A 40-year-old male who has been HIV positive for 6 years is experiencing a new increase in his viral load along with a corresponding decrease in his CD4+ count. Which of the following aspects of his immune system is likely to remain most intact?
A. Activation of B lymphocytes
B. Phagocytic function of monocytes and macrophages
C. Orchestration of natural killer cells as part of cell-mediated immunity
D. Presentation of major histocompatibility molecules on body cells