Answer:
The Human Immunodeficiency Virus (HIV) seems to only infect the CD4 (or T-helper) cells of the immune system. The CD4 cells are responsible for activating and directing other immune system cells.
HIV also infects macrophages and microglial cells that express the CD4 molecule on their surface. The virus can also infect a subtype of myeloid dendritic cells MDC-1.