Final answer:
HIV targets Helper T cells (CD4+ T cells), which are crucial for immune response regulation. The virus's replication within these cells depletes their numbers and weakens immunity, increasing susceptibility to other infections.
Step-by-step explanation:
The cell type targeted by the human immunodeficiency virus (HIV) is primarily the Helper T cells (specifically CD4+ T cells). These cells play a vital role in the immune system by regulating the immune response. HIV infects these cells, as well as macrophages and dendritic cells, and uses their machinery to replicate itself. This leads to a depletion in CD4+ T cells and, consequently, a weakened immune defense, making the body more vulnerable to opportunistic infections. An illustration of how the HIV infects the CD4+ T cell is shown in Figure 20.6.8.
Moving to the other immune system cells, Macrophages are known to phagocytize pathogens and produce chemicals that promote inflammation. Helper T cells and cytotoxic T cells are different in nature and function: while Helper T cells are CD4+ and release cytokines to regulate immune responses, cytotoxic T cells are CD8+ and their role is to directly kill infected cells.