Final answer:
HIV primarily infects helper T cells, specifically CD4+ T cells, leading to a depletion of these cells and impaired immune function in patients with overt AIDS.
Step-by-step explanation:
HIV primarily infects helper T cells (specifically CD4+ T cells) and leads to a depletion of these cells, resulting in impaired immune function in patients with overt AIDS. The virus kills infected CD4+ T cells directly and also triggers an immune response that attacks these T cells. CD4+ T cells are critical for the immune system's response and their loss leads to a loss of cell-mediated immunity, making the body more susceptible to opportunistic infections.