Question

what cells are affected by the HIV virus?

Answer 1

Lymphocytes

Answer 2

WillTaft is correct in stating that lymphocytes are affected. More specifically, HIV infects CD4+ T helper lymphocytes, dendritic cells and macrophages. CD4+ T helper lymphocytes are killed directly by infection but these cells are also more susceptible to killing by cytotoxic T killer cells (CD8+) which recognize them as infected and hence a threat. The infected T helper cells are also more likely to die via programmed cell death (which is called apoptosis). There's a good summary here:

http://en.wikipedia.org/wiki/HIV