The immune response to HIV infection

 HIV infection leads to the activation of CD8+ T helper cells (cytotoxic T lymphocytes (CTL)). This usually occurs before seroconversion (production of humoral antibodies) is observed. Since the virus particle number in the plasma falls before apparent seroconversion, the CTL response may be more critical than the humoral response. CTLs recognize HIV peptides presented by antigen-presenting cells in association with class I MHC antigens and the infected cells are lyzed. The CTLs can also induced apoptosis in infected cells via Fas/Fas-ligand interactions. Interaction of CTLs with HIV-infected cells also results in chemokine release. As noted elsewhere, chemokine receptors are the co-receptors for HIV infection of CD4+ cells and this can suppress infection of CD4+ cells as a result of blocking of the co-receptor.

Humoral antibodies also seem to play a minor role in counteracting an HIV infection since sera from HIV patients do not seem to reduce viral infectivity to a substantial degree; moreover, the virus population can rapidly escape from the neutralizing antibodies as a result of mutations in Gp120.