Abstract
Although it is clear that HIV can lyse HIV-infected CD4 T cells, it is still controversial whether the depletion of CD4 T cells seen in HIV-infected patients after years of asymptomatic disease is caused by the direct cytopathic effects of the virus or is mediated by the immune response. Assuming the initial decline in viraemia during highly active antiretroviral therapy (HAART) is caused by the death of cells productively infected with HIV, I investigate how the rate of the virus decline is affected by the efficiency of the cytotoxic T-lymphocyte (CTL) response. I find that whether the stronger immune response causes a more rapid virus decline depends critically on how the virus is controlled by the CTL response (lytic versus non-lytic mechanisms). Moreover, variation in the efficiency of the immune response does not always cause variation in the rate of the virus decline (and, therefore, in the death rate of infected cells), implying that the constancy of the virus decline rate measured in different patients does not necessarily indicate that the virus is cytopathic. The potential problems associated with the model and the approach undertaken are also discussed.