Impact of antigen specificity on CD4+ T cell activation in chronic HIV-1 infection

BACKGROUND HIV infection induces chronic immune activation which is associated with accelerated disease progression; the causes of this activation, however, are incompletely understood. We investigated the activation status of CD4+ T cells specific for chronic herpes viruses and the non-persistent antigen tetanus toxoid (TT) in HIV positive and HIV negative donors to assess whether persistent infections contribute to chronic CD4+ T cell activation. METHODS Untreated HIV+ patients and healthy, aged matched controls were recruited and activation levels assessed and compared between cells specific for persistent and non-persistent antigens. Activation levels on antigen-specific CD4+ T cells were measured by intracellular cytokine staining following in vitro stimulation with various recall antigens (CMV, EBV, HSV, VZV and TT) in conjunction with cell surface phenotyping. RESULTS Activation levels of herpes virus-specific CD4+ T cell populations, assessed by co-expression of CD38 and HLA-DR, were significantly elevated in HIV+ individuals compared to normal controls and compared to TT-specific responses. In contrast, we found similar levels of activation of TT-specific CD4+ T cells in HIV+ and HIV- donors. CONCLUSIONS These results show a disparate distribution of immune activation within CD4+ T cell populations depending on their specificity and suggest that the elevated level of immune activation that characterizes chronic HIV infection may be influenced by the persistence of other antigens.