Functional dichotomy of CD4+ T helper lymphocytes in asymptomatic human immunodeficiency virus infection

The majority of asymptomatic, human immune deficiency virus seropositive (HIV+) individuals exhibit a defect in CD4+ T helper cell (Th) function that is selective for responses to recall antigens, but not to HLA alloantigens. The CD4-dependent Th response to HLA alloantigens (Allo) can be mediated by two distinct Th pathways: self-restricted CD4+ Th that recognize allogeneic determinants processed and presented by autologous or self accessory or antigen-presenting cells (sAC); and allo-restricted, CD4+ Th that recognize allogeneic determinants directly on allogeneic accessory or antigen-presenting cells (aAC). In contrast, the Th response to recall antigens requires CD4+ Th and sAC and is therefore limited to the major histocompatibility complex (MHC) self-restricted pathway. Peripheral blood leukocytes from 56 asymptomatic HIV+ patients that exhibited a selective defect in CD4+ Th function were analyzed to determine whether the Th response to Allo was entirely functional, or whether one of the CD4-mediated components of the Allo Th response was also defective. By depletion of AC and/or CD8+ Th subsets (to analyze CD4+ Th function), we demonstrated that HIV+ patients who were selectively deficient in Th function to recall antigens were also unresponsive to Allo presented by autologous AC (HLA self-restricted Th pathway), but retained Allo Th activity presented by allogeneic AC (allo-restricted CD4+ Th pathway). These findings indicate that the CD4+ Th defect seen in the majority of asymptomatic, HIV+ individuals is not limited to recall antigens, but also extends to the component of the response to HLA alloantigens that involves the self-restricted, CD4+ Th pathway. Thus, the Th defect observed in asymptomatic, HIV+ patients does not involve a CD4+ Th defect per se, but is limited to the HLA self-restricted component of Th function.