CD4 and HIV-1 infection: Using conventional and novel immunologic assays in parallel, we have demonstrated that functional defects in HIV-1-specific CD4 HTL in chronic HIV-1 infection include an inability to proliferate and produce IL-2 in response to HIV-1 antigens, although secretion of anti-viral cytokines such as IFN-γ and TNF-α remained unimpaired (Wilson et al., 2000).