Enumeration of viral antigen-reactive helper T lymphocytes in human peripheral blood by limiting dilution for analysis of viral antigen-reactive T-cell pools in virus-seropositive and virus-seronegative individuals.

A limiting-dilution analysis technique was developed which enumerates human T cells with the capacity to secrete T-cell growth factors such as interleukin 2 after contact with herpes simplex virus type 1 (HSV-1) or cytomegalovirus (CMV) antigens (operationally defined as virus-reactive helper T cells [HTL]). By using this limiting-dilution analysis technique, the peripheral blood of HSV-seropositive individuals was analyzed for the frequency of HSV antigen-reactive HTL and for the ability either to proliferate or to secrete detectable T-cell growth factors in conventional HSV antigen-stimulated lymphocyte cultures. We found that the magnitudes of the latter two responses did not correlate directly with the frequency estimates of HSV antigen-reactive HTL. The study was expanded to analyze both HSV and CMV reactivities within individuals. Those who were seropositive for HSV or CMV were found to have relatively high HTL frequencies for the viral antigens to which they were sensitized. However, those who were seronegative for one of the viruses often had HTL reactive with that virus in their peripheral blood. These latter HTL frequencies were highly variable and ranged from undetectable to quite prominent, even within the same individual at different times. In general, it was found that viral antigen-reactive serologic activity does not necessarily reflect the status of viral antigen-reactive cell-mediated immunity in humans and that viral antigen-induced T-cell responses may be unexpectedly complex, rather than absent, in individuals who are seronegative for a particular virus.