Determination of human T cell activity in response to allogeneic cells and mitogens: An immunochemical assay for γ-interferon is more sensitive and specific than a proliferation assay

Abstract

T lymphocytes proliferate and secrete lymphokines in response to allogeneic cells, mitogens and other stimuli. Cell proliferation as measured by [ 3H]thymidine ([ 3H]Tdr) incorporation into DNA has been routinely used to determine T cell responses in research and clinical laboratories. We have compared the sensitivity of an immunoradiometric assay (IRMA) for human γ-interferon (IFN-γ) (Chang et al., 1984), with that of the conventional [ 3H]Tdr incorporation assay in the measurement of T cell responses to antigens and mitogens in culture. Peripheral blood mononuclear cells (PBMs) were incubated in the presence and absence of phytohemagglutinin (PHA) or mononuclear cells from another individual for various periods of time. The culture fluids were collected for determining IFN-γ and the cells were assayed for [ 3H]Tdr incorporation. Results of measurements were expressed in terms of stimulation indices. Both IFN-γ secretion and thymidine incorporation were measurable in mixed lymphocyte cultures after incubation for 3 days, and in PHA stimulated culture after 24 h of incubation. The stimulation indices reflecting increased γ-interferon were found to be more pronounced and more consistent than those of [ 3H]Tdr incorporation.