Detection of intracellular expression and secretion of interferon‐γ at the single‐cell level after activation of human T cells with tetanus toxoid in vitro

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Abstract
Activation of Tcells results in intracellular expression and secretion of cytokines such as interferon (IFN)‐γ. Here we have used three different assays for determination of IFN‐γ in tetanus toxoid‐ or mitogen‐activated human T cell cultures. Two of these assays [intracytoplasmic immunofluorescence and enzyme‐linked immuno spot assay (ELISPOT)] determined the expression and secretion of IFN‐γ at the single‐cell level while the third assay enzyme‐linked immunosorbent assay (ELISA) measured IFN‐γ secreted into the culture supernatant. Comparison of all three tests revealed a good correlation between the ELISPOT assay and the ELISA, whereas expression of intracellular IFN‐γ showed a qualitative but not a quantitative correlation with the latter. Both the immunospot assay and the immunofluorescence may be used to detect approximate numbers of specific T cells even when present at low frequencies. With the use of the immunospot assay antigen‐specific T cells could be detected even in the absence of detectable IFN‐γ in the culture supernatants. However, the ELISA assay should be more convenient for screening large clinical material.