In situ hybridization of interferon-gamma producing peripheral blood mononuclear cells.

Individual interferon-gamma (IFN-gamma) producing cells in activated human peripheral blood mononuclear cells (PBMC) were characterized by in situ hybridization using [35S]-labelled antisense RNA probes. The proportion of positive cells expressing IFN-gamma mRNA varied according to the substances used for stimulation. IFN-gamma mRNA expressed a relatively low percentage of 1-8% PBMC after a single stimulus with mitogens or OKT-3 antibody and 20-30% of the cells were identified to synthesize IFN-gamma mRNA after stimulation with PHA + P-MA + OKT-3 antibody. The expression of IFN-gamma mRNA and production of the lymphokine was dependent on accessory cells. If accessory cells were replaced by recombinant interleukin-1 (IL-1) plus interleukin-6 (IL-6), then T-cell proliferation to phytohaemagglutinin (PHA) could be partially restored and measurable amounts of IFN-gamma were detected. The addition of interleukin-2 (IL-2) or phorbol-12-myristate-13-acetate to T cells stimulated with PHA, IL-1 and IL-6 did not restore the production of IFN-gamma to an extent comparable to that produced by T cells stimulated in the presence of accessory cells. In further studies, depletion of T-cell subsets showed that CD3+, CD4+, CD8+, CD29+ and CD45RA+ cells were involved in IFN-gamma production after mitogenic stimulation. In conclusion, our data demonstrate that IFN-gamma production is dependent on signals from accessory cells and IFN-gamma is synthesized by only a small proportion of T cells, that did not belong to a unique population, characterized by conventional cellular surface antigens.