BASIC FIBROBLAST GROWTH-FACTOR AND INTERLEUKIN-4 AND INTERLEUKIN-6 STIMULATE THE RELEASE OF IFN-GAMMA BY INDIVIDUAL NK CELLS

Both the secretory and cytotoxic activity of natural killer (NK) cells are known to be regulated by such cytokines as interleukin-2 (IL-2) and interferon-gamma (IFN-γ). In the present study we have used the reverse hemolytic plaque assay to investigate either the direct effects of the protein kinase activator, phorbol myristate acetate (PMA), or exposure to recombinant human interleukins 2, 4, and 6 (IL-2, IL-4, and IL-6) tumour necrosis factor α (TNF-α) and basic fibroblast growth factor (bFGF) on the release of IFN-γ by individual, immunoidentified NK cells isolated from peripheral blood. This sensitive immunoassay was adapted and coupled with immunocytochemistry not only to immunophenotype and enumerate cells secreting IFN-γ in a given cell population, but also to quantify the amount of this cytokine released per individual cell. These studies have confirmed mononuclear cells with the morphology of large granular lymphocytes and the immunophenotype of CD3-/CD16+ NK cells to be the predominant source of spontaneously released IFN-γ in vitro. In contrast to this, fewer than 2% of the CD3+ T cells secreted detectable levels of this cytokine during the assay, irrespective of the stimulus applied. Whilst TNF-α had no significant effect on IFN-γ release by NK cells, a 6-hr exposure to IL-2 or PMA stimulated an increase in the amount secreted per single cell. Furthermore, bFGF and interleukins 4 and 6 elicited a marked, dose-dependent stimulation of IFN-γ secretion by this cell type. However, exposure to these cytokines did not alter the number of cells capable of releasing detectable levels of IFN-γ during the assay. These studies demonstrate that (i) both the spontaneous and stimulated release of IFN-γ by NK cells can be visualized and quantified at the single-cell level using this sensitive immunoassay, and (ii) bFGF and interleukins 2, 4, and 6, but not TNF-α, are potent stimulants of IFN-γ secretion by CD3-/CD16+ NK cells. © 1991.