The enhancement of avian NK cell cytotoxicity by thymulin is not mediated by the regulation of IFN-γ production

Preincubation with either thymulin or IFN-γ can enhance NK activity. In addition, overnight in vitro pre-treatment with thymulin and IFN-γ increases NK activity further than either treatment alone. It has been hypothesized that thymulin increases the responsiveness of immune cells to IFN-γ by either increasing the expression of IFN-γR or by increasing the production and/or secretion of IFN-γ. The effects of thymulin on IFN-γ production and secretion were examined in this study. While an overnight incubation with the polyclonal activator Con A increased the number of cells positive for intracellular IFN-γ, a similar incubation with thymulin produced no change in the percentages of cells labeling positive for intracellular IFN-γ when compared to the media control cells. In addition, IFN-γ was not secreted by splenocytes following an overnight incubation with thymulin, but increased secretion was induced by Con A stimulation. Taken together, these results suggest that thymulin does not increase IFN-γ production or induce IFN-γ secretion by avian splenocytes.