The effects of thymulin on macrophage responsiveness to interferon-γ

Abstract

The effect of in vivo and in vitro thymulin treatments on macrophage responsiveness to interferon-γ was evaluated in chickens. Seven-week-old chickens were treated with 0, 1, 10, or 100 ng thymulin per 100 g body weight. Abdominal exudate cells (AEC), a source of macrophages, were harvested and cultured in the presence of graded levels of recombinant chicken interferon-γ (ChIFN-γ). Responsiveness to ChIFN-γ was determined by measuring the induction of nitric oxide production. One and 2-day thymulin treatment at 10 and 100 ng per 100 g body weight doses significantly increased responsiveness to ChIFN-γ while 1 ng per 100 g body weight had no effect. Other experiments compared the effect of thymulin treatments in Cornell K strain chickens, having normal serum thymulin levels with sex-linked dwarf (SLD) chickens which are deficient in serum thymulin. The dose of thymulin treatment required to significantly increase responsiveness to ChIFN-γ differed between strains. Finally, the effect of direct in vitro thymulin treatments on macrophage responsiveness to ChIFN-γ was evaluated. There were no significant increases in responsiveness to ChIFN-γ between treatment groups within the macrophage cell line, HD-11, when cultured in the presence of 0–200 pg thymulin/ml. These data suggest that the effect of thymulin on AEC responsiveness to ChIFN-γ is indirectly mediated.