The effects of thymulin on macrophage responsiveness to interferon-gamma.

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