Gamma-interferon production by human low-density lymphocytes induced by T-cell mitogens

Low-density lymphocytes prepared by Percoll fractionation of human peripheral blood mononuclear leucocytes were found to produce large amounts of interferon-gamma (IFN-gamma) in response to different T-cell mitogens in the absence of macrophages, whilst higher density lymphocytes were strongly dependent on the presence of macrophages for significant IFN-gamma production. The addition of macrophages to the low-density lymphocytes made little difference to their IFN-gamma production. Subsets of the low-density lymphocytes prepared by rosetting with sheep red blood cells produced markedly less IFN-gamma than did the original population; IFN-gamma production could be largely restored by recombining the two low-density fractions. This suggests that IFN-gamma production by low-density lymphocytes whilst macrophage-independent does require co-operation between different cell types. The low-density lymphocytes were enriched for cells bearing the Leu 11 and OKM1 antigens, and for natural killer cell activity. The rosetting fraction was enriched for OKT3 antigen-bearing cells, and the non-rosetting fraction was enriched for Leu 11, OKM1 antigen-bearing cells. Depletion of B cells (surface Ig-positive) by nylon-wool chromatography had no effect on IFN-gamma production by low-density lymphocytes.