A suppressive lymphokine derived from Ts clone 13G2 is IL-10

CD8+ suppressor T cell (Ts) clone 13G2 produced a soluble suppressive lymphokine, termed the T-cell growth inhibitory factor (TGIF), which suppressed the proliferation of type 1 helper T-cell (Th1) clone 3D20 cells. The specific activity of TGIF was concentrated approximately 66,000-fold (3.7 x 10(6) U/mg of protein) by sequential chromatography from the culture supernatant of 13G2 cells. The suppressive activity of the highly purified TGIF toward the proliferation of Th1 cells was neutralized by the anti-IL-10 monoclonal antibody, and was replaced by IL-10. We detected the IL-10 molecule in the highly purified TGIF by using immunoblotting with the anti-IL-10 antibody. A PCR study showed that mRNA of IL-10 was expressed in the 13G2 cells. From these results, we conclude that TGIF produced from CD8+ T-cell clone 13G2 was IL-10. The suppressive activity of the whole supernatant was also completely blocked by the anti-IL-10 antibody, suggesting that IL-10 could play an important role in immune suppression by Ts cells.