REVERSAL OF MACROPHAGE-AUGMENTED MLR REACTIVITY BY TUMOR-INDUCED SPLENIC SUPPRESSOR T-CELLS AND THEIR SOLUBLE FACTOR(S)

Augmenting concentrations of macrophages or their supernatants failed to reverse T[thymus-derived]-cell hyporeactivity in tumor-bearing mice (TBM). Serial passaging over nylon wool columns depleted TBM spleen cells of a mildly adherent tumor-induced suppressor cell and restored mixed lymphocyte reaction (MLR) reactivity to the purified TBM T cell population. The tumor-induced suppressor cell was extensively plated to remove macrophages and characterized as a T cell by its anti-Thy 1 serum sensitivity. This suppressor T cell, when added to normal T cells, abrogated all enhancing effects caused by addition of macrophages. Suppressor T-cell inhibition was non-contact dependent, since suppressor T cell supernatants inhibited MLR activity in T cells treated with enhancing concnetrations of macrophage supernatants. Tumor-induced T cell debilitation is apparently a reversible phenomenon, mediated not by macrophages but by soluble factor(s) from a nonphagocytic, mildly adherent, suppressor T cell.