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-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 concentrations of macrophage supernatants. Thus it appears that tumor-induced T-cell debilitation is a reversible phenomenon, mediated not by macrophages but by soluble factor(s) from a nonphagocytic, mildly adherent, suppressor T cell.