Comparative studies on tumor and adjuvant (BCGcw)-induced nonspecific suppressor cells in rats.

Comparative studies on tumor and adjuvant-induced depression of in vitro mitogen responses were carried out using spleen cells obtained from syngeneic tumor bearing (TB) ACI rats or from rats which had been immunized with BCG cell walls attached to oil droplets (BCGcw). These in vitro studies demonstrated that: 1) the spleen cells from TB rats (TB-spleen cells) showed strongly depressed mitogen responses to concanavalin-A (Con-A), phytohemagglutinin-P (PHA-P) and lipopolysaccharide (LPS), 2) the mitogen response of lymph node cells from TB rats was slightly depressed, 3) the removal of plastic or nylon-wool adherent cells or phagocytic cells from TB-spleen cells resulted in a restoration of the mitogen response, 4) the Con-A response of normal spleen cells could be suppressed by the addition of TB-whole spleen cells, 5) the suppressor cell activity was not abrogated by the in vitro treatment with x-irradiation (2000 rads), 6) carbonyl-iron treated TB-spleen cells showed a normal level of mitogen response, and on addback to normal spleen cells no suppressive activity was detected in them. Similar results were observed when spleen cells were obtained from BCGcw immunized rats. These results suggest that in ACI rats tumor-induced nonspecific suppressor cells detected by in vitro assay are the same cell populations as BCGcw-induced nonspecific suppressor cells.