Suppression of immune anti-tumor lymphocytes by macrophages of advanced tumor bearing rats, across a cell impermeable membrane.

In experiments using double and triple chamber cultures it was demonstrated that suppressive macrophages from advanced T8-Guérin tumor (diameter 5--6.5 cm) bearing rats produced a dialysable factor which suppressed the killer activity of lymphocytes from non-advanced T8-Guérin tumor (diameter 0.5--0.7 cm) bearing rats, as well as from nonadvanced h 18R tumor bearing rats and from Ehrlich ascites bearing mice, against T8-Guérin ascitic cells and, respectively, against h 18R ascitic and Ehrlich ascitic cells. The dialysable suppressive factor inhibits immune lymphocytes but has no effect on the lymphotokin itself already produced.