Tumour-induced suppressor macrophages in rats: differences in their suppressive effects on the Con A and PHA responses.

Spleen cells obtained from ACI rats bearing a syngeneic hepatoma (9098) (TBR spleen cells) showed a strongly depressed mitogen responses to concanavalin A (Con A) and to phytohaemagglutinin-P (PHA) at various concentrations of the tested mitogens. The activity of suppressor cells in TBR spleens was demonstrated in mixtures with normal spleen cells where a marked depression of the mitogen response was observed. The properties of tumour-induced suppressor cells were adherent to plastic or nylon wool, phagocytic, and radioresistant (maybe macrophages). The Con A response of TBR spleen cells was more completely restored than was the PHA response after the removal of adherent or phagocytic cells. The suppression when TBR spleen cells (2,000 rad) were added to normal spleen cells at 0, 24, and 45 h after culture initiation was greater in the PHA response than in the Con A response. The PHA assay appeared to be more sensitive method than the Con A assay for the detection of suppressor cell activity in tumour bearing rats.