Tumour-induced suppression of delayed-type hypersensitivity in the mouse: independence of cyclophosphamide-sensitive suppressor cells.

Delayed-type hypersensitivity (DTH) responses to sheep red blood cells and ovalbumin were markedly reduced in mice receiving viable Landschütz ascites tumour cells at the time of immunization. Similar inhibitory effects were observed in control immunized animals when cell-free ascitic fluid or tumour bearer serum was administered together with antigen at the challenge site. Normal mouse serum exhibited much less pronounced inhibitory activity over the range of concentrations tested. High-dose cyclophosphamide (Cy) prior to immunization enhanced DTH responses to both antigens in normal mice. However, in animals also given tumour or soluble tumour-associated material, the immunosuppressive effect which had been observed in non-Cy-treated controls was preserved. It is concluded that the observed suppression of DTH is not dependent on Cy-sensitive T suppressor cells or on the presence of immunosuppressive factors during induction of the immune response.