Cellular requirements for the suppression of leucocyte adherence inhibition reactions by serum factors from tumour-bearing mice.

Tumour-bearing mice produce circulating serum factors that block cell-mediated immunological reactions in vitro. The mechanism by which these specific suppressor factors (SF) block leucocyte adherence inhibition (LAI) was studied. It had previously been shown that the antigen-reactive effector cells in the LAI assay are Ly-1+ T cells. We have now found that Ly-2+, I-J+ cells are required in the reactive cell population to observe the blocking action of SF from serum. Tumour-bearer spleen cells (containing Ly-2+, I-J+ lymphocytes) reacted only with the specific tumour-related serum factor (SF1) and relevant tumour antigen, to produce a non-specific suppressor factor (SF2). Specificity studies were conducted with contact-sensitized mice: hapten-specific spleen cells reacted only with hapten-related SF1 and the relevant hapten, to produce a similar SF2. SF2 differed from SF1 in suppressing allogeneic as well as syngeneic cells, in suppressing populations depleted of Ly-2+, I-J+ cells, and in being unaffected by absorption with immobilized anti-I-J antibody. Gel-filtration of SF2 revealed two forms of differing MW (greater than 190,000 and 20,000-50,000).