Humoral Factors Involved in the Mechanism of Reactivity of the Microplate Leukocyte Adherence Inhibition Assay

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Abstract
To study If specific antigen(s)-induced adherence inhibition is due to direct cell contact or mediated by a soluble factor, spleen cells and enriched populations of B-cells and T-cells from normal C57B1/6J mice and mice bearing progressively growing MCA-38 tumors were incubated with MCA-38 tumor antigen(s) and control B-16 melanoma antigen(s) for one hour at 37d`C. The supernatants of these cultures were harvested and evaluated for their ability to induce adherence inhibition of normal peritoneal cells. Supernatants of MCA-38 sensitized B-cells but not T-cells could induce adherence inhibition of normal peritoneal cells. Furthermore, supernatants of MCA-38 sensitized spleen cells could not induce adherence inhibition of normal peritoneal cells, despite the fact that these cells can directly undergo specific antigen(s)-induced adherence inhibition. However, the sensitized spleen cells, after removal of the supernatant, were less adherent than comparable cells incubated with- media alone, suggesting that the reactive cell within the spleen cell population adsorbed the soluble mediator as it was being generated. Affinity chromatography studies revealed that the biologically active soluble mediator contained IgG. Gel filtration studies indicated that the soluble mediator had a molecular weight greater than 190,000 daltons. Thus, in this murine tumor model, leukocyte adherence inhibition is dependent upon the interaction between sensitize B-cells and specific tumor antigen(s) to produce a soluble mediator and is an antibody-mediated phenomenon.