Role of T-cells in the mechanism of reactivity of the microplate leukocyte adherence inhibition assay.

To characterize the role of mononuclear cells in the microplate leukocyte adherence inhibition assay, enriched populations of T-cells, B-cells, macrophages, and a nylon wool-adherent fraction consisting of B-cells and macrophages were prepared by a two-stage adherence procedure from spleen cells of normal C57BL/6J mice and mice bearing progressively growing murine colon adenocarcinoma 38 (MCA-38) tumors. These studies indicate that the reactive cell undergoing specific antigen-induced adherence inhibition was present in the macrophage fraction. This cell was programmed to undergo specific antigen-induced adherence inhibition by an MCA-38-sensitized B-cell. An enriched population of MCA-38-sensitized T-cells but not normal T-cells abolished the in vitro leukocyte adherence inhibition response of MCA-38-reactive cells. Pretreatment of the MCA-38-sensitized T-cell fraction with anti-Thy 1:2 serum and complement but not anti-immunoglobulin and complement or carbonyl iron to selectively deplete macrophages abolished the regulatory effect of the MCA-38-sensitized T-cell fraction. MCA-38-sensitized T-cells could prevent MCA-38-sensitized B-cells from programming normal macrophages in vitro but could not abolish the leukocyte adherence inhibition response of presensitized macrophages. Temporal studies of suppressor T-cell activity were performed throughout different phases of progressive tumor growth. Suppressor T-cell could be detected as early as 4 days post-MCA-38 tumor cell inoculation and persisted throughout MCA-38 progressive tumor growth. Titration studies of suppressor T-cells revealed the need for 4 times the number of MCA-38-sensitized T-cells from small tumor bearers (Day 4) in comparison to large tumor bearers (Day 20) to achieve the same degree of suppression. Thus, in the MCA-38 system, sensitized T-cells programming of normal macrophages. This negative regulatory influence increased in magnitude with the progressive growth of the MCA-38 tumor.