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Role of T-Cells in the Mechanism of Reactivity of the Microplate Leukocyte Adherence Inhibition Assay¹

Department of Surgical Oncology, Tumor Immunology Laboratory, Roswell Park Memorial Institute, Buffalo, New York 14263

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-cells 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 exert a negative regulatory influence by preventing B-cell programming of normal macrophages. This negative regulatory influence increased in magnitude with the progressive growth of the MCA-38 tumor.

¹ This work was supported in part by Grant CA22931 awarded by the National Large Bowel Cancer Project, National Cancer Institute, Department of Health, Education and Welfare.

² Present address: Department of Surgery, New Jersey Medical School, 100 Bergen St., Newark, N. J. 07103.

³ Present address: Department of Neurology, Johns Hopkins School of Medicine, Baltimore, Md. 21205.

⁴ To whom requests for reprints should be addressed.

Received 12/10/80. Accepted 7/15/81.