Positive and negative immunoregulation of normal and tumor-bearing mouse T cell blastogenesis

Abstract

Using the mixed lymphocyte reaction (MLR) as a correlate of cell-mediated immunity, an examination was made of positive and negative blastogenic immunoregulation by syngeneic peritoneal macrophages (MΦ) and splenic T cells from tumor-bearing mice (TBM). As analysis of T cell proliferative response progressed an intricate pattern of immunoregulatory checks and balances unfolded involving both MΦ and TBM cells. In their capacity as regulators, MΦ acted, not only to enhance MLR reactivity, but to inhibit it. Results indicated that: i) MΦ regulation was a concentration dependent phenomena -- high concentrations of MΦ (or their supernatants) inhibited MLR reactivity, while low doses enhanced MLR reactivity; ii) inhibition occurred via a non-toxic, heat stable, nondialyzable (and therefore non-thymidine) factor; iii) enhancement occurred via a heat labile nondialyzable factor. Since normal MΦ possessed a factor which, in high concentrations, inhibited T cell blastogenesis, tests were run to determine if the MLR hyporeactivity of T cells from TBM could be attributed to a unique tumor-induced inhibitory MΦ. Contrary to expectations, TBM MΦ supernatants, when compared to their normal counterparts on a volume-to-volume basis. showed an increased (not decreased) ability to enhance MLR reactivity. In light of results showing TBM MΦ enhancement of MLR reactivity, T cell hyporeactivity in TBM was explained after observation of the following dual regulatory mechanism of suppression: i) on a purely quantitative basis, the high in vivo concentration of MΦ in spleens of TBM inhibits spleen cell response to alloantigen; ii) there also exists a population of mildly nylon wool adherent tumor-induced splenic T cells which elaborate a soluble factor capable of overriding any MΦ enhancing effect. In their capacity as regulators, tumor-induced splenic T-cells act, both to enhance and inhibit MLR reactivity. Whereas MΦ regulation is concentration dependent, in the case of the T cell regulator, regulation is based, not upon the relative concentration of the regulator cell, but upon the level of responder cell activity, i.e. MΦ-depleted MLR cultures (showing minimal proliferation) were enhanced by regulator TEM T cell addition, while MΦ augmented MLR cultures or PHA stimulated cultures (with a high rate of blastogenesis) were inhibited by the same concentration of TBM regulator cells. Centering around more stringent biophysical and biochemical characterization of MΦ supernatants, the latest work has resulted in the biochemical separation of MΦ supernatants into inhibitor and enhancing components. Using anion exchange chromotography and slab gel electrophoresis, inhibitor and enhancing factors have been separated by charge. Treatment of MΦ with indomethacin did not abrogate release of inhibitor factor, suggesting that it was not prostaglandin. Enhancing factor, obtained from MΦ sonicates as well as supernatants, could be distinguished from lymphocyte activating factor by its inability to induce a thymocyte PHA response. Thus, analysis of regulation in the cell-mediated immune system has resulted in the elucidation of a most elaborate scheme of immunoregulation involving both MΦ and T cells.