Alloreactive cells generated by in vitro stimulation of C57BL/6 (H-2b) spleen lymphocytes with irradiated MOPC 315 or MOPC 104E (H-2d) cells were shown to lyse 51Cr-labeled myeloma targets at high effector:target ratios under conditions of maximal cell contact. After coculture at low effector:target ratios under conditions of inefficient cell contact, the alloreactive cells cause variable and frequently minimal lysis of myeloma targets but markedly suppress antibody secretion even by viable myeloma cells. The suppressor cells are radioresistant T cells lacking I-J subregion-encoded surface determinants; their precursors are insensitive to cyclophosphamide; suppression is H-2 specific and not mediated by secreted factors; and the suppression is blocked by Cytochalasin B, a known inhibitor of T cell-mediated cytolysis. These properties are typical of cytolytic T lymphocytes (CTL) and not of defined suppressor T cells, suggesting that inhibition of myeloma function probably represents a pre-lytic effect of the alloreactive CTL, although a CTL-like suppressor cell effect cannot be definitively excluded. These results are discussed with reference to the possible relationships between suppressor and cytolytic T lymphocytes.

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This work was supported by National Institutes of Health Grant AI 14478 from the United States Public Health Service.

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