CHARACTERIZATION OF CELLS THAT SUPPRESS CYTOTOXIC ACTIVITY OF T LYMPHOCYTES .1. QUANTITATIVE MEASUREMENT OF INHIBITOR CELLS

Abstract

Target cell [C3H and SADZ mouse sarcoma cells] lysis by sensitized cytolytic [mouse] T [thymus-derived] lymphocytes (CTL) may be conveniently quantitated by 52Cr release. By fitting to the formula, P (% specific release) = 100 (1-e-N.alpha.t), .alpha., the relative frequency of CTL in N lymphoid cells was obtained. Using a microassay, an unexpected decrease in lysis was observed whenever effectors obtained from a graft-vs.-host reaction were tested at high concentrations. This inhibition was not observed with CTL generated by a mixed lymphocyte culture reaction. Inhibition could not be explained by nonspecific mechanical crowding, reutilization of released isotope, suppression of release from dead target cells or the particular strain combination and target used. By modifying the formula to allow suppression of CTL by a stochastic cell-cell interaction with a suppressor cell, P = 100 (1-e-Nate-n.gamma.) adequately fitted the data, where N.gamma. is proportional to inhibitor content. An 18-24 h incubation at 37.degree. C but not 4.degree. C allowed selective depletion or enrichment of inhibitors; in mixing experiments, parameters N.alpha.t and N.gamma. behaved stoichiometrically as independent cellular properties. The inhibitor was resistant to concentrations of [rabbit] anti-T cell (RAMB) serum + [guinea pig] complement which killed CTL. A similar inhibitor arose in vivo during an anti-tumor allograft response. The ability to quantitate CTL and inhibitor activities from titration curves provides a technique for studying the identity and mechanism of suppressor cells acting at the effector stage of cell-mediated immunity.