In Vitro Inhibition of Cellular Immune Responses by Benzodiazepines and Pk 11195 Effects on Mitogen-and Alloantigen-driven Lymphocyte Proliferation and on IL-1, IL-2 Synthesis and IL-2 Receptor Expression

Abstract

In vitro mitogen-driven lymphocyte proliferation tests (Con A, LPS) on murine lymph node and spleen cells revealed inhibition of T and B cell stimulation by different benzodiazepines and by PK 11195, with IC50 values in the low micromolar range. T cell responses as a consequence of recognition of alloantigens, as measured in mixed lymphocyte cultures (MLC), were affected in an analogous way. In all systems, agonists at peripheral type benzodiazepine receptors (Ro 5–4864 and the non-benzo-diazepine compound PK 11195) and diazepam which acts on both, central and peripheral type benzodiazepine receptors, were most potent; clonazepam, a central type agonist, proved about half as active. the central type antagonist Ro 15–1788 failed to antagonize the action of diazepam and clonazepam. Variations among cells from several congenic strains of mice were modest. Cytotoxicity could not be made responsible for drug effects. the most susceptible stage of mitogen-triggered T and B lymphocyte proliferation was found to be at incipience. Radioresistant, adherent spleen cells, upon LPS-stimulation formed only small amounts of the cytokine IL-1. Its release was affected only at very high drug concentrations. Similar small amounts of IL-1 were generated during MLC; in this case, the drugs were about 10times less potent than in mitogen-induced proliferation assays. Peripheral agonists were more active on IL-1 synthesis. Spleen cells stimulated with Con A and cultivated with the highest concentration of diazepam and clonazepam formed markedly greater amounts of IL-2 than those cultivated in medium, while at this concentration PK 11195 allowed no formation of the lymphokine. Flow cytometry revealed increased formation of IL-2R for 10-⁴M diazepam, Ro 5–4864 and PK 11195, with little difference to medium controls for other compounds and molarities. IL-2 formation during MLC was inhibited by central and peripheral agonists with IC50s in the micro-molar range. In presence of diazepam, these MLC cells displayed frequencies of IL-2R similar to those stimulated with Con A.