A selective inhibitor of the elicitation of immune-mediated reactions.

6-Chloro-17 alpha-hydroxypregna-1,4,6-triene-3,20-dione (CHP), a steroid having a progestin-type structure yet not having progestational activity, was found to exhibit moderate anti-inflammatory activity in a number of conventional tests for corticoid potency (e.g., thymolytic, granuloma, carrageenin edema). CHP was essentially equipotent, however, with cortisol in models of inflammation mediated via delayed hypersensitivity such as experimental allergic encephalomyelitis, adjuvant-induced arthritis, mouse skin graft, and mouse skin delayed hypersensitivity. In contrast to cortisol, which inhibits both 19-s and 7-s antibody formation, CHP does not diminish the number of cells producing either antibody.