Purification of a product from Salmonella typhimurium with the ability to inhibit mitogen-induced proliferation of murine splenic T-lymphocytes.

We attempted to purify a substance that inhibits mitogen-induced proliferation of murine splenic T-lymphocytes from Salmonella typhimurium. The soluble fraction of a suspension of bacteria disrupted by sonication was chromatographed serially on Mono Q HR, Superdex 200 HR and HiLoad Superdex 75 p.g. columns. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that the purified active substance migrated as a single band corresponding to a molecular mass of 87 kDa. We designated the purified substance S. typhimurium-derived inhibitor of T-cell proliferation (STI), which, at 0.2 microgram/ml and above, inhibited proliferation and augmented CD25 expression of phytohemagglutinin-stimulated murine splenic lymphocytes. These findings suggested that the immunosuppression induced by Salmonella infection may be attributable to STI.