Polyclonal activation of human peripheral blood lymphocytes by bacterial porins and defined porin fragments

Bacterial porins were isolated from Escherichia coli B and Salmonella typhimurium S 1135. The proteins were cleaved either by cyanogen bromide treatment or by enzymatic digestion into a variety of small fragments, and the compounds were characterized by SDS-polyacrylamide gel electrophoresis. Both the porins and the porin fragments constituted potent mitogens for human peripheral blood lymphocytes, comparable to the human B-lymphocyte activator pokeweed mitogen. In the cultures, B-lymphocytes were stimulated into immunoglobulin production, as measured by ELISA. In all experiments, the activity of the mitogens extracted from S. typhimurium was superior to that of the compound isolated from E. coli B. The well-defined porins constitute valuable tools for investigating the molecular mechanism of human lymphocyte activation.