Ketotifen-induced histamine release, inhibition of histamine secretion and modulation of immune response

In concentrations above 0.1 mM Ketotifen (KT) induced secretion of histamine from rat and mouse mast cells, but not from human basophils. In the same concentrations KT inhibited histamine release from rat mast cells, induced by compound 48/80 and histamine release from basophils, induced by anti-IgE-antibodies and concanavalin A. At low concentration (0.05-0.005 mM) KT enhanced in vitro phytohemagglutinin-induced proliferative response of human lymphocytes. The immunostimulating effect of KT was confirmed in vivo. In doses 0.18-1.4 micrograms/mouse KT significantly increased the number of antibody-producing cells (APC) in spleens of mice immunized by sheep red blood cells (SRBC). KT stimulated both IgM- and IgG-immune response to SRBC.