Expression of recombinant human ICOS and in vitro characterization of its bioactivity on B lymphocytes.

Inducible costimulator (ICOS) is a novel costimulatory molecule expressed in activated T cell and has critical regulation effect on special immune response. In this study, the cDNA encoding human ICOS was cloned from activated tonsil cells via RT-PCR, and was expressed in E. coli on pET28 expression vector. The recombinant ICOS protein expressed from E. coli showed a molecular weight of 14 kD on SDS-polyacrylamide gel electrophoresis and was further confirmed by Western blot. In presence of IL-10, the purified rhICOS significantly increased in vitro B cell growth stimulated by pokeweed mitogen (PWM), and enhanced the secretion of IgG from B cells.