Intercellular communication in the immune system: differential expression of connexin40 and 43, and perturbation of gap junction channel functions inperipheral blood and tonsil human lymphocyte subpopulations

The distribution and function of connexins (integral membrane proteins asse mbled into gap junction intercellular communication channels) were studied in human lymphocyte subpopulations. The expression of mRNA encoding connexi ns in peripheral blood and tonsil-derived T, B and natural killer (NK) lymp hocytes was examined. Connexin43 (Cx43) mRNA was expressed in peripheral bl ood and tonsil lymphocytes, but Cx40 mRNA expression was confined to tonsil -derived T and B lymphocytes; Cx26, Cx32, Cx37 and Cx45 were not detected b y reverse transcription-polymerase chain reaction (RT-PCR). Western blot an alysis also demonstrated the presence of Cx40 and Cx43 proteins in T and B lymphocytes in a manner coincidental to the mRNA detection. Stimulation in vitro of T and B lymphocytes with phytohaemagglutinin (PHA) and lipopolysac charide (LPS), respectively, increased Cx40 and Cx43 protein expression. Fl ow cytometric analysis, using antibodies to extracellular loop amino acid s equences of connexins, confirmed the surface expression of connexins in all lymphocyte subpopulations. Assembly of connexins into gap junctions provid ing direct intercellular channels linking attached lymphocytes was demonstr ated by using a dye transfer technique. The exchange of dye between lymphoc ytes was inhibited by a connexin extracellular loop mimetic peptide and alp ha-glycyrrhetinic acid, two reagents that restrict intercellular communicat ion across gap junctions. Dye coupling occurred between homologous and hete rologous co-cultures of T and B lymphocytes, and was not influenced by thei r stimulation with PHA and LPS. The connexin mimetic peptide caused a signi ficant decrease in the in vitro synthesis of immunoglobulin M (IgM) by T- a nd B-lymphocyte co-cultured populations in the presence or absence of stimu lation by PHA. The results identify connexins as important cell surface com ponents that modulate immune processes.