Nitric oxide synthase: Expression of the endothelial, Ca2+/calmodulin-dependent in human B and T lymphocytes

Nitric oxide (NO) is a pleiotropic mediator of a variety of cellular processes such as vasorelaxation, neurotransmission, anti cytotoxicity. We studied the expression of the human endothelial, Ca2+/calmodulin-dependent NO synthase (NOS) isoform (ccNOS) in highly purified human lymphocytes from peripheral blood and tonsillar tissue. ecNOS mRNA was detected in IgD(-) or IgD(-) B cells. peripheral blood and tonsillar cells. Upon stimulation. ecNOS mRNA expression decreased in all these lymphocyte subpopulations. Germinal center T cells and follicular dendritic cells did not express ecNOS mRNA either in an unstimulated or in a stimulated state. ecNOS expression by human lymphocytes was further substantiated by its mRNA detection in lymphoid cell lines such as Raji, Daudi, and Jurkat. By the use of a specific monoclonal antibody, ecNOS was shown to be present in T cells front peripheral blood and in various germinal center cells of frozen tonsillar sections. These data are the first to demonstrate the expression of the endothelial ccNOS at mRNA and protein level in human lymphocytes.