Expression of vasoactive intestinal peptide in lymphocytes: a possible endogenous role in the regulation of the immune system.

Experimental evidence is accumulating showing that vasoactive intestinal peptide (VIP) acts as an immunoregulatory peptide. Findings from our laboratory and others indicate that cells of the immune system are able to produce VIP. We have detected immunoreactivity for VIP in lymphocytes by immunohistochemical methods at specific locations of both central and peripheral lymphoid organs. Double immunofluorescence staining and flow cytometry analysis indicate that both T and B lymphocytes contain VIP that has been proved to be mostly VIP 1-28 by high-performance liquid chromatography and radioimmunoassay. VIP has been also demonstrated by 'in situ' hybridization and reverse transcription followed by polymerase chain reaction. We have also detected induction of VIP in splenic lymphocytes after mitogenic stimulation. Lymphocytes should be sensitive to the endogenously produced VIP because we have also detected VIP receptor expression in different populations of lymphocytes. All this evidence indicates that VIP is an endogenous autocrine modulator of immune function.