[Alpha 1-antitrypsin/lymphocyte interactions: cytofluorometry study]

Purified alpha 1-antitrypsin (alpha 1AT) was previously shown to prevent primary antibody response and lymphocyte DNA synthesis. We have reported that radiolabelled alpha 1-AT could bind to human lymphocytes and inhibit surface proteolytic activity. However, the radiolabelling method brings no information on the eventual heterogeneity of alpha 1AT distribution among the population nor on the presence of alpha 1AT on untreated lymphocytes. In this report, we have investigated these two points using indirect fluorescence followed by flow cytofluorometric analysis. The presence of alpha 1AT was revealed on a variable percentage of untreated peripheral blood and tonsillar lymphocytes. The incubation of cells with additional alpha 1AT induced an increase of the percentages of fluorescent lymphocytes. This binding was specific and could be inhibited by pretreatment with the protease inhibitor tosyl-L-phenylalanine-chloromethyl-ketone (TPCK) (2 X 10(-5)M). Furthermore, TPCK and EDTA (3 mM) could displace alpha 1AT initially bound to the lymphocyte surface.