INVOLVEMENT OF P-GLYCOPROTEIN IN THE TRANSMEMBRANE TRANSPORT OF INTERLEUKIN-2 (IL-2), IL-4, AND INTERFERON-GAMMA IN NORMAL HUMAN T-LYMPHOCYTES

The physiological role of the multidrug resistance P-glycoprotein (P-g p), which is expressed by normal human T lymphocytes, is still largely unknown. To investigate whether or not P-gp is involved in the transp ort of cytokines, peripheral blood lymphocytes were stimulated with ph ytohemagglutinin (PHA) in the absence or presence of P-gp inhibitors, and concentrations of cytokines (interleukin-2 [IL-2], IL-4, IL-6, int erferon-gamma [IFN-gamma]) in the supernatants of these cultures were quantitated by enzyme-linked immunosorbent assay. P-gp inhibitors incl uded verapamil (Ver), tamoxifen (Tmx), and the P-gp specific monoclona l antibody UIC2. Release of IL-2 was significantly suppressed by these inhibitors at concentrations that were also effective in blocking eff lux of Rhodamine-123 from normal T lymphocytes. IL-2 mRNA expression i n lymphocytes was not different between PHA control and the cultures w ith P-gp inhibitors. Ver and Tmx did not interfere with T-cell activat ion as determined by CD25 and CD69 expression. In a nonhematological m odel, the P-gp expressing HCT-8 adenocarcinoma cell line, exogenously added IL-2 was shown to exert an inhibitory effect on P-gp mediated Rh odamine-123 efflux. In addition, transepithelial transport of IL-2 by electrophysiologically tight and polarized HCT-8 monolayers was examin ed. A time-dependent flux of IL-2 across dense monolayers, which was p artially inhibited by Ver, was observed. We also investigated whether or not P-gp inhibitors suppressed release of other cytokines produced by activated T cells (IL-4, IL-6, IFN gamma). Release of IL-4 and lFN- gamma was significantly inhibited by Ver, Tmx, and UIC2; however, rele ase of IL-6 remained unaffected. These data show P-gp mediated transme mbrane flux of IL-2 in T lymphocytes and HCT-8 cells. We conclude that P-gp participates in the transport of cytokines (IL-2, IL-4, and lFN- gamma) in normal peripheral T lymphocytes. (C) 1996 by The American So ciety of Hematology.