J. Drach et al., INVOLVEMENT OF P-GLYCOPROTEIN IN THE TRANSMEMBRANE TRANSPORT OF INTERLEUKIN-2 (IL-2), IL-4, AND INTERFERON-GAMMA IN NORMAL HUMAN T-LYMPHOCYTES, Blood, 88(5), 1996, pp. 1747-1754
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.