Activation of human peripheral blood T cells does not lead to increased P-glycoprotein expression.
The expression of P-glycoprotein (Pgp) on normal human lymphocytes, and its drug exclusion capacity, implies that Pgp might be involved in cytokine secretion. We used two-color flow cytometry to detect simultaneously Pgp expression and IL-2 accumulation in resting and mitogen-activated human lymphocytes. Among resting lymphocytes from five healthy donors less than 1% were Pgp+ as determined by reactivity with the anti-Pgp monoclonal antibody (mAb) 4E3. The percentage of Pgp+ lymphocytes increased to 3% after 24 hr of mitogenic stimulation that induced maximal production of cytoplasmic IL-2. The percentage of lymphocytes that coexpressed membrane Pgp and cytoplasmic IL-2 accounted for < 10% of the total IL-2 producing lymphocytes. Finally, mitogen-induced cytoplasmic IL-2 accumulation was enhanced by stimulation in the presence of monensin but not the Pgp functional inhibitor verapamil. Because mAb 4E3 detected lower than expected numbers of Pgp+ lymphocytes, we compared the binding of mAbs MRK16 and 4E3 concomitant with doxorubicin (DOX)-uptake by K562 and R7 tumor cells and purified CD8+ lymphocytes. The MRK16 mAb was found to be sensitive but not very specific (30%). In contrast, the sensitivity of 4E3 was equivalent to MRK16 (98%) and was highly specific (98.5%). There was also a positive association between DOX efflux and the level of Pgp expression as detected by 4E3 but not MRK16. Thus, human T cells do not markedly up-regulate their expression of functional Pgp molecules as detected by mAb 4E3 following activation, suggesting that Pgp does not play a major role in IL-2 secretion by activated T cells.
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Department of Pharmacology, University of Kentucky, Lexington, USA.
Gosland
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MP
Bartik
M M
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Schimmelpfennig
J
J
Kay
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NE
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis* / Q000276:immunology; D000911:Antibodies, Monoclonal; D000918:Antibody Specificity; D004317:Doxorubicin / Q000378:metabolism; D006801:Humans; D007376:Interleukin-2 / Q000096:biosynthesis*; D008213:Lymphocyte Activation; D008934:Mitogens / Q000494:pharmacology; D008985:Monensin / Q000494:pharmacology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D014700:Verapamil / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000911:Antibodies, Monoclonal; D007376:Interleukin-2; D008934:Mitogens; D004317:Doxorubicin; D008985:Monensin; D014700:Verapamil