These events include phosphorylation of the CD3ζ chain, ZAP70, and LAT 37. Moreover, the Scr-family kinase LCK is inhibited 38, 39 which leads to a modulation of the calcium signaling 39. Therefore, while the inhibition of LFA-1
accumulation by dexamethasone is probably mediated by the inhibition of L-plastin phosphorylation, the additional defective accumulation of the TCR/CD3 complex in dexamethasone-treated T cells might be due to the inhibition of TCR/CD3-induced tyrosine phosphorylation and calcium signaling by dexamethasone. In contrast to other actin-binding proteins, such as cofilin or Arp2/3, the expression of L-plastin is restricted to leukocytes and certain tumors 47, potentially making it a valuable target for immunosuppression. Supporting this assumption, Wang et al. 46 demonstrated that LPL−/− mice showed a less severe experimental autoimmune encephalomyelitis (EAE). Moreover, they found that Palbociclib in vivo L-plastin expression has an important role in delayed, but not immediate
allograft rejection in the murine system. Therefore, interference with L-plastin phosphorylation and/or functions may be a sophisticated approach to modulate T-cell immune responses in order to prevent transplant rejection or to treat T-cell-mediated autoimmune diseases in humans. Abs employed were specific for the following markers: CD3 (mouse mAks, clone OKT3 or SK3), CD2 (mouse mAb, clone 3PT2H9, kindly provided by S. F. Schlossman, Dana Farber Cancer Institute, Boston, MA, USA), CXCR4 (R&D Systems, Wiesbaden-Nordenstadt, Germany) CD28 (CD28.2), and CD3-PerCP, LFA-1 (CD18-FITC, CD18-PE or CD11a-FITC), MEK inhibitor CD28-PE (mouse mAb, BD Biosciences, Heidelberg, Germany). The CD3-PeTxR Ab was purchased from Caltag (Buckingham, UK) and the actin antiserum from Sigma-Aldrich (Hamburg, Germany). The GFP Ab was from Clontech. Unconjugated anti-mouse and horseradish peroxidase-conjugated anti-rabbit Abs were purchased from Dianova (Hamburg,
Germany). The L-plastin polyclonal antiserum was produced against recombinant L-plastin protein 8. Phalloidin-AlexaFluor647 and Hoechst33342 was from Invitrogen (Darmstadt, Germany). Dexamethasone was purchased from Calbiochem (Bad Soden, Germany) and Ru486 (mifepristone) was from Sigma-Aldrich. All inhibitors and drugs were reconstituted Thiamet G in DMSO. Thus, the respective controls in the experiments were performed as solvent controls with the relevant concentration of DMSO. In the titration experiment, the highest concentration of DMSO was used as solvent control. Human PBMCs were obtained by Ficoll-Hypaque (Linaris, Wertheim-Bettingen, Germany) density gradient centrifugation of heparinized blood from healthy volunteers upon approval by the local ethics committee. T cells were subsequently isolated with magnetic associated cell sorting using pan T-cell negative isolation kit II (Miltenyi Biotec, Bergisch Gladbach, Germany) 5.