The ratio of LILRB1/SHP-1 has been determined by densitometry

The ratio of LILRB1/SHP-1 has been determined by densitometry. incubation of activated T cells with OKT3/IL2 in the presence of HLA-G5-coated beads. B: The ration of p-CD3/Actin has been determined by densitometry.(TIF) pone.0022776.s002.tif (513K) GUID:?7148E5FC-2481-49D6-BE7C-31C1473218D6 Abstract Human leukocyte antigen G (HLA-G) is involved in regulating T-cell responses through its interaction with inhibitory receptors belonging to the immunoglobulin-like transcript family (ILT). In this context, we investigated the pathways involved in the control of cell-cycle entry of T cells following HLA-G interaction with its inhibitory receptor. We show that HLA-G acts through its conversation with the LILRB1 receptor expressed on T lymphocytes. Both HLA-G and LILRB1 antibodies block the inhibitory effect of HLA-G and restore T-cell proliferation. The conversation of HLA-G with T lymphocytes is usually associated with phosphorylation of SHP-2 phosphatase, but not SHP-1. In Rabbit Polyclonal to RPL40 addition, in activated T cells, their incubation with HLA-G is not associated with a decrease in the TCR or CD28 downstream pathways, but is usually associated with dephosphorylation of the mTOR molecule and p70S6K. In contrast, Akt, which acts upstream of mTOR, is usually not affected by HLA-G. The inhibition of SHP-2 by NSC-87877(5 M), a chemical inhibitor of SHP-2, or the use of siRNA, abrogates dephosphorylation of mTOR and impairs the overexpression of p27kip in the presence of HLA-G. Together, these results indicate that HLA-G is usually associated with activation of phosphatase SHP-2, which inhibits the mTOR pathway and favors the inhibition of the cell-cycle entry of human-activated T cells. Introduction Human leukocyte antigen G (HLA-G) participates in graft SID 26681509 tolerance and inhibits proliferation of allogenic T cells. HLA-G is usually a non-classical MHC class I molecule with a limited polymorphism and has restricted tissue distribution: it SID 26681509 is only expressed in physiological conditions in medullary thymic epithelial cells [1], in the cornea [2], and in extra-embryonic tissues. During pregnancy, HLA-G is usually expressed around the cytotrophoblast and is believed to inhibit maternal NK cell cytotoxicity, thus allowing development of the embryo [3]. During human-organ transplantation, HLA-G expression correlates with improved allograft acceptance [4]C[7] in cardiac, lung, combined liverCkidney, or kidney transplantations. em In vitro /em , HLA-G modulates the function of several immune effectors: it acts on natural killer cells (NK) by inhibiting their cytotoxicity [8]C[10] and their transendothelial-migration properties [11]. HLA-G also inhibits antigen-specific CD8+ T cell cytolytic function [12], [13], interacts with CD4 T cells and dendritic cells (DC), which are involved in the initiation of the CD4-cell activation cascade during the alloimmune response and favor the growth of regulatory T cells [14]. HLA-G suppresses CD4+ T cell proliferation in response to allogeneic stimulation [15]C[17] and promotes (Th2)-type responses. It also inhibits DC maturation [18], [19], thus increasing allogeneic skin-graft survival. The inhibitory mechanism of HLA-G on activated T cells remains controversial. HLA-G has been demonstrated to induced apoptosis of T cells activated by phytohemagglutinin (PHA) [20] and a fraction of PHA-activated CD8 cells through the Fas pathway, leading to activation of caspases [13], [21]. In contrast, we have observed that T cells activated through engagement of their T-cell receptor (TCR) are inhibited by HLA-G, but do not undergo apoptosis. This process is usually associated with inhibition of cell-cycle entry. HLA-G receptors on immune cells belong to the killer immunoglobulin-like receptor (KIR) [22] and immunoglobulin-like transcript (ILT) families [23], [24]. LILRB1 is mostly expressed on NK cells, and is also expressed intracellularly by most CD4 and CD8 T cells, and by a significant fraction at their surface [25], whereas LILRB4 is usually expressed on dendritic cells. This suggests that HLA-G can regulate their functions through its conversation SID 26681509 with these receptors. em In vitro /em , we have shown that this inhibitory properties of HLA-G depend on its conversation with LILRB1 at the cell surface of lymphocytes whereas the regulatory effect of HLA-G on DC is usually mediated by LILRB2 and LILRB1. CD85j (LILRB1) is usually a 110-kDa surface glycoprotein detected on the surface of NK and T-cell subsets, B cells, dendritic cells, and monocytes [1], [2]. CD85j includes four Ig-like C2 domains in its extracellular region, which interact with the alpha domain name of HLA-G and with UL18, a human cytomegalovirus (HCMV) protein homologous to HLA class I molecules [26], [27]. Its intracellular domain name contains four ITIM-like sequences [4] that have been exhibited in Jurkat cells to interact with phosphatase SHP-1 and thereby inhibit the phosphorylation of MAP kinases [28]. In addition, crosslinking of LILRB1 is usually.