FCRL6 receptor is a more recently identified representative of the FCRL family. We generated a panel of mouse mAbs to baculovirus-derived recombinant FCRL6 protein. The clone 7B2 was found to specifically recognize a 63kDa protein expressed preferentially on the surface of CD8 T and CD56 NK cells in human peripheral blood and spleen. The clone 7B2 reacts with FCRL6 in Western blotting, FACS, and immunohistochemistry. In the T cell lineage, FCRL6 functions in antigen-experienced cells. Mitogenic stimulation of PB leukocytes in vitro resulted in an abrogation of the FCRL6 gene expression. We found a significant decrease in the FCRL6 gene expression in peripheral T cells of patients with certain autoimmune and blood diseases, and its upregulation at the late stages of HIV infection. Study of the FCRL6 association with signaling molecules showed its ability to recruit SHP-1, SHP-2, SHIP-1, and SHIP-2 phosphatases, and also adaptor protein Grb2 through phosphorylated cytoplasmic tyrosines. The current results demonstrate inhibitory potential of FCRL6 and suggest its possible involvement in modulation of CTL effector functions in various immune disorders.
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