| Summary: | 碩士 === 國立陽明大學 === 微生物及免疫學研究所 === 95 === Fc receptor-like proteins(FcRLs) are a group of proteins homologous to the receptors for the Fc portion of immunoglobulins (FcR), and their functions are still unknown. Human FcRL1 has 3 extracellular immunoglobulin-like domains, an acidic glutamic acid residue in the transmembrane region, and 2 ITAM-like morifs in cytoplamic region. Previous studies have shown that FcRL1 has the potential to serve as an activating coreceptor on B cells by FcRL1 ligation. In order to study the function of FcRL1, we have tried to identify its ligand. Using a fusion protein expressing FcRL1 extracellular domain fused to IgG1 Fc, we have screened cell lines, such as HL-60、THP-1、U937、HT-29、Ramos and RAW 264.7, and found that FcRL1 fusion protein did not bind to any one of them. In addition, we did not observe the association of FcRL1 fusion protein with mononuclear cells purified form peripheral blood, even after the cells are activated by PMA plus ionophore. These results imply that FcRL1 ligand(s) is not expressed on these cells. Furthermore, we have also looked for the membrane partner of FcRL1. when FcRL1 and CD19 were overexpressed in 293T cells, FcRL1 co-immunoprecipitated with CD19. the co-localization of FcRL1 and CD19 is also seen on the surface of 293T cells by confocal microscopy. These data demonstrated that FcRL1 may associate with CD19. The interaction between FcRL1 and CD19 may be mediated by the extracellular domain of FcRL1 because the glutamic acid in its transmembrane or the intracellular region of FcRL1 was not essential for the association. Therefore, FcRL1 may associate with CD19 and serve a coreceptor in the initiation of B cell receptor signaling.
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