| Summary: | 碩士 === 國立陽明大學 === 微生物及免疫學研究所 === 106 === Fc receptor like protein (FcRL) is a group of receptor proteins with homologous sequence to the Fc receptors. FcRL1 has three extracellular Ig-like domains, one transmembrane region (TM) containing a negatively charged glutamic acid, and two immunoreceptor tyrosine-based activation motif (ITAM)-like motifs in the intracellular region. FcRL1 can serve as a co-receptor to B cell receptor (BCR), and after co-ligation with IgM, FcRL1 enhances B cell proliferation and intracellular Ca2+ concentration; however, the physiological function of FcRL1 in B cell activation remains unclear. To test the role of FcRL1 in BCR-mediated B cell activation, we established four FcRL1 knockdown cell lines. At a suboptimal concentration, anti-IgM stimulation did not change CD69 expression or CXCL10 secretion in 3 out of 4 FcRL1 knockdown cell lines. In addition, we confirmed our previous findings that FcRL1 co-ligation enhanced the phosphorylation of CD19, the recruitment of PI3K to CD19, and the phosphorylation on Y1217 of PLC2. Because FCRL1 has a glutamic acid in the TM region, we tested if it interacts with IgM which contains positively polar amino acids in the TM. Using co-immunoprecipitation assay, we found that IgM did not bind FcRL1. We also checked the intracellular proteins associated with FcRL1 and found that Lyn was associated with FcRL1 before and after FcRL1 ligation. The results of this study verify the mechanisms by which FcRL1 enhanced B cell activation. Furthermore, knockdown of FcRL1 in human B cell lines did not affect CD69 expression and chemokine production after cross-linking of IgM.
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