| Summary: | 碩士 === 國立陽明大學 === 微生物及免疫學研究所 === 96 === Fc receptor-like 2 (FcRL2), a member of the Fc receptor-like molecules (FcRLs), is a B cell-specific receptor with unknown function. There are one immunoreceptor tyrosine-based activation motif (ITAM) -like motif and two immunoreceptor tyrosine-based inhibition motifs (ITIMs) located on its intracellular region. To characterize FcRL2 expression at different stages of B cells, we used specific anti-FcRL2 monoclonal antibody and real-time RT-PCR to examine FcRL2 expression in human B cells. In the tonsils, we found that FcRL2 protein is expressed mainly on a subpopulation of naïve and pre-germinal center B cells. In the peripheral blood, FcRL2 protein is expressed on a subpopulation of both naïve and memory B cells, and FcRL2 mRNA is also detected in both subsets of B cells. The surface expression of FcRL2 was reduced 1 day after cell activation and then up-regulated from day 2 to day 3 in the blood B cells. FcRL2 mRNA was reduced about 80% and remained the same level until 72 hr after activation. To test if FcRL2 defines a subpopulation of naïve B cells in the peripheral blood, we characterized the properties of FcRL2+ B cells. FcRL2+ naïve B cells contain higher levels of surface IgM and IgD. The levels of CD69, CD5, or CD86 are similar in FcRL2+ and FcRL2- naïve B cells. Interestingly, after stimulated with fixed Staphylococcus aureus, FcRL2+ cells showed a much stronger proliferative response than FcRL2- cells did. The stronger proliferative response of FcRL2+ cells was also observed by the stimulation of TLR2 ligand, Pam3CSK4. However, there was no significant difference when both subsets were stimulated with anti-CD40 antibody plus IL-2 and IL-10. Our preliminary result showed that FcRL2+ cells secreted higher levels of IgM while FcRL2- cells produced more IgG. Taken together, FcRL2 may be used as a marker to define a subpopulation in naïve B cells. We hypothesized that FcRL2+CD27- cells are likely human B-1 B cells which have not been well-characterized before.
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