FcRH1: an activation coreceptor on human B cells.
B-cell activation and differentiation is regulated through the coordinated function of a dynamic array of cell surface receptors. At different stages in their differentiation, human B cells may express one or more members of a large family of immunoglobulin Fc receptor homologs (FcRH) with regulatory potential. Among these newly identified transmembrane molecules, FcRH1 is unique in having 2 immunoreceptor tyrosine-based activation motif (ITAM)-like motifs in its intracellular domain. Here we used the Fab fragments of new monoclonal anti-FcRH1 antibodies and mRNA analysis to evaluate FcRH1 expression and function during B-cell differentiation. FcRH1 expression begins in pre-B cells, reaches peak levels on naive B cells, and is down-regulated after B cells are activated to begin to form germinal centers. This FcRH1 down-regulation coincides with dramatic enlargement of the pre-germinal center cells, cell cycle entry, and other overt signs of activation that include CD80 and CD86 up-regulation and immunoglobulin D (IgD) down-regulation. In vitro analysis indicates that ligation of FcRH1 leads to its tyrosine phosphorylation and to modest B-cell activation and proliferation. Concomitant FcRH1 ligation enhances B-cell antigen receptor (BCR)-induced Ca(2+) mobilization and proliferation. FcRH1 thus has the potential to serve as an activating coreceptor on B cells.
Leu
Chuen-Miin
CM
Division of Developmental and Clinical Immunology, University of Alabama at Birmingham, WTI378, Birmingham, AL 35294-3300, USA.
Davis
Randall S
RS
Gartland
Lanier A
LA
Fine
W David
WD
Cooper
Max D
MD
D000818:Animals; D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000276:immunology; D017209:Apoptosis / Q000502:physiology; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000502:physiology; D001483:Base Sequence; D002118:Calcium / Q000502:physiology; D002454:Cell Differentiation; D002460:Cell Line; D017931:DNA Primers; D006801:Humans; D051379:Mice; D016133:Polymerase Chain Reaction; D011961:Receptors, Fc; D011971:Receptors, Immunologic / Q000276:immunology*
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D017931:DNA Primers; C452186:FCRLA protein, human; D011961:Receptors, Fc; D011971:Receptors, Immunologic; D002118:Calcium