Fc receptor-like 5 promotes B cell proliferation and drives the development of cells displaying switched isotypes.
The biological roles of B cell membrane proteins in the FCRL family are enigmatic. FCRL proteins, including FCRL5, were shown to modulate early BCR signaling, although the subsequent, functional consequences of receptor engagement are poorly understood. We found that FCRL5 surface protein itself was induced temporarily upon BCR stimulation of human, naive B cells, indicating precise control over timing of FCRL5 engagement. Cross-linking of FCRL5 on cells induced to express FCRL5 enhanced B cell proliferation significantly. This enhancement required costimulation of the BCR and TLR9, two signals required for optimal proliferation of naive B cells, whereas T cell help in the form of anti-CD40 and IL-2 was dispensable. In addition, we found that FCRL5 stimulation generated a high proportion of cells displaying surface IgG and IgA. Optimal development of cells expressing switched isotypes required T cell help, in addition to stimuli found necessary for enhanced proliferation. Surprisingly, cells that developed upon FCRL5 stimulation simultaneously displayed surface IgM, IgG, and IgA. Cells expressing multiple Ig isotypes were described in hairy cell leukemia, a disease in which FCRL5 is overexpressed. Enhanced proliferation and downstream isotype expression upon FCRL5 stimulation could reflect a physiological role for FCRL5 in the expansion and development of antigen-primed B cells. In addition, FCRL5 may promote growth of malignant cells in hairy cell leukemia and other FCRL5-expressing tumors.
Division of Monoclonal Antibodies, Center for Drug Evaluation and Research, Food and Drug Administration, Silver Spring, Maryland 20993, USA.
Jessica
J
Dement-Brown
Christopher S
CS
Newton
Tomoko
T
Ise
Bazarragchaa
B
Damdinsuren
Satoshi
S
Nagata
Mate
M
Tolnay
D017951:Antigen Presentation / Q000502:physiology; D000940:Antigenic Variation / Q000276:immunology; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism; D002454:Cell Differentiation / Q000276:immunology*; D049109:Cell Proliferation; D006801:Humans; D007070:Immunoglobulin A / Q000096:biosynthesis; D007074:Immunoglobulin G / Q000096:biosynthesis; D007132:Immunoglobulin Isotypes / Q000502:physiology*; D007075:Immunoglobulin M / Q000096:biosynthesis; D011947:Receptors, Antigen, B-Cell / Q000096:biosynthesis; D011956:Receptors, Cell Surface / Q000235:genetics / Q000502:physiology*; D011961:Receptors, Fc; D015398:Signal Transduction / Q000276:immunology
C432367:FCRL5 protein, human; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D007132:Immunoglobulin Isotypes; D007075:Immunoglobulin M; D011947:Receptors, Antigen, B-Cell; D011956:Receptors, Cell Surface; D011961:Receptors, Fc