CD21 and FCRL5 form a receptor complex with robust B-cell activating capacity.
In: International Immunology, Jg. 30 (2018-12-01), Heft 12, S. 569-578
Online
academicJournal
Zugriff:
The B-cell response to antigen is critically regulated by co-receptors. CD21 (complement receptor 2) amplifies the response to antigen linked to its ligands, specific C3 fragments. In contrast, human Fc receptor-like 5 (FCRL5), a novel IgG receptor, was reported to inhibit B-cell receptor (BCR) signaling. Here, we show that CD21 and FCRL5 physically associate, suggesting that immune complexes containing both C3 fragment and IgG could simultaneously engage the pre-assembled receptors. We found that activating signaling molecules such as CD19, active PLCγ2 and BTK were rapidly recruited to FCRL5 upon engagement, suggesting a novel activating function for FCRL5. We confirmed that FCRL5 through its ITIMs (immunoreceptor tyrosine-based inhibitory motif) inhibited BCR signaling in the absence of CD21 stimulation. In contrast, triple engagement of FCRL5, CD21 and the BCR led to a superior calcium response compared to CD21 and BCR co-stimulation, in both cell lines and tonsil B cells. Furthermore, the novel activating function was independent of established FCRL5 signaling motifs. While human peripheral B cells express either FCRL5 or CD21, we identified a sizable subset of tonsil B cells which co-express the two receptors. We propose that FCRL5 has dual signaling capacity, while CD21 co-engagement serves as molecular switch, converting FCRL5 from a negative to a positive co-receptor. In tissues, B cells that co-express FCRL5 and CD21 could robustly respond to IgG immune complexes loaded with C3 fragments. [ABSTRACT FROM AUTHOR]
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CD21 and FCRL5 form a receptor complex with robust B-cell activating capacity.
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Autor/in / Beteiligte Person: | Franco, Andrea ; Kraus, Zachary ; Li, Huifang ; Seibert, Naomi ; Dement-Brown, Jessica ; Tolnay, Mate |
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Zeitschrift: | International Immunology, Jg. 30 (2018-12-01), Heft 12, S. 569-578 |
Veröffentlichung: | 2018 |
Medientyp: | academicJournal |
ISSN: | 0953-8178 (print) |
DOI: | 10.1093/intimm/dxy052 |
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