Antibodies Encoded by FCRL4-Bearing Memory B Cells Preferentially Recognize Commensal Microbial Antigens

FCRL4, a low-affinity IgA Ab receptor with strong immunoregulatory potential, is an identifying feature of a tissue-based population of memory B cells (Bmem). We used two independent approaches to perform a comparative analysis of the Ag receptor repertoires of FCRL4 and FCRL4 Bmem in human tonsils. We determined that FCRL4 Bmem displayed lower levels of somatic mutations in their Ag receptors compared with FCRL4 Bmem but had similar frequencies of variable gene family usage. Importantly, Abs with reactivity to commensal microbiota were enriched in FCRL4 cells, a phenotype not due to polyreactive binding characteristics. Our study links expression of the immunoregulatory FCRL4 molecule with increased recognition of commensal microbial Ags.