Abstract
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.