Fc receptor-like 4 (FCLR4) and Fc receptor-like receptor 5 (FCRL5) define and control human atypical memory B cells [RNA-Seq]

We performed NGS on Ig heavy chain V sequences amplified from RNA obtained from human tonsillar B cell subsets. From these NGS data, we reconstructed ongoing B cell responses as lineage trees, providing crucial in vivo developmental context. Each memory subset typically maintained its lineage, denoting mechanisms enforcing their phenotypes. FCRL4-FCRL5+ cells were the most represented memory subset in lineage trees, indicating robust participation in ongoing responses. Affinity maturation of both FCRL4-FCRL5+ and FCRL4+FCRL5+ atypical memory cells was stalled in chronic streptococcus infection, conceivably due to negative feedback from IgG immune complexes. We propose that FCRL4 and FCRL5 function as sensors of immune complexes, thus controlling atypical memory B cell responses. Overall design: B cells were isolated from human tonsil cells and FACS-sorted into subsets on the basis of CD19-, IgD CD38, FCRL4, and FCRL5 surface expression. CD38-IgD- memory cells were sorted into three subsets: FCRL4- FCRL4+ (F5), FCRL4- FCRL5- (DN) and FCRL4+ FCRL5+ (DP). In addition, IgD+CD38- naïve/IgD+ memory cells(Naive), IgD-D38+ GC cells(GC) , and IgD-CD38++ plasmablasts (PB) subsets were also sorted . IgM, IgA or IgG HC variable regions were separately amplified from each sorted subset and these amplified samples were subjected to deep sequencing.