Fc Receptor–like 5 Expression Distinguishes Two Distinct Subsets of Human Circulating Tissue–like Memory B Cells

Abstract

Fc receptor–like (FCRL) 5 is a novel IgG binding protein expressed on B cells, with the capacity to regulate Ag receptor signaling. We assessed FCRL5 expression on circulating B cells from healthy donors and found that FCRL5+ cells are most enriched among atypical CD21−/lo/CD27− tissue-like memory (TLM) B cells, which are abnormally expanded in several autoimmune and infectious diseases. Using multicolor flow cytometry, FCRL5+ TLM cells were found to express more CD11c and several inhibitory receptors than did the FCRL5− TLM subset. The homing receptor profiles of the two TLM subsets shared features consistent with migration away from lymphoid tissues, but they also displayed distinct differences. Analysis of IgH V regions in single cells indicated that although both subsets are diverse, the FCRL5+ subset accumulated significantly more somatic mutations. Furthermore, the FCRL5+ subset had more switched isotype expression and more extensive proliferative history. Microarray analysis and quantitative RT-PCR demonstrated that the two TLM subsets possess distinct gene expression profiles, characterized by markedly different CD11c, SOX5, T-bet, and RTN4R expression, as well as differences in expression of inhibitory receptors. Functional analysis revealed that the FCRL5+ TLM subset responds poorly to multiple stimuli compared with the FCRL5− subset, as reflected by reduced calcium mobilization and blunted cell proliferation. We propose that the FCRL5+ TLM subset, but not the FCRL5− TLM subset, underwent Ag-driven development and is severely dysfunctional. The present study elucidates the heterogeneity of TLM B cells and provides the basis to dissect their roles in the pathogenesis of inflammatory and infectious diseases.

Atypical memory B cells in human chronic infectious diseases: An interim report

“…These results suggest the possibility of a functional heterogeneity among aMBCs differentiating within an individual. Relevant to these observations, Li et al (29) reported that FcRL5 expression distinguished two subsets of aMBCs in healthy individuals that have distinct gene expression profiles. FcRL5 + aMBCs expressed more CD11c and inhibitory receptors as compared to FcRL5 − aMBCs and responded poorly to multiple stimuli.…”

“…T-bet has been detected in MBCs and plasmablasts in healthy adults, but at lower levels than other T-bet + lymphocytes (60). T-bet expression in circulating CD21 − CD27 − has been described in healthy adults, in whom CD21 − CD27 − B cells are a relatively rare population (8, 29) and T-bet + , CD11c + B cells appear to be expanded in healthy elderly individuals (61). But whether CD21-CD27 − T-bet + B cells in healthy adults represent the same population of CD21 − CD27 − T-bet + aMBCs that are expanded in settings of chronic infections remains unclear.…”

T-bet+ B cells are induced by human viral infections and dominate the HIV gp140 response

“…Interestingly, CD85j lo B cells, the CD21 -Tbet -counterpart of our cells of interest, were more similar to the antigen-inexperienced subsets (naive, transitional; Figure 4B), suggesting these are relatively unrelated to T-bet hi CD85j hi cells and confirming the previously described population heterogeneity within the TLM phenotype (CD21 -CD27 -; ref. 40). We next set out to establish a functional connection between T-bet and the transcriptional targets it might regulate in T-bet hi population because they can be identified and sorted via negative selection, avoiding potential ligation effects of CD85j-specific antibodies.…”

T-bet-expressing B cells during HIV and HCV infections

“…TLM B cells tend to be enriched for polyreactivity and are expanded in several autoimmune diseases, suggesting this population may contribute to pathology [14,92,95]; however, polyreactivity has also been hypothesized to enhance antiviral humoral immunity and may be a beneficial property during antiviral responses [96]. Lastly, with regard to the aforementioned points, it becomes difficult to extrapolate from TLM B cell findings as most TLM B cell studies are complicated by CD21 − CD27 − population heterogeneity: we and others identified significant differences between the T-bet + and T-bet − subsets that together comprise the TLM B cell population [13,97], but studies have generally assessed the TLM population as a whole. Accordingly, additional studies are necessary to further define the stimuli that best activate T-bet + TLM B cells, the relationship of this population during HIV infection to its counterpart in non-inflamed individuals, and any potential role for T-bet + TLM B cells during HIV.…”