Description

B-cell antigen receptor expression governs signaling potential and protection from apoptosis

Kanutte Huse^1,2, Cara Wogsland³, Hannah Polikowsky⁴, Kirsten Diggins⁴, Jillian Wise^1,2, Erlend B. Smeland^1,2, Jonathan Irish^3,4, June Myklebust^1,2

¹Centre for Cancer Biomedicine, University of Oslo, Oslo, Norway; ²Department of Cancer Immunology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway; ³Department of Pathology, Microbiology and Immunology, and ⁴Department of Cancer Biology, Vanderbilt University, Nashville, TN, United States

Mature B cells depend on expression of a signaling-capable B-cell antigen receptor (BCR) for survival. However, the exact role of antigen-induced and tonic BCR signaling in fate decisions like survival and differentiation during human germinal center (GC) reaction is not fully known. viSNE analysis of 27-dimensional mass cytometry data was used to identify and characterize B-cell subsets present throughout the germinal center reaction. Next, fluorescens phospho-flow was used to measure signaling responses induced by FITC-conjugated anti-IgM, enabling direct comparison of signaling responses in B-cell subsets according to stage, isotype, and per-cell expression of IgM. Before controlling for isotype and level of BCR stimulation, human GC B cells were observed to have weaker BCR signaling responses compared to naïve and memory B cells. This result was attributed to the observations that 1) BCR expression was significantly lower in GC B cells, and 2) BCR engagement (measured by per-cell binding of anti-IgM-FITC) was correlated with the degree of subsequent SYK, BLNK, PLCγ and SFK phosphorylation. After controlling for isotype and per-cell BCR expression level, potentiated BCR signaling was observed in GC B cells. Similarly, degree of caspase-3 cleavage in cells cultured in vitro was directly compared to BCR-expression level. Spontaneous apoptosis was inversely correlated with the level of BCR expression in GC B cells. These results indicate that BCR expression levels govern the strength of human GC BCR signaling and protection from apoptosis, suggesting an important role in the GC reaction.