Using mass cytometry to identify novel B cell subsets in red meat allergy

Previous studies have identified a novel food allergy driven by IgE antibodies specific for galactose-α-1,3-galactose (alpha-gal), an oligosaccharide found in red meat. While it is known that B cells play an important role in allergy as the producers of IgE antibodies that drive the allergic response, little is known about the phenotype of these B cells. The number of markers used to identify the major human B cell subsets by flow cytometry has been limited to common B cell proteins and thus precludes high dimensional immune phenotyping of B cell subsets, including unique phenotypes present in allergic individuals. We have addressed this problem by using mass cytometry (CyTOF), which enables the simultaneous analysis of up to 40 markers in a single staining panel. Here we analyzed the expression of 23 cell surface markers in PBMCs from 19 alpha-gal-allergic patients and 20 non-allergic controls by CyTOF. Additionally, we combined our CyTOF data with clinical endpoints to identify markers that may correlate with allergic disease. Our data reveals substantial heterogeneity within major B cells subsets on an individual level. Furthermore, our analysis identifies a number of markers that vary significantly in their expression in allergic versus non-allergic B cells and correlate with serum alpha-gal IgE titers. We hypothesize that B cells with this phenotype play an important role in mediating alpha-gal allergy. These findings demonstrate the power of using CyTOF and analytical tools to extract a hierarchy from high dimensional cytometry data in an unsupervised manner to identify known B cell subsets as well as to find novel B cell populations that differ between alpha-gal allergic and non-allergic individuals.