Glycosylation of mucosal B cells modulates gut inflammation as a result of cytokine imbalance.

CUTINE, ANABELA M.; MOROSI, LUCIANO; MANSELLE COCCO, MONTANA; CAGNONI, ALEJANDRO J.; MARTINEZ ALLO, VERONICA; MORALES, ROSA; GATTO, SABRINA; MAY, MARÍA; RABINOVICH, GABRIEL A.; TOSCANO, MARTA A; MARIÑO, KARINA V.

Brisbane

Congreso; 19th International Congress on Mucosal Immunology; 2019

Society of Mucosal Immunology

The glycome of immune cells can regulate cellular processes relevant to immune tolerance and disease, in the context of inflammatory bowel diseases (IBD) it has been suggested that altered glycosylation of T cells is a key player regulating the development of inflammation. We hypothesized that inflammatory mediators in the gut could alter the glycome of mucosal B lymphocytes and plasma cells resulting in an altered B cell functionality in IBD.We investigated the glycome of mucosal B cells in the experimental model of DSS-induced chronic colitis in C57BL6j. We analyzed the surface glycophenotype of B cells and IgA+ plasma cells (IgA PC) isolated from the colonic lamina propria (cLP) using different biotinylated lectins that recognize specific glycoepitopes followed by flow cytometry. During the development of chronic colitis, the level of α2,6-linked sialic acid (α2,6sia), detected through binding of Sambucus nigra agglutinin (SNA), was diminished on the surface of B cells and IgA PC. SNA binding was abolished in IgA PCs from ST6Gal1 deficient mice, the glycosyltransferase that adds α-2,6sia to N-glycans, meaning that α2,6sia is restricted to N-glycans in these cells.To study the functional consequences of this alteration during inflammation we studied B cells from ST6Gal1-/- mice, as they mimic the aberrant glycophenotype observed during inflammation. We employed the chronic T cell transfer model of colitis in RAG2-/- mice and co-transferred colitogenic WT CD4+CD45RBhi T cells with WT or ST6Gal1-/- splenic B cells. Co-transfer of T cells with WT B cells reduced colonic T cell infiltration and inflammation, however, co-transfer with ST6Gal1-/- B cells resulted in higher inflammation compared to WT B cells measured by the histological inflammatory score. Additionally, we found lower amounts of both fecal IgA and IgA PCs in the colon of ST6Gal1-/- transferred mice. Thus, in this model α2,6sia on B cells exerts a regulatory role during colitis controlling T cell infiltration to the colon and promoting expansion of tolerogenic IgA PCs.Finally, to elucidate the role of the cytokine milieu in regulating α2,6sia of B cells and IgA PC we used an in vitro strategy; splenic B cells were differentiated with TGF-b, IL-5 and LPS to induce IgA PC differentiation and then the cells were incubated with pro and anti-inflammatory cytokines. We found that IFN-g, IL-4 and IL-17A induced α2,6 sialylation on IgA PCs and B cells as detected by an increase in SNA binding, whereas IL-5, IL-10, IL-6, TGF-b, TNF-a had no effect. In order to contextualize these findings, we measured colonic-cytokines in healthy and DSS-treated mice and found reduced levels of IL-17, a similar tendency for IL-4 and increased levels of IFN-g during DSS-induced colitis. Considering that IL-17 and IL-4 induce α2,6sia in vitro, we propose that downregulation of these cytokines could be in part responsible for the decrease in α2,6sia on PCs during chronic colitis.These results suggest that α2,6-linked sialic acid exerts a regulatory role on B cells during IBD and provide a potential mechanism for the modulation these glycan residues on inflamed intestinal tissues.