Galectin-3 regulates germinal centers formation, autoreactive and long-lived antibody response

BECCARIA CG; AMEZCUA VESELY MC; FIOCCA VERNENGO F; GOROSITO SERRÁN M; RAMELLO MC; TOSELLO BOARI J; MUCCI J; CAMPETELLA O; MONTES CL; ACOSTA RODRIGUEZ EV; GRUPPI A

Congreso; LVII Reunión Anual de la Sociedad Argentina de Inmunología; 2014

We previously observed that B cells undergoing differentiation to antibody-secreting cells (ASC) downregulate the expression of Gal3 and that inhibition increases terminal B cell differentiation. In agreement, we observed that Gal3 knock-out (KO) mice showed a higher frequency of IgM and IgG ASC (p<0.05) and higher serum levels of IgM, IgG3 and IgG2a than wild type (WT) mice (p<0.001). By flow cytometry, we observed that Gal3KO showed higher % of plasma cells, Germinal Center (GC) B cells (B220+Fas+GL-7+; p<0.005), T Follicular Helper (Tfh) cells (CD4+ICOS+CXCR5+Foxp3-; p<0.05) and increased Tfh/Tfr ratio (p<0.05), in comparison to WT mice. Presence of GC was also observed by immunofluorescence in spleen sections from Gal3KO mice but not in WT mice. CD4+T cells from Gal3KO mice produced high amounts of INFg (p<0.05), IL-21 and IL-4 (p<0.005). This phenotype of Gal3KO is compatible with autoimmunity. Accordingly, 8 month-old Gal3KO mice presented higher % of spleen GC, Tfh and IFNg+ cells and increased antinuclear antibodies compared to WT controls. Using mixed bone marrow (BM) chimeric mice, generated with 50% BM from CD45.1 WT mice and 50% BM from CD45.2 Gal3KO mice, we observed GC B cell only in CD45.2+ cells indicating that absence of Gal3 in B cells mediates GC formation. Interestingly, B cells from Gal3KO mice expressed higher levels of CXCR4 (p< 0.005), suggesting that Gal3 could regulate this chemokine receptor, key molecule involved in the initial GC formation. Upon immunization with T-Independent and T-dependent Ags, Gal3KO mice presented higher levels of specific-IgM and IgG and higher frequency of ASC than immunized WT (p<0.05). Using cyclophosphamide, that depletes proliferating short-lived cells, we determined that Ag-specific ASC generated in Gal3KO mice are long-lived (p<0.05). Our results indicate that intracellular Gal3 is a negative regulator of the GC reaction and, therefore, its absence induces autoreactive and long-lived specific B cell response.