GALECTIN-3 REGULATES THE FORMATION OF GERMINAL CENTERS, PD-L1 EXPRESSION IN B CELLS, AND THE GENERATION OF LONG-LIVED ANTIBODY-SECRETING CELLS.

BECCARIA, CRISTIAN G; AMEZCUA VESELY, MARIA CAROLINA; FIOCCA VERNENGO, FACUNDO; GOROSITO SERRAN, MELISA; RAMELLO, MARIA CECILIA; TOSELLO BOARI, JIMENA; MONTES CAROLINA L; CAMPETELLA , OSCAR; ACOSTA RODRIGUEZ E V; GRUPPI, ADRIANA

Los Cocos

Jornada; LXI Reunión Anual de la sociedad argentina de Inmunología .; 2013

Sociedad Argentina de Inmunologia

We previously observed that B cells undergoing differentiation to antibody-secreting cells (ASC) downregulate the expression of Galectin-3 (Gal-3) and that inhibition of Gal-3 expression increases terminal B cell differentiation. In agreement, Gal-3 knock-out (KO) mice showed a higher frequency of IgM and IgG ASC and higher serum levels of IgM, IgG3 and IgG2a than wild type (WT) mice. The aim of this study was to identify the mediators through which Gal-3 regulates the generation of ASC. By flow cytometry, we observed that, in comparison to WT mice, Gal-3 KO mice showed higher percentage of Germinal Center (GC) B cells (identified as B220+ Fas+ GL-7+) and T Follicular Helper (Tfh) cells (identified as CD4+ PD-1+ ICOS+). Furthermore, both subsets were significantly increased in Gal-3 KO mice immunized with the T-cell independent antigen, NP-Ficoll. Consistent with these data, the presence of GC was observed by immunofluorescence in the spleen sections from both non-immunized and NP-Ficoll-immunized Gal-3 KO mice but not in sections from WT mice. Analyzing molecules involved in GC formation, we determined by flow cytometry that, when compared to WT B cells, Gal-3 KO B cells showed significantly decreased ICOSL expression and significantly increased PD-L1 expression while PD-L2 was equally expressed. To address whether the bone-marrow resident ASC from Gal-3 KO mice are short- or long-lived plasma cells, NP-Ficoll-immunized mice were treated with cyclophosphamide that depletes proliferating short-lived cells. We observed that the number of anti-NP IgM ASC remained unchanged in cyclophosphamide-treated Gal-3 KO mice, indicating that the ASC generated in Gal-3 KO mice are long-lived. Our results suggest that Gal-3 downregulates PD-L1 expression, and that the high PD-L1 expression in Gal-3 KO mice may be responsible for the enhanced response to NP-Ficoll resulting in increased GC generation and long-lived ASC differentiation.