Galectin-3 binds highly galactosylated IgG1 and is crucial for the IgG1 complex mediated inhibition of C5aReceptor induced immune responses.

Changes in the glycosylation of immunoglobulins have been shown to modulate immune homeostasis and disease pathology. In this sense it has been shown that highly galactosylated but not agalactosylated IgG1 immune complexes (ICs) inhibit C5aR-mediated pro-inflammatory immune responses via the assembly of FcγRIIB-Dectin-1 receptor complexes. In this study we demonstrated that Galectin-3, a galactose-binding lectin that is known to cross-link proteins on cell-surfaces via binding their N-glycans, bound to highly-galactosylated, but not agalactosylated IgG1. Further, Galectin-3 was essential for the IC-mediated inhibition of C5a-induced neutrophil chemotaxis in vitro. Taken together our results indicate that Galectin-3 mediates the interaction of ICs with the FcγRIIB-Dectin-1 receptor complex for delivering immunoregulatory signals to inhibit C5aR-mediated immune responses.