Galectin-8 Favors the Presentation of Surface-Tethered Antigens by Stabilizing the B Cell Immune Synapse

Abstract

SummaryComplete activation of B cells relies on their capacity to extract tethered antigens from immune synapses by either exerting mechanical forces or promoting their proteolytic degradation through lysosome secretion. Whether antigen extraction can also be tuned by local cues originating from the lymphoid microenvironment has not been investigated. We here show that the expression of Galectin-8—a glycan-binding protein found in the extracellular milieu, which regulates interactions between cells and matrix proteins—is increased within lymph nodes under inflammatory conditions where it enhances B cell arrest phases upon antigen recognition in vivo and promotes synapse formation during BCR recognition of immobilized antigens. Galectin-8 triggers a faster recruitment and secretion of lysosomes toward the B cell-antigen contact site, resulting in efficient extraction of immobilized antigens through a proteolytic mechanism. Thus, extracellular cues can determine how B cells sense and extract tethered antigens and thereby tune B cell responses in vivo.

Galectin-8 Enhances T cell Response by Promotion of Antigen Internalization and Processing

“…Since actin remodeling was shown to be involved in antigen pinocytosis of newly activated DCs (West et al, 2004), it is conceivable to pose that Gal-8-induced cell spreading could also participate in antigen uptake enhancement. In support of our findings, Obino et al (2018) have reported that exposure of specific B cells to particulate-antigen coated with Gal-8 increased their internalization capacity in vivo, reinforcing a role for extracellular Gal-8 in favoring the phagocytosis process as well.…”

“…Co-administration of recombinant Gal-8 and inactivated foot-and-mouth disease virus (FMDV) elicited a major protective antibody-mediated response in BALB/cJ mice, compared with the immunization with only viral antigen (Carabelli et al, 2017). In agreement with our findings, Obino et al (2018) showed that exogenously added Gal-8 is able to increase the number of antigen-specific germinal center B cells and T follicular helper cells. As a mechanism of action, these authors demonstrated that Gal-8 enhances particulate-antigen acquisition by B cells in vivo, promoting its presentation by stabilizing the B-immune synapse and enhancing B cell responses.…”

“…It has been previously shown that Gal-8 expression is incremented in inflammatory conditions in several tissues and cells (reviewed in Tribulatti et al, 2020), suggesting a role for the endogenous Gal in immune response and inflammation. Endothelial cells from both lymphatic and vascular vessels may constitute an important in vivo source for secreted Gal-8 in different peripheral tissues, with the potential to deliver lectin activity to immature APCs (Cattaneo et al, 2014;Cueni and Detmar, 2009;Obino et al, 2018;Stancic et al, 2011;Thijssen et al, 2008). Gal-8 is also found in primary and secondary lymphoid organs, and Gal-8 mRNA was observed specifically in the paracortical T zone area of lymph nodes (Obino et al, 2018;Tribulatti et al, 2007Tribulatti et al, , 2009.…”

Dopaminergic stimulation leads B-cell infiltration into the central nervous system upon autoimmunity

“…S6A-B). Furthermore, the APC ability of Drd3 +/+ and Drd3 -/-B-cells was evaluated in vitro using huMOG-coupled beads as antigen and CD4 + T-cells expressing a MOG-specific TCR as described before 54 . The results show that Drd3-deficiency in Bcells did not affect neither T-cell proliferation nor T-cell differentiation (Fig.…”

“…The extent of cell death was quantified using the ZAq Fixable Viability kit (Biolegend).In vitro Antigen presentation assays. huMOG protein or pMOG35-55 were coupled to glutaraldehyde-activated amino beads (40x10 6 beads for 20 g huMOR or pMOG) together with F(ab')2 anti-mouse-IgM fragments in equal concentrations, as previously described(Obino, 2018). Splenic CD19 + B-cells were sorted from Drd3 +/+ or Drd3 -/animals and then incubated with huMOG-or pMOG35-55-coated beads in a B-cell-to-bead ratio 1:1 for 5h at37°C to allows the uptake and processing of antigens.…”