We identified B cells as a major source for rapid, innate-like interleukin 17 (IL-17) production in vivo in response to Trypanosoma cruzi infection. IL-17+ B cells exhibited a plasmablast phenotype, outnumbered TH17 cells and were required for optimal response to this pathogen. Using both murine and human primary B cells, we demonstrate that exposure to parasite-derived trans-sialidase in vitro was sufficient to trigger modification of the cell surface mucin, CD45, leading to Btk-dependent signaling and IL-17A or IL-17F production via an ROR-γt and AHR-independent transcriptional program. Our combined data suggest that generation of IL-17+ B cells may be an unappreciated feature of innate immune responses required for pathogen control or IL-17-mediated autoimmunity.

Highlights d PoEMs, PDPN-expressing macrophages, localize in the proximity to tumor lymphatics d PDPN activates b1 integrin, mediating PoEM binding to GAL8-expressing lymphatics d PDPN in PoEMs promotes extracellular matrix remodeling d Pdpn deletion in macrophages reduces breast tumor lymphangiogenesis and lymphoinvasion

The intracellular parasite Trypanosoma cruzi, the etiological agent of Chagas disease, sheds a developmentally regulated surface trans-sialidase, which is involved in key aspects of parasite-host cell interactions. Although it shares a common active site architecture with bacterial neuraminidases, the T.cruzi enzyme behaves as a highly efficient sialyltransferase. Here we report the crystal structure of the closely related Trypanosoma rangeli sialidase and its complex with inhibitor. The enzyme folds into two distinct domains: a catalytic β-propeller fold tightly associated with a lectin-like domain. Comparison with the modeled structure of T.cruzi trans-sialidase and mutagenesis experiments allowed the identification of amino acid substitutions within the active site cleft that modulate sialyltransferase activity and suggest the presence of a distinct binding site for the acceptor carbohydrate. The structures of the Trypanosoma enzymes illustrate how a glycosidase scaffold can achieve efficient glycosyltransferase activity and provide a framework for structure-based drug design.

Gals (galectins) are proteins with glycan affinity that are emerging as mediators of atherosclerosis. Despite the similarities in structure and sequence, different Gals exert distinct effects on their target cells. We have shown that Gal-1 triggers platelet activation, suggesting a role for Gals in thrombus formation. Since Gal-8 is expressed upon endothelial activation and also contributes to inflammation, to understand further the role of these lectins in haemostasis, we evaluated the effect of Gal-8 on human platelets. Gal-8 bound specific glycans in the platelet membrane and triggered spreading, calcium mobilization and fibrinogen binding. It also promoted aggregation, thromboxane generation, P-selectin expression and granule secretion. GP (glycoprotein) αIIb and Ib-V were identified as putative Gal-8 counter-receptors by MS. Studies performed using platelets from Glanzmann's thromboasthenia and Bernard-Soulier syndrome patients confirmed that GPIb is essential for transducing Gal-8 signalling. Accordingly, Src, PLC2γ (phospholipase C2γ), ERK (extracellular-signal-regulated kinase) and PI3K (phosphoinositide 3-kinase)/Akt downstream molecules were involved in the Gal-8 signalling pathway. Gal-8 fragments containing either the N- or C-terminal carbohydrate-recognition domains showed that activation is exerted through the N-terminus. Western blotting and cytometry showed that platelets not only contain Gal-8, but also expose Gal-8 after thrombin activation. These findings reveal Gal-8 as a potent platelet activator, supporting a role for this lectin in thrombosis and inflammation.