N-linked glycosylation is a central regulatory factor that influences the immune system in varied and profound ways, including leukocyte homing, T cell receptor signaling and others. Moreover, N-glycan branching has been demonstrated to change as a function of infection and inflammation. Our previous findings suggest that complex-type N-glycans on the class II major histocompatibility complex play an important role in antigen selection within antigen presenting cells (APCs) such that highly branched N-glycans promote polysaccharide (glycoantigen, GlyAg) presentation following Toll-like receptor 2 (TLR2)-dependent antigen processing. In order to explore the impact of N-glycan branching on the myeloid-derived APC population without the confounding problems of altering the branching of lymphocytes and non-hematopoietic cells, we created a novel myeloid-specific knockout of the β-1,2-N-acetylglucosaminyltransferase II (Mgat2) enzyme. Using this novel mouse, we found that the reduction in multi-antennary N-glycans characteristic of Mgat2 ablation had no impact on GlyAg-mediated TLR2 signaling. Likewise, no deficits in antigen uptake or cellular homing to lymph nodes were found. However, we discovered that Mgat2 ablation prevented GlyAg presentation and T cell activation in vitro and in vivo without apparent alterations in protein antigen response or myeloid-mediated protection from infection. These findings demonstrate that GlyAg presentation can be regulated by the N-glycan branching pattern of APCs, thereby establishing an in vivo model where the T cell-dependent activity of GlyAgs can be experimentally distinguished from GlyAg-mediated stimulation of the innate response through TLR2.

Typhoid fever caused by Salmonella enterica serovar (S.) Typhi differs in its clinical presentation from gastroenteritis caused by S. Typhimurium and other non-typhoidal Salmonella serovars. The different clinical presentations are attributed in part to the virulence-associated capsular polysaccharide (Vi antigen) of S. Typhi, which prevents phagocytes from triggering a respiratory burst by preventing antibody-mediated complement activation. Paradoxically, the Vi antigen is absent from S. Paratyphi A, which causes a disease that is indistinguishable from typhoid fever. Here, we show that evasion of the phagocyte respiratory burst by S. Paratyphi A required very long O antigen chains containing the O2 antigen to inhibit antibody binding. We conclude that the ability to avoid the phagocyte respiratory burst is a property distinguishing typhoidal from non-typhoidal Salmonella serovars that was acquired by S. Typhi and S. Paratyphi A independently through convergent evolution.

Here we identified a population of bone marrow neutrophils that constitutively expressed the transcription factor RORγt and produced and responded to interleukin 17A (IL-17A (IL-17)). IL-6, IL-23 and RORγt, but not T cells or natural killer (NK) cells, were required for IL-17 production in neutrophils. IL-6 and IL-23 induced expression of the receptors IL-17RC and dectin-2 on neutrophils, and IL-17RC expression was augmented by activation of dectin-2. Autocrine activity of IL-17A and its receptor induced the production of reactive oxygen species (ROS), and increased fungal killing in vitro and in a model of Aspergillus-induced keratitis. Human neutrophils also expressed RORγt and induced the expression of IL-17A, IL-17RC and dectin-2 following stimulation with IL-6 and IL-23. Our findings identify a population of human and mouse neutrophils with autocrine IL-17 activity that probably contribute to the etiology of microbial and inflammatory diseases.

Capsular polysaccharides are common virulence factors of extracellular, but not intracellular bacterial pathogens, due to the antiphagocytic properties of these surface structures. It is therefore paradoxical that Salmonella enterica subspecies enterica serovar Typhi, an intracellular pathogen, synthesizes a virulence-associated (Vi) capsule, which exhibits antiphagocytic properties. Here, we show that the Vi capsular polysaccharide has different functions when S. Typhi interacts with distinct subsets of host phagocytes. The Vi capsular polysaccharide allowed S. Typhi to selectively evade phagocytosis by human neutrophils while promoting human macrophage phagocytosis. A screen of C-type lectin receptors identified human DC-SIGN as the receptor involved in macrophage binding and phagocytosis of capsulated S. Typhi. Consistent with the anti-inflammatory activity of DC-SIGN, purified Vi capsular polysaccharide reduced inflammatory responses in macrophages. These data suggest that binding of the human C-type lectin receptor DC-SIGN by the Vi capsular polysaccharide contributes to the pathogenesis of typhoid fever. IMPORTANCE Salmonella enterica subspecies enterica serovar Typhi is the causative agent of typhoid fever. The recent emergence of S. Typhi strains which are resistant to antibiotic therapy highlights the importance of vaccination in managing typhoid fever. The virulence-associated (Vi) capsular polysaccharide is an effective vaccine against typhoid fever, but the role the capsule plays during pathogenesis remains incompletely understood. Here, we identify the human C-type lectin receptor DC-SIGN as the receptor for the Vi capsular polysaccharide. Binding of capsulated S. Typhi to DC-SIGN resulted in phagocytosis of the pathogen by macrophages and induction of an anti-inflammatory cytokine response. Thus, the interaction of the Vi capsular polysaccharide with human DC-SIGN contributes to the pathogenesis of typhoid fever and should be further investigated in the context of vaccine development.