How proteoglycan receptors affect antigen cross-presentation and immunity

Topic Intracellular pathogens are some of the most successful mammalian parasites. They have evolved many tricks to avoid host detection and our body often struggles to clear them. One important method for their elimination by the immune system is antigen cross-presentation. Here, exogenous antigen is routed from the endocytic MHC-II presentation pathway into the pathway used for presentation of endogenous cytosolic components (MHC-I pathway). The fate of exogenous antigen that enters the endosomal route has been shown to be determined by what endocytic receptors are engaged upon its uptake by professional antigen presenting cells. Carbohydrate pattern receptors on such cells route it into either the classical MHC-II pathway or into MHC-I cross-presenting endosomes, but how this decision is made is poorly understood. Current tools do not allow for the elucidation of their pattern recognition properties and the effect this has on cross-presentation. Approach Here I propose to chemically modify a rigid inert scaffold protein with defined carbohydrate arrays, such that a library of probes for carbohydrate pattern receptors is obtained. With this library, the carbohydrate pattern-binding properties of these receptors can be studied. The probes will be fused to a peptide which has the ability to restore activity of an inactive form of beta-galactosidase (alpha-complementation). This complementation strategy will permit tracking of the escape of internalized antigens from endosomes, the first step in cross-presentation into the MHC-I pathway. The inactive beta-galactosidase will be introduced into model antigen presenting cell-like cell lines or in primary cells and cross-presentation and T cell priming will be evaluated. Importance Using the stage-specific probes envisioned I hope to elucidate what glycan patterns best engage these MHC-I/MHC?II targeting receptors and what effects their specific engagement has on cross-presentation. This will aid the understanding of immune activation by cross-presentation and its role in intracellular pathogen clearance. Keywords cross-presentation, protein modification, carbohydrate-lectin interaction, glycoprotein synthesis