The unexpected role of the nurse shark pancreas as a secondary immune organ 2227

Abstract Description Cartilaginous fishes (sharks, skates, chimeras) are the oldest extant vertebrate lineage to possess an adaptive immune system founded on Ig-based receptors. The shark spleen has long been known to function as a secondary lymphoid organ (SLO), while B cell selection was recently shown to occur within the well-organized B cell follicles residing in the splenic white pulp. Given that sharks (and other exotherms) lack lymph nodes and prior studies have shown many shark organs possess at least some immune function, we hypothesized that some of these organs may also function as SLOs to help monitor and protect the periphery. Here we investigated the nurse shark pancreas using a combination of immunofluorescent microscopy and RNAscope in situ hybridization to determine if it also functions as an SLO. We identified B cell follicles within the pancreas that exhibited many of the hallmarks of B cell selection previously found in nurse shark splenic follicles. Also, we showed that antigen-specific Ig is generated by the shark pancreas following immunization. Together, our data supports the designation of nurse shark pancreas as an SLO. Importantly, distribution of SLO function among organs, as observed here, provides a means by which adaptive immune surveillance of the periphery can be successfully achieved in vertebrate lineages that emerged prior to the evolution of lymph nodes. Funding Sources Supported by T32AI095190 Topic Categories Veterinary and Comparative Immunology (VET)