Reptilian immune systems are believed to rely more heavily on the innate response than the adaptive response. Past research on reptilian immune systems has indicated that natural antibodies (NAbs) play an important role in fighting antigens as the first responder and initiating the innate immune response. However, there is a gap in research on NAbs in reptiles as there is little data on how they may influence parasite prevalence in reptiles. Furthermore, no studies have examined NAbs at mucosal sites, which represent an important point of entry for parasites. We investigated NAbs in male and female red-eared slider turtles (Trachemys scripta) in order to begin to fill this gap in our understanding. Plasma and mucosal samples were collected from T. scripta to determine total immunoglobulin levels in relation to intestinal parasite load, which was determined from fecal samples. We also determined antibody levels to various antigens to examine if NAbs are present in mucosal samples and how levels compare to plasma NAbs. In female turtles, parasite intensity decreased with increasing host age and mucosal antibody levels. We also found that the levels of antibodies that bind to a novel antigen and an antigen they are likely to have encountered were significantly related in both plasma and mucosal samples, indicating a NAb response. This study contributes to our understanding of how reptiles may rely on a broad innate response that allows them to resist potential pathogens while potentially avoiding some negative consequences of immunosenescence.

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