Red-Eared Slider Turtles Lack Response to Immunization with Keyhole Limpet Hemocyanin but Have High Levels of Natural Antibodies

While the specific humoral response of reptiles is slow and does not typically increase in titer or binding affinity upon secondary immunization, reptiles produce polyreactive natural antibodies (NAbs) that have low binding affinity and are produced in the absence of antigen stimulation. Given the poor specific response, NAbs may be an important protective resource in reptiles. In order to investigate the relative contributions of natural and specific antibodies, we immunized turtles with the novel antigen keyhole limpet hemocyanin (KLH). We did not detect an increase in antibody titers. However, preimmunization titers to KLH, as well as to a series of other novel antigens, were high in the turtles, indicating a strong NAb response. Interestingly, we found an age-associated increase in NAb titers in adults. Overall, our data suggest that reptiles may use NAbs as part of a strong innate immune response rather than relying on slower specific humoral responses.