Relationships between parasitic infection and natural antibodies, age, and sex in a long‐lived vertebrate

Abstract

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.

Mucosal antibody quantity but not avidity predicts likelihood of Salmonella infection in red‐eared slider turtles (Trachemys scripta)

“…Further, the increased antibodies could help to improve phagocytosis and the respiratory burst of macrophages (Pasmans et al, ). This relationship is similar to that found previously in sliders between the total immunoglobulin levels and the number of intestinal parasites from fecal samples (Stromsland & Zimmerman, ), suggesting that a common mechanism may be used against both intracellular and extracellular pathogens.…”

“…For example, captive male tuatara have been found to be more reactive against Salmonella saintpaul and Citrobacter koseri than females due to food bowl domination over contaminated feed (Middleton et al, ). We previously found that male slider turtles had a higher number of intestinal parasites than females (Stromsland & Zimmerman, ). This current study did not reflect a pattern between Salmonella distribution and sex (Figure ).…”

“…There was no association found between the amount of plasma LPS‐Abs and likelihood of infection. Past studies have established that the B cells of T. scripta are likely of the B‐1 subset (Stromsland & Zimmerman, ; Zimmerman, Clairardin, et al, ). Studies of B‐1 cells in mice indicate that two subsets of B‐1 cells exist: One that develops in the bone marrow and spleen and one that develops in the peritoneal cavity.…”

“…This study opened the question of how the NAbs are used in immune defense in the turtles against potential pathogens. Recently, it was found that sliders with greater amounts of total mucosal antibodies have a decrease in extracellular, intestinal parasite numbers (Stromsland & Zimmerman, ). However, it is unknown if this pattern holds true for intracellular pathogens or more generally, for other types of pathogens such as bacteria, viruses, or fungi.…”

Mosquito-Independent Transmission of West Nile virus in Farmed Saltwater Crocodiles (Crocodylus porosus)

“…Notably, antibodies to St. Louis encephalitis virus, a flavivirus circulating in southern USA and South America, have never been detected in crocodilians [7,8,45]. Future studies of the host-virus interaction in WNV-infection of crocodilians should therefore also focus on innate and adaptive antiviral defenses as well as the potential role of co-infections and the gut microbiota [8,46,47]. In this study, we detected maternal antibodies to WNV in a number of the clutches used, i.e., passive immunity acquired through the egg yolk, which persisted beyond 4 months in a few animals.…”