Is there an effect of environmental temperature on the response to an antigen and the metabolic rate in pups of the rodent Octodon degus ?

Acute-Phase Immune Response Involves Fever, Sickness Behavior, and an Elevated Metabolic Rate in the Subterranean Rodent Ctenomys talarum

AbstractThe acute-phase response (APR) is an induced innate response and may involve pronounced physiological and behavioral changes. One of the most common assays to study the APR involves the use of a lypopolysaccharide (LPS) from the cell wall of gram-negative bacteria. In this study, we determined the energetic costs of the APR in the subterranean rodent Ctenomys talarum, as well as the effects of the exposure to LPS on body temperature, body mass loss, and behavior in this species. Furthermore, we monitored levels of circulating endotoxin after LPS exposure. Our results suggest that in C. talarum, the APR is energetically costly, resulting in a 14% increase in metabolic rate. Animals exposed to LPS experienced a short-term thermal response, weight loss, and changes in their behavior that included more time spent resting and with their eyes totally or partially closed. However, the magnitude of the effects of LPS exposure varied between sexes and among animals. Also, there was a clear peak in circulating endotoxin levels in plasma 3 h postinjection (hpi) and a significant decrease of these levels 24 hpi, but peak endotoxin concentration values recorded were highly variable among animals. In light of these results, ecological determinants of immune function variation in tuco-tucos are discussed considering the roles of pace of life, habitat, and degree of pathogen exposure in these subterranean rodents.

Nutritional ecology and ecological immunology in degus: Does early nutrition affect the postnatal development of the immune function?

Environmental conditions experienced by developing animals have an impact on the development and maturity of the immune system. Specifically, the diet experienced during early development influences the maintenance and function of the immune system in young and adult animals. It is well known that exposure to low-protein diets during early development are related to an attenuation of immunocompetence in adulthood. While this functional linkage has been widely studied in altricial models' mammals, it has been little explored how the nutritional history modulates the immune function in precocial animals. We evaluated the effect of dietary protein consumed during early development on the immune function and the oxidative costs in the precocial Caviomorph rodent Octodon degus, or degu. We evaluated components of the acute phase response (APR) and oxidative parameters before and after immune challenge. We found that after the immune challenge, the juveniles on the low-protein dietary treatment exhibited an attenuation of body temperature but showed higher levels of lipid peroxidation than juvenile degus on the high-protein diet. We did not find a significant effect of the interaction between diet and immune challenge on body mass, levels of inflammatory proteins, nor in the total antioxidant capacity. Our results suggest that some components of the immune function and the oxidative status in the degu can be modulated by diet during development. However, the modulation would depend on the immune variables analyzed, and the characteristics of the immune system of precocial rodents.

Food restriction, but not seasonality, modulates the acute phase response of a Neotropical bat

Season and food intake are known to affect immune response of vertebrates yet their effects on metabolic rate have been rarely explored. We tested the effect of season and acute food restriction and their interaction on the energetic cost of immune response activation of a tropical vertebrate, the Seba's short-tailed fruit bat (Carollia perspicillata). We specifically stimulated the acute phase response (APR) with bacterial lipopolysaccharide (LPS) to measure metabolic changes along with changes in body temperature (T_b), body mass (M_b), white blood cell counts and the Neutrophil/Lymphocyte ratio (N/L). We found no effect of season on the different factors associated to the activation of the APR. In contrast to our expectations, unfed bats reached similar T_b increments and RMR peak values and had higher RMR scope values and higher caloric costs than fed bats after LPS injection. However, food deprivation led to delayed metabolic response indicated by longer time required to reach peak RMR values in unfed bats. Both food-deprived and fed bats did not present leukocytosis after APR activation and their WBC counts were similar, but unfed bats had a significant increase of N/L. APR activation represented a small fraction of the bat daily energy requirements which might explain why unfed bats were not limited to mount a metabolic response. Our study adds to recent evidence showing that activating the innate immune system is not an energetically expensive process for plant-eating bats.

Ecoimmunology in degus: interplay among diet, immune response, and oxidative stress

The relationships between immunity, oxidative stress, and diet have not often been studied together. Despite this, it has been shown that dietary proteins can have effects on the functioning of the immune system and the oxidative status of animals. Here we evaluated the effects of dietary proteins on the response to an antigen and oxidative status of Octodon degus (Rodentia). We acclimated adult individuals to high-protein and low-protein diets and evaluated several aspects of the acute phase response and variables associated with oxidative status. After the immune challenge, animals acclimated to the high-protein diet had more inflammatory proteins and body mass losses than the group acclimated to a low-protein diet. Overall, the immune challenge increased the production of inflammatory proteins, total antioxidant capacity, lipid peroxidation, and duration of rest periods. In contrast, we did not find an interaction between diet and the challenge with the antigen. Overall, our results do not reveal an enhanced response to an antigen nor effects on the oxidative status of degus individuals subjected to a high-protein diet.