Assessing the energetic costs and trade-offs of a PHA-induced inflammation in the subterranean rodent Ctenomys talarum: immune response in growing tuco-tucos

Varying intensity of simulated infection partially affects the magnitude of the acute-phase immune response in the subterranean rodent Ctenomys talarum

The acute phase response (APR), coordinated by a complex network of components of the immune and neuroendocrine systems, plays a key role in early immune defense. This response can be elicited by a wide variety of pathogens at different intensities (frequencies and doses), hence experimental immune challenges with antigen gradients makes it possible to evaluate sickness progression with a better representation of what occurs in natural systems. However, how infection intensity could shape the APR magnitude in wild species is still poorly understood. Here, the immune response was activated in the subterranean rodent Ctenomys talarum with a gradient of lipopolysaccharide (LPS) doses (0.5, 1, 1.5, and 2 mg/kg of body mass). Changes in body temperature, body mass, and energetic costs were evaluated over time. We also assessed cortisol levels, white blood cells counts and neutrophil: lymphocyte ratios, before and after injection. Results indicated that during the APR, C. talarum shows a hyperthermic response, which is maintained for 6 h, with slight differences among antigen doses in the pattern of thermal response and body mass change. A maximum increase in body temperature of 0.83°C to 1.63°C was observed during the first hour, associated with a metabolic cost that ranged from 1.25 to 1.41 ml O₂ /gh. Although no clear effects of treatment were detected on leukocyte abundance, we found increments in neutrophil: lymphocyte ratios and gradual increases in cortisol levels corresponding to the intensity of simulated infection, which may indicate redistribution of immune cells and enhancement of immune function. An evident sickness syndrome was observed even at the lowest LPS dose that was characterized by an increase in body temperature, energy expenditure, and N: L ratio, as well as a dose-dependent increase in cortisol levels. Although in nature, other constraints and challenges could affect the magnitude and costs of immune responses, C. talarum mounts an effective APR with a low increase in their daily energy expenditure, regardless of LPS dose.

Food Restriction Affects Inflammatory Response and Nutritional State in Tuco-tucos (Ctenomys talarum)

Insufficient or unbalanced food intake typically has a negative impact on immune responses. The understanding of this effect is, however, hampered by the effect that food has on general condition, which, in turn, affects immunity, and the interaction among general condition, immunocompetence, and concurrent infections. The goal of this study was to determine the effects of food restriction and methionine supplementation on immunity in tuco-tucos (Ctenomys talarum). Effects of diet manipulations on nutritional state, inflammatory response to phytohemagglutinin (PHA), and other immune parameters (bacterial killing capacity, natural antibodies, and leukocyte profile) were evaluated. Health and stress parameters and endoparasite loads were assessed to understand more deeply potential effects of treatments on immune status. Individuals under food restriction presented an altered nutritional state as well as increased stress levels (higher N: L ratios) compared with individuals fed ad libitum, and a marked reduction in the inflammatory response to PHA. Supplementation with methionine did not affect any of the parameters analyzed. Endoparasite loads were not affected by treatments. Our results support the idea that food insufficiency can modulate the individual's immune responsiveness through the lack of adequate essential nutrients, metabolic fuel and energetic reserves, or by a detrimental effect of the stress caused by nutrient limitation. We show that the response to PHA previously reported as nonenergetically costly for C. talarum, implies a nutritional cost; an opposite pattern to that previously found for the adaptive antibody response to sheep red blood cells in the same species.

Parasite infection negatively affects PHA-triggered inflammation in the subterranean rodent Ctenomys talarum

Magnitude and effectiveness of immune responses vary greatly between and within species. Among factors reported to determine this variation, parasitism is a critical one, although controversial effects of parasites over immunological indices have been reported. Information regarding immune strategies in species with different life histories is crucial to better understand the role of immune defenses in an ecological and evolutionary context. Here, we examine the influence of the parasite community on immune responsiveness of a solitary subterranean rodent, Ctenomys talarum. To do this, we assessed the impact of the natural parasite community and the experimental infection with Eimeria sp. on the phytohemagglutinin (PHA)-response, as well as other immune, condition, nutrition, and stress parameters. PHA-triggered inflammation was similarly impaired by Eimeria sp. infection alone or co-occurring with a number of gastrointestinal nematodes. None of the other physiological parameters studied were affected by parasitism. This indicates that parasitism is a general key factor modulating immune responsiveness of the host, and in particular for C. talarum, it could explain the great inter-individual variation previously observed in the PHA-response. Thus, our results highlight the importance of taking the parasite community into account in ecoimmunological studies, particularly when using immunological indices.