LAUSR

Objectives Our goal in these studies was to quantitatively determine the metabolic phenotype of intracellular bacterial infection, immune response, and clearance. Mounting an immune response to a bacterial infection is metabolically taxing to the host. During infection, the host exhibits sickness syndrome characterized by fever, lethargy and anorexia. Cells of the immune system also shift cellular metabolic pathways, which alters the metabolic and nutritional needs of the host. Previous studies of the metabolic demands of sickness have used model antigens, mitogens or pattern associated molecular patterns, which do not represent the full spectrum of response to a live pathogen infection. Thus, our study is the first of its kind to assess the full spectrum of metabolic, nutritional, immunological, and behavioral demands of live pathogen infection. Methods Mice were administered either a mock intraperitoneal (ip) injection of PBS (Control) or ip dose of Listeria and individually housed over the course of 12 days in Promethion metabolic cages to monitor their metabolic phenotype. In a parallel study, groups of mice were equivalently treated, yet conventionally housed and sacrificed at 3, 5, 7 and 10 days over the course of infection to determine splenic bacterial burden, Listeria-specific T cell response, and cellular metabolic status. Results We observed that the period of the innate immune response (days 1-4) had the most metabolic demand, indicated by weight loss (P < 0.05), reduced activity (P < 0.05), increased sleep (P < 0.05), and decreased energy expenditure (P < 0.05). During the period of the adaptive immune response (days 5-10), there was little to no metabolic impact in the infected animals when compared to the uninfected control animals. We also observed increased GLUT1 expression (P < 0.05) on the membranes of myeloid cells during the period of highest metabolic demand, indicating shifts in cellular metabolism of innate immune cells during the early stages of infection. Conclusions The innate immune response is more metabolically taxing on the host compared to the adaptive immune response and places an increased metabolic demand on infected animals. Funding Sources Departmental startup funds to Elizabeth Hiltbold Schwartz.