(Uploaded by Plazi for the Bat Literature Project) Bats play a key role as host for multiple microorganism and virus without showing clinical manifestations of disease. After recognition of a potential threat, innate immunity triggers acute phase response, a systemic reaction that contributes to restrain microbial and viral growth. APR is characterized by fever, leukocytosis, and production of acute phase proteins, but also by behavioral changes, including somnolence, lethargy, and anorexia. Deploying immune responses, such as acute phase response, represents an energetic cost for vertebrates. In bats, it has been suggested that higher metabolic rates reached during flight might subsidize any inherent cost of raising metabolism to activate an immune response. Therefore, a central question is whether immune response represents a significant cost to bats and, if so, how much is the metabolic cost of these responses. Here, we assess the resting metabolic rate of Artibeus lituratus in response to challenge with LPS. In addition, we assessed parameters of acute phase response including fever, body mass loss, and leukocytosis in this specie. We found that challenge with LPS leads to an increase of 40% in resting metabolic rate of A. lituratus, concomitant with body mass loss and an increase in body temperature of 1.5 °C.