The acute phase response in bats (Carollia perspicillata) varies with time and dose of the immune challenge.

The acute phase response (APR) is a core component of the innate immune response and represents the first line of immune defense used in response to infections. Although several studies with vertebrates reported fever, a decrease in food intake and body mass, and an increase in neutrophil/lymphocyte ratio and total white blood cell count after lipopolysaccharide (LPS) inoculation, there was great variability in the magnitude of these responses. Some of these differences might reflect, to some extent, differences in the time of endotoxin inoculation (during active or rest periods) and dose. Therefore, our study tested the interplay between LPS dose and time of injection on selected physiological (fever and increase in total white blood cell count and neutrophil/lymphocyte ratio) and behavioral (food intake) components of the APR using a Neotropical fruit-eating bat (Carollia perspicillata) as a model organism. We predicted that LPS would trigger a dose- and time-dependent response in APR components. APR components were assessed in rest and active periods after injection of three doses of LPS (5, 10 and 15 mg kg-1 LPS). The results indicate a more robust decrease in food intake at higher doses during the active period, while increased neutrophil/lymphocyte ratio was more robust during the active period regardless of dose. Furthermore, the skin temperature increase lasted longer at higher doses regardless of the timing of injections. Our study offers important insights into the dependence of time as well as the LPS dosage effect in the APR of bats, and how they deal with the magnitude of infections at different times of day.

Bats respond to simulated bacterial infection during the active phase by reducing food intake.

Sickness triggers a series of behavioral and physiological processes collectively known as acute phase response (APR). Bats are known as reservoirs of a broad variety of pathogens and the physiological changes resulting from APR activation have been tested predominantly during the resting phase (daytime) in several species exposed to lipopolysaccharide (LPS). In contrast, behavioral consequences of sickness for bats and other wild mammals have received less attention. We examined the physiological and behavioral consequences of APR activation in a fruit-eating bat (Carollia perspicillata) challenged with LPS during the active phase (nighttime). We measured changes in food intake, body mass, body temperature, total white blood cell counts, and the neutrophil/lymphocyte ratio (N/L). No fever and leukocytosis were observed in bats injected with LPS, but food intake decreased, bats lost body mass and their N/L ratio increased. The effect of LPS on daily energy balance is remarkable and, along with the increase in N/L ratio, it is assumed to be beneficial to fight disease. On the basis of our findings and those with other bats, it is probable that the physiological and behavioral components of the immune response to LPS follow circadian rhythms, but a formal test of this hypothesis is warranted.