Leptin regulates energetic tradeoffs between body fat and humoural immunity

Mounting an immune response requires a relatively substantial investment of energy and marked reductions in energy availability can suppress immune function and presumably increase disease susceptibility. We have previously demonstrated that a moderate reduction in energy stores via partial surgical lipectomy (LIPx) impairs humoural immunity of Siberian hamsters (Phodopus sungorus). Here we tested the hypothesis that LIPx-induced decreases in immunity are mediated by changes in the adipose tissue hormone leptin. Hamsters received bilateral surgical removal of inguinal white adipose tissue (IWATx) or sham surgeries (Sham). Half the animals in each group received osmotic minipumps containing murine leptin (0.5 μl h(−1) for 10 days) whereas the remaining animals received minipumps containing vehicle alone; all animals were subsequently challenged with the novel antigen keyhole limpet haemocyanin (KLH). In general, serum leptin and anti-KLH antibodies were significantly correlated with one another with higher levels generally indicating enhanced immunity. In addition, IWATx hamsters had significantly lower serum anti-KLH IgG compared with sham animals. Exogenous leptin, however, attenuated LIPx-induced immune suppression but did not affect humoural immunity in sham animals. These results suggest that reductions in energy availability lead to impairments in humoural immunity and that leptin can serve as a neuroendocrine signal between body fat and immunity regulating humoural immune responses

Body condition, sex and elevation in relation to mite parasitism in a high mountain gecko

Parasitism is one of the main selective forces in nature, strongly affecting host fitness. Still, knowledge is incomplete concerning how variation in probability and intensity of infestation depends on body condition, sex or geographic variables. Here, I study the variation in probability and intensity of infestation of bloodsucking mites parasitizing the Atlas day gecko (Quedenfeldtia trachyblepharus) depending on host body condition, sex and elevation, in the High Atlas (Morocco). Parasite prevalence was 58.75%, and probability of infection decreased with host body condition. However, parasitism intensity tended to increase with body condition. The parasite load ranged from 0 to 16 mites per individual, with a mean intensity of 3.0 ± 0.37 (se) in infested geckos. Prevalence was higher in males (2/3 parasitized) than in females (1/2 parasitized), but intensity did not significantly differ with sex. Neither prevalence nor intensity varied with elevation. In conclusion, geckos in better body condition harboured heavier parasite loads, but animals with the highest body condition were not infested. These findings suggest that animals with good body condition may tolerate heavier mite infestations, but only animals with the highest body condition may resist infestation