Changes in body surface temperature play an under-appreciated role in the avian immune response

Fever and hypothermia are well characterized components of systemic
inflammation. However, our knowledge of the mechanisms underlying such
changes in body temperature is largely limited to rodent models and other
mammalian species. In mammals, high dosages of an inflammatory agent
(e.g., lipopolysaccharide, LPS) typically leads to hypothermia (decrease
in body temperature below normothermic levels), which is largely driven by
a reduction in thermogenesis, and not changes in peripheral vasomotion
(i.e., changes in blood vessel tone). In birds, however, hypothermia
occurs frequently, even at lower dosages, but the thermoeffector
mechanisms associated with the response remain unknown. We
immune-challenged zebra finches (Taeniopygia guttata) with LPS and
monitored changes in subcutaneous temperature and energy balance (i.e.,
body mass, food intake), and assessed surface temperatures of, and heat
loss across, the eye region, bill, and legs. We hypothesized that if birds
employ similar thermoregulatory mechanisms to similarly-sized mammals,
LPS-injected individuals would reduce subcutaneous body temperature and
maintain constant surface temperatures when compared with saline-injected
individuals. Instead, LPS-injected individuals showed a slight elevation
in body temperature, and this response coincided with a reduction in
peripheral heat loss, particularly across the legs, as opposed to changes
in energy balance. However, we note that our interpretations should be
taken with caution due to small sample sizes within each treatment. We
suggest that peripheral vasomotion, allowing for heat retention, is an
underappreciated component of the sickness-induced thermoregulatory
response of small birds.

发热与体温过低是全身性炎症的典型特征性表现。然而，学界对这类体温变化背后的调控机制的认知，目前仍主要局限于啮齿类动物模型与其他哺乳类物种。在哺乳类动物中，高剂量炎症刺激剂（如脂多糖（lipopolysaccharide, LPS））通常会引发体温过低——即体温降至正常温域以下——这一过程主要由产热减少驱动，而非外周血管张力（即血管舒缩状态）的改变。但在鸟类中，即便使用较低剂量的刺激剂，也常能观察到体温过低现象，但其关联的体温调节效应机制至今仍不明晰。

我们对斑胸草雀（Taeniopygia guttata）施以脂多糖免疫刺激，监测其皮下温度与能量平衡（即体质量、摄食量）的变化，并评估了眼部、喙部与腿部的表面温度及热散失情况。我们提出假说：若鸟类采用与体型相近的哺乳类相似的体温调节机制，那么与注射生理盐水的对照组个体相比，脂多糖注射组的皮下体温应会降低，且表面温度保持稳定。

但实际结果显示，脂多糖注射组个体的体温仅出现轻微升高，且该响应与外周热散失减少（尤以腿部为甚）相关，而非能量平衡的改变。不过需注意，由于各处理组的样本量较小，本研究的解读需谨慎。我们认为，介导热量潴留的外周血管舒缩活动，是小型鸟类疾病诱导性体温调节响应中被长期低估的关键环节。