Molt dampens pro-inflammatory cytokine production during the acute phase response to lipopolysaccharide in the domestic chicken (Gallus domesticus)

There are a variety of nutritionally costly life stages that birds must balance with investments in the immune system, yet much remains unknown about how the process of molt impacts immunity. For chickens, similar to other birds, molt is characterized by periodic feather shedding and replacement along with broader physiological changes like reproductive quiescent. To investigate how molt modulates innate immunity, mRNA expression and the plasma concentration of key cytokines were evaluated following an acute phase response induced by lipopolysaccharide (LPS-APR). Laying hens were challenged with an intraperitoneal injection of LPS at 1.5 mg/kg of body weight during the peak feather production period of an induced molt. Cytokine expression was evaluated in the liver, spleen, and plasma 4 h post-injection. Molting hens had reduced expression of certain pro-inflammatory cytokines, with the most significant reduction occurring in expression of IL-6 in the liver. This trend occurred even when the number of molted feathers varied in the fully feather UCD-003 or sparsely feathered Scaleless High hens. Importantly, molting hens failed to significantly increase plasma levels of IL-1β and IL-6 to those observed in the non-molting birds in response to LPS. A reduction in the expression of key pro-inflammatory cytokines, especially those involved in the febrile response and hepatic immune function, suggest that molt may reduce the availability of nutrients and energy needed to support the acute phase response to LPS. This attenuation is likely a mechanism to allow both molt and an innate immune response to progress during an energetic or nutritional bottleneck.