Hibernation induces immune changes in the lung of 13-lined ground squirrels (Ictidomys tridecemlineatus)

During hibernation, significant changes occur in the systemic and intestinal immune populations. We found that the lungs of hibernating 13-lined ground squirrels (Ictidomys tridecemlineatus) also undergo shifts in immune phenotype. Within the population of mononuclear cells, the percentage of T cells increases and the percentage of CD11b/c+ cells decreases in hibernators. E-selectin, which promotes endothelial attachment, increases during arousal from torpor. Levels of the anti-inflammatory cytokine interleukin (IL)-10 in the lung are lower during hibernation while levels of the pro-inflammatory cytokine, tumor necrosis factor (TNF)-α remain constant. Expression of suppressor of cytokine signaling (SOCS) proteins is also decreased in torpid hibernators. Our data point to a unique immune phenotype in the lung of hibernating ground squirrels in which certain immunosuppressive proteins are downregulated while some potentially inflammatory proteins are maintained or amplified. This indicates that the lung houses an immune population that can potentially respond to antigenic challenge during hibernation.