Classical pathway serum complement activity throughout various stages of the annual cycle of a mammalian hibernator, the golden-mantled ground squirrel, Spermophilus lateralis.

Little is known about the changes in the immune system that coincide with the annual cycle of hibernating mammals. This study investigates classical pathway complement activity in the serum of the golden-mantled ground squirrel, a mammalian hibernator. Complement activity varied significantly among discreet stages of the annual cycle and is lowest during torpor and greatest during stages of arousal. C3 mRNA levels follow a pattern similar to that of complement-mediated hemolysis throughout the year but do not vary significantly among hibernation states. The classical pathway of the serum complement system is able to function in vitro at 5 degrees C, although at a slower rate than at 34 degrees C. The classical pathway of the serum complement system is active throughout all phases of the annual cycle of the golden-mantled ground squirrel.