The Development of Complement Activating Ability as an Age Related Factor in Murine Brains

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Abstract
We recently reported on the ability of the myelin fraction of the murine brain to activate the complement system through the classical pathway, which might be important in the induction of secondary inflammation in various pathological conditions where brain tissue has been exposed to the complement. The present study was undertaken to investigate the relationship between the appearance of complement activity in the mouse brain and the synthesis of myelin in ICR micce up to 90 days of age. Here, we show that anti-complementary activity in the murine brain is closely related to murine brain weight and that its activity seems to be dependent on the amount of myelin in the murine brain. Myelin was isolated from brains of equal weight taken from both 2-day old and 90-day-old mice, and we found that 90-day-old myelin consumed a much greater amount of complement (C) than 2-day-old myelin. However, for equal concentrations of myelin, almost an equal amount of C was consumed by the myelin of the 2-day-old mice and by that of the 90-day-old mice. It was suggested that the difference of anti-complementary activity was caused by the myelin contents of the murine brains, but thepossibility of maturation of myelin was not excluded. The mechanism involved in the anti-complementary activity of the myelin was found to be related to the consumption of complement, mainly via the classical pathway but also less activity via the alternative pathway.