C3 and infection: However, given that the cleavage products of C3 and C5 (C3a and C5a) have been reported to help in the initiation of inflammatory responses during infection (50), and that alternative and classical complement activation is higher in the relatively resistant C57BL/6 mice following T. congolense infection (51, 52), it is conceivable that complement activation may contribute to optimal resistance to certain species of African trypanosomes.