[Early immunological aspects in rats infected by Trypanosoma cruzi. II. Soluble antigen circulation and the modifications of serum complement from animals in sucessive days of the infection (author's transl)].

A group of rats was infected by the Y strain of T. cruzi and three animals were bled daily from the 4th to the 13th days. The sera obtained each day, after being mixed, were used for dosing serum complement and for acting as antigens in the CFT with a Chagas' disease serum. The amount of circulating antigen increased gradually, reached a maximum in the 5th and 6th days and then decreased up to the 10th day; thereafter it increased attaining a new maximum in the 11th day and again decreased up to the 13th day. The dosage of the complement showed that the 50 per cent unit was about 70 x 10(-4) in the first few days of the infection, reached 130 -- 135 x 10(-4) in the 7th and 8th days, and was back again to the initial levels in the 13th day. These results suggest a relation between the circulation of antigens, the formation of antigen antibody complexes, and the fixation of the complement by such complexes.