Antigenicity of Fractions of a Somatic Antigen of Trypanosoma cruzi

Abstract

A delipidized somatic Trypanosoma cruzi antigen was mechanically fractionated in a Sephadex G-200 column, and the fractions were separated according to complement fixation (CF) (Fraction Ia) and indirect hemagglutination (IHA) activity (Fractions III, IV). The reaction of the active fractions against chronic infected human sera was quite similar to the reaction of the unfractionated antigen. The CF active fraction was the only one with measurable amounts of DNA and was associated with the largest molecules. No precipitation activity was detected in this fraction. Precipitinogens had a wide size variation; they were present in the IHA active fractions as well as in other fractions. The two last fractions (VI and VII) did not show any antigenic activity. Fife and Kent (1960) prepared a protein antigenic fraction from epimastigotes of Trypanosoma cruzi for complement fixation (CF). In many laboratories, diagnostic tests are performed with crude extracts of the whole parasite without any characterization other than their reactivity in serologic tests (Knierim and Saavedra, 1966). Delipidized somatic antigens have been prepared by Chaffee et al. (1956) and Maekelt (1960, 1964). The antigen prepared as suggested by Maekelt (1960) is active in the complement fixation (CF) and indirect hemagglutination (IHA) tests. In sera from immunized rabbits this antigen detects also precipitins. In the present study a somatic antigen prepared as suggested by Maekelt (1960), but with a higher protein concentration, was fractionated by gel filtration chromatography, and the fractions were evaluated serologically. The purpose was to initiate a study of the physical and chemical characterization of the components responsible for the serologic reactivity. MATERIALS AND METHODS