Antibody maturation in Trypanosoma cruzi-infected rats

Abstract

The study of antibody avidity changes during infection has improved the understanding of the pathologic processes involved in several infectious diseases. In some infections, like toxoplasmosis, this information is being used for diagnostic purposes. Results of the evolution of antibody avidity for different specific antigens in Trypanosome cruzi-infected rats are presented. A Western blotting technique, combined with avidity analysis to identify antigens that elicit high-avidity antibodies, is suggested. In this system, antibodies showed high avidity values only during the chronic phase of infection and only in relation to antibodies against 21-, 33-, 41-, 42-, 56-, 58-, 66-, and 72-kDa antigens. Finally, a 97-kDa T. cruzi antigen, which was recognized by high-avidity antibodies and occurred in noninfected rats, was identified. These results allow us to evaluate the different antigens in chagasic infection. Our results show that with the correct choice of antigen it is possible to detect differences in maturation of antibodies and to discriminate, in an experimental model, between recent (acute) and chronic infections.

FIG. 1

Evolution of parasitemia and antibody levels in rat sera. (A) Clearance of blood-circulating parasites in T. cruzi-infected rats. The bars represent means ± standard deviations of parasites in 100 fields. (B) Kinetics after T. cruzi infection in control and infected rats on days 7, 15, 30, and 60 p.i. ▵, total antibody after inoculation in controls rats; ▴, IgG-specific antibody after inoculation in control rats; □, total antibody after inoculation in infected rats; ■, IgG-specific antibody after inoculation in infected rats. Points are averages of triplicate experiments. Standard deviations are less than 10%. All groups were assayed on the same ELISA plate. OD was obtained for each group with both conjugates in order to assess the serological response from the onset of the infection.

FIG. 2

Evolution of the avidity index in sera pools from infected rats on days 15, 30, and 60 p.i. Differences were statistically significant at day 60 p.i. (P < 0.0002).

FIG. 3

(A) WB of sera from different groups of infected rats; non-urea-eluted antibodies (a) and urea-eluted antibodies (b) were measured on days 7, 15, 30, and 60 p.i. (B) WB of control sera on days 7, 15, 30, and 60 p.i., with non-urea-eluted antibodies (a) and urea-eluted antibodies (b). Strips were incubated with peroxidase-conjugated anti-rat IgG. Apparent molecular mass is shown on the left.