A new method for diagnosis of Chagas' disease: diffusion-in-gel enzyme-linked immunosorbent assay.

The diffusion-in-gel enzyme-linked immunosorbent assay (DIG-ELISA) for antibodies to Trypanosoma cruzi was evaluated using formalinized epimastigotes as antigen. The results obtained by DIG-ELISA were compared with those obtained with the indirect hemagglutination test. The results of the DIG-ELISA showed that the reaction zone diameters obtained with sera from individuals with past or present exposure to T. cruzi were significantly greater than those obtained with normal human sera. All the sera from Chagasic individuals had a positive reaction in the test, whereas sera from normal individuals and individuals with toxoplasmosis or cutaneous leishmaniasis had a negative result. A close correlation was observed between the reaction zone diameters and antibody concentration (expressed as log2 of the serum dilution). Excellent correlation was observed between results obtained by the 2 serological tests. The data suggest that the DIG-ELISA is a promising serological test for measuring antibodies to T. cruzi.

Plasmodium berghei: characterization of antigens and their role in inducing immunity to infection.

In vitro, Plasmodium berghei infected erythrocytes incorporated 35S-methionine into 31 polypeptides with molecular weights from 21 kd to 300 kd. Hemoglobin and additional smaller molecular weight polypeptides were labelled with 35S-methionine by a population of uninfected, reticulocyte-rich rat erythrocytes. 3H-glucosamine was incorporated into at least 3 components by Plasmodium berghei infected erythrocytes. Uninfected, reticulocyte-rich rat erythrocytes did not incorporate 3H-glucosamine. Rabbit antisera against small, free plasmodia formed complexes which contained between 12 and 22 of the 31 labelled polypeptides in the 35S-methionine labelled antigen preparation. Rabbit antisera against soluble antigens washed from small, free plasmodia formed complexes containing many of the same labelled plasmodial polypeptides, however the reactions were particularly strong with those components which yielded polypeptides with molecular weights of 25 kd and 31 kd. Rabbit origin antisera against the 2 preparations did not form detectable complexes with the 3H-glucosamine labelled plasmodial components. Sera from rats undergoing progressive P. berghei infection formed complexes containing an increasing number of 35S-methionine labelled plasmodial polypeptides. Hyperimmune rat serum, the only serum protective upon passive transfer into mice, formed complexes containing 7 polypeptides with molecular weights of 35 kd, 75 kd, 80 kd, 92 kd, 100 kd, 150 kd and 190 kd. Antigens containing 1 or more of these polypeptides may be important in the induction of a protective antibody response against the parasite.