Repeated antigenic stimulation overcomes immunosuppression in experimental Chagas' disease.

Mice infected with Trypanosoma cruzi, and profoundly suppressed in their ability to respond to sheep erythrocytes (SRBC), were found to become highly responsive to these antigens when given two injections of SRBC at 4- or 6-day intervals. Two injections at intervals of 2, 8 or 10 days did not restore responsiveness. The ability to overcome immunosuppression via two challenges with antigen was found to be antigen-specific, in that if the first injection was with SRBC and the second with horse RBC there was no enhancement of plaque-forming cells to either antigen. Homologous challenges with SRBC or HRBC, however, did overcome immunosuppression. It is suggested that the ability to overcome immunosuppression by two injections of antigens at 4- or 6-day intervals is due to stimulation of a small number of T-helper cells in the first injection and an expansion of these cells in the second injection resulting in sufficient help to induce specific B-cell responses.