E-031. B-Cell Activation in Response to the Trypanosoma cruzi Mitogen TcPRAC

M. A. Bryan, K. A. Norris;
Univ. of Pittsburgh, Pittsburgh, PA.

Chagas disease is caused by the eukaryotic parasite Trypanosoma cruzi. In about a third of patients, parasite persistence causes progression to chronic phase disease, in which cardiac arrest and sudden death can occur. During acute phase infection, polyclonal B cell activation occurs and is thought to delay specific humoral responses, contributing to parasite persistence. TcPRAC has been identified as a T. cruzi B cell mitogen and was cloned from Y strain parasite. Stimulation of splenocytes with 25 ug/mL of rTcPRAC for 72 hours induced proliferation of 37.5±10.3 percent of B cells; all B cell subsets proliferate. rTcPRAC causes dose-dependent B cell proliferation that titrates out between 1 and 5 ug/mL. In a time-course experiment, rTcPRAC upregulated expression of cell surface activation markers that peaked at 48 hours. Proliferation occurred at 48, 72, and 96 hours, with the maximal proliferation of B cells evident at 72 hours. rTcPRAC induced IgG and IgM production increased from 24 to 96 hours compared to controls. These data show that rTcPRAC induces B-cell proliferation, activation, and antibody secretion in vitro. To test the possibility that an antigen-specific TcPRAC response may lead to immune-mediated protection from infection, mice were injected with high (50 ug/ml) and low (10 ug/ml) doses of TcPRAC. The results indicate that 50 ug of rTcPRAC induces B cell proliferation within 96 hours, whereas 10 ug of protein is not stimulatory. These results suggest that for immunization studies, 10 ug of rTcPRAC will be sub-mitogenic and potentially antigenic.