Trypanosoma cruzi: detection of a surface antigen cross-reactive to human C-reactive protein.

C-reactive protein (CRP) is an acute phase protein secreted by liver hepatocytes, and is also found on the surface of lymphocytes and as a membrane-associated protein expressed on rat liver macrophages and human monocytes. C-reactive protein levels increase in the sera of children infected with Trypanosoma cruzi, during the acute phase of Chagas' disease, but its role in the course of this infection is unknown. Experiments designed to detect the binding of CRP to circulating forms of T. cruzi failed to observe it because anti-human CRP antibodies bind to the parasite. The present work intended to further clarify this novel question related to the anti-CRP cross-reactivity with the parasite. Indirect immunofluorescence, immunoenzymatic, flow cytometry, and Western blot assays showed that three different polyclonal anti-human CRP antibody preparations bind to T. cruzi surface. This binding is dose-dependent, saturable, and is inhibited when anti-CRP antibodies from different species were allowed to compete, indicating the specificity of the reactivity. The antibodies recognized a protein band below 23 kDa in Western blot analysis of parasite extracts. The divalent cation chelators EDTA and EGTA impaired the antigen recognition by the antibodies. The binding to parasite surface was also observed with some available monoclonal antibodies raised against human CRP. A polyclonal anti-human CRP presented an inhibitory effect on invasion of heart muscle cells by T. cruzi. Our results indicate that a molecule antigenically related to CRP, a possible CRP-like molecule, is expressed on the surface of T. cruzi.