Figure 2.

ATA Inhibit T. cruzi Infection of PC12 Cells A: Visualization of T. cruzi (Silvio strain) infection of PC12^wt cells by fluorescence microscopy. PC12^wt cells were infected with T. cruzi (∼30 parasites/cell) for 3 days in the presence of 0.3 μg/ml non-chagasic IgG (panel a) or ATA (#1) (panel b), fixed in paraformaldehyde, stained with 4,6-diamidino-2-phenylindole (to visualize host cell nuclei) and chagasic IgG/secondary Alexa-labeled anti-human IgG (to identify intracellular parasites). Arrows in panel a indicate host cells fully loaded with amastigotes. Non-Ch, non-chagasic IgG. B: Dose-response of ATA-induced inhibition of T. cruzi infection of PC12 cells. Protocol similar to that in (A) except infection was performed in the presence of various concentrations of ATA (#1, unadsorbed) and visualized by phase contrast microscopy after staining with Diff-Quik. Also shown is the effect of ATA adsorbed on TrkA^ECD-Fc/protein G-Sepharose (ATA ads on protein G) and on p75^ECD-Fc/protein G-Sepharose (p75 ads on p75/proteinG). Results plotted as inhibition of infection relative to infection in the presence of non-chagasic IgG (open squares). The lack of inhibition by non-chagasic IgG (average of the protein G-Sepharose-purified IgG from three sera) is indicated by open triangles. Experiment repeated twice with similar results.