High Circulating Levels of Fibronectin and Antibodies against Its RGD Adhesion Site during Mouse Trypanosoma cruziInfection: Relation to Survival

The levels of fibronectin (FN), a multifunctional glycoprotein known to mediate in vitro Trypanosoma cruzi-host cell adhesion, were measured in the plasma of T. cruzi-infected BALB/c mice. The infection induced a long-lasting increase of fibronectin levels during the acute parasitemic phase of the disease. Immunoblotting analysis showed the occurrence of lower-molecular-size FN fragments in the plasma of acutely infected animals, suggesting an infection-related FN degradation. FN levels were found to be significantly lower in dying mice harboring higher parasitemias than in surviving animals. A weak level of natural IgM against the RGD adhesion site of FN was detected before and during the first 3 weeks of infection. The level was significantly higher in surviving mice. From the fourth week postinfection, a significant increase in the levels of anti-RGD antibodies coincided with a decrease of circulating FN. These antibodies were mainly of the IgM, IgG1, and IgG2a isotypes. Taken together, these data suggest that both FN and anti-FN antibodies may contribute to the outcome of T. cruziinfection in mice.