Trypanosoma cruzi: aberrant expression of class II major histocompatibility complex molecules in skeletal and heart muscle cells of chronically infected mice.

In isolated skeletal, heart, and smooth muscle cells from BALB/c and C3H/HeJ mice infected with different strains of Trypanosoma cruzi the presence of class II MHC molecules was investigated by immunocytochemical techniques. We employed single muscle fibers instead of conventional cryostat sections to obtain a more accurate antigen localization. Approximately half of the skeletal muscle cells isolated from the rectus femoris expressed Ia antigens on their surface, irrespective of the mouse or parasite strain combination. Ia expression was apparent only at 30 days postinfection and thereafter. The heart muscle cells expressed class II molecules only at 1 and 3 months postinfection. In no case did the smooth muscle cells from infected mice express Ia antigens. Studies of the same molecules in the noninfected animals gave constantly negative results. We conclude that in the course of the chronic infection of mice with T. cruzi, ectopic expression of class II MHC molecules occurs at the surface of skeletal and heart muscle cells, providing a possible mechanism for explaining the anti-striped muscle autoreactivity present in Chagas' disease.