The occurrence and localization in trypanosomes and other endo-parasites of an antigen cross-reacting with mitochondrial antibodies of primary biliary cirrhosis.

1. A mitochondrion-associated antigen to primary biliary cirrhosis (PBC) in man has been shown by solid-phase radioimmunoassay and immunoautoradiography to occur in several parasitic protozoa (Trypanosoma, Plasmodium and Eimeria spp.) and in the helminths Ascaridia galli and Nippostrongylus brasiliensis. 2. Stercorarian trypanosomes and T. brucei procyclics, with more highly-developed mitochondria, appear to contain more PBC antigen than the salivarian trypomastigote, in accordance with the known mitochondrial association of the antigen. 3. Trypanosoma lewisi and A. galli gave consistently high reactivity for PBC antigen, the antigen of the former being localized predominantly to the microsomal fraction.