Identification of two liver proteins recognized by autoantibodies elicited in mice infected with mouse hepatitis...

Western blot experiments showed that sera from mice infected with the mouse hepatitis virus strain A59 (MHV-A59) contained autoantibodies (autoAb) that bound to a 40-kDa protein present in liver and kidney extracts. No reaction was observed with extracts of the heart, muscles, spleen, brain and lung. The Ab cross-reacted with a 40-kDa protein from human, rat and sheep liver, but not with liver extracts from the silver side fish (Odontesthes bonariensis). No correlation was found between the development of the hypergammaglobulinemia that followed the viral infection and the occurrence of the autoAb. Reactive immunoglobulins pertained to the IgG1, IgG2a and IgG2b subclasses, recognized cryptic epitopes and were detected from 10 days up to 8 weeks after MHV-infection. The 40-kDa protein was purified from mouse liver extracts by ion-exchange chromatography, gel filtration and SDS-PAGE. Because the N-terminal was blocked, we digested the protein in-gel with trypsin and sequenced various peptides. Results indicated a 100% homology of sequence between the protein recognized by the autoAb and liver fumarylacetoacetate hydrolase (FAH), the enzyme that mediates the last step of tyrosine catabolism. Additionally, a second protein recognized by the autoAb was detected during FAH purification steps and was identified as liver alcohol dehydrogenase.