Molecular cloning of the liver-specific rat F antigen.

F antigen is a 43-kDa widely conserved liver protein that has been intensively used in studies of immunogenicity and tolerance; two murine allotypes have been identified. Immunization of specific responder inbred strains with liver homogenates from the opposite allotype leads to precipitating antibody and cell-mediated immunity against F. The antibodies produced are autoantibodies as they react equally well with self. We have identified a cDNA clone from rat liver that reacts with alloantisera to F. The fused polypeptide produced by the clone was shown to correspond to F by several experiments. First, alloantisera to F antigen reacted with the cloned fused polypeptide, but not control recombinant clones. Second, mice immunized with the fused polypeptide generate an antibody response that reacts specifically with the 43-kDa protein of mouse liver homogenates and with highly purified F antigen. Finally, both anti-F allosera and sera from mice immunized with the fused polypeptide react with the same 43-kDa liver protein on two-dimensional immunoblots. The nucleotide and deduced amino acid sequence of the clone are presented and the sequence was found to have a significant homology with L28, an Escherichia coli ribosomal protein. The availability of recombinant F antigen will allow definitive questions to be addressed with respect to epitopes and specifically the identification of the T cell epitope which allows for autoimmune responses.