IDENTIFICATION OF WOODCHUCK CLASS-I MHC ANTIGENS USING MONOCLONAL-ANTIBODIES

Two class I major histocompatibility complex (MHC) proteins with molec ular masses of 43- and 39-kDa were identified in the cell surface memb ranes of normal woodchucks using a newly developed anti-woodchuck clas s I monoclonal antibody (mAb) B1b.B9 and immunoblotting. B1b.B9 was ge nerated by immunizing mice with viable woodchuck peripheral blood mono nuclear cells and was selected for anti-class I MHC reactivity using a cellular enzyme-linked immunoassay, indirect immunofluorescence on ti ssue sections and flow cytofluorimetry. The distribution pattern of cl ass I MHC antigen on woodchuck lymphoid cells was found to be similar to that reported in other species. Also, the antigen expression on nor mal woodchuck hepatocytes was comparable to that observed on normal hu man liver parenchymal cells; thus, the antigen was not detected on hep atocytes by staining of liver tissue sections, but was found by indire ct immunofluorescence staining of isolated liver cells. Western blot a nalysis of the plasma membranes from normal woodchuck hepatocytes reve aled the presence of a single species of class I MHC heavy chain prote in with a molecular mass of 43-kDa, whereas splenocyte plasma membrane s showed intense expression of a 43-kDa species, as well as the presen ce of a 39-kDa protein. The 39- and 43-kDa proteins were extracted wit h Triton X-114 to the hydrophobic protein phase, suggesting that they both contain a hydrophobic transmembrane domain. The data obtained ind icate that the B1b.B9 identifies a nonpolymorphic epitope of woodchuck class I MHC heavy chains, providing an important reagent for the stud y of the pathogenesis of hepatitis B virus infection in a woodchuck mo del.