SUMMARYWe have previously used Epstein-Barr virus transformation to establish two clonal lymphoblastoid cell lines (48-1 and S-I) producing monoclonal antibodies against microtubular aggregates that appear in the hepatocytes of chimpanzees with non-A, non-B hepatitis (NANBH). To obtain additional antibodies directed against the same structure, the mouse hybridoma method was employed. Partially purified microtubular aggregates were prepared from liver homogenates of a chimpanzee with NANBH and used as the immunogen. Hybridoma cultures were first screened by radioimmunoassay against the partially purified antigen and secondly by immunofluorescence (IF) using liver sections from a chimpanzee with NANBH. Twenty-seven cultures exhibited positive IF reactions similar to those observed with the original antibodies, 48-1 and S-I, and were cloned by limiting dilution. The specificities of the monoclonal antibodies were tested by IF on liver biopsy specimens from chimpanzees with hepatitis A, B, D or NANBH and from normal chimpanzees. All the antibodies proved to be IgG. Immunoelectron microscopy revealed that all 27 antibodies bound to the same structure, the microtubular aggregates, in hepatocytes of chimpanzees with NANBH. To determine the size of the antigen polypeptide recognized by these antibodies, polyacrylamide gel electrophoresis and Western blot assays were performed. Nine of the 27 antibodies specifically reacted with a single polypeptide of Mr 44K (p44). The remaining 18 antibodies detected no antigen polypeptide on the filters. The anti-p44 antibodies were then tested using cross-competition assays with lzSI-labelled antibodies, and were found to be classifiable into three groups. In addition, the results indicate that at least three distinct epitopes are located on p44: epitope A recognized by group 1, epitope B recognized by group 2 and epitope C recognized by group 3.
The 48-1 antibody, initially reported to react specifically with non-A, non-B infected liver tissue, has been found to react also with liver specimens from chimpanzees infected with hepatitis delta virus (HDV). To clarify further the relation between HDV and appearance of the antigen reacting with the 48-1 antibody (48-1 Ag), immunoperoxidase studies were carried out on serial liver specimens from chimpanzees infected with HDV. Immunohistochemical and serological findings suggested that the appearance of 48-1 Ag paralleled that of HDV. Double immunoperoxidase staining revealed HDAg in the nucleus and 48-1 Ag in the cytoplasm of the same hepatocytes as well as in different hepatocytes separately. The course of appearance of microtubular aggregates paralleled that of 48-1 Ag. The present results suggested that expression of 48-1 Ag was related to infection with HDV, probably because expression of this antigen is induced from the host genome.
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