Mouse hybridomas producing antibodies against structural proteins of canine distemper virus (CDV) were produced by fusion of Sp2/0 myeloma cells with spleen cells from BALB/c mice immunized with purified preparations of Vero cell-grown CDV. Ascites fluids collected after intraperitoneal inoculation with 149 CDV antibody-producing hybridoma cell lines were characterized by different serological tests. By immune precipitation tests with [S]methionine-labelled extracellular virions and intracellular virus polypeptides, 57 clones were found to produce antibodies against the nucleocapsid protein (NP), 22 against the polymerase (P) protein, 10 against the fusion (F) protein and nine against the large uncleaved glycoprotein (named H in analogy with measles virus). By competitive binding enzyme-linked immunosorbent assay (ELISA) tests with monoclonal antibodies against each structural component, a minimum of 18, six, three and seven separate antigenic determinants were identified on the NP, P, F and H proteins, respectively. The reactions of clones directed against F and H surface components of the virus were tested for their ability to inhibit the infectivity of both CDV and measles virus in the absence and presence of anti-γ-globulin. In addition, the inhibitory activity of the clones on measles haemagglutinating (HA) and haemolysis (HL) activity were examined. Monoclonal antibodies against six of the seven antigenic determinants of the H protein could neutralize the infectivity of the virus. After addition of anti-γ-globulin to the test, increases of titres varying from twofold to several hundredfold were observed with the different clones. None of all the clones against H could block measles virus infectivity, HA or HL activity. The 10 clones directed against the F protein could not neutralize the infectivity of CDV even in the presence of anti-γ-globulin. Further, the antibodies could not inhibit measles HA and HL activity in the absence of anti-γ-globulin. However, after the addition of anti-γ-globulin, antibodies against two of the three sites were found to block measles virus HL activity. The reactions of all clones were tested in immune fluorescence, ELISA and immune precipitation tests with three strains of CDV. Each strain had a few unique antigenic sites. Variation was found in four, one and three different antigenic sites of the NP, P and H proteins, respectively.


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