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Abstract
Monoclonal antibodies specific for the ‘latent membrane protein’ (LMP) of Epstein-Barr virus (EBV), one of the effector proteins of EBV-induced B cell transformation, have been generated from mice immunized with a β-galactosidase fusion protein containing the carboxyl half of the B95. 8 strain LMP sequence. Four monoclonal IgG1 antibodies, designated CS. 1, CS. 2, CS. 3 and CS. 4, which together recognized at least three different epitopes on the molecule, were used to examine various aspects of LMP expression in B cell lines transformed in vitro. The pooled CS. 1 to 4 reagent detected the LMPs encoded by each of 20 geographically distinct EBV isolates, despite a degree of inter-isolate heterogeneity in the size and antigenicity of the protein. In cell lines carrying the prototype B95. 8 virus strain, particularly if these were virus producers, an additional lower molecular weight LMP was also detected; this appeared to correspond to the truncated form of the protein already predicted to exist from the analysis of B95. 8 lytic cycle mRNAs. Attempts were made to identify an analogous truncated form of LMP in cell lines carrying other virus isolates after treatment with phorbol ester and/or sodium butyrate to induce virus production. Surprisingly these experiments showed that expression of the full length LMP molecule was itself strongly inducible by these agents; when monitored at the single cell level, this was a generalized response and was not restricted to cells entering a lytic cycle. Expression of LMP in EBV-transformed B cells therefore appears to be subject to a distinct type of regulation.
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