Identification of epitope expression on the internal proteins of rinderpest virus which is dependant upon virion maturation events

Monoclonal antibodies (MAb) identified the existence of both maturation-dependent and maturation-independent epitopes on rinderpest virus antigens. The former were divided into (i) post-maturation antigenic determinants, which were dependent upon the maturation of viral antigen into complete virions; and (ii) pre-maturation antigenic determinants, which were only expressed on what appeared to be immature particles before ‘budding’ into the extracellular environment. Epitope expression could be related to the kinetics of virus production, with the ‘post-maturation’ sites requiring the production of mature/infectious virions, but the ‘pre-maturation’ sites being lost when mature virus was formed (these ‘pre-maturation’ determinants were strongly cell-associated). MAb against the different virion proteins of measles virus, when reacting with rinderpest virus did not demonstrate the same relationship to virion maturation as did the anti-rinderpest virus MAb: the anti-measles virus MAb detected maturation-independent epitopes. This work demonstrates the caution which should be taken when preparing antigens for diagnostic and epidemiological purposes, especially when MAb are being used to identify antigenic differences between isolates, and/or to compare antigenically isolates with vaccine viruses.