Properties and characterization of monoclonal antibodies to Tacaribe virus

Monoclonal antibodies prepared against Tacaribe and Junin viruses have been used to define further the serological relationships between arenaviruses of the Tacaribe complex. A close relationship was found between these two viruses and the heterologous Amapari and Machupo viruses, with Pichinde virus and Parana virus being more distantly related. Among the antibodies specific for Tacaribe virus, five were found to react with viral antigens at the surface of infected cells and to neutralize virus infectivity in vitro. These five antibodies could be differentiated by competitive immunoassay as recognizing at least two antigenically distinct epitopes. The kinetics of reaction between antibody and virus were examined for all five neutralizing antibodies. One antibody (2.25.4) effectively neutralized all infectious virus. The remaining four directed against a second epitope gave significant persistent fractions which could be reduced by addition of complement, anti-mouse immunoglobulin, or antibody 2.25.4. Variants of Tacaribe virus resistant to neutralization by antibody 2.25.4 were obtained by growth in the presence of this antibody and neutralization kinetics were reexamined using the heterologous monoclonal neutralizing antibodies. Several different neutralization profiles were obtained, suggesting that point mutations resulted in conformational changes at topographically selected distinct epitopes recognized by the remaining antibodies.