Monoclonal antibodies to guinea-pig cytomegalovirus: an immunoelectron microscopic study.

Three groups of monoclonal antibodies which reacted with cells infected by guinea-pig cytomegalovirus (GPCMV) were prepared. The first group of antibodies immunoprecipitated a 50 000 mol. wt. (50K) polypeptide of GPCMV-infected cells. This polypeptide was identified as part of the nuclear inclusion by immunofluorescence. This nuclear fluorescence was markedly diminished when the infected cells were incubated in the presence of phosphonoacetic acid. By immunoelectron microscopy the antibodies reacted mainly with filamentous structures (26 to 28 nm in diameter) in nuclear inclusions and occasionally stained nucleocapsids. Neither intracytoplasmic nor extracellular virions reacted with the antibodies. Therefore, the 50K protein with which the monoclonal antibodies reacted was nuclear inclusion-specific and a non-structural protein. The second group of antibodies reacted with a 76K polypeptide of the infected cells which was a matrix protein found in both cytoplasmic inclusions and extracellular dense virions. The third group of antibodies mainly reacted with a virion core protein by immunoelectron microscopy.