Experimental subacute sclerosing panencephalitis: selective disappearance of measles virus matrix protein from the Central nervous system.

Subacute sclerosing panencephalitis (SSPE) is caused by a cell-associated or defective form of measles virus. The matrix protein of measles virus may be absent in patients with SSPE which could explain the defective nature of the virus in these patients. In an experimental model of SSPE in hamsters, measles virus in brain tissue is known to convert from a complete infectious form to a cell-associated or defective form eight to 12 days after intracerebral inoculation. Rabbit sera containing antibodies to two individual measles virus polypeptides, the nucleocapsid protein and matrix protein, were used in immunofluorescent and ultrastructural immunoperoxidase studies to label these proteins in brains of hamsters. During the early phase of infection when complete infectious virus could be isolated from brain tissue, both proteins were labeled. However, by 17 days after inoculation, when only cell-associated virus could be rescued from brain tissue, the nucleocapsid protein remained but the matrix protein had disappeared.