Antibody response to structural proteins of measles virus in patients with natural measles and subacute sclerosing panencephalitis

The SI strain of measles virus derived from a patient with subacute sclerosing panencephalitis possesses typical genome alterations and unique amino acid changes that modulate receptor specificity and reduce membrane fusion activity

Subacute sclerosing panencephalitis (SSPE) is a fatal sequela associated with measles and is caused by persistent infection of the brain with measles virus (MV). The SI strain was isolated in 1976 from a patient with SSPE and shows neurovirulence in animals. Genome nucleotide sequence analyses showed that the SI strain genome possesses typical genome alterations for SSPE-derived strains, namely, accumulated amino acid substitutions in the M protein and cytoplasmic tail truncation of the F protein. Through the establishment of an efficient reverse genetics system, a recombinant SI strain expressing a green fluorescent protein (rSI-AcGFP) was generated. The infection of various cell types with rSI-AcGFP was evaluated by fluorescence microscopy. rSI-AcGFP exhibited limited syncytium-forming activity and spread poorly in cells. Analyses using a recombinant MV possessing a chimeric genome between those of the SI strain and a wild-type MV strain indicated that the membrane-associated protein genes (M, F, and H) were responsible for the altered growth phenotype of the SI strain. Functional analyses of viral glycoproteins showed that the F protein of the SI strain exhibited reduced fusion activity because of an E300G substitution and that the H protein of the SI strain used CD46 efficiently but used the original MV receptors on immune and epithelial cells poorly because of L482F, S546G, and F555L substitutions. The data obtained in the present study provide a new platform for analyses of SSPE-derived strains as well as a clear example of an SSPE-derived strain that exhibits altered receptor specificity and limited fusion activity.

Altered translation of the matrix genes in Niigata and Yamagata neurovirulent measles virus strains

Niigata and Yamagata strains measles virus were isolated from subacute sclerosing panencephalitis patients. These viruses were defective in virion production and expression of matrix (M) protein. The Niigata M protein-coding frame was interrupted by an in-frame termination codon, whereas the Yamagata M gene lacked the normal translational initiation codon. These mutations prevented translation of a normal M protein. However, RNA derived from the cloned Niigata and Yamagata M genes was translatable in vitro into low levels of aberrant proteins that reacted with M-specific antiserum. These proteins were also translated from poly(A)+ RNA from cells infected by Niigata and Yamagata virus strains. The aberrant M protein of Niigata virus was initiated at a downstream AUG codon created by a second mutation. The Yamagata M gene produced two aberrant proteins: one initiated mainly in vitro at an ACG codon, and a second species initiated at a downstream site both in vitro and in vivo. These results define the abnormal translational functions of the Niigata and Yamagata M genes, and further implicate the involvement of M protein defects in chronic central nervous system infections by measles virus.

Maturation of measles virus hemagglutinin glycoprotein

The processing of measles virus hemagglutinin glycoprotein (H) in infected cells was studied by pulse-chase method and two-dimensional isoelectric focusing and SDS-polyacrylamide slab gel electrophoresis. H glycoprotein was synthesized initially as polypeptides smaller than H glycoprotein present in the virions. They were then processed into a cohort of polypeptides of larger molecular size and with reduced charge. The change was associated with the expression of H glycoprotein on the cell surface. The removal of sialic acid from carbohydrate chain of H glycoprotein resulted in the shift of isoelectric point to a more basic range. The entire process of maturation of H glycoprotein required approximately 5 hours. Carbohydrate content in H was determined to be approximately 12 per cent by weight. Mannose, galactose, fucose, N-acetylglucosamine, and N-acetylneuraminic acid were the constituent monosaccharides.

Detection of antibody to M protein of measles virus in patients with subacute sclerosing panencephalitis: a comparative study on immunoprecipitation

Consistent results have not been obtained yet on the presence of antibody to the M protein of measles virus in the sera of patients with subacute sclerosing panencephalitis (SSPE). We performed a comparative study on various immunoprecipitation systems which appeared in the literature and found that the difference in the composition of the solubilizing buffer produced a large variety of results on the immunoprecipitation. [35S]Methionine-labeled Vero cells infected with the Edmonston strain of measles virus were solubilized by 10 different buffers and reacted with hyperimmune rabbit serum to whole virus, monospecific antisera to H, NP, and M proteins of the virus, normal adults' sera, and the sera from 16 SSPE patients. The immune complex was absorbed by protein A and both solubilization and precipitation rates were compared with each viral protein. Although viral proteins were solubilized by all buffers, the solubilization rate varied considerably. M protein was solubilized and was not coprecipitated nonspecifically with any of the other viral proteins. Purified protein A conjugated to Sepharose was preferable to Staphylococcus aureus for absorption of the immune complex since the latter absorbed both viral and host proteins nonspecifically. The precipitation rates of the viral proteins also varied according to the buffers. Better solubilization of the viral proteins seemed to reduce their rate of precipitation for which the presence of SDS may be responsible, and the presence of the protease inhibitors may also affect the results of immunoprecipitation. Detection of M protein in the immunoprecipitates was largely influenced by the kind of buffer used: some buffers could detect it clearly, but others could not defect it at all. Among the solubilizing buffers tested, Saleh's buffer (Virology 93: 369-376 (1979)),, which contains 0.5% DOC and 0.5% Triton X-100, was most reliable for detection of the anti-M antibody in the rabbit serum, because it showed a high solubilization and high precipitation rates of viral proteins without nonspecific absorption by protein A or coprecipitation of M proteins with any of the other proteins. Using this buffer, we could definitely detect M proteins in the immunoprecipitates from the sera of all six healthy adults and 15 out of 16 patients with SSPE. It was found, however, that the amount of M proteins in SSPE patients was lower than that in healthy adults and varied considerably.

Chronic encephalomyelitis with specific increase in intrathecal mumps antibodies

Symptoms of severe encephalomyelitis developed in a 31-year-old man in 1967. He had a high serum antibody titre to mumps virus associated with a polymorphic cell reaction and an increased protein concentration in cerebrospinal fluid (CSF). He recovered considerably within a year and was able to resume work. In 1975 his condition deteriorated again; it improved during the following few years, but a further deterioration then occurred. In March, 1981, the complement-fixing antibody titre to mumps virus was 1/32 in the serum and 1/4 in the CSF. In November, 1981, the CSF IgG index was increased and the altered serum/CSF antibody ratio persisted. The specificity of the altered antibody ratio was confirmed by the single radial haemolysis test and an immunoassay specific for mumps virus. Antibodies against the mumps virus envelope glycoprotein, M-protein, and nucleoprotein could be demonstrated by immunoprecipitation and the antibody patterns in serum and CSF were similar. Antibodies against other microorganisms were not detected in the patient's CSF, and mumps antibodies were not found in the CSF specimens of 57 control patients. This case may be an example of a new disease-chronic mumps virus infection in the central nervous system.