Characteristics of viruses derived from nude mice with persistent measles virus infection

Abstract

Measles virus (MV) isolates from patients with subacute sclerosing panencephalitis (SSPE) differ from wild-type MV virologically. However, few animal models have reported viruses with characteristics of the SSPE virus. The MV Edmonston strain was inoculated into the subarachnoid space of nude mice. All nude mice displayed weight loss and required euthanasia, with a mean survival duration of 73.2 days. The viral load in the brain was 4- to 400-fold higher than the inoculated load, and brain infection was confirmed by immunostaining. Gene sequencing of the viruses revealed that amino acid mutations occurred more frequently in matrix proteins. The most common mutation was a uridine-to-cytosine transition. The virus exhibited lower free virus particle formation ability than the Edmonston strain. When nude mice were challenged with 2 × 10(2) PFU of the brain-derived virus, the mean survival duration was 34.7 days, which was significantly shorter than that of the mice challenged with 4 × 10(4) PFU of the Edmonston strain (P < 0.01). This study indicated that MV in a nude mouse model of persistent infection exhibited characteristics of the SSPE virus. This model may prove useful in elucidating the pathogenic mechanism of SSPE and developing potential therapeutics.

Fig 1

Percent survival of nude mice infected with the Edmonston strain. Black solid line, mice infected with 4.0 × 10⁴ PFU of the Edmonston strain (Ed) (n = 12); gray solid line, mice infected with 2.0 × 10² PFU of the Yamagata-1 (Ya-1) (n = 10) strain. Euthanasia was performed if mice exhibited more than 20% weight loss relative to their maximum weights.

Fig 2

Pathology of harvested brain. Hematoxylin-eosin staining (A and B) and staining of a polyclonal antibody against the measles virus nucleoprotein (C and D) were used. The histology is representative of three animals examined 58 to 84 days after inoculation of medium (A) or the Edmonston strain (B to D). (A, B, and D) Cortex; (C) around the cerebellum, positivity in Purkinje cells (arrows). The images in panels A, B, and D were captured by an Olympus FSX100 microscope. The image in panel C was captured using a Coolpix P5000 camera (Nikon) connected to a DSZT-44E microscope (Carton). Bars: 50 μm (A and B), 400 μm (C), and 25 μm (D).

Fig 3

Amino acid mutations in viruses derived from brains of mice with persistent MV infection resulting from mutations in the coding region of each gene. The genes are listed on the horizontal axis. Each horizontal axis tick represents 50 amino acids. The number of amino acid mutations is presented on the vertical axis. Among the 10 clones, when any 1 clone had an amino acid mutation at a position, it was counted as one mutation. Overlapping mutations at the same position in multiple clones were counted as a single mutation.

Fig 4

Free virus particle formation ability of persistent virus strains in the nude mouse brain. (A) Viral load in the supernatant; (B) number of infected cells. Gray bars, Edmonston strain; black bars, virus isolated from mouse 2 (M2). The number of plaques at 24 and 48 h after inoculation are shown for each virus in both graphs. The viral load in one well was estimated using 50 μl of the supernatant or cell suspension. Error bars indicate standard errors of the means. The experiment was performed three times independently.

Fig 5

Percent survival of nude mice after inoculation with each virus. Black solid line, mice inoculated with 2.0 × 10² PFU of the virus derived from mouse 2 (M2) (n = 10); gray solid line, mice inoculated with 2.0 × 10² PFU of the Edmonston strain (Ed 2.0 × 10²) (n = 10); broken line, mice inoculated with 4.0 × 10⁴ PFU of the SSPE Edmonston strain (Ed 4.0 × 10⁴) (n = 10).