Autoimmunity-related demyelination in infection by Japanese encephalitis virus

Abstract

Japanese encephalitis (JE) virus is the most common cause of epidemic viral encephalitis in the world. The virus mainly infects neuronal cells and causes an inflammatory response after invasion of the parenchyma of the brain. The death of neurons is frequently observed, in which demyelinated axons are commonly seen. The mechanism that accounts for the occurrence of demyelination is ambiguous thus far. With a mouse model, the present study showed that myelin-specific antibodies appeared in sera, particularly in those mice with evident symptoms. Meanwhile, specific T cells proliferating in response to stimulation by myelin basic protein (MBP) was also shown in these mice. Taken together, our results suggest that autoimmunity may play an important role in the destruction of components, e.g., MBP, of axon-surrounding myelin, resulting in demyelination in the mouse brain after infection with the JE virus.

Figure 1

Detection of viral RNA by RT-PCR in brains of mice inoculated with Japanese encephalitis virus. The size of the amplified fragment was estimated to be 291 bp. Viral RNA was observed in all mice with evident clinical symptoms (m1, m2, and m4). A mouse (c1) inoculated with culture medium was used as the control. In addition, viral RNA was detected from both the cerebrum (marked with B) and the cerebellum (marked with b) of brains of infected mice. The lane marked "v" is the positive control taken from a cultured virus suspension.

Figure 2

Pathological changes with severe inflammation in a mouse brain infected with Japanese encephalitis virus. (A) Inflammatory infiltrate around the vessel in the brain. The blood vessel is congested with inflammatory cells. (B) Degenerating neurons (pink) shown in the brain of symptomatic mice are being engulfed by phagocytes (arrow). Hematoxylin and Eosin staining. Original magnification: × 400.

Figure 3

Demyelination shown in the brain of mice infected with the Japanese encephalitis virus. (A) Severely demyelinating axons extensively distributed in the brain, primarily the cerebrum, of symptomatic mice. (B) Demyelinated axons present a loose composition of myelin. (C) Normal axons were surrounded by a myelin sheath that was condensed with intraperiodic lines. Scale bar = 5 μm for A, 500 nm for B, and 100 nm for C.

Figure 4

Detection of an anti-MBP antibody in mouse sera collected from JE virus-infected mice. Average titers of the anti-MBP antibody (IgG) from mice with impaired movement were significantly higher than those in asymptomatic ones (Student's t-test, p < 0.05). S, Sera from symptomatic mice; AS, sera from asymptomatic mice.

Figure 5

T-cell proliferation in mice infected with the Japanese encephalitis virus after treatment with 50 μg/ml of the myelin basic protein (MBP). A stimulation index (SI) was used to express the efficacy of T-cell proliferation for each mouse compared to that from a mouse inoculated with culture medium only. Mouse s1~s3: mice with symptoms of movement disability; Mouse ns1~ns2: mice without evident symptoms.