Indirect role of T cells in development of polioencephalitis and encephalomyelitis induced by encephalomyocarditis virus

Serendipity: Reflections on Being Mentored by Dr. Peter Doherty

This is a semiautobiographical and scientific account of my time in the Doherty Laboratory from 1994 to 1999. It includes personal vignettes as well as discussion of how our work has impacted the fields of influenza, respiratory infections and immunity. I also point out the long-term impacts on my career.

Role of invariant NKT cells in lipopolysaccharide-induced lethal shock during encephalomyocarditis virus infection

Viral infections can give rise to secondary bacterial infections. In the present study, we examined the role of invariant natural killer T (iNKT) cells in lipopolysaccharide (LPS)-induced lethal shock during encephalomyocarditis virus (EMCV) infection. Wild-type (WT) mice and Jα18 gene knockout (Jα18 KO) mice were inoculated with EMCV, 5days prior to challenging with LPS. The survival rate of Jα18 KO mice subjected to EMCV and LPS was significantly higher than that of WT mice. TNF-α and nitric oxide (NO) production were increased in WT mice, than that in Jα18 KO mice, after the administration of EMCV and LPS. EMCV infection increased the number of iNKT cells and IFN-γ production by iNKT cells in WT mice. Moreover, EMCV infection enhanced the expression of Toll-like receptor 4 (TLR4) in the lung and spleen. IFN-γ also increased the expression of TLR4 in splenocytes. These findings indicated that EMCV infection activated iNKT cells, and IFN-γ secreted from the iNKT cells up-regulated the expression of TLR4 in various tissues. As a result, EMCV-infected mice were susceptible to LPS and easily developed the lethal shock. In conclusion, iNKT cells were involved in the development of LPS-induced lethal shock during EMCV infection.

High susceptibility to lipopolysaccharide-induced lethal shock in encephalomyocarditis virus-infected mice

Secondary bacterial infection in humans is one of the pathological conditions requiring clinical attention. In this study, we examined the effect of lipopolysaccharide (LPS) on encephalomyocarditis virus (EMCV) infected mice. All mice inoculated with EMCV at 5 days before LPS challenge died within 24 h. LPS-induced TNF-α mRNA expression was significantly increased in the brain and heart at 5 days after EMCV infection. CD11b⁺/TLR4⁺ cell population in the heart was remarkably elevated at 5 days after EMCV infection, and sorted CD11b⁺ cells at 5 days after EMCV infection produced a large amount of TNF-α on LPS stimulation in vivo and in vitro. In conclusion, we found that the infiltration of CD11b⁺ cells into infected organs is involved in the subsequent LPS-induced lethal shock in viral encephalomyocarditis. This new experimental model can help define the mechanism by which secondary bacterial infection causes a lethal shock in viral encephalomyocarditis.

Experimental encephalomyocarditis virus infection in small laboratory rodents

Encephalomyocarditis virus (EMCV) is a cardiovirus that belongs to the family Picornaviridae. EMCV is an important cause of acute myocarditis in piglets and of fetal death or abortion in pregnant sows. Small rodents, especially rats, have been suspected to be reservoir hosts or carriers. This virus also induces type 1 diabetes mellitus, encephalomyelitis, myocarditis, orchitis and/or sialodacryoadenitis in small laboratory rodents. This paper reviews the pathology and pathogenesis of experimental infection with EMCV in small laboratory rodents.

Non-suppurative meningoencephalitis of unknown origin in cats and dogs: an immunohistochemical study

Non-suppurative meningoencephalitis of unknown cause is a frequent finding in dogs and cats. Fifty-three dogs and 33 cats with non-suppurative meningoencephalitis of unknown aetiology were examined immunohistochemically for 18 different infectious agents, including viruses, bacteria and prion protein^Sc. In 14 (26%) of the dogs and 13 (39%) of the cats a causative agent was identified in the central nervous system (CNS), two dogs and one cat giving positive results for two infectious agents simultaneously. The study revealed infections with known causative agents (porcine herpes virus 1, feline infectious peritonitis virus, Escherichia coli) and a new disease pattern of parvovirus infection in the CNS of dogs and cats. Infection of the CNS with feline leukaemia virus was found in a cat. Five dogs and four cats gave positive results for West Nile virus (WNV) antigen. In one dog, canine parainfluenza virus antigen was detected in the brain. Four dogs and four cats gave positive results for encephalomyocarditis virus (EMCV). The significance of the detection of WNV and EMCV antigen requires further study. The aetiology remained undetermined in 39 dogs (74%) and 20 cats (61%). Although it is possible that non-infectious causes play a more important role than previously thought, infections with hitherto unrecognized agents cannot be ruled out.

The Role of CD4+ T Cells in Biphasic Hind Limb Paralysis Induced by the D Variant of Encephalomyocarditis Virus (EMC-D) in DBA/2 Mice

DBA/2 CrSlc mice infected with the D variant of encephalomyocarditis virus (EMC-D) (10 PFU/head) developed biphasic hind limb paralysis due to spinal cord lesion. The early phase lesion was characterized by demyelination with infiltration of macrophages in the funiculus lateraris and the late phase lesion by degeneration of motor neurons with infiltration of CD4(+) T cells in the cornu ventrale. In the present study, treatment with anti-Mac1 monoclonal antibody (MAb) or anti-CD4 MAb prior to virus infection (-3 to -1 days) reduced the early phase lesion and the incidence of the first paralysis. Signals of viral RNAs were observed only in a few oligodendrocytes in the funiculus lateraris. Treatment with anti-CD4 MAb from 31 to 33 days post infection when mice showed recovery from the first paralysis reduced the late phase lesion and prevented the second paralysis. Signals of viral RNAs were still detected in a few degenerated neurons in the cornu ventrale. These results indicate that while macrophages and CD4(+) T cells participate in the early phase lesion and paralysis and only CD4(+) T cells in the late phase lesion and paralysis.

Distribution of viral RNA in the spinal cord of DBA/2 mice developing biphasic paralysis following infection with the D variant of encephalomyocarditis virus (EMC-D)

DBA/2 mice infected with the D variant of encephalomyocarditis virus (EMC-D) (10(1) PFU/head) developed biphasic hind limb paralysis. As a first step in clarifying its pathogenesis, we examined the distribution of viral RNA in the spinal cord using in situ hybridization. At 3 days post inoculation (DPI), in the spinal cord of mice showing slight paralysis, viral RNA was observed in capillary endothelial cells and a few adjacent glia cells in the funiculus lateralis from thoracic to lumbar enlargement. At 7 DPI, in the spinal cord of mice showing apparent paralysis, viral RNA was observed in a larger number of glia cells in the demyelinated lesion associated with infiltration of macrophages in the funiculus lateralis and in a small number of degenerated neurons in the cornu ventrale. In the funiculus lateralis, viral RNA could not be observed after 28 DPI. On the other hand, viral RNA was observed in degenerated neurons in the cornu ventrale of mice showing the second phase paralysis at 42 DPI. Many CD4+T cells infiltrated around these degenerated neurons. These results suggest that: (1) the viral entry zone was the capillary endothelial cells in the funiculus lateralis; (2) first phase paralysis was due to demyelination caused by EMC-D and associated with macrophage infiltration; (3) second phase paralysis was due to degeneration of motor neurons bearing viral RNA associated with infiltration by CD4+T cells.

Picornavirus-specific CD4+ T lymphocytes possessing cytolytic activity confer protection in the absence of prophylactic antibodies

Picornaviruses are a family of positive-strand RNA viruses that are responsible for a variety of devastating human and animal diseases. An attenuated strain of mengovirus (vMC24) is serologically indistinguishable from the lethal murine wild-type mengovirus and encephalomyocarditis virus (EMCV). Immunogen-specific stimulation of vMC24-immune splenocytes in vitro demonstrates preferential activation of CD4+ lymphocytes. vMC24-immune splenocytes adoptively transferred to naive recipients conferred protection against lethal EMCV challenge. Immune splenocytes, expanded in vitro, were > 92% CD4+ T lymphocytes. Interestingly, adoptive transfer of these expanded cells engendered protection against lethal challenge. In vivo depletion of CD4+ T lymphocytes prior to lethal challenge abrogated survival of transfer recipients, confirming that CD4+ T lymphocytes were essential for protection. Subsequent rechallenge of vMC24-immune splenocyte recipients with a greater EMCV dose elicited serum neutralizing antibody titers paralleling the high titers observed in vMC24-immunized mice. Unexpectedly, an augmented humoral response was absent in vMC24-specific CD4+ T-cell recipients after the secondary challenge. Moreover, comparably low serum neutralizing antibody titers failed to protect passive transfer recipients when correspondingly challenged. vMC24-immune splenocytes expanded in vitro (> 94% CD4+) lysed vMC24-infected A20.J target cells. The ability to transfer protection with primed CD4+ T cells, in the absence of primed B lymphocytes or immune sera, is novel for picornaviral infections. Consequently, mechanisms such as CD4+ cytolytic T-lymphocyte activity are implicated in mediating protection.

Biphasic disease of central nervous system induced in DBA/2 mice by the D variant of encephalomyocarditis virus (EMC-D)

DBA/2 mice infected with the D variant of encephalomyocarditis virus (EMC-D) (10(1) PFU/head) developed biphasic hind limb paralysis. At 12 days post inoculation (12 DPI), 60% of the infected mice developed hind limb paralysis and two-thirds of them showed recovery by 33 DPI. Thereafter, about 30% of the mice which once showed paralysis developed hind limb paralysis again by 56 DPI. Histopathologically, the spinal cord lesion of paralysed mice was characterized by demyelination associated with infiltration of macrophages in the funiculus lateralis and by degeneration of neurons in the cornu ventrale. Virus antigens were detected in the cytoplasm of degenerated neurons and oligodendrocytes in the demyelinated lesions from 3 to 14 DPI. At 28 DPI, demyelinated lesions reduced in size due to prominent remyelination. At 56 DPI, infiltration of mononuclear cells mainly composed of anti-L3T4-positive (CD4+) T cells were observed in the cornu ventrale of the mice showing recurrence of hind limb paralysis. These results suggested that the early paralysis was mainly due to demyelination in funiculus lateralis caused by EMC-D and macrophages and that the late paralysis was due to degeneration of motor neurons, probably brought about by CD4+ T cells.

ts1, a temperature-sensitive mutant of Moloney murine leukemia virus TB, can infect both CD4+ and CD8+ T cells but requires CD4+ T cells in order to cause paralysis and immunodeficiency

When neonatal FVB/N mice were inoculated with ts1, a temperature-sensitive mutant of Moloney murine leukemia virus TB, they developed a progressive bilateral hindlimb paralysis and immunodeficiency leading to death 4 to 6 weeks after inoculation. T lymphocytes have been shown to be primarily responsible for this ts1-induced syndrome. Here we compare the role played by each subset of T lymphocytes, i.e., CD4+ and CD8+ T cells, in disease development. Mice were depleted of a specific subset for the first 10 days of their lives by using either anti-CD4 or anti-CD8 monoclonal antibodies in vivo. Disease development in these mice was then monitored. Depletion of CD4+ T cells significantly attenuated the ts1-induced syndrome: virus replication was decreased, disease latency was extended, and death was prevented in 60% of the mice. Similar treatment with anti-CD8 antibody had almost no effect on disease progression. However, when depletion was begun 2 weeks after neonatal ts1 inoculation, CD4+ T cell depletion did not affect disease development. ts1 infected CD4+ and CD8+ T lymphocytes equally well in vivo, as shown by flow cytometric analysis, but virus replication was restricted primarily to the CD4+ subset of T cells, as found by in vitro assay. Hence, CD4+ T lymphocytes play an important role in the development of ts1-induced paralysis and immunodeficiency. The mechanism of this CD4+ T-cell-mediated disease production by ts1 is not clear; however, increased replication of ts1 in the CD4+ T cells, especially in the early stages of the disease, seems to play a crucial role.