Dr. Tom Jerrells and his laboratory have been working with CVB3 since 2002 with a mouse model of CVB3-mediated pancreatitis and the mechanisms of chronic alcohol abuse that affect the production of chronic alcoholic pancreatitis and fibrosis. The research is based on epidemiologic data that shows that 70 to 80% of the diagnosed cases of acute and chronic pancreatitis in human beings are associated with chronic of alcohol abuse, but interestingly only 15-20% of the people who abuse alcohol for these times develop pancreatitis. These data argue for a co-factor that is involved in the development of pancreatitis. On the basis of the finding that alcoholic liver disease has similar epidemiologic characteristics and it has been clearly shown that hepatic viral infections (i.e., hepatitis B and C viruses) are robust co-factors for the development of alcoholic liver disease, we posed the hypothesis that viral infections of the pancreas would be a co-factor for the development of alcoholic pancreatitis.
In fact, the animal model developed in collaboration with other member of the Enterovirus Research Group (Drs. Chapman and Tracy) showed exactly what was predicted. Infection of mice that were provided ethanol in drinking water for extended time showed statistically significant increases in serum concentrations of amylase and lipase, which are commonly used for clinical diagnosis of acute pancreatitis. Histologic evaluation of the pancreas showed marked destruction of the exocrine pancreas (acinar cells) and no apparent damage to the islets after infection with the strain of CVB3 that is tropic for the pancreas. Interestingly, the pancreas regenerated rapidly. Recent studies have shown that alcohol consumption by the relatively resistant strain of inbred mice results in an inability to control the viral infection and low levels of active cytolytic virus is demonstrable up to 28 days after infection. Control mice in the same experiments clear the virus around 10 days after the infection. Of particular interest is the finding that a persistent non-lytic infection can be demonstrated up to 28 days after the infection. The demonstration of continued viral infection, either an active or persistent infection, appears to be a factor for the development of chronic pancreatitis and, importantly, pancreatic fibrosis. We have shown with a number of approaches that there is a cell in the pancreas with similar characteristics as the stellate cells in the liver that are induced by various factors, to include TGF-b and other cytokines, to produce type 1 collagen to produce the fibrosis. It is our hypothesis that the continued viral replication, especially the slowly replicating persistent virus in the pancreas continues to stimulate the innate and acquired immune system to continue a low level of inflammation and stellate cell activation, thus chronic pancreatitis and fibrosis occurs. Published data from this laboratory shows that there is an increased number of CD4+ and CD8+ T cells in the pancreas obtained from infected mice that has been provided alcohol for extended times, which supports two suggestions. First, it is likely that the continued presence of T cells is the result of continued expression of either viral proteins as a result of persistent viral infection of the acinar cells or a continued response of autoreactive T cells. Secondly, it is clear that some changes in the cells of the pancreas mediated by metabolism of alcohol in the pancreas “sensitizes” the acinar cells to exaggerated damage mediated by activated T cells or proinflammatory cytokines. It is hypothesized that the sensitization of the pancreas to a “second hit” mediated by viral infection is depletion of antioxidants (i.e., glutathione) or endoplasmic stress that results from accumulation of unfolded or misfolded proteins in the endoplasmic reticulum as a result of alcohol metabolism or the processing of the viral proteins.
We recently discovered that the CVB3 infection is associated with the development of antibodies that recognize proteins obtained from pancreata from non-infected mice, which support the suggestion that one aspect of the pathogenicity of CVB3 in terms of the development of chronic pancreatitis is an autoimmune response. Studies are in progress to better define this phenomenon and to determine whether there is a T-cell-mediated autoimmune response as well as the autoimmune antibody response. It is not surprising that autoimmunity occurs on the basis of the extensive tissue damage in the pancreas mediated by the virus infection.
We have shown that the infection induces high serum concentrations of proinflammatory cytokines that is believed to damage other organs, especially the lungs and liver. Data have been generated to support this suggestion and this is an active area of research in the laboratory.
We have also developed a model of autoimmune pancreatitis and fibrosis that is induced by infection with the murine cytomegalovirus (MCMV). MCMV is a herpes virus that reproduces the pathogenic effects of human CMV in various mouse strains. We are interested in this model because of the well-studied effect of changes in the immune system that reactivate the virus to produce a second round of pathogenic infection. It has been shown in the lungs that MCMV will activate the immediate early gene that is involved in the early stages of viral replication and the gene product is not only necessary for viral replication but is the immunodominant viral antigen that induces CD8+ T-cell-responses. It our hypothesis that latent viral infections of the pancreas and heart ultimately results in autoimmune responses and pathogenicity because of the random reactivation of small numbers of latent virus in these organs, which is essentially the same mechanism of continued immune responses in these organs as described for the persistent CVB3 infections of the pancreas and heart (for complete details of CVB3-mediated myocarditis see the write up provided by Dr Chapman).
One recent interest in the laboratory is the effects of acute infections of the pancreas and the robust production of proinflammatory cytokines, especially tumor necrosis factor associated with the infection. The infection results in high concentrations of tumor necrosis factor in the serum and this seems to mediate damage of the liver, which is independent of the viral infection of the liver. Studies are in progress to definitively show that tumor necrosis factor is mediating this collateral damage of the liver in mice that consume alcohol for chronic periods. Another effect of the infection is the potential collateral damage of the lungs mediated by tumor necrosis factor. Recent studies in collaboration with Dr Steve Carson show that the viral infection alone produces obvious changes in the lungs that are clearly associated with the infection and increase in severity over the time of the infection. It appears that the virus infects cells of the lungs to induce changes in tight junctions of pulmonary epithelial cells to induce changes in permeability and leakage. In fact, the infection appears to be associated with erythrocytes in pulmonary wash outs, which further supports the hypothesis that there are changes in permeability in the lungs that would include endothelial cells. These preliminary data are being expanded to determine the possibility of direct viral effects in the lungs, pulmonary damage mediated by proinflammatory cytokines, or both.
Work in the laboratory also involves the use of cell culture models of viral infections of the pancreas and pulmonary epithelial cells. These studies are designed to use a system that can be manipulated to define in detail the cellular mechanisms that are involved in the viral infection of these cell types and the effects of alcohol on the infection. In the near future, a stellate cell model will be developed to define the role of direct infection of this cell type, which is responsible for collagen production in the liver and pancreas, on the noted fibrosis seen in the chronic pancreatitis models.