Reversal of virus-induced systemic shock and respiratory failure by blockade of the lymphotoxin pathway.

At present, little is known about the pathogenesis of acute virus-induced shock and pulmonary failure. A chief impediment in understanding the underlying disease mechanisms and developing treatment strategies has been the lack of a suitable animal model. This study describes a mouse model of virus-induced systemic shock and respiratory distress, and shows that blockade of the lymphotoxin beta receptor pathway reverses the disease.

Evidence of Pasteurella haemolytica linked immune complex disease in natural and experimental models.

The pathogenesis of bovine pneumonic pasteurellosis is not completely understood, and studies have not established that Pasteurella haemolytica A1 (Ph1) virulence is exclusively responsible for the development of acute pulmonary lesions. The purpose of this investigation was to determine if immune complex disease is involved in the pathogenesis of bovine pneumonic pasteurellosis. A retrospective immunohistologic study of lung tissue from natural cases of bovine pneumonic pasteurellosis (44) as performed, and immune complexes were observed in alveloar spaces and walls in 88% of these cases. To study this pathologic mechanism experimentally, groups of mice were immunized with purified Ph1 outer membranes (OMs) or sham immunized on days 0 and 14. Mice were challenged intratracheally on day 24 with either live Ph1 or Ph1 OMs, and pulmonary lesions were assessed 24 h after challenge. Placebo immunized mice developed focal infiltrates of neutrophils and macrophages centered around large caliber bronchi. Mice immunized with Ph1 OMs and challenged with live Ph1 or OMs developed severe bronchointerstitial pneumonia with diffuse neutrophilic infiltration, focal necrosis, hemorrhage and edema, that is histologically similar to bovine pneumonic pasteurellosis. Immunohistology revealed flocculent aggregates of IgG and complement positive material within alveolar spaces and walls from mice challenged with live Ph1, and fine granular deposits of IgG and complement positive material were observed lining the alveolar walls from mice challenged with Ph1 OMs. Immunized mice exhibited high serum IgG antibody titers to Ph1 outer membrane proteins (OMPs). Results of this study suggest that immune complex disease plays a role in the pathogenesis of bovine pneumonic pasteurellosis.

Sequential distribution of neurovirulent and avirulent strains of bluetongue virus in neonatal mice by RT-PCR.

Neurotropism of bluetongue virus (BLU) has been demonstrated in the developing brain of fetal ruminants and neonatal mouse models. Two strains of BLU serotype 11, UC8 and UC2, differentiated by their electrophoretic characteristics and abilities to cause brain lesions in bovine fetuses and neonatal mice were investigated to determine differences in tissue distribution in new born mice following subcutaneous inoculation. Tissue analysis by reverse transcriptase-polymerase chain reaction (RT-PCR) showed selective distribution of both BLU strains to the brain and spleen as early as 3 h post-inoculation (PI) but viral RNA was not detected in the blood or other tissues for the duration of the 15 day experiment. UC2 persisted within the brain and spleen until 9 h PI without development of CNS lesions. In contrast, UC8 persisted within the spleen for 24 h and in the brain through the end of the experiment. UC8 infected mice developed necrotizing lesions throughout the cerebrum and cerebellum that were most severe on PI days 11 and 13. Immunohistochemical staining for BLU identified infected cells within the brains of UC8 inoculated mice before inflammatory lesions were present and gave supportive evidence of the ability of UC2 to infect brain cells. Our results show that both UC8 and UC2 selectively target the brain and spleen in neonatal mice early after inoculation and suggest that the differences in neurovirulence between these strains are due to differences in replicative efficacy within host target cells.

Growth of a neuroinvasive strain of bluetongue virus in suckling mice.

Some strains of bluetongue virus cause congenital brain damage in bovine and ovine fetuses, as well as in neonatal mice. Two strains of bluetongue virus serotype 11 (UC-2 and UC-8) which differ in neuroinvasiveness were used to determine the biological basis for this difference. UC-2 and UC-8 were inoculated subcutaneously into newborn mice and virus was titrated from blood, plasma and brain tissues over 14 days. For the invasive UC-8 strain, 50-175 plaque forming units of virus per ml was found associated with the blood cells and no virus was detected in the plasma. The virus was detected in the brain at day one post inoculation, and again at day 7, increasing to day 11. The results indicate that UC-8 was able to reach the brain soon after inoculation and to replicate and/or remain in the blood circulation better than UC-2. Immunohistochemical examination of frozen brain sections revealed a sudden, multifocal appearance of UC-8 at day 9, with more viral antigen seen at days 11 and 13, which was barely detected by day 15. Viral antigen was not associated with blood vessels in the brain, indicating that the viral invasion was not from infected vascular endothelium. No virus was detected in the mice infected with strain UC-2.

The pathogenesis of bluetongue virus infection of bovine blood cells in vitro: ultrastructural characterization.

Cattle are proposed to be reservoir hosts of bluetongue virus (BTV) because infected animals typically have a prolonged cell-associated viremia. Enriched populations of bovine monocytes, erythrocytes and lymphocytes were inoculated with BTV serotype 10 (BTV 10) and the infected cells then were examined by transmission electron microscopy to characterize the interaction of BTV with bovine blood cells. Replication of BTV 10 in monocytes and stimulated (replicating) lymphocytes was morphologically similar to that which occurred in Vero cells, with formation of viral inclusion bodies and virus-specific tubules. In contrast, BTV 10 infection of unstimulated (non-replicating) lymphocytes and erythrocytes did not progress beyond adsorption, after which virus particles persisted in invaginations of the cell membrane. Studies with core particles and neutralizing monoclonal antibodies established that outer capsid protein VP2 is necessary for attachment of BTV 10 to erythrocytes. These in vitro virus-cell interactions provide a cogent explanation for the pathogenesis of BTV infection of cattle, especially the prolonged cell associated viremia that occurs in BTV-infected cattle.