The effects of bovine respiratory syncytial virus on the phagocytic and antigen-presenting capacity of peripheral blood monocytes and monocytic cell lines derived from lambs and calves

Failure of respiratory defenses in the pathogenesis of bacterial pneumonia of cattle

The respiratory system is well defended against inhaled bacteria by a dynamic system of interacting layers, including mucociliary clearance, host defense factors including antimicrobial peptides in the epithelial lining fluid, proinflammatory responses of the respiratory epithelium, resident alveolar macrophages, and recruited neutrophils and monocytes. Nevertheless, these manifold defenses are susceptible to failure as a result of stress, glucocorticoids, viral infections, abrupt exposure to cold air, and poor air quality. When some of these defenses fail, the lung can be colonized by bacterial pathogens that are equipped to evade the remaining defenses, resulting in the development of pneumonia. This review considers the mechanisms by which these predisposing factors compromise the defenses of the lung, with a focus on the development of bacterial pneumonia in cattle and supplemented with advances based on mouse models and the study of human disease. Deepening our understanding of how the respiratory defenses fail is expected to lead to interventions that restore these dynamic immune responses and prevent disease.

Reduced clearance of respiratory syncytial virus infection in a preterm lamb model

Respiratory syncytial virus (RSV) causes significant respiratory disease in children worldwide. For the study of severe RSV disease seen in preterm infants, a suitable animal model is lacking. The novel hypothesis of this study was that preterm lambs are susceptible to bovine RSV (bRSV) infection, an analogous pneumovirus with ruminant host specificity, and that there would be age-dependent differences in select RSV disease parameters. During RSV infection, preterm lambs had elevated temperatures and respiration rates with mild anorexia and cough compared to controls. Gross lesions included multifocal consolidation and atelectasis with foci of hyperinflation. Microscopic lesions included multifocal alveolar septal thickening and bronchiolitis. Immunohistochemistry localized the RSV antigen to all layers of bronchiolar epithelium from a few basal cells to numerous sloughing epithelia. A few mononuclear cells were also immunoreactive. To assess for age-dependent differences in RSV infection, neonatal lambs were infected similarly to the preterm lambs or with a high-titer viral inoculum. Using morphometry at day 7 of infection, preterm lambs had significantly more cellular immunoreactivity for RSV antigen (P <0.05) and syncytial cell formation (P <0.05) than either group of neonatal lambs. This work suggests that perinatal RSV clearance is age-dependent, which may explain the severity of RSV infection in preterm infants. The preterm lamb model is useful for assessing age-dependent mechanisms of severe RSV infection.

Pathogenic and immunosuppressive effects of avian pneumovirus in turkeys

Avian pneumovirus (APV) causes a respiratory disease in turkeys. The virus has been associated with morbidity and mortality due to secondary infections. Our objective was to determine if APV caused immunosuppression in the T-cell or B-cell compartments and to study the pathogenesis of the disease in APV maternal antibody-lacking 2-wk-old commercial turkeys. APV was administered by the eyedrop/intranasal route. Observations were made for gross lesions, viral genome, and T-cell mitogenesis and cytokine secretion at 3, 5, 7, 14, and 21 days postinoculation (DPI). During the acute phase of the disease that lasted for about 1 wk, the turkeys exposed to APV showed clinical signs characterized by nasal discharge and sinus swelling. Virus genome was detected by in situ hybridization in cells of turbinates and trachea at 3 and 5 DPI. At 3 and 5 DPI, spleen cells of the birds infected with APV markedly decreased proliferative response to concanavalin A (Con A). Con A and lipopolysaccharide stimulation of spleen cells from virus-exposed turkeys resulted in accumulation of nitric oxide-inducing factors (NOIF) in the culture fluid. NOIF were not detected in culture fluids of Con A-stimulated spleen cells of virus-free turkeys. APV did not compromise the antibody-producing ability of turkeys against several extraneous antigens such as Brucella abortus and tetanus toxoid.

The immunology of the bovine respiratory disease complex

The bovine respiratory disease complex continues to be an economically important syndrome in an era when immunologic control is likely to become increasingly important. Recent studies have yielded a better understanding of the interaction, at the molecular level, of various pathogens with the bovine immune system. Improved challenge models for important viral pathogens such as bovine viral diarrhea virus and bovine respiratory syncytial virus have provided evidence of the efficacy of immune responses stimulated by vaccination. This article highlights recent advances in understanding of the role of the immune response in the pathogenesis and prophylaxis of bovine respiratory disease complex.

Infection of primary human monocytes by Epstein-Barr virus

Previous studies have reported that infection of monocytes by viruses such as cytomegalovirus and human immunodeficiency virus weakens host natural immunity. In the present study, we demonstrated the capability of Epstein-Barr virus (EBV) to infect and replicate in freshly isolated human monocytes. Using electron microscopy analysis, we observed the presence of EBV virions in the cytoplasm and nuclei of approximately 20% of monocytes. This was confirmed by Southern blot analysis of EBV genomic DNA sequences in isolated nuclei from monocytes. Infection of monocytes by EBV leads to the activation of the replicative cycle. This was supported by the detection of immediate-early lytic mRNA BZLF-1 transcripts, and by the presence of two early lytic transcripts (BALF-2, which appears to function in DNA replication, and BHRF-1, also associated with the replicative cycle). The late lytic BcLF-1 transcripts, which code for the major nucleocapsid protein, were also detected, as well as EBNA-1 transcripts. However, attempts to detect EBNA-2 transcripts have yielded negative results. Viral replication was also confirmed by the release of newly synthesized infectious viral particles in supernatants of EBV-infected monocytes. EBV-infected monocytes were found to have significantly reduced phagocytic activity, as evaluated by the quantification of ingested carboxylated fluoresceinated latex beads. Taken together, our results suggest that EBV infection of monocytes and alteration of their biological functions might represent a new mechanism to disrupt the immune response and promote viral propagation during the early stages of infection.