Acute and persistent alterations in pulmonary inflammatory cells and airway mast cells induced by Sendai virus infection in neonatal rats.

Neonatal rats inoculated with parainfluenza type 1 (Sendai) virus develop alveolar dysplasia and bronchiolar hypoplasia by 30 to 110 days after inoculation. Weanling rats do not develop these abnormalities. Because neonatal animals have hyporesponsive immune and inflammatory cell functions, and because neonatal rats support pulmonary viral replication for longer duration and are delayed in their viral antibody response compared to weanling rats, we compared inflammatory and immune responses of two age groups of rats following viral inoculation. Data from quantitative bronchoalveolar lavage 1 to 29 days following viral inoculation demonstrated that neonates had significantly fewer (P less than 0.05) lymphocytes and macrophages in their bronchoalveolar fluid per cm2 alveolar surface than weanlings. Magnitude of neutrophil responses in neonatal rats compared to weanlings were not depressed. Pulmonary interferon activity was lower in neonates than in weanlings at 2, 3, 4, and 5 days after viral inoculation. Neonates failed to make antibody following intraperitoneal inoculation of inactivated viral antigen, whereas weanling rats had detectable viral antibody by 3 to 5 days after injection of antigen. At 90 days after inoculation of neonates, viral-inoculated rats had over 100-fold greater numbers (P less than 0.05) of mast cells in enzyme-dissociated lung preparations compared to age-matched controls. Viral-inoculated rats had two- to three-fold greater densities of mast cells (#/mm) in bronchiolar walls (P less than 0.02) than did control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathogenesis of bronchiolitis and pneumonia induced in neonatal and weanling rats by parainfluenza (Sendai) virus.

The objective of this research was to identify potential mechanisms that might account for the greater susceptibility of neonatal rats (5 days old) as compared with weanling rats (25 days old) to viral-induced lung injury. Sites of viral replication, the sequential development of bronchiolitis and pneumonia, and systemic humoral immune responses were compared between neonatal and weanling rats from 2 to 17 days after being inoculated intranasally with parainfluenza Type 1 (Sendai) virus. In both neonatal and weanling rats, viral antigen was demonstrated by immunoperoxidase technique and viral nucleocapsids, and budding virions were demonstrated by transmission electron microscopy in bronchiolar ciliated and nonciliated epithelial cells as early as 2 days after inoculation. Similar evidence of viral replication was also demonstrated in both ages of rats in alveolar Type I and Type II epithelial cells and in macrophages. Neither virus nor viral antigens was identified in endothelial cells or interstitial cells of interalveolar septa. Bronchiolitis was induced as early as 2 days after inoculation in both ages of rats and was characterized by necrosis, erosion, and hyperplasia of epithelial cells. Multifocal to locally extensive interstitial pneumonia centered on bronchioles, was characterized by alveolar epithelial cell damage and by infiltration of neutrophils, macrophages, and lymphocytes in alveolar septa and spaces and was observed as early as 2 days after inoculation in both age groups of rats. Interstitial pneumonia of maximal severity occurred in weanling rats at 5 days after inoculation, whereas maximal pneumonia of comparable severity occurred in neonatal rats at 8 days after inoculation. Epithelial repair and resolution of bronchiolitis and pneumonia were largely complete in both ages of rats by 17 days after inoculation. Virus was recovered from lung homogenates of neonatal and weanling rats as early as 2 days after inoculation. In weanling rats, infective virus could not be recovered from lung beyond 6 days after inoculation, whereas in neonatal rats virus could be recovered from lung as late as 10 days after inoculation. Viral persistence in neonatal rats was associated with a delayed onset of serum antibody to the virus, compared with weanling rats. The results indicate that the cellular sites of viral replication and the pattern of inflammatory reactions are closely comparable between neonatal and weanling rats inoculated with Sendai virus.(ABSTRACT TRUNCATED AT 400 WORDS)

Live temperature-sensitive equine influenza virus vaccine: generation of the virus and efficacy in hamsters.

Temperature-sensitive (ts) reassortants of an equine influenza virus, subtype A-1, were produced by mating a human influenza ts donor virus with an equine influenza A/Cornell/16/74 wild-type virus and by isolating a ts reassortant virus possessing the equine hemagglutinin and neuraminidase surface antigens. Two equine its reassortant clones, 8B1 and 71A1, were produced which had an in vitro shutoff temperature for plaque formation of 38 and 37 C, respectively. The human ts donor virus had ts mutation(s) on the polymerase 3 (P3) and nucleoprotein genes so that a ts equine reassortant virus could have either or both of these ts genes. It was found by complementation analysis that reassortant clone 8B1 had a ts lesion on the P3 gene and clone 71A1 had ts lesions on the nucleoprotein and P3 genes. An analysis of the parental origin of the genes in each ts equine reassortant virus indicated that clone 8B1 received 6 of its 8 genes and clone 71A1, 3 of its 8 from the equine parent virus, the remainder genes being from the human ts donor virus. The growth of both clones was restricted in the lungs of hamsters, but similar to that of the equine wild-type virus in the nasal turbinates. Each virus isolate obtained from the hamster's lungs or nasal turbinates retained the ts phenotype. These findings form the basis for further evaluation of the equine ts reassortant viruses for their level of attenuation and immunogenicity in horses.