Effect of pH on the growth and cytopathogenicity of avian infectious bronchitis virus in chick kidney cells

The growth of avian infectious bronchitis virus (IBV) in chick kidney cells at different pH values in the range 6.0-9.0 demonstrated that although the virus was released at a much faster rate at the higher pH values the titre tended to drop more quickly. At the acid pH values the virus was released more slowly but reached a maximum titre similar to that at the higher pH values and showed only minimum reduction in infectivity up to 49 hours post inoculation. The stability of virus in tissue culture medium was shown to be directly related to pH 6.0-8.0, being more stable at the acid pH values. The degree of cytopathogenicity induced in chick kidney cells following infection with IBV was directly related to the pH at which the cells were incubated, occurring earlier and more extensively in cells at the higher pH values. Cell macromolecule synthesis in chick kidney cells was inhibited following infection with IBV and was apparently due to cell damage and death.     

Plaque formation by avian infectious bronchitis virus in primary chick embryo fibroblast cells in the presence of trypsin

Summary Ten strains of avian infectious bronchitis virus (IBV) were titrated as plaqueforming units in primary chick embryo fibroblast cells. In the absence of trypsin, plaques were only formed by Beaudette-42 and Iowa-609 strains. When trypsin was incorporated in the overlay medium of cell monolayers, all the IBV strains tested produced plaques within 4 days after inoculation. Incorporation of 20–40 µg of trypsin per ml of the overlay medium seemed to be suitable for plaque formation of IBV. A preliminary investigation was made of the mode of action of trypsin.With 2 Figures     

Cytopathology of chick renal epithelial cells experimentally infected with avian infectious bronchitis virus

The renal ducto-tubular epithelial cells of chicks infected with the MA-87 strain of avian infectious bronchitis virus (IBV) were examined ultrastructurally. Infected epithelial cells containing IBV particles were more numerous in the collecting ducts, collecting tubules, distal convoluted tubules and Henle's loops than in the proximal convoluted tubules. Virus particles invaded host cells through endocytotic vesicles. Cytopathologic changes in the infected epithelial cells were manifested by a variety of organlle alterations including swelling of mitochondria, dilation of Golgi vesicles and an increase in the amount of rough endoplasmic reticulum (RER). Virus particles were produced by budding into RER and, rarely, toward the perinuclear space. As virus replication progressed, virus particles were enclosed mainly in the dilated RER, cytoplasmic vesicles or virus-containing electron-dense bodies. Virus particles were also found in vesicles of Golgi complex, the dilated perinuclear space, in some autophagic vacuoles or free in the cytoplasm. Virus particles were released by exocytosis through cytoplasmic vesicles, or appeared to be discharged through disrupted cell membranes. It was concluded that epithelial cells of lower nephron and ducts are the primary target cells in IBV-infected kidneys.     

Replication and cytopathogenicity of avian infectious bronchitis virus in chicken embryo kidney cells

Archives of Virology - The formation of syncytia and their subsequent necrosis were the characteristic cytopathic effects produced in chicken embryo kidney cell cultures infected with the IBV 42...     

Intracloacal infection with avian infectious bronchitis virus

An infectious bronchitis virus (IBV) strain HS-91 isolated from kidneys of chicks which died of nephrosis was inoculated via the cloaca of specific pathogen-free (SPF) chicks. These chicks showed more severe clinical signs, grosser kidney lesions and higher mortality than chicks inoculated with the same IBV strain via the trachea.     

The polypeptide composition of avian infectious bronchitis virus

Summary Avian infectious bronchitis virus grownin ovo was purified by differential centrifugation and isopycnic sedimentation in density gradients. The purified virus was analysed by SDS polyacrylamide gel electrophoresis and found to comprise up to sixteen polypeptides, four of which were glycopeptides. Bromelain treatment of the particles removed three polypeptides and two glycopeptides.With 3 Figures     

Two particle types of avian infectious bronchitis virus

Two distinct types of avian infectious bronchitis virus (IBV) particles were isolated on sucrose density gradients. The higher density particles banded at 1.18 g/ml, had typical coronavirus morphology and contained all the structural polypeptides and a complete genome. The less dense particles of density 1.13 g/ml appeared to have typical coronavirus morphology, although they were much more flattened than the more dense particles. Furthermore, these particles lacked the ribonucleoprotein polypeptide and the genome, although all the other polypeptides were present in the same amounts as in the denser particles.     

Antigenic variation in strains of avian infectious bronchitis virus

Summary Fifteen british field strains of IBV were compared using cross serum neutralization tests in embryonated eggs with seven standard reference strains of IBV. While the British field strains were considered to form a relatively homogeneous group considerable antigenic variation did occur. It was considered that it was not feasible at this time to describe accurately a serotype classification for IBV, similar to that described for other virus groups.     

Antigenic variation of avian infectious bronchitis virus during replication in BHK-21 cells

Summary Avian infectious bronchitis virus Beaudette-42 strain showed antigenic variation during serial passages in BHK-21 cells. The same strain serial passaged in chicken cells or five times in the presence of antibody did not change its antigenicity.With 1 Figure     

Pathogenicity of Australian strains of avian infectious bronchitis virus

The pathogenicity of 25 strains of infectious bronchitis virus (IBV) isolated in Australia between 1961 and 1994 was compared in white leghorn specific pathogen-free chicks. Twelve strains were nephropathogenic and 10 respiratory, the other three being of mixed pathogenicity. The IBV strains identified as nephropathogenic induced clinical nephritis, gross and histological kidney lesions, and mortality of 5-90%. According to the severity of these features, the nephropathogenic strains could be further subdivided into strains of high, moderate or low pathogenicity. The three strains of mixed pathogenicity induced tracheitis, mild clinical nephritis and kidney lesions but no mortality. The 10 respiratory strains caused histological lesions in the trachea but not in the kidney, and did not induce clinical nephritis or mortality. Of 12 IBV strains isolated between 1961 and 1976, nine were nephropathogenic, inducing mortality of 15-90%. In contrast, of 13 strains isolated between 1981 and 1994, only three were nephropathogenic, inducing mortality of 5-37%, whereas nine were respiratory. Seven of these nine strains, unlike other respiratory strains, failed completely to replicate in the kidney. The results indicated a change in the prevalent IBV strains from highly nephropathogenic (1960s to 1970s) to respiratory (1980s to early 1990s); moreover, the late 1980s saw the emergence of respiratory strains with altered tissue tropism.     

The polypeptide composition of avian infectious bronchitis virus particles

Summary Egg grown avian infectious bronchitis virus (IBV) centrifuged on sucrose density gradients was found to consist of a major virus peak of density 1.17 to 1.18 g/cm³ and occasionally two minor virus peaks of density 1.21 to 1.22 g/cm³ and 1.13 g/cm³. Three different IBV strains were examined and no morphological differences were detected between virus particles of different densities or from different strains. The polypeptides of the different density virus particles from the three IBV strains were analysed on polyacrylamide gels. In all cases 7 polypeptides were observed, although there were differences in the proportions of these polypeptides in particles of different densities and those from the different strains. The polypeptides have been called VP1 (molecular weight 130,000), VP2 (105,000), VP3 (97,000), VP4 (81,000), VP5 (74,000), VP6 (51,000) and VP7 (33,000). Additional polypeptides were produced if slightly harsher treatments were used.With 4 Figures     

Studies on avian infectious bronchitis virus (IBV)

Summary The growth of ten strains of avian infectious bronchitis virus (IBV) in several cultured cells was examined. The cultured cells used were chick kidney (CK), chick embryo (CE), HeLa and BHK-21 cells. The results obtained can be summarized as follows. 1. All the strains showed similar growth curves in CK cells. Progeny viruses appeared in the culture medium 4 to 6 hours after inoculation and peak virus titers of 10^6.5–10^8.5 TCID₅₀ per 0.1 ml were obtained after 36 hours. A cytopathogenic effect (CPE) was detected within 24 hours. No distinct CPE and low multiplicities were observed on culturing at 30° C. 2. All strains replicated in CE cells, although only small amounts of virus were produced. No CPE was observed. 3. Only Beaudette-42 and Holte strains grew in BHK-21 cells. 4. No IBV strains grew in HeLa cells.With 6 Figures     

Studies on avian infectious bronchitis virus (IBV)

Summary The resistance of avian infectious bronchitis virus (IBV) to several chemical and physical treatments was studied. Ten strains, including four Japanese strains, were used.1. All strains were sensitive to heating at 56° C for 15 minutes; although two of them, KH and Massachusetts-41, were resistant to heating at 45° C for 90 minutes. 2. All strains were resistant to pH 3.0 and most of the strains were sensitive to pH 11.0. 3. All strains were completely inactivated by chloroform and sodium deoxycholate and all except Beaudette-42 and Connaught were relatively stable to ether. 4. All strains rapidly lost their infectivities upon ultraviolet irradiation. 5. Trypsin did not affect the infectivity of any strain. 6. From these results, the ten strains were classified into three groups based on their stabilities to exposure to heating at 45° C for 90 minutes and to ether.With 2 Figures     

Studies on avian infectious bronchitis virus (IBV)

Summary The induction of interferon by avian infectious bronchitis virus (IBV) and the sensitivity of IBV to interferon were studied. The results of experiments with ten IBV strains are summarized as follows. 1. All the IBV strains tested induced interferon in chick embryo (CE) cells, chicken kidney (CK) cells and embryonated eggs. The Iowa-609 strain induced about 1000 units of interferon in CE cells while the Beaudette-42 strain induced about 200 units of interferon in embryonated eggs; the interferon titers induced by other strains usually ranged from 5 to 60 units. No IBV strain induced interferon in HeLa or BHK-21 cells. 2. IBV particles inactivated by ultraviolet irradiation or by heating lost their ability to induce interferon. 3. The properties of the interferon produced in the present study are similar to those of other interferons produced in chicken cells. 4. HeLa or BHK-21 cells did not acquire resistance to virus infection, after incubation with interferon produced in CE cells. On the other hand, CK cells acquired the same degree of resistance to virus infection as CE cells after incubation with interferon produced in CE cells. 5. All the IBV strains tested were sensitive to interferon in CK cells. The sensitivities of Massachusetts-41 and Holte strains to interferon were similar to that of vesicular stomatitis virus.With 2 Figures     

Electron microscope observations on the entry of avian infectious bronchitis virus into susceptible cells

Summary Infectious bronchitis virus was observed to enter cells of chicken chorioallantoic membrane by viropexis. There was no support for the suggestion that entry took place by fusion of viral and plasma membranes. The results of electron microscopy showed that virus attachment occurred both at 4° and at 37° C. Viropexis was not observed until the preparations were warmed. Similar results were obtained using chicken kidney cells. Quantitative data obtained from a plaque counting system employing chicken kidney cells indicated that attachment was the same at both temperatures and that some virus particles were taken up at 4° C.Virus uptake was triggered by attachment of the virus to the cell membrane and the subsequent process of virus entry visualised by E. M. appeared to proceed without the involvement of lysosomal enzymes. No intracellular virus was located by electron microscopy in warmed preparations when virus was treated with specific antiserum, either before or after adsorption to the cells.With 6 Figures     

Biological properties of the chick infectious bronchitis virus isolated in Russia

A field chick infectious bronchitis virus (IBV) was isolated from the pathological material on chick embryos. The nucleotide sequence of the S1 gene was determined and comparatively analyzed with some sequences of this gene of foreign and Russian vaccine strains and isolates. A cross-neutralization test using sera to various IBV seroptypes was performed. The isolate was shown to antigenically differ from the reference strains. Bioassay was carried out, by using one-day chicks and the immunogenic properties of the virus were investigated.