Veterinary Pathology

Hooser, S. B.; Beasley, V. R.; Waite, L. L.; Kuhlenschmidt, M. S.; Carmichael, W. W.; Haschek, W. M.

doi: 10.1177/030098589102800401pmid: 1949504

The morphologic effects of microcystin-LR (MCLR) were examined in vitro and in vivo to identify the specific cell type(s) affected and to characterize the actin filament changes occurring in hepatocytes. Male Sprague Dawley rats were used for all studies. For in vitro studies, hepatic cells were isolated by collagenase perfusion of liver, while parenchymal cells (hepatocytes) and nonparenchymal cells were prepared by pronase digestion and metrimazide gradient centrifugation. Cell suspensions and primary hepatocyte monolayer cultures were treated with MCLR at doses up to 10 μg/ml; cultured hepatocytes were also treated with phalloidin or cytochalasin B at a dose of 10 μg/ml; and rats were treated intraperitoneally with MCLR at 180 mg/kg. Cultured hepatocyte preparations and frozen liver sections were stained with rhodamine-labeled phalloidin for filamentous actin. In cell suspensions. MCLR did not affect nonparenchymal cells but caused rapid, progressive, blebbing of the plasma membrane in hepatocytes. In cultured hepatocytes, MCLR caused plasma membrane blebbing as well as marked reorganization of actin microfilaments. These alterations were dose and time dependent. Cultured hepatocytes treated with phalloidin or cytochalasin B also showed extensive plasma membrane blebbing and actin filament alterations; however, actin filament changes were morphologically distinct from those induced by MCLR. In vivo, MCLR-induced hepatocyte actin alterations occurred at the same time as, or slightly preceded, histologic changes that began 30 minutes after dosing. These studies suggest that early MCLR-induced morphologic changes occurring both in vivo and in vitro are due to alterations in hepatocyte actin filaments.

Ackermann, M. R.; Cheville, N. F.; Gallagher, J. E.

doi: 10.1177/030098589102800402pmid: 1949505

Seven-day-old gnotobiotic pigs were inoculated intranasally with Pasteurella multocida and euthanatized 2, 5, 9, and 14 days after inoculation. Tissues from the oropharynx and respiratory tract of pigs were cultured quantitatively and analyzed microscopically. Pigs remained afebrile and alert, except one that died of acute fibrinopurulent pneumonia. Pasteurella multocida was isolated in greatest numbers from the pharyngeal tonsils, but only in low numbers from turbinate, trachea, lung, spleen, and liver. Significant histologic changes were limited to the tonsil. Infected pigs developed mild tonsillitis with lymphocytic hyperplasia, and accumulation of cell debris and bacteria in crypts. Capsular antigens of P. multocida, identified on tissue sections with rabbit anti-capsular polysaccharide antibody and immunocytochemical reagents, were confined to the crypt lumen. Ultrastructurally, bacteria were free within crypt material or within phagosomes of macrophages or neutrophils. In a second experiment, 5-day-old pigs were infected with Streptococcus suis type 2, followed by toxigenic Pasteurella multocida at 7 days of age; one pig died of streptococcal septicemia. Pigs developed a mild tonsillitis, and both bacteria were cultured from the tonsillar crypts for up to 14 days after infection. These studies show that a toxigenic strain of Pasteurella multocida, which is a causative agent of atrophic rhinitis, can colonize the tonsil and respiratory tract of gnotobiotic pigs for up to 14 days. In addition, colonization can occur concurrently with Streptococcus suis type 2.

Whiteley, L. O.; Maheswaran, S. K.; Weiss, D. J.; Ames, T. R.

doi: 10.1177/030098589102800403pmid: 1949506

Eighteen male Holstein calves were divided into groups of three and inoculated intratracheally with 5 x 109 logarithmic phase or ultraviolet light-killed Pasteurella haemolytica biotype A serotype 1. Serial coagulation profiles were done on one calf from each group during the first 24 hours after inoculation. One calf from each group was necropsied at 4, 12, and 24 hours after inoculation and lesions were characterized with light and transmission electron microscopy. We found that 1) the pulmonary intravascular macrophage may have an important role in the early intravascular inflammatory events; 2) there was morphologic evidence for local initation of the coagulation cascade in the lung early in the disease process but it was not a consumptive process; and 3) killed-bacteria were capable of causing fibrin exudation, platelet aggregation and alveolar epithelial damage similar to live bacteria, but the degenerative changes in neutrophils, endothelial cells and intravascular fibrin formation that occur with live bacteria were not seen.

Bryson, D. G.; McConnell, S.; McAliskey, M.; McNulty, M. S.

doi: 10.1177/030098589102800404pmid: 1949507

Ultrastructural changes occurred in alveolar epithelium in the acute and repair stages of induced respiratory syncytial virus pneumonia induced in eight calves (calf Nos. 1–7, 3 to 6 days old and calf No. 8, 2 weeks old), using a bovine strain of respiratory syncytial virus. Five of the calves were Friesians, three were Hereford x Friesians, and all were male. Tissues from three mock-infected control calves (two Friesian, one Hereford x Friesian) were also examined. Evidence of respiratory syncytial virus infection was observed in both type I and type II pneumocytes from day 4 to day 8 after infection. Infection of type I pneumocytes frequently resulted in necrosis. The response of type II pneumocytes to respiratory syncytial virus infection varied and included hypertrophy, hyperplasia, and syneytial formation. In some infected type II pneumocytes, there were numerous irregular projections of the cell surface, associated with viral budding. Hypertrophy and hyperplasia of type II pneumocytes, epithelial syncytium formation, and irregular cytoplasmic projections from epithelial cells caused considerable thickening of respiratory membrane and occlusion of alveolar lumina. Neutrophils were frequently observed in close association with virus-infected epithelial cells, but evidence of respiratory syncytial virus infection and replication was not observed in alveolar macrophages or neutrophils.Proliferation of type II pneumocytes appeared to play a major role in maintaining the integrity of the alveolar epithelium during the acute stage of the experimental pneumonia. Increased numbers of type II pneumocytes were present on alveolar walls, particularly from 4 to 8 days after infection, and some alveoli were lined entirely by this cell type. In some areas, however, squamous epithelial cells were also involved in covering exposed alveolar basement membrane.

Bryson, D. G.; Platten, M. F.; McConnell, S.; McNulty, M. S.

doi: 10.1177/030098589102800405pmid: 1949508

Ultrastructural changes were observed in bronchioles in acute and repair stages of respiratory syncytial virus pneumonia induced in eight young calves (calf Nos. 1–8) using a bovine strain of respiratory syncytial virus. Five of the calves were Friesians and three were Hereford x Friesians and all were male. Tissues from three mock-infected control calves (two Friesian, one Hereford x Friesian) were also examined. Calves were from 3 to 6 days old at the time of first inoculation, with the exception of calf No. 8, which was 2 weeks old. In the acute stage of the induced pneumonia, evidence of respiratory syncytial virus replication and release was demonstrable in both ciliated and non-ciliated bronchiolar epithelial cells, with the virus-releasing process most obvious at 4 and 5 days after infection. Respiratory syncytial virus infection of bronchiolar epithelium was associated with various changes, including hypertrophy, hyperplasia, and formation of syncytia. Necrosis of epithelial cell structures usually appeared to be preceded by their desquamation from bronchiolar walls. Respiratory syncytial virus infection resulted in considerable damage to the bronchiolar ciliary apparatus. Such damage was seen as early as 1 day post-infection and was still obvious at 10 days post-infection. Neutrophils were closely associated with respiratory syncytial virus infected epithelial cells and evidence of neutrophil fusion with infected epithelial cells was seen. These observations suggest that neutrophils may be involved in killing respiratory syncytial virus infected cells and that neutrophils might play an important role in early antiviral defense against respiratory syncytial virus at a time when antibody levels are low and other cellular defenses are not fully in play. Bronchiolar repair was evident from 6 days after infection and was well advanced at 10 and 13 days after infection.

Latimer, K. S.; Rakich, P. M.; Steffens, W. L.; Kircher, I. M.; Ritchie, B. W.; Niagro, F. D.; Lukert, P. D.

doi: 10.1177/030098589102800406pmid: 1949509

The nature of feather inclusions was characterized in 32 psittacine birds (30 cockatoos, one peachfaced lovebird (Agapornis roseicollis), and one red-lored Amazon parrot (Amazona autumnalis autumnalis)) with naturally-acquired psittacine beak and feather disease. Intranuclear inclusions within feather epithelial cells and intracytoplasmic inclusions within macrophages in the feather epithelium and pulp cavity contained psittacine beak and feather disease viral antigen when stained by the avidin-biotin complex immunoperoxidase technique. Ultrastructurally, inclusions were observed primarily within macrophages and to a lesser extent within epithelial cell nuclei. Macrophage inclusions appeared as paracrystalline arrays of viral particles. Intranuclear inclusions were less well defined, although scattered viral particles were present. Intracytoplasmic and intranuclear particles in ultrastructural preparations were identified by colloidal gold labeling as psittacine beak and feather disease virus. Feather epithelium was more frequently and severely involved in the disease process than was adjacent follicular epithelium. Plucked feathers with an intact epidermal collar and feather epithelium were preferred to follicular biopsies for histopathologic examination.

Adkison, D. L.; Sundberg, J. P.

doi: 10.1177/030098589102800407pmid: 1949510

In a retrospective study, 37 male and 19 female inbred laboratory mice, from 1 to 36 weeks of age, were diagnosed with “lipomatous” hamartomas or choristomas from nearly 10,000 mice examined at necropsy over a 24-month period. Hamartomas and choristomas were found to be rare, noninherited tumorlike conditions that occurred spontaneously in 18 inbred strains of mice with a predominance of the conditions in the C3H/HeJ and C57BL/6J strains. Prevalence between strains ranged from 0.6 to 6.2 cases per hundred thousand mice. The 56 cases studied had soft, raised masses that arose on the dorsal midline, primarily above the sutures of the skull. The lesions were prominent on gross examination due to abnormally long hair, change in direction of the hairs, and a change in hair color compared to the normal pelage.Microscopically, the masses consisted of normal adipose tissue in the reticular dermis and subcutis that sometimes extended through the cranial sutures, entering the brain, or expanding into the ventricles. Large masses occasionally contained normal appearing thyroid, intestine, respiratory epithelium lined cysts, squamous epithelial cysts, bone and marrow, cartilage, glands, and angiomatous anomalies. In all cases, the epidermis was intact. Hair follicles were larger in the affected areas of many cases compared to those in adjacent skin.Breeding studies did not yield affected offspring, indicating this is a congenital, noninherited abnormality. This condition resembles “lipomatous” hamartomas, a congenital defect in human beings.

Sundberg, J. P.; Hanson, C. A.; Roop, D. R.; Brown, K. S.; Bedigian, H. G.

doi: 10.1177/030098589102800408pmid: 1719689

Myoepitheliomas are subcutaneous tumors that arise from myoepithelial cells of various exocrine glands. In a retrospective study of 142 tumors observed over a period of 3 years, myoepitheliomas occurred spontaneously in A/HcJ, A/J, BALB/cJ, BALB/cByJ, LLC,A/Ckc, and NOD/Lt inbred strains of mice. Tumors presented primarily in the subcutaneous tissues of the ventral neck (74% of the myoepitheliomas evaluated) but were observed in several other subcutaneous locations, including the head, perineum, and ventral abdomen. These areas were adjacent to salivary, mammary, clitoral, preputial, and Harderian glands. Forty myoepitheliomas were tested by the avidin-biotin complex technique with a panel of antisera specific for mouse keratins, intermediate filaments, and other cytoskeletal proteins to determine the cell type from which this neoplasm originated. Antibodies directed against the specific mouse keratins K5, K6, and K14, and a broadly crossreactive cytokeratin antibody stained acinar and ductal myoepithelial cells in normal mammary, salivary, and Harderian glands, and neoplastic cells in all cases. Antisera directed against a smooth muscle actin (anti-α-sm-1) stained acinar myoepithelial cells of the glands and vascular smooth muscle but neither ductular myoepithelial cells nor tumor cells. This supports the notion that these tumors originate from extraglandular ductular myoepithelial cells. Southern blots, prepared from DNA extracted from nine myoepitheliomas, did not show restriction fragment length polymorphisms when mouse mammary tumor virus (MMTV) cDNA or Int-1 genomic DNA probes were used; this implies that a retrovirus is not the etiologic agent.

Baumgärtner, W.; Krakowka, S.; Durchfeld, B.

doi: 10.1177/030098589102800409pmid: 1659020

In vivo and in vitro properties of two strains of canine parainfluenza virus(CPIV) were investigated. One strain, designated CPIV(+), induced syncytial giant cell formation and cytolysis in vitro, whereas the second strain, CPIV(−), caused only a mild strand-forming cytopathic effect with few, small syncytial giant cells. Vero cells infected with CPIV(+) or CPIV(−) were 100% positive for CPIV antigen as determined by immunofluorescent staining; however, 100% of CPIV(+) and less than 10% of CPIV(−) infected cells were hemadsorption positive. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis revealed no differences in electrophoretic mobility of viral polypeptides between both strains; however, in CPIV(−) reduced or absent synthesis of the putative HN and F1 proteins was observed. Isopyenic separation of CPIV(+) progeny virions showed a high proportion of viral particles with a buoyant density of 1.18 g/cm3. In contrast, CPIV(−) progeny virions had a heterogeneous density profile ranging from 1.08 to 1.18 g/cm3. Intracerebral infection of six ferrets with CPIV(+) resulted in moderate lymphocytic and histiocytic choroiditis, meningitis, and ependymitis, whereas CPIV(−) infection caused only mild to moderate inflammation. Immunohistologically, CPIV antigen was prominent in ependymal lining cells of the ventricles in CPIV(+)-infected ferrets and was reduced or lacking in CPIV(−)-infected ferrets (n = 6). Sham-injected ferrets (n = 6) did not have histologic lesions and no viral antigen was identified. The present findings suggest that certain changes in the activities of CPIV glycoproteins may lead to alterations of CPIV virulence in vivo.

Murnane, R. D.; Hartley, W. J.; Prieur, D. J.

doi: 10.1177/030098589102800410pmid: 1949511