G L Watson’s research while affiliated with Michigan State University and other places

Renal cysts in the cortex of a juvenile Belgian Malinois dog with acute renal failure were studied by means of light, scanning and transmission electron microscopy, immunohistochemistry for intermediate filaments, and binding for wheat germ agglutinin (WGA), peanut agglutinin (PNA), and Maclura pomifera agglutinin (MPA) lectins to determine the morphological and histochemical features of the epithelial cells of these cysts. The cysts were renal corpuscles with expanded urinary space. Glomerular tufts were small with poorly developed capillary loops and increased mesangial matrix. Continuity with the proximal tubule was evident in some cystic glomeruli. Two cell types lined Bowman's capsule. One was squamous with a central cilium and microvilli. The other had morphological and histochemical features of immature podocytes (parietal podocytes). These cells were round and protruded into the urinary space; they had thick cytoplasmic projections that resembled foot processes of podocytes, microvilli, and filtration slits. The parietal podocytes expressed vimentin and cytokeratins and had affinity for WGA as do normal immature podocytes. These features suggest that the parietal podocytes are derived by metaplasia of the parietal cells. The basement membrane of Bowman's capsule was irregularly thickened and showed multifocal glycosylation changes with lectin histochemistry (WGA, PNA, MPA) in areas adjacent to the parietal podocytes. Histologic and ultrastructural findings in this dog are consistent with glomerulocystic kidney disease. This is the second report of canine glomerulocystic kidney disease. Features are similar to those of the human counterpart, but it is unclear whether genetic defects cause the disease in the dog. The presence of parietal podocytes in all cysts suggests that abnormal differentiation may play an important role in the pathogenesis of this type of polycystic kidney disease.

Immunohistochemistry, using a monoclonal antibody to Melan A and a polyclonal antibody to S100 protein, was applied to 48 formalin-fixed, paraffin-embedded specimens of feline melanoma. Forty-two cutaneous, three oral, one mucocutaneous, and two metastatic melanomas comprised the tumors. Thirty-two tumors (67%) were positive for Melan A and 42 (87.5%) were positive for S100. All but one of the tumors that were positive for Melan A were also positive for S100. S100 was detected in 11 of 16 tumors that were negative for Melan A. Seventy-five percent (9 of 12) of amelanotic melanomas were negative for Melan A. Normal adrenal cortex, the cerebellum, and the skin had cells that were positive for Melan A. Sebaceous adenoma was the only nonmelanocytic tumor examined that reacted with antibody to Melan A. Although less sensitive than S100 protein, Melan A is more specific for melanoma and is useful in differentiating feline cutaneous melanoma from the more common pigmented basal cell tumor.

The monoclonal antibody A103 to the melanocytic differentiation antigen Melan A stains human steroid-producing cells and their tumors. A total of 200 formalin-fixed, paraffin-embedded canine normal tissues and hyperplastic and neoplastic lesions of the adrenal gland, testis, and ovary were immunohistochemically tested for Melan A with antibody A103. Leydig cell tumors (23/23, 100%), Sertoli cell tumors (14/15, 93%), and adrenocortical adenomas (12/13, 92%) were consistently positive. Adrenocortical carcinomas (23/35, 65%) and granulosa cell tumors (10/17, 59%) were less frequently positive. All pheochromocytomas, seminomas, and dysgerminomas were negative. The pattern of staining was cytoplasmic, but nuclear staining was also frequently seen in normal Leydig cells and their tumors. As in human tumors, immunohistochemistry for Melan A stains many canine steroid-producing tumors and can be used to distinguish these tumors from those of nonstereidogenic cells.

Rhodococcus equi infection was diagnosed in two goats from the same herd. At necropsy, numerous caseating granulomas were disseminated throughout the liver, lungs, abdominal lymph nodes, medulla of right humerus, and the right fifth rib of goat No. 1, and the liver of goat No. 2. Histopathologic examination confirmed the presence of multiple caseating granulomas in these organs. Numerous gram-positive and Giemsa-positive coccobacilli were identified within the cytoplasm of macrophages. Aerobic bacterial cultures of the liver and lung from both goats yielded a pure growth of R. equi. R. equi antigens were immunohistochemically identified in caseating granulomas from both goats. However, the 15- to 17-kd virulence antigens of R. equi were not detected, suggesting possible infection by an avirulent strain of this organism.

Intestinal extramedullary plasmacytomas (EMPs) are rare tumours in dogs. Three cases of canine intestinal EMP with amyloid deposits are described in this report. These tumours, which were located in the rectal submucosa, had variable numbers of well-differentiated plasma cells and fewer multinucleated giant cells of plasmacytoid and histiocytic morphology, admixed with abundant amyloid. Two cases had metaplastic cartilage and bone within the amyloid deposits. Immunohistochemically, the plasma cells of all three tumours reacted for lambda-light chains of immunoglobulins but not for kappa-chains, indicating monoclonality. Plasma cells of two tumours were also positive to CD79a antiserum. Amyloid deposits were labelled with an A lambda (amyloid of immunoglobulin lambda-light chain origin) antiserum but not with antisera against its precursor protein, the immunoglobulin lambda-light chains, indicating possible conformational changes of amyloidogenic proteins during their transformation into amyloid.

Samples from rectal plasmacytoma in three adult dogs that were diagnosed by light microscopy and immunohistochemistry were examined by electron microscopy. The most common cell type had typical plasmacytoid features. A second cell type was a plasmacytoid giant cell with single or multiple eccentric nuclei, irregular nuclear membrane, abundant and dilated rough endoplasmic reticulum, and numerous electron-dense granules. The third cell type was a histiocytic giant cell that intermingled with plasmacytoid cells. All three tumors had abundant amyloid, mainly in the interstitium but also within histiocytic cells and less commonly in plasma cells or plasmacytoid giant cells. Extracellular and intracellular amyloid fibrils and the contents of membrane-bound electron-dense bodies of plasma cells reacted with antibody to lambda-light chain of immunoglobulins by immunogold staining.

To evaluate a thyroglobulin autoantibody (TgAA) assay and determine a diagnostic threshold. Serum samples from dogs with various endocrine abnormalities and from 30 obese adult female Beagles. TgAA were determined by use of the ELISA. Six experiments were done: 1, definition of positive results for TgAA using samples from normal and T3 autoantibody (T3AA) positive dogs; 2, establishment of prevalence of positive results in 91 clinically normal dogs; 3, evaluation of positive results for sera from dogs with nonthyroidal illnesses; 4, testing of samples from dogs with primary hypothyroidism but absence of T4AA or T3AA, or both; 5, determination of prevalence of false-negative results in dogs that are T4AA and/or T3AA positive, which were (18 dogs) or were not (22 dogs) receiving L-thyroxine replacement therapy; and 6, examination of thyroid biopsy specimens from 18 dogs (8 TgAA positive and 10 TgAA negative). Positive results were defined as at least twice (200%) the optical density of the negative-control sample. False-positive results were obtained for only 3.4% of 146 dogs with nonthyroidal illness. Thirty-seven percent of dogs with primary hypothyroidism, but no evidence of T4AA or T3AA, or both, were TgAA positive. False-negative results were found in 1 of 22 and 2 of 18 T3AA-positive dogs with and without thyroid replacement therapy, respectively. Thyroid biopsy specimens from 8 TgAA-positive dogs had evidence of lymphocytic thyroiditis, whereas those from 10 TgAA-negative dogs did not. The assay is sensitive and specific for identification of lymphocytic autoimmune thyroiditis in dogs, and has potential for aiding early diagnosis of thyroiditis in dogs and identifying dogs likely to perpetuate hypothyroidism in breeding programs.

Morphologic, microbiologic, and polymerase chain reaction amplification techniques were used to evaluate an alpaca (Lama pacos) with splenitis and intestinal volvulus. The intestinal volvulus produced a severe necrosuppurative typhlocolitis associated with vascular thrombosis and was most likely the cause of death of this animal. In addition, this animal had multiple coalescing abscesses affecting most of the splenic tissue. The isolation of Actinomyces spp. from the spleen and the morphology of the colonies when stained with Gram and Steiner stains support a diagnosis of splenic actinomycosis.

Macroscopic, histologic, ultrastructural, microbiologic, in situ hybridization (ISH) and PCR detection results in three 8-week-old pigs naturally infected with Pneumocystis carinii (PC) are described. All animals had a nonsuppurative interstitial pneumonia and intra-alveolar Pneumocystis organisms with foamy eosinophilic and PAS positive appearance. Ultrastructurally, PC trophozoites and cysts were observed in pigs No. 2 and No. 3, with the former being much more numerous. PC organisms were located on the alveolar surface or within the alveolar septa. Trophozoites had numerous filopodia and were thick-walled. Cysts had no or few filopodia, were thick-walled and contained intracystic bodies. Using non-isotopic ISH on formalin-fixed, paraffin-embedded lung tissue sections, PC DNA from pigs No. 2 and No. 3 hybridized with a probe specific for PC ribosomal RNA (rRNA). Using primers specific for mitochondrial rRNA gene (pAZ102-E/pAZ102-H), and for the internal transcriber spacers of ribosomal gene of PC, PCR methods amplified a product in the lung of pigs No. 2 and No. 3 using either frozen or formalin-fixed and paraffin-embedded lung tissue. DNA from Pig No. 1 samples did not amplify with any primer. This is the first time that molecular biology techniques (in situ hybridization and PCR) have been applied to the study of porcine pneumocystosis.

This report describes the clinical, microscopic, and ultrastructural findings in mink with muscular sarcocystosis. Three 2-3-mo-old mink were killed because they were ill with signs of progressive neurological disease. One mink had variable numbers of sarcocysts in multiple skeletal muscles. Sarcocysts were up to 300 microm in long and 20 microm wide. Ultrastructurally, the sarcocyst wall had numerous elongated 1.7-2.0-microm x 250-nm villar protrusions (VP). The VP had microtubules and irregularly distanced minute undulations. Both metrocytes and bradyzoites were present in sarcocysts. The mink with sarcocysts in muscles also had nonsuppurative meningoencephalitis and meningomyelitis. Similar brain lesions were found in other 2 mink from the same farm, but sarcocysts were not observed in the skeletal muscle of these animals. This is the first report of muscular sarcocystosis in mink.