APMIS zyxwvutsrqp 98: zyxwvutsr 255-268, 1990 Peyer’s patches zyxw in experimental Salmonella dublin infection in calves zyx Microvascular and epithelial changes contributing to atrophy of lymphoid follicles T. LANDSVERK, B. LIUM, J. A. MATOVELO, E. LIVEN and K. NORDSTOGA Department of Pathology, the Norwegian College of Veterinary Medicine and the National Veterinary Institute, Oslo, Norway Landsverk, T., Lium, B., Matovelo, J. A., Liven, E. & Nordstoga, K. Peyer’s patches in experimental Salmonella dubfin infection in calves. Microvascular and epithelial changes contributing to atrophy of lymphoid follicles. APMIS zyxwvutsr 98: 255-268, 1990. Six calves were infectedper zyxwvuts 0s with Salmonella dublin and killed nine hours to seven days later. Early changes included occlusion of capillaries with a hyaline material, particularly in the ileal Peyer’s patch (PP). Central areas of the follicles contained hemorrhages and edema. In later stages the follicle-associated epithelium (FAE) of both the jejunal and ileal PP was fused with the adjacent epithelium and the follicleswere collapsed. As judged from 5’nucleotidase histochemistry, follicles were depleted of lymphocytes whereas reticular cells were retained. Carbonic anhydrase (CA) histochemistry showed a decreased reaction in the ileal FAE and a reduced amount of CA reactive material in the folliclesof the ileal PP, indicating loss of FAE differentiation and function. Hyaline material and fibrinous thrombi were seen occluding the blood capillaries and the lymphatics, respectively. The villi were atrophied and covered with thick fibrin deposits. Using antifibrino- gen antibodies, immunoperoxidase stained fibrin in the lymphatics and the lumenal deposits but not the hyaline material in the capillaries. Reaction for CA indicated that this hyaline material originated from erythrocytes. Factors contributing to the follicle atrophy may include anoxia due to stasis in the microcirculation with the formation of erythrocyte thrombi, and reduced lymphopoiesis due to a decrease in the stimulating factors provided by the FAE. Key words: Follicle-associated epithelium; erythrocyte thrombi; fibrin; immunohistochemistry; enzyme histochemistry; S’nucleotidase; carbonic anhydrase; calf. T. Landsverk, Dept. Pathol., Norwegian College of Veterinary Medicine, P.O. Box 8 146, Dep. 0033, Oslo 1, Norway. One of the main manifestations of salmonella infections is involvement of the intestine. Fibri- nous enteritis characterized by inflammatory changes of the intestinal mucosa with exudation and emigration of leucocytes is typical zyxwvut (Williams Smith & Jones 1967). Salmonella cholerae-suis infection in pigs causes extensive superficial necro- Received July 10, 1989. Accepted September 27, 1989. sis of the mucosa with microthrombosis of the capillaries as an initial event (Nordstoga & Fjolstad 1970). Salmonella have been reported to have affinity for PP in rabbits, mice and rats (Maenza et al. 1970, Gianella et al. 1973, Hohmann et al. 1978) and destructive inflammatory lesions of PP have been observed in calves and pigs (Williams Smith & Jones 1967, Reed et al. 1986, Wray & Sojka 1978). The purpose of the present study was to examine aspects of intestinal pathology and pathogenesis of 255