Pathomorphology of peripheral organs of immunogenesis in cats with spontaneous feline infectious peritonitis

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This article presents the results of pathomorphological research on the spleen and mesenteric lymph nodes of 23 dead cats aged from 3 months to 7 years, which in their lifetimes (according to anamnesis, clinical signs, laboratory-instrumental methods of examination and VetExpert FCoV Ab express test) had been diagnosed with infectious peritonitis. All the animals were domestic. Blood was drawn from the subcutaneous vein of the forelimb of the diseased cats. We determined ESR, morphological parameters of blood and content of hemoglobin. For histological and histochemical examinations, we selected samples of spleen and mesenteric lymph nodes, which were fixated in 10% aqueous solution of neutral formalin, Carnoy’s and Bouin’s solutions. The prepared histological sections were stained using haematoxylin and eosin, Van Gieson’s stain, methyl green-pironin stain (Brashe), PAS-reaction (McManus), alcian blue and Congo red. Hematological parameters during 3 weeks of clinical progression of the disease among the cats demonstrated a decrease in the hemoglobin content and in the number of erythrocytes and leukocytes. Possible decrease in the number of lymphocytes indicated the development of an immune-deficiency state. Also, during the development of disease, the animals had possible increase in ESR, which indicated the development of an inflammatory process in the organism and decrease in the number of thrombocytes, which conditioned development of disseminated intravascular coagulation. The anatomical pathology autopsy showed that in most animals the spleen was diminished in size, the surface of the organ was tuberous, the capsule was wrinkled and mat, the edges were sharpened. The histostructural change was accompanied by a sharp depletion of the lymph nodes and reduction in the number of micro- and macrophages, which indicated the reduction of white pulp, rapid inhibition of the activity of T- and B-lymphocytes, plasmacytic and macrophage reaction and manifested in development of immune-deficient condition of the organism. In this process, the reticular carcass of the lymph nodes saturated with PAS-positive and eosinophilic masses was clearly manifested, which indicated formation of fibrinoid. In the spleen of 5 individuals, during staining using Congo red, we found deposition of amyloid masses both in the intima of the blood vessels and along the reticulary fibers of the lymph nodes. In the cytoplasm of macrophages, we found pyroninophilic formations. In two cases, we observed blood accumulation of red pulp and bleeding following the reduction of white pulp, and in one case fibrinogenous perisplenitis. In the mesenteric lymph nodes of most of the cats which had suffered from infectious peritonitis, we determined that edema, exposure of the reticular soft skeleton (stroma) of adrenal and paracortical zones, dilation of the border and central sinuses and thrombosis of vessels were followed by steep decrease in the number of T- and B-lymphocytes, plasma cells, micro- and macrophages, which indicated the development of atrophic processes of lympoid tissue and immune-suppression. In three cases, in mesenteric lymph nodes of cats, we determined development of sinus histiocytosis. The changes determined in the spleen and lymph nodes of the cats which had suffered from FIP indicate immune-suppressed condition and steep decrease in the functional ability of the organs and organism in general.