Experimental mucosal disease in cattle: changes in the number of lymphocytes and plasma cells in the mucosa of the small and large intestine.

Changes in the number of lymphocyte and plasma cell subtypes were investigated in the lamina propria and in the epithelium of the small and large intestine of cattle with mucosal disease. Mucosal disease had been induced experimentally in seven out of 13 animals persistently viremic with non cytopathogenic BVD-virus by inoculation with a matching cytopathogenic BVD-virus. For comparison, six clinically healthy, persistently viremic cattle were used. IgA+, IgM+ and IgG1+ plasma cells, BoCD4+, BoCD8+ and gamma delta + T-lymphocytes, and the antigen of the cytopathogenic BVD-virus were demonstrated in tissue sections by immunohistochemistry. Distribution of cellular subtypes in the controls was consistent with data reported from non infected cattle. In cattle with mucosal disease, a decrease in the number of plasma cells which was significant for IgA+ and IgM+, but not for IgG1+ plasma cells was found in the lamina propria. The number of BoCD4+ T-lymphocytes was reduced in the small intestine, whereas their number per mm2 of mucosa was increased in the large intestine. Numbers of intraepithelial BoCD8+ and gamma delta + T-lymphocytes were severely decreased. Antigen of the cytopathogenic BVD-virus was detected predominantly in epithelial cells of the crypts. Overall there is a severe loss of effector cells which are essential components of the humoral and cell mediated immune protection of the mucosal barrier. The decrease of immunoregulatory cells in the lamina propria and epithelium may contribute to the transformation of mucosal architecture in mucosal disease.