EXPERIMENTAL MUCOSAL DISEASE IN CATTLE - CHANGES OF LYMPHOCYTE SUBPOPULATIONS IN PEYERS-PATCHES AND IN LYMPHOID NODULES OF LARGE-INTESTINE

Changes in the number and distribution of lymphocyte subtypes were investigated in Peyer's patches in the jejunum and ileum, and mucosa-associated lymphoid nodules in the proximal colon and rectum of cattle with end-stage mucosal disease. Mucosal disease had been induced experimentally in seven of 13 animals by inoculation with cytopathogenic bovine viral diarrhea virus (cp BVD-virus). For comparison, six clinically healthy, persistently viremic cattle were used. IgM +, IgA +, BoCD4 +, BoCD8 + and gamma delta TCR + lymphocytes, and the cp BVD-viral antigen were visualized in tissue sections by immunohistochemistry. In cattle with mucosal disease, the size of lymphoid follicles was significantly decreased in all localizations resulting in decreased numbers of B-lymphocytes per average follicular area. In most animals domes were missing and epithelium was invaginated into the lymphoid follicles. Numbers of BoCD4 + and BoCD8 + T-lymphocytes were increased per mm(2) of lymphoid follicle. Conversion of these counts into number of cells per average follicular area revealed, however, that the absolute number of BoCD4 + T-lymphocytes had decreased within lymphoid follicles and there was no distinct change of BoCD8 + T-lymphocytes in comparison to the controls. Interfollicular areas were less densely populated due to reduced numbers of BoCD4 + and BoCD8 + T-lymphocytes. cp BVD-viral antigen was detected predominantly in epithelial cells and in cells with dendritic morphology within lymphoid follicles. This may indicate that the severe depletion of B-lymphocytes in the lymphoid follicles is due to alterations of the microenvironment. The decrease of BoCD4 + and BoCD8 + T-lymphocytes does not support the hypothesis of T-cell-mediated tissue damage. Destruction of mucosa-associated lymphoid nodules does not only lead to local disruption of the gastrointestinal barrier, but will reduce the seeding of effector cells to the mucosa and therefore impair the defense mechanisms of the gastrointestinal barrier.