ABSTRACT
To investigate the involvement of thymic function in the development of diseases with poor prognosis in calves, this study conducted a survey for the assessment of thymus cell composition in immature Japanese Black cattle with poor prognosis. Histopathological evaluation of 47 cattle showed signs of acute thymic involution in most cases. Less than half of the cases had a cortex predominant over the medulla in the thymic parenchyma, and a quarter of the cases indicated severe histological condition with an unclear boundary between the cortex and medulla. Correlation analysis revealed a close relationship between the corresponding stages of acute involution, cortical occupancy, and the expression of CD4, CD8B, and CD205. When cases were grouped by cortical occupancy, the expression of CD4 and CD8B expression was lower in the severe group with less than 25 % cortical occupancy, and the expression of CD205 was lower in the group with an unclear cortical-medullary boundary. Meanwhile, there was no difference in the expressions of IL7, CD80, FEZF2, and FOXN1 according to cortical occupancy. Immunohistochemistry has shown that cytokeratin-positive thymic epithelial cells are more densely populated in the severe thymus. UEA-I-binding medullary thymic epithelial cells were also present, but CD205-positive cortical thymic epithelial cells were rare in severe thymus. Moreover, there were significantly fewer Ki-67-positive cells in cattle with severe thymus. Therefore, these results indicate that thymic histological abnormalities frequently occur in immature cattle with a poor prognosis, and the presence of CD205-positive cortical thymic epithelial cells is associated with the severity of the abnormalities.
