Only thymic epithelial cells and other stromal components are present. In a sense, the entire thymus of a CID foal resembles the thymic medulla of a normal foal. The normal lymph node is divided into cortex, paracortex, and medulla. Lymph node-normal animal Notice the lack of cortex, paracortex, and medulla. The remaining cells consist of fibroblasts, macrophages and perhaps NK cells.
Lymphocytes are virtually absent from the PALS and there are no lymphoid follicles.
Figure 23 . This photograph contains one thymus lobule. Like the thymus in Figure 19, there is poor distinction between the cortex and the medulla. However, unlike CID, the thymus in this case was formed normally, but subsequently depleted by canine distemper virus. Canine distemper virus replicated within lymphocytes prior to localizing in the brain and lungs.