Postnatal Development of Non-Lymphoid and Lymphoid Cell Populations in Situ in Diabetes-Prone BB Rats

Abstract

The BB rat serves as an animal model for human insulin-dependent diabetes mellitus (1). Independent of the development of diabetes mellitus, BB rats show a profound T-cell lymphocytopenia (2–7,18). Both the T-helper lymphocyte and the T-suppressor/cytotoxic subsets are depressed (3,5–7) and T-cell mediated immuneresponses in vitro are impaired (3,4,6,7). There are indications, that this T-cell immunoincompetence in adult rats is a defect in T-cell maturation or differentiation which manifests either in the thymus(6) or has a postthymic origin (3,5). However, few data are available on the mlcroenvlronment in the BB rat where T-cell maturation takes place,. namely the thymus and the other lymphoid organs. In the T-cell areas of these organs interdigitating cells are thought to figure in the homing process of T lymphocytes (8–10,22) or in the creation of a suitable environment for T-cell proliferation and differentiation (11–13). Furthermore, the epithelial component of the thymic stroma (29) and thymic macrophages (24,25) probably play a prominent role in this process.