Human Thymic Epithelial Cell Cultures

The thymus is a very complex organ that regulates T-cell production Thymocytes (immature T-cells) constitute by far the largest cellular population in the organ (several billions of thymocytes in a child’s thymus), but small numbers of other hematopoietic cells are found in the intrathymic microenvironment, such as thymic monocytes, macrophages, interdigitating dendritic cells, and B-cells Stromal cells of nonhematopoietic origm comprise thymic epithelial cells (TEC) organized in a network throughout the organ, thymic fibioblasts of the capsule and interlobular septae, and endothelial cells of the thymic vasculature The proportion of these thymic cellular components varies with age (1 ). Fat infiltration becomes significant at puberty and increases throughout adulthood. Intrathymic T-cell maturation is supported in part by TEC, which express cell-surface molecules interacting with counterreceptors on the maturing thymocytes (2 –4 ) Importantly, TEC induce positive selection and major histocompatibility complex restriction of T-cells (5 ) In vitro studies have shown that TEC produce numerous cytokines (4 , 6 , 7 ), which may directly and/or indirectly contribute to T-cell maturation. Reciprocally, TEC functions are affected by interactions with T-cells (t4 , 8 ). Monolayer cultures of TEC provide in vitro systems to study the biology of TEC (2 –7 ) However, investigators should be aware that monolayer cultures may not be representative of a three-dimensionally structured TEC network, and the function of isolated cells may differ from that of cells in the midst of a complex environment One method to obtain highly purified monolayer cultures of human TEC is described here Nontransformed human TEC can be propagated and passaged up to six times before cells become senescent. Careful “budgeting” of the cell stocks by freezing early passages can provide a long-lasting supply of purified TEC strains with determined purity