COLONIZATION OF THE THYMUS BY T-CELL PROGENITORS - MODELS FOR CELL-CELL INTERACTIONS

The early events of T-cell generation, i.e. seeding of bone marrow-der ived progenitor cells onto the thymic stroma, involve a small fraction (up to 1%) of thymus cells and are not presently observable. However, these events are crucial in determining the outcome of thymic coloniz ation. In previous studies we utilized an experimental in vitro model of thymic reconstitution by bone marrow cells to compare normal thymoc yte development with the development in conditions of T-cell deficienc y, and, in particular, in aging. These studies showed that progenitor cells from old donor bone marrow are deficient in their ability to col onize the thymus, in spite of their ability to divide earlier upon see ding. In this study we apply mathematical and computer modelling in or der to analyse early T-cell development and the causes for the develop mental disadvantage of old donor bone marrow cells. The results indica te that the competition for seeding niches in the thymic stroma determ ines the outcome of colonization.