Figure 2.

A model showing the consequence of skewed X-chromosome inactivation on tolerance induction in the thymus. Thymocytes enter the thymus and proceed on a pathway that exposes them to thymic-deleting elements, mainly dendritic cells in the thymic medulla. Dendritic cells are schematically illustrated here as grey or black, depending on which of the two parental X chromosomes are predominantly active in each cell. On the left hand side of the figure, transiting thymocytes will be exposed to dendritic cells that express both parental X chromosome, and thus will be tolerant (ie deleted) to X-linked antigens from both parents. On the right hand side of the figure, transiting thymocytes will likely be exposed only to the `grey' dendritic cells, which express only one of the two parental X chromosomes. Thus, T cells that exit the thymus will not be tolerized to X-linked antigens from the other parent (the `black' dendritic cells).