Positive and negative selection of the T cell repertoire in MHC class II transgenic mice.

Nowhere has the power of transgenic mouse technology been more evident than in the field of immunology. It has become possible to ordain the specificities expressed by an animal's B and T cells, to stipulate where and when these cells encounter antigen, and to influence how they respond to it by controlling the appearance of cell-surface or soluble regulatory molecules. This new ability to manipulate the immune system from within' has tremendous potential for answering some previously intractable questions about the shaping of the T cell repertoire. Amongst these are where and when the various repertoire selection events take place. We and others have recently addressed these two questions by creating and characterizing transgenic mice with altered patterns of major histocompatibility complex (MHC) class II gene expression. Results from these studies are the focus of this review.