Class II MHC genes (for example, the humanHLA-DRAgene) are expressed at the cell surface in many professional and nonprofessional anti-gen-presenting cells in a variety of anatomical locations. Here, we report about 13 mouse transgenic lines (11 of which have not been previously des-cribed) generated with four distinct sets of DRAtransgenes carrying pro-gressive, informative 5¢ and 3¢ deletions.