MRAP and ankylosing spondylitis: These are generated via recycling of unstable fully folded HLA -I heterotrimers on the cell surface of a variety of cells such as human lymphoid cell lines [109], as well as on stimulated lymphoid cells from B27+ transgenic rats and on mononuclear cells of synovial and peripheral blood of B27+ patients with ankylosing spondylitis [110,113,114].