Two loxP sites were inserted so as to flank the two exons encoding the extracellular Ig-like domains as well as an FRT enclosed neomycin resistance gene (Icosltm2Cdon. These two exons and the neomycin gene were subsequently removed by crossing F1 mice with a cytomegalovirus-cre transgenic mouse. Absence of protein product was confirmed immunologically. (J:86697)