A loxP site was inserted 3 the J alpha 18 (J alpha 281) gene segment and an FRT-flanked neomycin cassette followed by a second loxP site was placed 3 to the gene segment. The neomycin selection cassette was removed via FLP-mediated recombination. The J alpha 18 segment and neo cassette were removed via cre-mediated recombination of the loxP sites. (J:249268)