C57BL/6 mice deficient in D^b were generated by homologous recombination in the laboratory of Dr. Francois Lemonnier of The Institut Pasteur, Paris France. Generation of H2-D^b knockout mice: The H2-D^b gene was disrupted using an insert containing LacZ and a neo cassette flanked by a 4-kb HindIII-XbaI 5' and 1-kb KpnI-SpeI 3' fragment of the D^b gene resulting in the loss of the first three exons. The targeting construct was introduced into a CGR-8 embryonic stem cell of 129/OLA origin. Clones that were confirmed for homologous recombination were injected into B6 blastocysts and germline chimeras were identified. The founders were crossed twice with C57BL/6Ji females and heterozygous N2 offspring were intercrossed to generate the H2-D^b homozygous strain. Inactivation of the H2-D^b was confirmed by Southern blot analysis on tail DNA and immunofluorescence assay. Subsequently the N2 mice were backcrossed another 10 times to C57BL/6Ji and then intercrossed to produce N12 homozygous H2-D^b-/- targeted mutation mice. Six pairs of the N12 homozygous mice were transferred from Dr. Lemonnier to the NIAID repository at Taconic in 2001 where they were embryo transfer derived.