Irg1−/− mice were generated after receiving embryonic stem cells (ESCs) from the Knockout Mouse Project Repository containing an insertion cassette between exons 3 and 4. This cassette prevents transcription of downstream exons 4 and 5 and production of mature protein. Irg1−/− C57BL/6N ESCs were microinjected into (Cg)-Tyrc-2J/J albino recipient female C57BL/6 mouse blastocysts. Chimeric mice with black coat color were selected and bred to wild-type C57BL/6N mice. Homozygous Irg1−/− mice were generated by intercrossing the heterozygous animals and confirmed by PCR. Irg1−/− mice were fertile and exhibited normal Mendelian frequencies, and BMDM from both sexes were used.