This project is directed at understanding the role of specific enzyme systems in generating and maintaining host immunity. The approach taken involves the creation of mice with discrete defects in host defenses by using homologous recombination of DNA into the host genome to disrupt relevant genes. Lesions will be introduced that either correspond to previously identified mutations in humans or that incapacitate systems probably involved in host defense. Therefore, this project relies upon a thorough understanding of the molecular and functional organization of the NADPH oxidase system and the mutations which disable it. Further, the dissection of specific phenotypes associated with defined genotypes may provide insight into the importance of certain functional domains of the genes of the NADPH oxidase and indicate which sites are most informative for further study. We have used the NADPH oxidase system as a paradigm for the creation of mice with a genetic defect similar to one found in humans, chronic granulomatous disease (CGD). To this end, we have cloned, characterized and disrupted genomic fragments from both the mouse p47phox and gp91phox genes. Disruption of these genes has provided the basis for a murine model of the autosomal recessive and X-linked forms of CGD, respectively. Embryonal stem cells with homologous recombination at the p47phox gene have been generated and successfully microinjected into mouse blastocysts. Chimeric fertile males have been generated which have successfully sired heterozygous knock-out pups. These animals are being bred to homozygosity. The disrupted gp91phox gene has been electroporated into embryonal stem cells and screening for the homologous recombinant clones is underway. In the course of this work we have 1) further characterized a family with ineffective granulomatous inflammation as demonstrated by disseminated Mycobacterium avium infection, 2) overcome the inflammatory defect in the family with disseminated Mycobacterium avium infection by treatment with interferon gamma, 3) identified immune defects in patients with this infection.