Leukocyte adhesion deficiency type I (LAD I) is a primary immunodeficiency disease resulting from mutations in the gene encoding CD18. Markedly reduced or absent expression of the leukocyte integrin component CD18 causes significant impairment in leukocyte mobilization to inflammatory sites. Clinically, patients have marked leukocytosis and recurrent infections involving soft tissues such as skin, the gastrointestinal tract and gingiva. Death due to infections in early infancy is common with the severe form of LAD I (CD18 expression less than 0.5%), but patients with the moderate phenotype (CD18 expression 1-10%) may survive into young adulthood. To date, therapy consists of antibiotic treatment for infections and bone marrow transplantation when possible. LAD I is also a candidate for future gene therapy. Recently, it has been shown that in vivo administration of interferon gamma (IFN-gamma) upregulates CD18 expression in normals and alters leukocyte trafficking. We hypothesize that modest increases in CD18 expression in LAD I patients with the moderate phenotype or alterations in CD18 independent trafficking could result in detectable clinical changes and possible clinical improvement.