Human neutrophil immunodeficiency syndrome is associated with an inhibitory Rac2 mutation

A 5-week-old male infant presented with severe bacterial infections and poo r wound healing, suggesting a neutrophil defect. Neutrophils from this pati ent exhibited decreased chemotaxis. polarization, azurophilic granule secre tion, and superoxide anion (O-2(-)) production but had normal expression an d up-regulation of CD11b. Rac2, which constitutes >96% of the Rac in neutro phils, is a member of the Rho family of GTPases that regulates the actin cy toskeleton and O-2(-) production. Western blot analysis of lysates from pat ient neutrophils demonstrated decreased levels of Rac2 protein. Addition of recombinant Rac to extracts of the patient neutrophils reconstituted O-2(- ) production in an in vitro assay system. Molecular analysis identified a p oint mutation in one allele of the Rac2 gene resulting in the substitution of Asp57 by an Asn (RaC2(D57N)). Asp57 is invariant in all defined GTP-bind ing proteins. RaC2(D57N) binds GDP but not GTP and inhibits oxidase activat ion and O-2(-) production in vitro. These data represent the description of an inhibitory mutation in a member of the Rho family of GTPases associated with a human immunodeficiency syndrome.