The effects of DOCK8 deficiency on human neutrophil functions

Neutrophil chemotactic defects have been reported in patients with Hyper IgE syndrome. Mutations in dedicator of cytokinesis 8 gene (DOCK8) gene cause a combined immunodeficiency that can be diagnosed as a hyper IgE syndrome and DOCK8 plays a role in reorganization of the F-actin cytoskeleton in NK and dentritic cells. However, data are lacking about the possible role of DOCK8 in neutrophil function. The expression of DOCK8 protein was assessed in neutrophils from healthy volunteers before and after stimulation with neutrophil activators: phorbol 12-myristate 13-acetate (PMA) or N-Formylmethionyl-leucyl-phenylalanine (fMLP). Neutrophil functions, including chemotaxis, phagocytosis and superoxide generation were studied in neutrophils from DOCK8 deficient patients compared to neutrophils from healthy controls. DOCK8 protein was found to be expressed in resting neutrophils with a significant up-regulation of DOCK8 after stimulation with PMA or fMLP. Neutrophil functions were assessed in 6 patients. All patients were homozygotes for the same mutation in the DOCK8 gene (c.C5134A, p.S1711X) causing a premature stop codon mutation in DOCK8. Lack of expression of the DOCK8 protein in T cells was revealed by flow-cytometry in one patient. A mild to moderate neutrophil chemotaxis defect was recorded in neutrophils from 2/6 (33.3%) of the patients while phagocytosis and superoxide generation were normal. We conclude that the DOCK8 protein is expressed in resting human neutrophils and is upregulated after stimulation with PMA or fMLP. Most patients with a disease-causing mutation in DOCK8 have normal neutrophil function, while a minority showed a mild to moderate chemotactic defect.