The effects of DOCK8 deficiency on human neutrophil functions

RATIONALE: 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.

METHODS: 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.

RESULTS: 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.

CONCLUSIONS: 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.