Introduction DOCK8 mutations are responsible for a rare autosomal recessive immunodeficiency syndrome associated with severe cutaneous viral infections, elevated IgE levels, environmental allergies, autoimmunity, and malignancy. DOCK8 activates CDC42, which is important for cell signalling and actin reorganisation. Natural killer cells play a vital role in tumour surveillance and defence against virally infected cells. NK cell function relies on the accumulation of actin at the NK cell immunologic synapse formed with target cells. Although abnormalities in T and B cell function have been described in DOCK8-deficient patients, the role of NK cells in this disease is poorly understood.

Objectives/Aims Given the susceptibility to severe cutaneous viral infection and malignancy, we hypothesised there was a substantive defect in NK cell function in patients with DOCK8 deficiency.

Methods 10 patients with genetically confirmed DOCK8 deficiency as well as NK cell lines with stably reduced DOCK8 expression were evaluated experimentally using in vitro NK cell cytotoxicity, F-actin content, and confocal immunofluorescence microscopy assays.

Results DOCK8-deficient patients and cell lines all had decreased NK cell cytotoxicity and function could not be restored after IL-2 stimulation. Importantly, DOCK8 deficiency did not affect NK cell F-actin content, but impaired F-actin accumulation at the lytic immunological synapse.

Conclusions DOCK8 deficiency results in severely deficient NK cell function owing to an inability to form a mature lytic immunological synapse via focal F-actin accumulation. This defect may underlie important and previously perplexing attributes of the DOCK8 deficiency clinical syndrome including the unusual susceptibility to viral infection.