Peripheral Natural Killer Cells Exhibit Qualitative and Quantitative Changes in Patients with Psoriasis and Atopic Dermatitis

Background: Psoriasis and atopic dermatitis are the most recurrent skin inflammatory disorders. Despite their distinct aetiology and clinical aspects, these diseases share several immunological features. Besides the largely documented role of T cells, emerging literature supports a potential involvement of innate immune effectors, the natural killer (NK) cells, in both pathologies. In the peripheral blood, NK cells consist of CD3-CD56dim and CD3-CD56bright cell subsets, harbouring a distinct cell surface phenotype, but both endowed with the main NK-cell effector functions: cytotoxicity and cytokine production.

Objectives: To determine whether the frequency, the cell surface phenotype and the functional properties of peripheral NK cells were affected in patients with psoriasis or atopic dermatitis.

Methods: Peripheral blood mononuclear cells were isolated from 11 patients with psoriasis, nine patients with atopic dermatitis and 16 healthy individuals. By using flow cytometry, we analysed the following parameters of peripheral NK cells: the frequency, the cell surface expression of several NK-cell receptors (NKR) and the activation of the effector functions upon various in vitro stimuli.

Results: Peripheral NK cells were significantly reduced in both skin diseases. The cell surface expression of various NKR was differently modified in peripheral NK cells of the two cohorts of patients. Finally, NK-cell natural cytotoxicity was affected only in atopic dermatitis, while interferon-γ production was defective in both groups of patients.

Conclusion: Psoriasis and atopic dermatitis are associated with quantitative and qualitative changes of peripheral NK cells, mostly shared by both diseases, supporting a common process implicating these innate effectors in skin inflammation.