No modulation of circulating natural killer cell and natural killer receptor bearing memory T cell subsets in patients with atopic dermatitis

NK cells and gamma delta+ T cells are phenotypically and functionally defective due to preferential apoptosis in patients with atopic dermatitis

Innate immune cells mediate a first line of defense against pathogens and determine the nature of subsequent acquired immune responses, mainly by producing profound amounts of cytokines. Given these diverse tasks, it is predictable that defective NK and gammadelta(+) T cell responses could be the underlying mechanism for the immunological alterations observed in atopic dermatitis (AD). Indeed, the frequencies of circulating NK cells and gammadelta(+) T cells were profoundly reduced in AD patients. They also displayed a defective ability to sustain TNF-alpha and IFN-gamma, but not IL-4, production after in vitro stimulation, and the defect was restricted to innate immune cells. Surprisingly, on the depletion of CD14(+) monocytes, this selective impairment of TNF-alpha and IFN-gamma production was restored to levels comparable to that observed in controls. Release of IL-10 from monocytes was not a major mechanism of the NK and gammadelta(+) T cell dysfunction. Apoptosis as revealed by annexin V binding, was preferentially observed in NK and gammadelta(+) T cells from AD patients when stimulated in the presence of monocytes, and depletion of monocytes significantly protected these cells from apoptotic cell death. Preferential apoptosis of NK cells by activated monocytes in AD patients was cell-contact-dependent. These results indicate that, once NK and gammadelta(+) T cells in AD patients are in immediate contact with activated monocytes, these cells are specifically targeted for apoptosis, leading to the reduced type 1 cytokine production, thereby directing subsequent acquired immune responses toward a type-2 pattern and increasing susceptibility to infection.

Natural killer and dendritic cell contact in lesional atopic dermatitis skin--Malassezia-influenced cell interaction

The regulation of dendritic cells is far from fully understood. Interestingly, several recent reports have suggested a role for natural killer cells in affecting dendritic cell maturation and function upon direct contact between the cells. It is not known if this interaction takes place also in vivo, or if a potential interaction of natural killer cells and dendritic cells would be affected by allergen exposure of the dendritic cells. The yeast Malassezia can act as an allergen in atopic eczema/dermatitis syndrome, and induce maturation of dendritic cells. Our aims were to study the distribution of natural killer cells in the skin from atopic eczema/dermatitis syndrome patients with the emphasis on possible natural killer cell-dendritic cell interaction, and to assess whether the interaction of Malassezia with dendritic cells would affect subsequent interaction between dendritic cells and natural killer cells. A few scattered natural killer (CD56+/CD3-) cells were found in the dermis of healthy individuals and in nonlesional skin from atopic eczema/dermatitis syndrome patients. In lesional skin and in biopsies from Malassezia atopy-patch-test-positive skin, however, natural killer cells were differentially distributed and for the first time we could show close contact between natural killer cells and CD1a+ dendritic cells. Dendritic cells preincubated with Malassezia became less susceptible to natural-killer-cell-induced cell death, suggesting a direct effect imposed by Malassezia upon interaction of dendritic cells with natural killer cells. These findings indicate that natural killer cells and dendritic cells can interact in the skin and that Malassezia affects the interaction between natural killer cells and dendritic cells. Our data suggest that natural killer cells may play a role in regulating dendritic cells in atopic eczema/dermatitis syndrome.