Natural killer cells in allergy

The prevalence of allergic disease has dramatically increased worldwide in the past 20 years. Allergic diseases are characterized by abnormal inflammatory responses to allergens with a bias towards T-helper type-2 cytokine production. Natural killer (NK) cells have been conventionally associated with immune surveillance of tumor cells as well as anti-viral defence. However, recent advances in phenotypic and functional characterization of NK cells support their capacity to regulate the immune response to allergens. NK cells play a role in the pathogenesis of allergic inflammation through their interaction with dendritic cells (DCs) and T cells. They potentially are also involved in two of the most commonly encountered allergic diseases: asthma and atopic dermatitis (AD). The role of NK cells in allergy remains elusive. NK cells are large granular lymphocytes that play a crucial role in innate immunity due to their cytotoxic ability to destroy virus-infected cells and tumor cells. NK cells may modulate allergic responses through their interactions with DCs, which are important cells in initiating and shaping adaptive immune responses. NK cells have been found in close contact with DCs in lesions of allergen-induced atopic eczema. NK cells lyse immature DCs, and this function appears to require pathogen-dependent activation of both NK cells and Dcs. NK cells may facilitate the development of eosinophilic airway inflammation and participate in IgE-mediated allergic response. On the other hand, deficiency of certain NK subsets with regulatory function may promote a highly polarized Th2 response characteristic of allergy. Further elucidation of the pathogenic mechanisms of NK cells in allergic diseases may provide insight in designing novel therapeutic approaches.