Natural killer cell activity in atopic dermatitis: a sequential study

Progressive accumulation of hyperinflammatory NKG2Dlow NK cells in early childhood severe atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease that often precedes the development of food allergy, asthma, and allergic rhinitis. The prevailing paradigm holds that a reduced frequency and function of natural killer (NK) cell contributes to AD pathogenesis, yet the underlying mechanisms and contributions of NK cells to allergic comorbidities remain ill-defined. Here, analysis of circulating NK cells in a longitudinal early life cohort of children with AD revealed a progressive accumulation of NK cells with low expression of the activating receptor NKG2D, which was linked to more severe AD and sensitivity to allergens. This was most notable in children co-sensitized to food and aeroallergens, a risk factor for development of asthma. Individual-level longitudinal analysis in a subset of children revealed coincident reduction of NKG2D on NK cells with acquired or persistent sensitization, and this was associated with impaired skin barrier function assessed by transepidermal water loss. Low expression of NKG2D on NK cells was paradoxically associated with depressed cytolytic function but exaggerated release of the proinflammatory cytokine tumor necrosis factor-α. These observations provide important insights into a potential mechanism underlying the development of allergic comorbidity in early life in children with AD, which involves altered NK cell functional responses, and define an endotype of severe AD.

Progressive accumulation of hyperinflammatory NKG2D low NK cells in early childhood severe atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease that often precedes the development of food allergy, asthma, and allergic rhinitis. The prevailing paradigm holds that a reduced frequency and function of natural killer (NK) cell contributes to AD pathogenesis, yet the underlying mechanisms and contributions of NK cells to allergic co-morbidities remain ill-defined. Herein, analysis of circulating NK cells in a longitudinal early life cohort of children with AD revealed a progressive accumulation of NK cells with low expression of the activating receptor NKG2D, which was linked to more severe AD and sensitivity to allergens. This was most notable in children co-sensitized to food and aero allergens, a risk factor for development of asthma. Individual-level longitudinal analysis in a subset of children revealed co-incident reduction of NKG2D on NK cells with acquired or persistent sensitization, and this was associated with impaired skin barrier function assessed by transepidermal water loss. Low expression of NKG2D on NK cells was paradoxically associated with depressed cytolytic function but exaggerated release of the proinflammatory cytokine TNF-α. These observations provide important insights into a potential mechanism underlying the development of allergic co-morbidity in early life in children with AD which involves altered NK-cell functional responses, and define an endotype of severe AD.

Elevated NK-cell transcriptional signature and dysbalance of resting and activated NK cells in atopic dermatitis

BACKGROUND

Altered quantities, activity, and composition of natural killer (NK) cells in blood as well as expression changes of genes involved in NK-cell function in skin lesions of patients with atopic dermatitis (AD) were recently reported.

OBJECTIVES

We sought to comprehensively analyze cutaneous NK-cell transcriptomic signatures in AD, and to examine changes under treatment.

METHODS

We analyzed NK-cell signatures in skin transcriptome data from 57 patients with moderate to severe AD and 31 healthy controls. In addition, changes after 12 weeks of systemic treatment (dupilumab n = 21, cyclosporine n = 8) were analyzed. Deconvolution of leucocyte fractions was conducted. Immunofluorescence staining of NK cells was performed on paraffin-embedded skin sections.

RESULTS

Immunofluorescence staining revealed a relatively high abundance of both NK cells and CD3⁺CD56⁺ cells in lesional as compared with nonlesional and healthy skin. Lesional and to a lesser extent nonlesional skin showed a strong upregulation of NK-cell markers together with a dysbalanced expression of inhibitory and activating receptors, which was not reverted under treatment. Digital cytometry showed a decrease in activated and an increase in resting NK cells in both lesional and nonlesional skin, which was reverted by both treatment with dupilumab and cyclosporine. The NK-cell transcriptomic signature remained upregulated after treatment, but there was a shift on the qualitative level, indicating a compositional change in NK-cell subsets toward CD56^bright NK cells.

CONCLUSIONS

Lesional AD skin shows a NK-cell dysregulation, which despite clinical improvement under systemic therapy was only partially reverted, and which may represent a yet underappreciated disease mechanism.

Innate Lymphocyte Mechanisms in Skin Diseases

Innate lymphocyte populations are emerging as key effectors in tissue homeostasis, microbial defense, and inflammatory skin disease. The cells are evolutionarily ancient and carry conserved principles of function, which can be achieved through shared or unique specific mechanisms. Recent technological and treatment advances have provided insight into heterogeneity within and between individuals and species. Similar pathways can extend through to adaptive lymphocytes, which softens the margins with innate lymphocyte populations and allows investigation of nonredundant pathways of immunity and inflammation that might be amenable to therapeutic intervention. Here, we review advances in understanding of innate lymphocyte biology with a focus on skin disease and the roles of commensal and pathogen responses and tissue homeostasis.

Cellular and molecular mechanisms in atopic dermatitis

Atopic dermatitis (AD) is a pruritic inflammatory skin disease associated with a personal or family history of allergy. The prevalence of AD is on the rise and estimated at approximately 17% in the USA. The fundamental lesion in AD is a defective skin barrier that results in dry itchy skin, and is aggravated by mechanical injury inflicted by scratching. This allows entry of antigens via the skin and creates a milieu that shapes the immune response to these antigens. This review discusses recent advances in our understanding of the abnormal skin barrier in AD, namely abnormalities in epidermal structural proteins, such as filaggrin, mutated in approximately 15% of patients with AD, epidermal lipids, and epidermal proteases and protease inhibitors. The review also dissects, based on information from mouse models of AD, the contributions of the innate and adaptive immune system to the pathogenesis of AD, including the effect of mechanical skin injury on the polarization of skin dendritic cells, mediated by keratinocyte-derived cytokines such as thymic stromal lymphopoietin (TSLP), IL-6, and IL-1, that results in a Th2-dominated immune response with a Th17 component in acute AD skin lesions and the progressive conversion to a Th1-dominated response in chronic AD skin lesions. Finally, we discuss the mechanisms of susceptibility of AD skin lesions to microbial infections and the role of microbial products in exacerbating skin inflammation in AD. Based on this information, we discuss current and future therapy of this common disease.

Smallpox vaccination: Risk considerations for patients with atopic dermatitis

As the threat of bioterrorism with pathogenic microbes such as smallpox virus (Variola major) increases, the question of widespread voluntary vaccination with smallpox (vaccinia) vaccines is being carefully considered. A major challenge lies in the ability to protect the population from the disease while minimizing the considerable side effects from the vaccine. Individuals with active or quiescent atopic dermatitis are at increased risk for vaccinia complications. The nature of these complications and other considerations are summarized in this rostrum.

Characterisation of lymphocyte subpopulations in the skin and circulation of horses with sweet itch (Culicoides hypersensitivity)

Circulating lymphocyte numbers are elevated in horses with the allergic skin disease sweet itch and skin lesions are typified by an infiltrate of eosinophils and mononuclear cells, the latter of which have not been fully characterised. The aim of the present study was to characterise the lymphocyte subpopulations in the circulation and skin of ponies with sweet itch by flow cytometry and a newly developed modified alkaline phosphatase immunohistochemical technique. Sweet itch ponies were found to have significantly greater numbers of circulating CD5+ and CD4+ T-lymphocytes than normal animals. Increased numbers of CD3+ T-lymphocytes, most of which were CD4+, and eosinophils were present in the skin of these animals following intradermal injection of a Culicoides antigen extract (97 +/- 21 vs. 449 +/- 49 CD3+ T-lymphocytes/mm2 in deep dermis of vehicle vs. antigen injected sites; 83 +/- 8% CD4+ T-lymphocytes at antigen injected site). T-lymphocytes, which are thought to be important in the pathogenesis of human allergic skin disease, may therefore contribute to the development of sweet itch lesions via the release of cytokines which can cause eosinophil accumulation and activation. An understanding of the pathology of this disease may lead to a more rational approach to therapy.

Control of IgE responses. II. Isotype specific suppression of peak hapten specific IgE antibody forming cell responses in BPO-KLH sensitized mice after oral administration of muramyldipeptide or murabutide

Muramyldipeptide (MDP) and murabutide (MB), a pyrogen free derivative of MDP, suppressed BPO specific IgE antibody forming cell (AFC) responses in vivo. To induce IgE responses, BALB/c mice were injected intraperitoneally (i.p.) with BPO-KLH (10 micrograms) in alum on days 0 and 21, or on days 0, 21 and 42. On day 44, mice were fed (gavage) or injected subcutaneously (s.c.) with MDP or MB (0.1-500 mg/kg). Mice were killed on days 45-70, and the numbers of BPO specific IgM, IgG1, IgE, and IgA antibody forming cells (AFC) in lymphoid organs determined in ELISPOT assay. With either immunization schedule, oral treatment with MDP or MB on day 44 suppressed BPO specific IgE AFC responses within 48 h (65-100%). With both molecules, the suppression was IgE isotype specific, dose dependent and transient. The suppression was also route specific since it was obtained only when MDP or MB was given by gavage, and not when injected s.c. These results show that peak antigen specific IgE responses can be suppressed in vivo, in isotype specific fashion, by a clearly defined class of molecules, one of which, MB, is a candidate for clinical studies in man. Pharmacologic agents of this type may be suitable for use in the therapeutic or prophylactic suppression of IgE and, hence, in the therapy of IgE mediated diseases such as allergic rhinitis, asthma, and other atopic diseases.

Differentiation of human in vivo antigen-induced lymphoblastoid B cell precursors can be prevented by natural killer cells

Tetanus toxoid (tet) immunization of normal humans leads to the transient appearance in the circulation of large lymphoblastoid (LB) B cells, which spontaneously secrete IgG-tet in short-term cultures. The present work examines the effect of endogenous natural killer (NK) cells, as defined as CD 16+ cells, on the LB B cell subset. NK cell depletion by monoclonal antibody (Leu11) and complement (C)-mediated lysis from LB B cell containing populations eliminated 76 +/- 7% of the cytotoxic activity against 51Cr-K-562 cells, and, in contrast, enhanced 2.7 +/- 0.3 times IgG-tet secretion. Cells untreated, treated with Leu11 alone, C alone, or with an irrelevant monoclonal antibody and C were used as controls. Furthermore, the increased IgG-tet production after NK depletion could be reversed by adding autologous CD 16(+)-enriched populations. Limiting dilution analysis revealed that the NK removal enhancement of IgG-tet production was due to an augmentation (3.18 +/- 0.63 times) of the precursor frequency of spontaneous antibody-secreting cells in NK-depleted cells with respect to control populations. Finally, the spontaneous IgG-tet-producing cells present in NK-depleted and control populations were the same since they produced similar quantities of antibody on a per cell basis and exhibited identical large size, as determined by 1 x G sedimentation technique. NK cells, therefore, exert a strong inhibitory effect on LB B cells by preventing the development of a considerable part of their precursors. This mechanism might be of importance in the control of LB B cells in vivo.

The effect of topical steroid application on natural killer cell activity

Peripheral blood natural killer (NK) cell activity of a group of 10 healthy non-atopic volunteers was reduced following the topical application of 15 g of 0.1% betamethasone valerate ointment to the skin nightly for 1 week. In contrast, no such effect was observed when the inactive base of the steroid ointment was used. NK cell activity dropped significantly by day 7 (P less than 0.05) and then recovered, although NK cell activity at day 22 was still lower than that observed at the start of the experiment. These findings suggest that topically applied steroid is absorbed in sufficient amounts to cause a systemic effect on NK cell function. This may have implications in a number of dermatological disorders, including atopic dermatitis, where topical steroids form the mainstay of treatment.

Reduced natural killer cell activity in patients with systemic sclerosis. Correlation with clinical disease type

Natural killer (NK) cell number and function were determined in 69 systemic sclerosis (SSc) patients (41 with diffuse cutaneous SSc, 24 with limited cutaneous SSc, and 4 with scleroderma in an overlap syndrome). The results were compared with those obtained from 5 patients with Raynaud's disease and from 27 normal controls. Natural and antibody-dependent killing was reduced in the total group of SSc patients compared with controls, but these differences were primarily attributable to patients with the diffuse form of the disease who were seen early in their illness (less than 5 years after onset). NK cell numbers were not significantly reduced in patients compared with controls, although lower numbers were observed in individuals with early diffuse disease. Other clinical parameters, such as treatment with D-penicillamine or the presence of scleroderma-specific autoantibodies, did not exert an independent effect on NK cell function. These findings suggest a possible central role for NK cells in the pathogenesis of SSc.

Immune responses to herpes simplex virus in patients with facial herpes simplex and those with eczema herpeticum

The immune response to herpes simplex virus (HSV) was studied in 59 patients with primary and recrudescent facial HSV infections. The patients included nine with atopic eczema, seven of whom had eczema herpeticum (EH). All patients had antibodies to HSV (measured by ELISA) and all but three had HSV-specific cell mediated immunity (CMI) (measured by in vitro lymphoproliferation). Thirteen control subjects were negative for both tests. All three patients with absent CMI to HSV had suffered from severe EH and had depressed CMI to HSV for several months following an attack. In two of these EH patients, a positive CMI response was produced by in vitro removal of CD8 + ve T lymphocytes from peripheral blood mononuclear cells using a panning technique. Thus the absence of CMI to HSV in these patients was due to suppressor cell function rather than a lack of specifically responsive cells. The other four EH patients with normal CMI to HSV had suffered less severe EH, but no association between the absence of CMI to HSV and serum IgE level or activity of the eczema was apparent in the atopic patients. No specific anti-HSV IgE antibody was detectable.

Natural killer and interleukin-2 induced cytotoxicity in asthmatics. I. Effect of acute antigen-specific challenge

Natural killer (NK) cell activity and interleukin-2 (IL-2) induced cytotoxicity to NK-resistant targets T24 in a group of patients with grass pollen seasonal asthma were investigated. Acute bronchial provocation with this antigen was also performed and blood samples were taken before and 15 min after the maximal clinical response. NK activity was elevated in this group but there was a significant decrease after acute challenge. IL-2 induced cytotoxicity was also increased and declined after antigen challenge. Limiting dilution analysis for minimal frequencies of precursors of the IL-2 induced killer cells was introduced and showed increased numbers of lymphokine-activated killing precursors in this group of patients. These data might indicate the aberrations of the IL-2 system in immediate type allergy but the clinical significance of these findings remains to be determined.

Production of interferon and lymphoproliferative response in whole blood cultures derived from patients with atopic dermatitis

Enhanced susceptibility to viral infections has been reported repeatedly in atopic dermatitis (AD). A difference in the capacity to produce interferons (IFN) in response to viral antigens may be the cause. In the present study we investigated the in vitro IFN production of leukocytes from AD patients in response to different stimuli. Furthermore, the lymphoproliferative responses were tested. The patients showed moderate to severe disease activity. Whole blood cultures of 25 AD patients and 21 healthy nonatopic controls were stimulated with the mitogens phytohemagglutinin (PHA), concanavalin A (ConA), and pokeweed mitogen (PWM), with tuberculin derivative (PPD) and tetanus antigen as IFN-gamma inducers, and with C. parvum, poly I-poly C, and herpes simplex virus (HSV) as inducers of IFN-a. Lymphoproliferation was assayed in 5-day cultures in parallel. In AD no significant difference of the IFN production was found in comparison with the controls with any stimuli tested. The lymphoproliferative response of leukocytes of patients with AD was significantly decreased upon stimulation with PHA, Con A, PWM, and PPD. We suggest that in AD the described susceptibility to viral infections is not due to an altered capability of leukocytes to generate IFN.