Jessica Strid

Acute upregulation of an NKG2D ligand promotes rapid reorganization of a local immune compartment with pleiotropic effects on carcinogenesis

The self-encoded ligands MICA (human) and Rae-1 (mouse) for the cytotoxic lymphocyte activating receptor NKG2D are highly expressed in carcinomas and inflammatory lesions and have been linked to immunosurveillance and graft rejection. However, whether NKG2D ligands have an intrinsic ability to acutely regulate tissue-associated immune compartments is not known. Here we show that epidermis-specific upregulation of Rae-1 induced rapid, coincident and reversible changes in the organization of tissue-resident Vγ5Vδ1 TCRγδ+ intraepithelial T cells and Langerhans cells, swiftly followed by epithelial infiltration by unconventional αβ T cells. Whereas local Vγ5Vδ1+ T cells limited carcinogenesis, Langerhans cells unexpectedly promoted it. These results provide unique insight into the early phases of tissue immunosurveillance and indicate that acute changes in NKG2D ligands may alone initiate a rapid, multifaceted immunosurveillance response in vivo.

Epicutaneous exposure to peanut protein prevents oral tolerance and enhances allergic sensitization.

Background Food allergies are an important cause of life‐threatening hypersensitivity reactions. Oral tolerance can be considered the default immune response to dietary antigens, with immune deviation resulting in allergic sensitization. However, primary sensitization to food allergens may not solely be through the gastrointestinal mucosa, as strong T‐helper type 2 (Th2)‐biased immunity can result from exposure to protein allergens on barrier‐disrupted skin.

Disruption of the stratum corneum allows potent epicutaneous immunization with protein antigens resulting in a dominant systemic Th2 response.

The skin is an important immunological organ with an outer protective layer, the stratum corneum forming a barrier between the skin‐associated lymphoid tissue and the environment. We show thatgently removing the stratum corneum with adhesive tape permits potent epicutaneous immunization to protein antigens. IL‐4 secretion by T cells from draining lymph nodes and high levels of specific IgE and IgG1 with no IgG2a showed that the immune responses induced following epicutaneous antigen exposure are strongly Th2 biased. Similar responses were obtained with different antigens and mousestrains. In contrast, subcutaneous immunization with antigen delivery into the dermis was less potent and gave predominantly Th1 responses. Removal of the stratum corneum increased expression of MHC class II, CD86, CD40, CD54 and CD11c on Langerhans cells, but did not cause them to migrate. Rapid migration from epidermis to draining lymph node was obtained, however, by exposure to antigen after removal of the stratum corneum, suggesting that maturation and migration of Langerhans cells are independently regulated events. These results suggest that antigen presentation by Langerhans cells gives predominantly Th2 responses. This may provide an explanation for allergic sensitization to some antigens. It may also be a useful non‐invasive, non‐adjuvant‐dependent method of vaccination.

A novel model of sensitization and oral tolerance to peanut protein.

The prevalence of food allergic diseases is rising and poses an increasing clinical problem. Peanut allergy affects around 1% of the population and is a common food allergy associated with severe clinical manifestations. The exact route of primary sensitization is unknown although the gastrointestinal immune system is likely to play an important role. Exposure of the gastrointestinal tract to soluble antigens normally leads to a state of antigen‐specific systemic hyporesponsiveness (oral tolerance). A deviation from this process is thought to be responsible for food‐allergic diseases. In this study, we have developed a murine model to investigate immunoregulatory processes after ingestion of peanut protein and compared this to a model of oral tolerance to chicken egg ovalbumin (OVA). We demonstrate that oral tolerance induction is highly dose dependent and differs for the allergenic proteins peanut and OVA. Tolerance to peanut requires a significantly higher oral dose than tolerance to OVA. Low doses of peanut are more likely to induce oral sensitization and increased production of interleukin‐4 and specific immunoglobulin E upon challenge. When tolerance is induced both T helper 1 and 2 responses are suppressed. These results show that oral tolerance to peanut can be induced experimentally but that peanut proteins have a potent sensitizing effect. This model can now be used to define regulatory mechanisms following oral exposure to allergenic proteins on local, mucosal and systemic immunity and to investigate the immunomodulating effects of non‐oral routes of allergen exposure on the development of allergic sensitization to peanut and other food allergens.

The intraepithelial T cell response to NKG2D-ligands links lymphoid stress surveillance to atopy.

Epidermal abrasion and T cells in the skin work together to drive the type of immune responses seen in allergy and asthma. Epithelial cells respond to physicochemical damage with up-regulation of major histocompatibility complex–like ligands that can activate the cytolytic potential of neighboring intraepithelial T cells by binding the activating receptor, NKG2D. The systemic implications of this lymphoid stress-surveillance response, however, are unknown. We found that antigens encountered at the same time as cutaneous epithelial stress induced strong primary and secondary systemic, T helper 2 (TH2)–associated atopic responses in mice. These responses required NKG2D-dependent communication between dysregulated epithelial cells and tissue-associated lymphoid cells. These data are germane to uncertainty over the afferent induction of TH2 responses and provide a molecular framework for considering atopy as an important component of the response to tissue damage and carcinogenesis.

A defect in bone marrow derived dendritic cell maturation in the nonobesediabetic mouse

The pathogenesis of diabetes in the nonobese diabetic (NOD) mouse is characterized by a selective destruction of the insulin‐producing β‐cells in the islets of Langerhans mediated by autoreactive T cells. The function of T cells is controlled by dendritic cells (DC), which are not only the most potent activators of naïve T cells, but also contribute significantly to the establishment of central and peripheral tolerance. In this study, we demonstrate that the NOD mouse (H2: Kd, Ag7, E°, Db) shows selective phenotypic and functional abnormalities in DC derived from bone marrow progeny cells in response to GM‐CSF (DCNOD). NOD DC, in contrast to CBA DC, have very low levels of intracellular I‐A molecules and cell surface expression of MHC class II, CD80, CD86 and CD40 but normal β2‐microglobulin expression. Incubation with the strong inflammatory stimulus of LPS and IFN‐γ does not increase class II MHC, CD80 or CD86, but upregulates the level of CD40. The genetic defect observed in the DCNOD does not map to the MHC, because the DC from the MHC congenic NOD.H2h4 mouse (H2: Kk, Ak, Ek, Dk) shares the cell surface phenotype of the DCNOD. DC from these NOD.H2h4 also fail to present HEL or the appropriate HEL‐peptide to an antigen‐specific T cell hybridoma. However all the DC irrespective of origin were able to produce TNF‐α, IL‐6, low levels of IL‐12(p70) and NO in response to LPS plus IFN‐γ. A gene or genes specific to the NOD strain, but outside the MHC region, therefore must regulate the differentiation of DC in response to GM‐CSF. This defect may contribute to the complex genetic aetiology of the multifactorial autoimmune phenotype of the NOD strain.

Skin Barrier Dysfunction and Systemic Sensitization to Allergens Through the Skin

Most allergic, atopic and hypersensitive reactions are associated with Th2-biased immune responses and allergen-specific IgE antibodies. Pathological allergic disorders are on an alarming increase in the industrialized world. Understanding the mechanism of primary sensitization to allergens is important in elucidating the pathogenesis of these diseases and for possibly preventing their development. In this article, we review recent information supporting that epidermal allergen exposure may contribute to systemic allergic diseases and that atopy may be secondary to skin barrier dysfunction in some dermatoses. The skin is an active immunological organ, which functions as a primary defence and biosensor to the external environment. The critical permeability barrier function is mediated by the outmost layer of the epidermis, the stratum corneum. Perturbation of the stratum corneum initiates a chain of event, which activates homeostatic responses in the underlying epidermis. Repeated barrier-disruption, whether environmentally or genetically determined, may however stimulate signaling cascades that lead to inflammation and epidermal hyperplasia. Skin barrier dysfunction may also allow entry of allergens, which can lead to primary systemic sensitization. The altered epidermal microenvironment in barrier-disrupted skin appears to be particularly well suited for the induction of potent Th2-type responses with production of allergen-specific IgE. Epidermal exposure to food antigens can prevent the normal induction of oral tolerance and also lead to airway eosinophilia following inhalation. Exposure to allergens on barrier-disrupted skin may as such serve as a natural sensitization pathway for food allergy and respiratory allergic disease.

Reconstruction of cell population dynamics using CFSE

BackgroundQuantifying cell division and death is central to many studies in the biological sciences. The fluorescent dye CFSE allows the tracking of cell division in vitro and in vivo and provides a rich source of information with which to test models of cell kinetics. Cell division and death have a stochastic component at the single-cell level, and the probabilities of these occurring in any given time interval may also undergo systematic variation at a population level. This gives rise to heterogeneity in proliferating cell populations. Branching processes provide a natural means of describing this behaviour.ResultsWe present a likelihood-based method for estimating the parameters of branching process models of cell kinetics using CFSE-labeling experiments, and demonstrate its validity using synthetic and experimental datasets. Performing inference and model comparison with real CFSE data presents some statistical problems and we suggest methods of dealing with them.ConclusionThe approach we describe here can be used to recover the (potentially variable) division and death rates of any cell population for which division tracking information is available.

Epicutaneous immunization converts subsequent and established antigen‐specific T helper type 1 (Th1) to Th2‐type responses

Epicutaneous immunization is a potential novel technique for topical vaccine delivery. It targets the immunologically rich milieu of the skin while having the advantage of being a non‐invasive immunization procedure. By disrupting the stratum corneum of the epidermis a natural adjuvant effect can be achieved through activation of resident Langerhans cells. This negates the normal need for co‐application of noxious adjuvants. Epicutaneous immunization on barrier‐disrupted skin induces potent antigen‐specific systemic immunity with a strong T helper type 2 (Th2) bias. We show here that epicutaneous immunization enhances the vigour of a subsequent T‐cell response to the same antigen. The induced systemic Th2 response prevents the development of Th1 responses induced through injection of antigen in complete Freunds adjuvant (CFA). Prior epicutaneous immunization results in reduced production of antigen‐specific interferon‐γ and immunoglobulin G2a (IgG2a) and enhanced interleukin‐4, IgG1 and IgE responses to immunization with CFA. Moreover, epicutaneous immunization converts an established Th1 response to a Th2 response, as demonstrated by the specific reduction of interferon‐γ and IgG2a and the enhancement of interleukin‐4 and IgE. This Th2 dominance of epicutaneous immunization may have direct therapeutic application as an immune‐modulating procedure in Th1‐dominant diseases such as autoimmune rheumatoid arthritis, type 1 diabetes, Hashimotos thyroiditis and multiple sclerosis.

Skin immune surveillance by T cells-A new order?

Although studies of the skin have provided fundamental models for innate and adaptive immune surveillance of body surfaces, there remains relatively little understanding of the role that epithelial cells play in sensing infection and/or organ dysfunction, and the pathways available to them to communicate with local and systemic immune cells. In particular, evidence is emerging for a novel stress response initiated by local lymphocytes, rather than dendritic cells, and based on their recognition of epithelial stress-induced antigens. Its consequences are to sustain tissue integrity by providing immunoprotection and novel modes of immunoregulation, whereas its dysregulation may promote body surface immunopathologies.