Cytokines and regulation of allergic sensitization to chemicals

Safety evaluation of the food enzyme asparaginase from the genetically modified Aspergillus oryzae strain NZYM-SP

The food enzyme asparaginase (l-asparagine amidohydrolase, EC 3.5.1.1) is produced with the genetically modified Aspergillus oryzae strain NZYM-SP by Novozymes A/S. The genetic modifications do not give rise to safety concerns. The food enzyme is considered free from viable cells of the production organism and its DNA. It is intended to be used to prevent acrylamide formation in food processing. Dietary exposure to the food enzyme-total organic solids (TOS) was estimated to be up to 0.101 mg TOS/kg body weight (bw) per day in European populations. Genotoxicity tests did not indicate a safety concern. The systemic toxicity was assessed by means of a repeated dose 90-day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 880 mg TOS/kg bw per day, the highest dose tested, which, when compared with the estimated dietary exposure, resulted in a margin of exposure of at least 8,713. A search for the similarity of the amino acid sequence of the food enzyme to known allergens was made and no match was found. The Panel considered that a risk of allergic reactions by dietary exposure cannot be excluded, but the likelihood is low. Based on the data provided, the Panel concluded that this food enzyme does not give rise to safety concerns under the intended conditions of use.

Safety evaluation of the food enzyme asparaginase from the genetically modified Aspergillus oryzae strain NZYM‐OA

The food enzyme asparaginase (l‐asparagine amidohydrolase; EC 3.5.1.1) is produced with the genetically modified microorganism Aspergillus oryzae strain NZYM‐OA by Novozymes A/S. The genetic modifications do not give rise to safety concerns. The food enzyme is free from viable cells of the production organism and its DNA. It is intended to be used in various food manufacturing processes to prevent acrylamide formation. Dietary exposure to the food enzyme–total organic solids (TOS) was estimated to be up to 0.051 mg TOS/kg body weight (bw) per day in European populations. Genotoxicity tests did not indicate a safety concern. The systemic toxicity was assessed by means of a repeated dose 90‐day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 1,182 mg TOS/kg bw per day, the highest dose tested, which, when compared with the estimated dietary exposure, resulted in a margin of exposure of at least 23,176. A search for the similarity of the amino acid sequence of the food enzyme to known allergens was made and no match was found. The Panel considered that, under the intended conditions of use, the risk of allergic reactions by dietary exposure cannot be excluded, but the likelihood is low. Based on the data provided, the Panel concluded that this food enzyme does not give rise to safety concerns, under the intended conditions of use.

Safety evaluation of the food enzyme asparaginase from the genetically modified Bacillus subtilis strain NZYM‐CK

The food enzyme asparaginase (l‐asparagine amidohydrolase EC 3.5.1.1) is produced with the genetically modified Bacillus subtilis strain NZYM‐CK by Novozymes A/S. The genetic modifications do not give rise to safety concerns. The food enzyme is free from viable cells of the production organism and its DNA. It is intended to be used in various food manufacturing processes to prevent acrylamide formation. Dietary exposure to the food enzyme–total organic solids (TOS) was estimated to be up to 0.361 mg TOS/kg body weight (bw) per day in European populations. Genotoxicity tests did not indicate a safety concern. The systemic toxicity was assessed by a repeated dose 90‐day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 1,207 mg TOS/kg bw per day, the highest dose tested, which, when compared with the estimated dietary exposure, results in a margin of exposure of at least 3,343. A search for the similarity of the amino acid sequence of the food enzyme to known allergens was made and no match was found. The Panel considered that, under the intended conditions of use, the risk of allergic reactions by dietary exposure cannot be excluded, but the likelihood is low. Based on the data provided, the Panel concluded that this food enzyme does not give rise to safety concerns under the intended conditions of use.

Differential regulation of sensitizer-induced inflammation and immunity by acute restraint stress in allergic contact dermatitis

Previously, we demonstrated that restraint stress applied before chemical sensitization modulates allergic contact dermatitis (ACD) differently than restraint applied before challenge. In this study, we asked if these dichotomous restraint-induced changes reflect modulation of the cutaneous microenvironment or changes in development of antigen-specific immunity in the lymph node (LN) of BALB/c mice. Our data confirm that restraint suppresses T cell-dependent immunity in ACD when applied prior to sensitization or prior to challenge and demonstrate that the stress-induced increase in ear swelling is due to heightened inflammation associated with ACD and is dependent upon the sensitization status of the mouse.

Modulation of phenotype, cytokine production and stimulatory function of CD34+-derived DC by NiCl(2) and SDS

One of the most promising alternatives to identify the sensitizing potency of new products is the in vitro culture of human dendritic cells (DC). In vivo, dendritic cells present in the skin are highly specialized antigen-presenting cells (APC) of the immune system, which play a crucial role in the induction of allergic reactions. The DC produce specific cytokines and upregulate specific co-stimulatory molecules in addition to the antigen-MHC complex in order to promote an optimal T-cell activation. The aim of our study is to assess the phenotype, cytokine production and autologous T-cell stimulatory capacity of the in vitro CD34+-derived dendritic cells after 24 hours of incubation with the metal allergen NiCl(2) (100-300 microM) and the irritant sodium dodecyl sulfate (SDS; 0.01%), in order to find a sensitive endpoint to discriminate between sensitizers and irritants. After exposure to Ni, a significant increase in the number of CD83+ and CD86+ cells was noticed. The intensity of CD86 as well as the intensity of the HLA-DR molecule on the DC also showed a significant increase. The expression of the co-stimulatory molecule CD80 was not changed after exposure. SDS was not able to increase the expression of any of the analysed markers. The production of IL-6 increased significantly after exposure of dendritic cells to Ni, but not after SDS exposure. Results on tumor necrosis factor-alpha (TNF-alpha) production are somewhat equivocal. Although not statistically significant, TNF-alpha was upregulated in one out of three experiments after 48 hours of exposure to the Ni allergen, but increases were also noticed after exposure to SDS (two out of three experiments). Both exposure to Ni and SDS caused an upregulation (not significant) in the IL-12 production by DC, but the production was higher in Ni-exposed DC compared to SDS-exposed cells. In none of the exposed DC cultures was it possible to detect IL-1 beta. The antigen-presenting capacity of the DC in autologous MLR could not be demonstrated. Nevertheless, T-cell proliferation after DC stimulation was noticed in allogenic MLR.

Restraint-induced modulation of allergic and irritant contact dermatitis in male and female B6.129 mice

Recent studies in rats have indicated that acute restraint enhances cutaneous hypersensitivity. We hypothesized that acute restraint would also modulate the development of allergic and irritant dermatitis in mice and that these restraint-induced changes would be reflected in the cutaneous cytokine profile and be gender-specific. For these studies, male and female B6.129 mice were sensitized and challenged with the contact sensitizer dinitrofluorobenzene or challenged with the irritant croton oil. Two-hour restraint was applied prior to chemical challenge. Restraint combined with chemical increased ear swelling in both genders in ACD, a change that was blocked by administration of RU-486 prior to restraint. Neither restraint nor RU-486 administration modulated development of ICD; however, IL-1beta was decreased by restraint in females only. TNF-alpha and IFN-gamma production were modified in ACD; TNF-alpha in both genders and IFN-gamma in female mice only. Our data demonstrate that acute restraint increases serum corticosterone in B6.129 male and female mice to comparable levels. Restraint modulated the murine ear swelling in ACD, but not ICD, in both genders, and the change in the ear swelling response and cytokine production were, at least in part, corticosterone-dependent.

Anatomical origin of dendritic cells determines their life span in peripheral lymph nodes

Dendritic cells (DCs) exhibit considerable heterogeneity in their anatomical location, surface phenotype, and functional properties. In this study, we demonstrate that peripheral lymph nodes contain at least four major, functionally separable, and independently derived, DC subsets, which can be clearly demarcated by their CD11c, CD40, and CD8 expression pattern. Surprisingly, all DCs derived directly from the bone marrow, the myeloid- and the lymphoid-related subsets, turned over fast with t(1/2) of a couple of days. In contrast, DCs exported from the skin, both dermal and epidermal, accumulated 3- to 4-fold slower, turnover that is dramatically increased by cutaneous inflammation.

Analyses of cutaneous fluoroquinolones photoreactivity using the integrated model for the differentiation of skin reactions

Currently available test models for the differentiation of photoallergic and photoirritant reactions are extremely time consuming and the protocols are very heterogeneous. In vitro tests are of proven value in predicting irritant or toxic effects, but these tests fail to predict chemical-induced allergic side effects. We developed test systems for this endpoint which is not easily detected by existing assays. In a previous publication we were able to discriminate between a contact sensitizer and a skin irritant with a combination of primary ear swelling analysis and cell counting of the ear-draining lymph nodes [Toxicol. Appl. Pharm. 153 (1998) 83; Arch. Toxicol. 73 (2000) 501]. This combination of tests was called the Integrated Model for the Differentiation of chemical-induced allergic and irritant Skin reactions (IMDS). In addition, it had been shown before that inclusion of UV irradiation in the local lymph node assay enables discrimination of photoallergic from photoirritant reactions after dermal application [Photodermatol. Photoimmunol. Photomed. 10 (1994) 57]. Because of the fact that fluoroquinolones are known to induce photoreactions after oral but not dermal treatment, the aim of the present study was to apply the IMDS for the fast and reliable differentiation of photoreactions due to fluoroquinolones after oral treatment. Enoxacin, lomefloxacin, ofloxacin, sparfloxacin and BAY y 3118 were tested in this system. We found a good correlation between the results of UV light-irradiated IMDS and a guinea pig model with the quinolones as far as photoirritancy was concerned. This holds true also for the photoallergic standard olaquindox and the photoirritant standard 8-methoxypsoralen. However, in contrast to the guinea pig assays the IMDS is fast and extremely predictive for the risk of both photosensitization and photoirritancy depending on the route of exposure. Thus, the UV light-irradiated IMDS turned out to be a good tool for the preclinical risk assessment procedure in terms of discriminating photoreactions. In addition, flow cytometric analyses were used to underline the fact that antigen-independent activation occurred after the induction of photoirritant reactions.

Epidermal cytokines in murine cutaneous irritant responses

Investigations on cytokines in skin irritancy or non-immunological irritant contact dermatitis (ICD) should improve our understanding of their complex mechanism. Numerous studies showed, however, that similar epidermal cytokines have been detected in irritant and allergic reactions, suggesting a lack of specific cytokines that clearly differentiate allergic from irritant reactions even though the pathomechanisms between allergic contact dermatitis (ACD) and ICD are distinguished. Recent data, however, indicate that some mediators may be restricted to allergic responses (contact hypersensitivity). This could provide the impetus to study their implication on irritant reactions. We overview the epidermal cytokines involved in irritant responses compared to those in contact hypersensitivity based on published results of studies using in vitro cell-cultured murine keratinocytes and in vivo murine models.

Thresholds in contact sensitization: theoretical and practical considerations

The existence of thresholds for both the induction and the elicitation of contact sensitization is an important issue for hazard assessment in this area of toxicology. In this paper, the evidence for such thresholds has been reviewed from both theoretical and practical perspectives. When the mechanisms of skin sensitization are considered, the existence of thresholds can be shown to occur at several stages. They are both quantitative, for example in terms of the degree of protein haptenation and in the sufficiency of the signals for Langerhans cell migration and maturation, as well as qualitative, in terms of the type of immune response that is engaged. Such considerations are evidenced by a substantial body of practical observation. In humans and in animal models of skin sensitization there is abundant evidence for the existence of thresholds for both the induction and the elicitation of reactions. In addition to, and in distinction from, the experimental situation, in the general human population there is extensive evidence for threshold effects. This evidence arises directly from the observation that only a proportion of those who are exposed become sensitized (i.e. are patch test positive), and of that latter group only a proportion develop allergic contact dermatitis.

Immunotoxicity of pesticides: a review

The intricate balance that is the hallmark of the immune system shows vulnerability to any chemical, including pesticides, that can cause structural and functional alterations to the system. The immunotoxic effects of xenobiotics include: histopathologic effects in immune tissues and organs; cellular pathology; altered maturation of immunocompetent cells; changes in B and T cell subpopulations; and functional alterations of immunocompetent cells. Pesticides, including fungicides, herbicides, and insecticides, are the only class of chemicals deliberately released into the environment because of their toxicity. Around the world, millions of people are exposed to pesticides at work and/or in their home. This article reviews evidence, from animal and human studies, on the effects of pesticides on the immune system.

An integrated model for the differentiation of chemical-induced allergic and irritant skin reactions

Contact and photocontact allergic as well as irritant and photoirritant skin reactions represent a major problem in clinical dermatology and during the development of new pharmaceuticals. Furthermore, there is a lack of in vitro and in vivo assays that provide a clear differentiation between allergic and irritant skin reactions. Here, we describe an integrated model to differentiate between chemical-induced allergic and irritant skin reactions by measuring objective and easy-to-determine parameters within both skin and skin-draining lymph nodes. Dose-response studies with standard contact and photocontact allergens as well as irritants and photoirritants revealed that irritants predominantly induced skin inflammation, which in turn stimulated draining lymph node cell proliferation. In contrast, the induction phase of contact or photocontact allergy was characterized by marginal skin inflammation, but a marked activation and proliferation of skin-draining lymph node cells. Therefore, a differentiation index (DI) was defined describing the relation between skin-draining lymph node cell activation (lymph node cell count index) and skin inflammation (ear swelling). A DI > 1 indicates an allergic reaction pattern whereas DI < 1 demonstrates an irritant potential of a chemical. Experiments with the contact allergen oxazolone, the photocontact allergen TCSA + UVA, the irritant croton oil, and the photoirritant 8-methoxypsoralen + UVA confirmed the predictive value of DI. Furthermore, flow cytometric analysis of lymph node-derived T- and B-cell subpopulations revealed that contact sensitizer, but not irritant, induced the expression of CD69 on the surface of I-A+ cells. In conclusion, further studies with a broad range of irritants and allergens will be required to confirm general applicability.

Value of animal models for predicting hypersensitivity reactions to medicinal products

Although hypersensitivity reactions induced by medicinal products and chemicals are relatively common, few predictive models are available. A major difficulty is our currently limited understanding of the mechanisms involved, and efforts should be paid to better defining drug immunogenicity, hapten formation and immune effector mechanisms. A second difficulty is the multiplicity of clinical manifestations presumably due to varying mechanisms. Available models can only predict a few of these reactions. Anaphylaxis models in guinea-pigs can be only used for the safety assessment of macromolecules which are neither humanized or of human origin, whereas guinea-pig or mouse models can detect the majority of human contact sensitizers. In addition to the extensive validation of existing models, promising avenues of research are expected to be found in the use of novel animal models, particularly those using genetically modified animals, such as transgenic and knock-out mice.

TDI inhalation in guinea-pigs involves migration of dendritic cells

Toluene diisocyanate (TDI) can cause occupational asthma, but the mechanism underlying sensitization to this chemical compound remains controversial. The present study aims to investigate whether tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) liberated in the lungs after TDI inhalation can contribute to the migration of dendritic cells from respiratory airways towards lung associated lymph nodes for presentation of TDI hapten. Exposure was studied in two modes: (1) acute exposure (experiment no. 1, 2 and 3) where animals were exposed to 2.962, 1.060, and 1.076 ppm TDI for 1, 4, and two periods of 4 h, respectively; (2) subacute exposure (experiment no. 4, 5 and 6) where animals were exposed to 0.066, 0.110, and 0.999 ppm TDI for 48 h for the two lower doses and 5 days for the highest dose. Depending on the modes of exposure, two to four post exposure times were selected. After acute exposure to 2.962 ppm TDI for 1 h, the increase in TNF-alpha and IL-6 levels in bronchoalveolar lavage (BAL) fluid was observed immediately at the end of inhalation exposure, whereas the maximum number of dendritic cells and total cells occurred at post exposure times of 48 h and 5 days, respectively. In two other acute exposures, the peak increases in TNF-alpha, IL-6 and total cell numbers were observed at 48 h post exposure time, whereas the peak increase in dendritic cells occurred at 24 h. After subacute exposure to 48 h TDI, where TDI concentrations were relatively low (0.006 or 0.110 ppm), a parallel increase in TNF-alpha and IL-6 levels, dendritic and total cell numbers were observed at 0 h post exposure time. This phenomenon was also apparent at 24 h post exposure time when the animals had been exposed to 1.999 ppm TDI for 5 days. From these results, we can conclude that dendritic cells could play a key role as antigen presenting cells in the development of TDI-induced respiratory sensitization, and that their migration toward lung-associated lymph nodes is probably conditioned by cytokine release in their micro-environment. Future work must delineate whether TNF-alpha and IL-6 are solely responsible for the migration of dendritic cells after TDI inhalation, for example by using antibodies to neutralize these cytokines.

Langerhans cells require signals from both tumour necrosis factor-alpha and interleukin-1 beta for migration

The induction phase of contact sensitization is associated with the movement of epidermal Langerhans cells (LC) from the skin and their migration, via afferent lymphatics, to draining lymph nodes where they accumulate as immunostimulatory dendritic cells (DC). It has been demonstrated previously that tumour necrosis factor-alpha (TNF-alpha) provides an important signal for LC migration and that in the absence of this cytokine, movement of LC from the epidermis to regional lymph nodes is inhibited. Recent evidence indicates that interleukin-1 beta (IL-1 beta), a cytokine produced in murine epidermis exclusively by LC, may also play a role in LC migration. The purpose of the investigations described here was to clarify, using relevant neutralizing anti-cytokine antibodies, the contributions made by TNF-alpha and IL-1 beta to the migration of LC from the epidermis. It was found that like anti-TNF-alpha, anti-IL-1 beta administered systemically to mice (by intraperitoneal injection), prior to skin sensitization with the contact allergen oxazolone, resulted in a marked inhibition of DC accumulation in draining lymph nodes. It was shown also that anti-IL-1 beta inhibited TNF-alpha-induced LC migration and DC accumulation and that; in similar fashion, the stimulation of LC migration and DC accumulation induced by IL-1 beta was compromised by prior treatment with anti-TNF-alpha. Based upon these data it is proposed that the stimulation of LC migration in response to skin sensitization requires the receipt by LC of two independent signals, one provided by TNF-alpha and the other by IL-1 beta. Morphological analyses of LC in epidermal sheets prepared from animals exposed to these cytokines with or without prior systemic treatment with anti-cytokine antibody suggested that the changes induced in LC by TNF-alpha and IL-1 beta may include the altered expression of adhesion molecules and acquisition of the ability to interact with and pass through the basement membrane.

Clinical and mechanistic aspects of photopheresis

Photopheresis is an extracorporeal form of photochemotherapy with 8-methoxypsoralen (8-MOP) and ultraviolet A (UVA) radiation. Photopheresis is used for the management of T-cell-mediated diseases, and such treatment leads to the induction of antigen-specific immune suppression directed to the pathogenic clone of T cells. Photopheresis is used to treat a wide variety of diseases--such as cutaneous T-cell lymphoma, systemic sclerosis; rheumatoid arthritis, lupus erythematosus--and is also successfully applied in the suppression of graft rejection. In addition to the clinical achievements, attention will be paid to results from animal studies. An important outcome of these studies is that photopheresis can be used to treat airway hyperreactivity. Furthermore, it was shown that the therapeutic strategy can be changed drastically: the presence of plasma during irradiation should be avoided and the amount of blood that must be treated to obtain the desired antigen-specific immunosuppression can be greatly decreased. Also, results from cellular experiments are discussed. An example of this is the increase in the major histocompatibility complex expression on the surface of cells found after treatment. The mechanism that underlies photopheresis has not yet been elucidated, but progress has been made. The following related points will be reviewed: models for investigation; and mechanistic aspects, with the emphasis on cellular biomacromolecules and on photosensitizers (drugs) other than 8-MOP.

The local lymph node assay: a viable alternative to currently accepted skin sensitization tests

The prospective identification of skin sensitizing chemicals is a vital prerequisite for their proper risk management. Traditionally this has been achieved largely by the conduct of guinea pig assays such as the maximization and Buehler tests. These methods are recommended by the Organisation for Economic Cooperation and Development (OECD) and are required by the European Union (EU) for the evaluation of new substances. However, a novel mechanistically based method, the local lymph node assay (LLNA), has been the focus of substantial validation activity in recent years. This material is reviewed in this paper. It is shown that the LLNA has been validated successfully by five interlaboratory assessments as well as by comparisons with guinea pig tests and human data. The method also offers clear advantages to the user in terms of objectivity, time and cost, and delivers important animal welfare benefits. In consequence, it is recommended that the LLNA be formally adopted by the OECD in Guideline 406 and accepted by the EU and US EPA as a method suitable for the classification of the skin sensitizing potential of chemicals.

Characterization of processing requirements and metal cross-reactivities in T cell clones from patients with allergic contact dermatitis to nickel

Metal ions such as nickel, cobalt, copper and palladium are known to be potent sensitizers in humans, but the antigenic determinants created by these metals as well as the mechanisms of recognition by specific T cell clones are still not elucidated. In this paper, nickel-specific T lymphocyte clones were isolated from four patients exhibiting contact dermatitis to this metal. A panel of 42 independent T cell clones was studied. They were shown to recognize nickel in the context of major histocompatibility complex (MHC) class II molecules and to belong to the CD4 subset. Using fixed autologous Epstein-Barr virus-transformed B cells as antigen-presenting cells (APC), we could distinguish two distinct groups of T cell clones on the basis of processing requirements: 40% of the T cell clones were strictly processing dependent, whereas the remaining 60% could proliferate in response to nickel even in the presence of glutaraldehyde-fixed APC. Furthermore, we present arguments indicating that individual Ni-specific T cell clones cross-react with some transition metals (e.g. Cu or Pd), but not with others (e.g. Co, Cr and Pt), presented by identical MHC class II molecules. These results thus provide an explanation for the multiple metal-reactivities observed in vivo in human patients: they indicate that for Cu and Pd, these co-reactivities in vivo might be due to cross-reactivity at the clonal level. Our findings also suggest that this is not the case for cobalt allergy, which might result from cosensitization of the patient to cobalt in addition to nickel.

Cytokine regulation of chemical sensitization

The skin is an immunologically active tissue. Epidermal cells, both keratinocytes and Langerhans cells (LC), produce constitutively or can be stimulated to produce a variety of cytokines, many of which play important roles in the induction and regulation of allergic responses to sensitizing chemicals. Tumor necrosis factor alpha (TNF-alpha) provides the signal for LC migration from the skin and granulocyte/macrophage colony-stimulating factor (GM-CSF), interleukin 1 (IL-1) and other cytokines effect the functional maturation of LC and their acquisition of immunostimulatory potential. The initial stimulus for induced or increased epidermal cytokine production derives from chemical exposure, or some other form of skin trauma. However, some epidermal cytokines are regulated in paracrine or autocrine fashion by other cytokines produced locally. The availability of epidermal cytokines has a major impact on the induction of sensitization and on the characteristics of immune responses to chemical allergens.