Approaches to the identification and classification of chemical allergens in mice

Effects of Exercise on Stress-induced Attenuation of Vaccination Responses in Mice

Studies suggest that exercise can improve vaccination responses in humans. Chronic stress can lead to immunosuppression, and there may be a role for exercise in augmenting immune responses.

PURPOSE

To investigate the effects of acute eccentric exercise (ECC) and voluntary wheel exercise training (VWR) on antibody and cell-mediated immune responses to vaccination in chronically stressed mice. We hypothesized that both ECC and VWR would attenuate chronic stress-induced reductions in vaccination responses.

METHODS

Mice were randomized into four groups: control (CON), stress (S)-ECC, S-VWR, and S-sedentary (SED). Stressed groups received chronic restraint stress for 6 h·d, 5 d·wk for 3 wk. After the first week of stress, S-ECC were exercised at 17 m·min speed at -20% grade for 45 min on a treadmill and then intramuscularly injected with 100 μg of ovalbumin (OVA) and 200 μg of alum adjuvant. All other groups were also vaccinated at this time. Stress-VWR mice voluntarily ran on a wheel for the entire experiment. Plasma was collected before, and at 1, 2, and 4 wk postvaccination. Enzyme-linked immunosorbent assay was performed to analyze anti-OVA IgG and IgM antibodies. After 3 wk of chronic stress, all mice were injected with OVA into the ear to determine the delayed-type hypersensitivity.

RESULTS

We found that chronic restraint stress significantly reduced body weight and caused adrenal hypertrophy. We also found both S-ECC and S-VWR groups had significantly elevated anti-OVA IgG (P < 0.05), whereas no significant differences between the two exercise groups. Neither S-ECC nor S-VWR altered anti-OVA IgM or delayed-type hypersensitivity responses compared with S-SED group.

CONCLUSIONS

Acute eccentric exercise and voluntary exercise training alleviated the chronic stress-induced anti-OVA IgG reductions in vaccination responses.

Effect of orally administered Eriobotrya japonica seed extract on allergic contact dermatitis in rats

The anti-allergic activity of Eriobotrya japonica seeds extract (ESE) was investigated. Oral administration of ESE dramatically inhibited ear swelling due to allergic contact dermatitis caused by repeated application of two antigens, 4-ethoxymethylene-2-phenyl-2-oxazolin-5-one (oxazolone) and dinitrofluorobenzene (DNFB), respectively. The increase of histamine content in inflamed ear tissue induced by oxazolone and DNFB was significantly antagonized by orally administered ESE. Eosinophil peroxidase and myeloperoxidase activity in both models was suppressed by orally administered ESE. Tumour necrosis factor-α in the inflamed region caused by repeated application of DNFB was also significantly suppressed. The findings suggest that ESE may be effective for treating allergic contact dermatitis.

Stress-induced augmentation of immune function--the role of stress hormones, leukocyte trafficking, and cytokines

Delayed-type hypersensitivity (DTH) reactions represent cell-mediated immune responses that exert important immunoprotective (resistance to viruses, bacteria, and fungi) or immunopathological (allergic or autoimmune hypersensitivity) effects. We initially utilized the skin DTH response as an experimental in vivo model to study neuro-endocrine-immune interactions in rodents. We hypothesized that just as an acute stress response prepares the cardiovascular and musculoskeletal systems for fight or flight, it may also prepare the immune system for challenges which may be imposed by a stressor. The skin DTH model allowed us to examine the effects of stress at the time of primary and secondary exposure to antigen. Studies showed that acute (2h) stress experienced before primary or secondary antigen exposure induces a significant enhancement of skin DTH. Importantly, this enhancement involved innate as well as adaptive immune mechanisms. Adrenalectomy eliminated the stress-induced enhancement of DTH. Acute administration of physiological (stress) concentrations of corticosterone and/or epinephrine to adrenalectomized animals enhanced skin DTH. Compared with controls, DTH sites from acutely stressed or hormone-injected animals showed significantly greater erythema and induration, numbers of infiltrating leukocytes, and levels of cytokine gene expression. In contrast to acute stress, chronic stress was immunosuppressive. Chronic exposure to corticosterone, or acute exposure to dexamethasone significantly suppressed skin DTH. These results suggest that during acute stress, endogenous stress hormones enhance skin immunity by increasing leukocyte trafficking and cytokine gene expression at the site of antigen entry. While these results are discussed from a mechanistic and clinical relevance perspective, it is acknowledged that much work remains to be done to elucidate the precise mechanisms mediating these bi-directional effects of stress and stress hormones and their clinical ramifications.

Acute stress enhances while chronic stress suppresses skin immunity. The role of stress hormones and leukocyte trafficking

Delayed-type hypersensitivity (DTH) reactions are antigen-specific, cell-mediated immune responses that, depending on the antigen, mediate beneficial (resistance to viruses, bacteria, fungi) or harmful (allergic dermatitis, autoimmunity) aspects of immunity. Contrary to the widely held notion that stress is immunosuppressive, we have shown that under certain conditions, stress can enhance immune function. DTH reactions can be studied in rats or mice by challenging the pinnae of previously sensitized animals with antigen. Studies have shown that acute stress administered immediately before antigen exposure significantly enhances skin DTH. In contrast, chronic stress significantly suppresses skin DTH. Stress-induced changes in leukocyte distribution may contribute to these bidirectional effects of stress, since acute stress induces a significant mobilization of leukocytes from the blood to the skin, whereas chronic stress suppresses leukocyte mobilization. In order to identify the hormonal mediators of the observed effects of stress, we first showed that adrenalectomy (ADX) eliminates the stress-induced enhancement of DTH. Acute administration (to ADX animals) of low doses of corticosterone and/or epinephrine significantly enhances skin DTH. In contrast, acute administration of high doses of corticosterone, low doses of dexamethasone, or chronic administration of moderate doses of corticosterone, suppress skin DTH. Thus, the timing and duration of stress may significantly affect the nature (enhancing versus suppressive) of the effects of stress on skin immune function. These results suggest that during acute stress, stress hormones may help enhance immune function by informing the immune system about impending challenges (e.g., wounding or infection) that may be imposed by a stressor (e.g., an aggressor). Thus, during acute stress, the brain may send a warning signal to the immune system, just as it does to other fight/flight systems in the body.

Morphine modulation of the contact hypersensitivity response: characterization of immunological changes

Previous investigations in our laboratory showed that systemic morphine administration 1 h prior to elicitation of the in vivo contact hypersensitivity (CHS) response produced a robust increase in inflammation at the site of antigen reexposure. The present study extended those findings by characterizing the effect of morphine on immunological processes important in the development of the CHS response. To induce contact hypersensitivity, the antigen 2,4-dinitrofluorobenzene was applied to the pinnae of previously sensitized rats. Morphine administration produced an increase in inducible nitric oxide synthase mRNA and the proinflammatory cytokine interleukin-6, at the site of antigen reexposure. In contrast, morphine did not alter expression of the anti-inflammatory cytokine interleukin-10. Morphine also produced an increase in the proliferation of lymphocytes from the peripheral (i.e., cervical) lymph nodes when assessed 72 h following challenge. These studies show that the morphine-induced increase in the in vivo CHS response involves immunologically specific alterations.

Cytokine fingerprinting and hazard assessment of chemical respiratory allergy

Allergic sensitization of the respiratory tract resulting in occupational asthma and other symptoms can be caused by a variety of chemicals and represents an important occupational health problem. Although there is a need to identify and characterize those chemicals that are able to cause respiratory allergy, there are currently no well validated or widely accepted predictive test methods. Some progress has been made with guinea pig assays, but our attention in this laboratory has focused instead on the development of novel approaches based on an understanding of the nature of immune responses induced in mice by chemical allergens. We have shown that whereas contact allergens provoke in mice selective type 1 immune responses, characterized by the secretion by draining lymph node cells (LNC) of high levels of the cytokine interferon gamma (IFN-gamma), chemical respiratory allergens stimulate instead preferential type 2 responses associated with comparatively high levels of interleukins 4 and 10 (IL-4 and IL-10). The divergent immune responses provoked by different classes of chemical allergens, and the phenotypes of selective cytokine secretion that characterize such responses, form the basis of a novel method-cytokine fingerprinting--that permits chemicals that have the potential to cause respiratory allergy to be identified and distinguished from those that are associated primarily with contact sensitization. In this article the immunobiological basis for cytokine fingerprinting is considered and the development, evaluation and practical application of the assay are reviewed.

Stress-induced enhancement of skin immune function: A role for gamma interferon

Contrary to the widespread belief that stress is necessarily immunosuppressive, recent studies have shown that, under certain conditions, stress can induce a significant enhancement of a skin cell-mediated immune response [delayed-type hypersensitivity (DTH) or contact hypersensitivity]. Adrenal stress hormones and a stress-induced trafficking of leukocytes from the blood to the skin have been identified as systemic mediators of this immunoenhancement. Because gamma interferon (IFNgamma) is an important cytokine mediator of DTH, the studies described here were designed to examine its role as a local mediator of the stress-induced enhancement of skin DTH. The effect of acute stress on skin DTH was examined in wild-type and IFNgamma receptor-deficient (IFNgammaR-/-) mice that had previously been sensitized with 2,4-dinitro-1-fluorobenzene. Acutely stressed wild-type mice showed a significantly larger DTH response than nonstressed mice. In contrast, IFNgammaR-/- mice failed to show a stress-induced enhancement of skin DTH. Immunoneutralization of IFNgamma in wild-type mice significantly reduced the stress-induced enhancement of skin DTH. In addition, an inflammatory response induced by direct IFNgamma administration to the skin was significantly enhanced by acute stress. Our results suggest that IFNgamma is an important local mediator of a stress-induced enhancement of skin DTH. These studies are clinically relevant because, depending on the nature of the antigen, DTH reactions mediate numerous protective (e.g., resistance to viral, bacterial, parasitic, and fungal infections) or pathological (e.g., autoimmune reactions and contact sensitivity reactions such as that to poison ivy) immune responses.

Enhancing versus suppressive effects of stress hormones on skin immune function

Delayed-type hypersensitivity (DTH) reactions are antigen-specific cell-mediated immune responses that, depending on the antigen, mediate beneficial (e.g., resistance to viruses, bacteria, and fungi) or harmful (e.g., allergic dermatitis and autoimmunity) aspects of immune function. Contrary to the idea that stress suppresses immunity, we have reported that short-duration stressors significantly enhance skin DTH and that a stress-induced trafficking of leukocytes to the skin may mediate this immunoenhancement. Here, we identify the hormonal mediators of a stress-induced enhancement of skin immunity. Adrenalectomy, which eliminates the glucocorticoid and epinephrine stress response, eliminated the stress-induced enhancement of skin DTH. Low-dose corticosterone or epinephrine administration significantly enhanced skin DTH and produced a significant increase in the number of T cells in lymph nodes draining the site of the DTH reaction. In contrast, high-dose corticosterone, chronic corticosterone, or low-dose dexamethasone administration significantly suppressed skin DTH. These results suggest a role for adrenal stress hormones as endogenous immunoenhancing agents. These results also show that hormones released during an acute stress response may help prepare the immune system for potential challenges (e.g., wounding or infection) for which stress perception by the brain may serve as an early warning signal.

Assessment of the sensitization potential of five metal salts in the murine local lymph node assay

The murine local lymph node assay (LLNA) has been proposed as a predictive test for the identification of sensitizing agents. We used this test to compare the sensitization potential of NiSO4, K2Cr2O7, CoCl2, Na2PtCl6 and BeSO4, salts of metals which have all been associated with allergic contact dermatitis and either bronchial asthma orinterstitial lung disease, by either humoral or cell-mediated allergic mechanisms. BALB/c mice (n = 3 per concentration studied, three concentrations studied per metal) received three daily applications of the metal salt (in DMSO) on the dorsum of both ears. On the fourth day the draining auricular lymph nodes were removed and the incorporation of [3H]-thymidine in the lymphocytes in culture was compared to that of concurrent vehicle-treated control mice, thus enabling to derive a stimulation index (SI), indicative of immunological sensitization potential. Each experiment was performed three times. Oxazolone and toluene diisocyanate, chosen as positive controls, yielded strongly positive SI values (> 20 and > 30 respectively). Na2PtCl6 (SI 2.6 +/- 1.0 at 2.5%), CoCl2 (SI 2.8 +/- 0.5 at 5%) and possibly also K2Cr2O7 (SI 2.1 +/- 1.2 at 0.5%) were positive in the LLNA, whereas NiSO4 (SI 0.9 +/- 0.2 at 5%) and BeSO4 (SI 1.3 +/- 0.6 at 4%) were negative. Although our results are still limited by the fact that only one mice strain was tested, they indicate that there is no strict relationship between the sensitization potential of metal salts, as evaluated in the murine LLNA, and their potential to cause either respiratory or dermal allergic disease. Consequently, caution should be exercised before proposing the murine LLNA as a valid test to predict the sensitization potential of low molecular weight chemicals.

Phenyl isocyanate is a potent chemical sensitizer

Diisocyanates, as a chemical class, are recognized for their ability to cause respiratory and dermal sensitization. By contrast, monofunctional isocyanates have not been associated with cases of clinical sensitization. We investigated the immunologic activity of phenyl isocyanate (PI), an aromatic monoisocyanate, which is a trace constituent in commercial diphenyl methane diisocyanate (MDI) products, since it is has been reported to cause an "asthma-like' syndrome in rats. The potency of PI as a contact sensitizer was assessed using the mouse ear swelling test. PI was found to be the most potent isocyanate tested yielding an SD50 (dose predicted to sensitize 50% of the mice) of 0.04 mumol/kg, compared with SD50 values of 0.5, 2.1, and 30.4 mumol/kg, for the diisocyanate sensitizers hexamethylene diisocyanate, MDI, and toluene diisocyanate (TDI), respectively. When tested for ability to stimulate humoral immune responses, antibody titers to PI were more than ten-fold greater than those induced by TDI. The mean hapten-specific IgG antibody titer to PI was 1.4 x 10(4), compared with 1.3 x 10(3) for TDI. The anti-PI IgG1 anaphylactic antibody titer (1.2 x 10(4) was significantly greater than the anti-TDI IgG1 titer of 6.4 x 10(2). Hapten-specific IgE was not detected to either isocyanate. These results indicate that phenyl isocyanate is a potent inducer of both cellular and humoral immune responses. This activity may be a significant contribution to the sensitization potential of commercial products in which it is a trace contaminant.

Experimental assessment of the sensitizing properties of formaldehyde

Formaldehyde causes upper respiratory tract irritation and has been reported in some investigations to be a cause of occupational allergic asthma. The data are equivocal, however, and it has proved difficult to confirm that exposure to formaldehyde induces respiratory sensitization or provokes the production of specific immunoglobulin E (IgE) antibody. In this study the sensitizing properties of formaldehyde were examined experimentally. This chemical elicited strong positive responses in three independent methods for the prospective identification of contact sensitizing chemicals-the guinea pig maximization test, the occluded patch test of Buehler and the murine local lymph node assay. In contrast, in a novel predictive test method for assessment of respiratory sensitization potential-the mouse IgE test-formaldehyde at the same test concentrations was negative. Furthermore, formaldehyde induced in mice a pattern of cytokine secretion by draining lymph node cells inconsistent with the stimulation of IgE antibody responses or respiratory sensitization. These data indicate that, although formaldehyde is a potent contact allergen, it lacks a significant potential to cause sensitization of the respiratory tract.

The local lymph node assay: developments and applications

The murine local lymph node assay is a predictive test method for the identification of contact allergens in which sensitizing activity is measured as a function of induced proliferative responses in lymph nodes draining the site of application. In this article the development and validation of the assay are described and comparisons with guinea pig predictive test methods discussed. In addition we examine the advantages and limitations of the method and consider new opportunities and applications of the assay in the context of the toxicological evaluation of sensitizing potential.