Contact allergic response to dinitrochlorobenzene (DNCB) in rats: insight from sensitization phase

Impact of Skin Exposure to Benzo[a]pyrene in Rat Model: Insights into Epidermal Cell Function and Draining Lymph Node Cell Response

The skin is a direct target of the air pollutant benzo[a]pyrene (BaP). While its carcinogenic qualities are well-studied, the immunotoxicity of BaP after dermal exposure is less understood. This study examines the immunomodulatory effects of a 10-day epicutaneous BaP application, in environmentally/occupationally relevant doses, by analyzing ex vivo skin immune response (skin explant, epidermal cells and draining lymph node/DLN cell activity), alongside the skin's reaction to sensitization with experimental hapten dinitrochlorobenzene (DNCB). The results show that BaP application disrupts the structure of the epidermal layer and promotes immune cell infiltration in the dermis. BaP exposure led to oxidative stress in epidermal cells, characterized by decreased reduced glutathione and increased AHR and Cyp1A1 expression. Production and gene expression of proinflammatory cytokines (TNF, IL-1β) by epidermal cells decreased, while IL-10 response increased. Decreased spontaneous production of IFN-γ and IL-17, along with unchanged IL-10, was observed in DLC cells, whereas ConA-stimulated production of these cytokines was elevated. Local immunosuppression caused by BaP application seems to reduce the skin's response to an additional stimulus, evidenced by decreased effector activity of DLN cells three days after sensitization with DNCB. These findings provide new insight into the immunomodulatory effects and health risks associated with skin exposure to BaP.

Expression of interleukin-1β, interleukin-4, interferon-γ and tumour necrosis factor α in different tissue in a dinitrochlorobenzene-induced ear swelling test in mice

OBJECTIVE

To study the expression of interleukin-1β (IL-1β), interleukin-4 (IL-4), interferon-γ (IFN-γ) and tumour necrosis factor α (TNF-α) in different tissue in a dinitrochlorobenzene (DNCB)-induced ear swelling test in mice and further evaluate the correlation between the cytokine expression in different tissues and the degree of ear swelling.

METHODS

The mice were sensitised with a 0.50% DNCB solution on their back for 3 days. After 7 days, the thickness of their ears was measured and grouped. Different concentrations of the DNCB solution were challenged in the left ear of each group of mice, and the right ear was used as the control. The thickness of both ears was measured every 24 h, and the mice were sacrificed 72 h after the challenge. The expressions of IL-1β, IL-4, IFN-γ and TNF-α in the mouse serum, lymph node and ear tissue were quantified by enzyme-linked immunosorbent assay, respectively.

RESULTS

There was a linear positive correlation between the swelling index of the mouse lateral ear and the challenge concentration of DNCB (r = 0.96, p < 0.01). The high expression of IL-1β and IL-4 in the lateral ear tissue of the mice was positively correlated with the ear swelling index 48 h after the challenge. The correlation coefficient was 0.78 (p < 0.01). Furthermore, IFN-γ and TNF-α had no significant correlation with the ear swelling index 48 h after the challenge.

CONCLUSION

There is a correlation between the degree of ear swelling in mice and the concentration of DNCB and the expression of IL-1β and IL-4 in the lateral ear tissue. There is a sub-clinical skin sensitivity state in contact allergy.

Neurokinin-1 Receptor Signaling Is Required for Efficient Ca2+ Flux in T-Cell-Receptor-Activated T Cells

Efficient Ca²⁺ flux induced during cognate T cell activation requires signaling the T cell receptor (TCR) and unidentified G-protein-coupled receptors (GPCRs). T cells express the neurokinin-1 receptor (NK1R), a GPCR that mediates Ca²⁺ flux in excitable and non-excitable cells. However, the role of the NK1R in TCR signaling remains unknown. We show that the NK1R and its agonists, the neuropeptides substance P and hemokinin-1, co-localize within the immune synapse during cognate activation of T cells. Simultaneous TCR and NK1R stimulation is necessary for efficient Ca²⁺ flux and Ca²⁺-dependent signaling that sustains the survival of activated T cells and helper 1 (Th1) and Th17 bias. In a model of contact dermatitis, mice with T cells deficient in NK1R or its agonists exhibit impaired cellular immunity, due to high mortality of activated T cells. We demonstrate an effect of the NK1R in T cells that is relevant for immunotherapies based on pro-inflammatory neuropeptides and its receptors.

The neurokinin 1 receptor (NK1R) induces Ca²⁺ flux in excitable cells. Here, Morelli et al. show that NK1R signaling in T cells promotes optimal Ca²⁺ flux triggered by TCR stimulation, which is necessary to sustain T cell survival and the efficient Th1- and Th17-based immunity that is relevant for immunotherapies based on pro-inflammatory neuropeptides.

Correlating the structure and reactivity of a contact allergen, DNCB, and its analogs to sensitization potential

We report a study that seeks to find a correlation between the overall sensitization potential quantified by the expression of IL-8 by stimulated monocytes and the chemical structure of a model contact allergen, 2,4-dinitrochlorobenzene (DNCB). We show that structure and reactivity of the chemical compounds play an important role in activation of the monocytes and subsequent inflammation in tissue. However, we observed a non-linear correlation between the rate of reaction and biological activity indicating a required balance of stability and reactivity.

Oral warfarin affects some aspects of systemic immunomodulation with topical dinitrochlorobenzene (DNCB) in rats

PURPOSE

The efficacy of topical dinitrochlorobenzene (DNCB) in the treatment of some skin dermatoses is based both on local and systemic effects. It is not known, however, whether it can be applied to patients receiving some other therapy associated with systemic immunomodulation. The aim of the present paper using a rat model was to examine whether oral warfarin (WF) intake, as shown by others and by us, had an immunomodulatory potential to interfere with effects of topical DNCB as systemic immunotherapy.

MATERIALS AND METHODS

Rats received 3.5 mg/l of WF sodium in drinking water for 30 days and were thereafter skin-sensitized with 0.4% DNCB. Changes in the oxidative activity (myeloperoxidase/MPO, reduction of nitroblue tetrazolium/NBT and nitric oxide/NO production) as well as tumor necrosis factor (TNF) production by peripheral blood polymorphonuclear cells (PMN) were measured and compared with PMN from sensitized unexposed to WF rats.

RESULTS

WF intake enhanced some aspects of PMN activity (intracellular MPO activity and unstimulated NO production) as well as their responsiveness to exogenous stimulation (NBT reduction and TNF production from sensitized animals). However, WF also decreased PMN responsiveness of NO production to stimulation. WF affected NO and TNF production solely by PMN, as no effect on these activities of peripheral blood mononuclear cells was seen.

CONCLUSION

Having in mind that polymorphonuclear leukocytes are the most abundant cell type in peripheral blood in humans, increase of basic aspects of PMN activity described in the present paper might be relevant for consideration of using WF as therapeutic modality in patients topically treated with DNCB.

Central neural activation following contact sensitivity peripheral immune challenge: evidence of brain-immune regulation through C fibres

This study tested the hypothesis that peripheral immune challenges will produce predictable activation patterns in the rat brain consistent with sympathetic excitation. As part of examining this hypothesis, this study asked whether central activation is dependent on capsaicin-sensitive C-fibres. We induced skin contact sensitivity immune responses with 2,4-dinitrochlorobenzene (DNCB), in the presence or absence of the acute C-fibre toxin capsaicin (8-methyl-N-vanillyl-6-nonenamide) to trigger immune responses with and without diminished activity of C-fibres. Innovative blood-oxygen-level-dependent functional magnetic resonance imaging data revealed that the skin contact sensitivity immune responses induced with DNCB were associated with localized increases in brain neuronal activity in treated rats. This response was diminished by pre-treatment with capsaicin 1 week before scans. In the same animals, we found expression of the immediate early gene c-Fos in sub-regions of the amygdala and hypothalamic sympathetic brain nuclei. Significant increases in c-Fos expression were found in the supraoptic nucleus, central amygdala and medial habenula following immune challenges. Our results support the idea that selective brain regions, some of which are associated with sympathetic function, process or modulate immune function through pathways that are partially dependent on C-fibres. Together with previous studies demonstrating the motor control pathways from brain to immune targets, these findings indicate a central neuroimmune system to monitor host status and coordinate appropriate host responses.

Total glucosides of paeony inhibit the inflammatory responses of mice with allergic contact dermatitis by restoring the balanced secretion of pro-/anti-inflammatory cytokines

The present study aimed to investigate the regulation exerted by the total glucosides of paeony (TGP) on the production of interleukin-2 (IL-2), IL-4, IL-10 and IL-17 in the serum and lymphocytes of mice with allergic contact dermatitis (ACD). ACD in mice was induced by the repeated application of 2,4-dinitrochlorobenzene (DNCB) to their skins. The mice were orally administered TGP (35, 70, and 140mg/kg/d) and prednisone (Pre, 5mg/kg/d) from day 1 to day 7 after immunization. The inflammatory responses were evaluated by ear swelling and histological examination. Thymocyte proliferation was assayed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H tetrazolium bromide assay. The cytokine production in the serum and lymphocytes supernatant was measured by enzyme-linked immunosorbent assay. The results indicated that the topical application of DNCB to the skin provoked obvious inflammatory responses. The oral administration of TGP (70 and 140mg/kg/d) and Pre (5mg/kg/d) significantly inhibited skin inflammation, decreased the thymus and spleen indices, and inhibited thymocyte proliferation in mice treated with DNCB. Further study indicated that TGP increased IL-4 and IL-10 production but decreased the production of IL-2 and IL-17 in the serum and lymphocyte supernatant. The correlation analysis suggested significantly positive correlations between IL-2 and IL-17 production and the severity of skin inflammation, whereas negative correlations were obtained for IL-4 and IL-10 production and skin inflammation. In summary, these results suggest that the therapeutic effects of TGP on ACD may result from its regulation of the imbalanced secretion of IL-2/IL-4 and IL-10/IL-17.

Inflammatory and immune mechanisms in contact hypersensitivity (CHS) in rats

Contact hypersensitivity (CHS) is a T-cell-mediated skin inflammatory reaction to cutaneous exposure to small sensitizing chemicals, haptens. Majority of CHS studies were conducted in mice and there is paucity of data in other experimental animals. In this review, after a brief survey of murine CHS, hitherto known characteristics of CHS in rats were presented including inflammatory and immune mechanisms of both sensitization and elicitation phases. Survey of literature of rat CHS is presented, with our data concerning the importance of genetic background both in the induction and in the expression of reaction to dinitrochlorobenzene. The knowledge of CHS in rats, preferred animal in immunopharmacological studies, might help development of immunomodulatory intervention in contact allergy.

Systemic immunomodulatory effects of topical dinitrochlorobenzene (DNCB) in rats. Activity of peripheral blood polymorphonuclear cells

Topical application of dinitrochlorobenzene (DNCB) is employed in the immunotherapy of skin diseases. Activation of T-cell mediated immune responses (Th1/type1) is the supposed mechanism of the clinical effect of DNCB, but there are no data concerning innate/inflammatory mechanisms. In this study, the effect of repeated topical DNCB application on peripheral blood polymorphonuclear (PMN) leukocytes has been examined in two rat strains which differ in the propensity to mount Th1/type1 or Th2/type2 responses. The dynamics of changes in PMN numbers and effector activities (respiratory burst, nitric oxide production and myeloperoxidase content), as well as in adhesion and TNF-α production following the rat skin sensitization with low (0.4%) and high (4%) DNCB doses were measured. Both priming and activation of PMNs were observed following skin sensitization with DNCB, with dose-dependent as well as time-dependent differences in some PMN activities. Obtained data might be relevant for understanding the immune mechanisms of topical DNCB therapy.

Percutaneous toxicity of dinitrochlorobenzene (DNCB) in rats

Contact hypersensitivity reaction (CHS) is a T-cell-mediated skin inflammatory reaction to cutaneous exposure to small sensitizing chemicals, haptens. While the significance of local inflammatory skin response to the hapten application in CHS induction and expression is known, there is paucity of data concerning systemic inflammation in CHS. In this study, changes in cellular (peripheral blood granulocytes) and humoral (plasma tumor necrosis factor (TNF)-α levels) components of inflammation during sensitization of rats with two consecutive applications of dinitrochlorobenzene (DNCB) were examined. The impact of sensitization on these parameters was determined by employing low (0.4%) and high (4%) hapten doses and by examining the dynamics (i.e. one and three days following the last application of DNCB) of these changes. Dose-dependent increase in relative numbers and priming (for respiratory burst and adhesion) effect of skin sensitization with DNCB on peripheral blood neutrophils in rats were noted. No changes in circulating TNF-α levels were observed following the sensitization. The increase in lung myeloperoxidase content and histologically evident presence of neutrophils was observed in lungs of the sensitized rats. The changes in granulocyte priming for adhesion might have accounted for the observed increase in lung neutrophil content in the sensitized rats.