Imunski mehanizmi indukcije i ekspresije reakcije kontaktne preosetljivosti kod pacova
Immune mechanisms of induction and expression of contact hypersensitivity reaction in rats
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Allergic contact dermatitis (ACD) is a common skin inflammatory disease in humans, affecting 15-20% of the general population. Large number of chemical agents that induce ACD (called haptens), together with lack of adequate conventional immunosuppressive therapy, make this disease a major challenge for public health and modern immunology. Pathophysiology of ACD is studied on animal models referred as contact hypersensitivity. Although the reaction of contact hypersensitivity (CHS) has been much studied, mostly in mice, the knowledge of its mechanisms is still far from complete. In addition, there is paucity of data about CHS in other experimental animals, beside mice, which might increase our understanding of the immunobiology of contact allergy. In light of this, in the present study the characteristics of CHS were analyzed in rats, using two strains, Dark Agouti (DA) i Albino Oxford (AO), which have been shown to differ in reactivity to certain inflammatory stimuli. CHS to hapten dinitrochlorobenzene (DNCB) was induced by applying two different hapten concentrations in sensitization and elicitation phases (sensitization/elicitation regime 0.4%/0.13% and 4%/1.3% DNCB). Mechanisms of CHS were studied in induction (sensitization) and expression (elicitation) phases, by evaluating dynamics in activity changes of draining lymph node (dLN) cells in sensitization phase and by evaluating production of inflammatory/anti-inflammatory mediators in conditioned medium of ear skin organ culture and activity changes of dLN cells in elicitation phase (24 hours after elicitation). The results showed increased in vivo (ear thickness) and ex vivo (patohistology analysis of ear skin) parameters of CHS reaction, in both rat strains following the treatment with high DNCB dose, but the reaction was more intensive in DA compared to AO rats. In sensitization phase it was showed: increased dLN cell number in both strains (higher in DA rats), changes in ratio of CD4+ and CD8+ subsets (increased ratio of CD4+/CD8+ cells in DA rats, because of increased relative number of CD4+ and decreased relative number of CD8+ cells and decreased CD4+/CD8+ ratio in AO rats, because of decreased relative number of CD4+ cells and increased CD8+ cells relative number), increased ex vivo proliferation of dLN cells and increased spontaneous and specific (induced by in vitro cell stimulation with hapten) production of inflammatory cytokines IFN-γ and IL-17 and Th2/anti-inflammatory cytokine IL-10 (more pronounced in DA rats). Similarly to DA rats, no changes in production and expression of Th2/anti-inflammatory cytokine IL-4 were noted in AO rats in sensitization phase. Increased ear thickness in elicitation phase was accompanied by increased production of TNF-α, NO, MPO, IFN-γ and IL-17 in conditioned medium of ear skin organ culture. Strain-dependent differences in CHS expression were related to differences in intensity (higher NO, MPO, IFN-γ, IL-17 in DA strain) and type of immune response (increased production of IL-4 only in AO rats). In addition, in this phase of the reaction it was showed the increase in dLN activity in DNCB-treated DA rats (increased spontaneous and specific proliferation, concomitantly with increased expression of growth factor IL-2 receptor α chain, as well as production of effector cytokines IFN-γ and IL-17, and gene expression of p35, p40 and T-bet, which are indicators of differentiation of Th1/type1 cells), compared to controls. The absence of changes in the activity of effector mechanisms in dLN of AO strain is accompanied by increased production of IL-4 and increased numbers of CD4+CD25+Foxp3+ cells, that phenotypically correspond to regulatory T cells (Treg). CHS to DNCB in rats (similarly to mouse model) is characterized by activation of Th1/type1 and Th17/type17 immune response, and differences in response intensity (in induction and expression phase) and response type (in expression phase) could be underlying mechanism of strain-dependent difference. Comparative analysis of CHS in more reactive (DA) and less reactive (AO) strains, can contribute to the further knowledge of the immunological mechanisms underlying the development and expression, as well as regulation of this reaction. Such findings might be useful in exploring the potential of therapeutic modalities to reduce skin damage caused by contact allergy, as well as in the elucidation of immunomodulatory potential of different chemicals, particularly those that gain access to the host system via skin.
Keywords:Contact hypersensitivity reaction; DNCB; Sensitization phase; Elicitation phase; DA and AO rats; Draining lymph nodes; Ear skin organ culture
Source:University of Belgrade, Faculty of Biology, 2013, 1-147