Immune mechanisms of induction and expression of contact hypersensitivity reaction in rats

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 (mor