DC migration into the draining lymph node also takes place in the elicitation phase of allergic contact dermatitis and this migration can be influenced by tacrolimus and rapamycin, and, to a lesser extent, by cilomilast.

No abstract

The in vitro and in vivo immunomodulatory effects of the phosphodiesterase 4 inhibitor cilomilast were compared to tacrolimus and rapamycin, immunosuppressive drugs used in organ transplantation. Tacrolimus is also registered for treatment of human atopic dermatitis. In vitro, the effect of the substances on the mixed leucocyte reaction (dendritic cell‐mediated T‐cell activation) was tested. Cilomilast and tacrolimus, as well as rapamycin, were able to inhibit proliferation in a dose‐dependent manner. In vivo, the substances were tested in a model of allergic contact dermatitis. Toluene‐2,4‐diisocyanate (TDI)‐induced allergic contact dermatitis in BALB/c mice is characterized by a Th2‐mediated allergic inflammatory reaction, demonstrated by an increase of IL‐4 and an unchanged level of IL‐12 in inflamed tissues. It was our aim to compare the inhibitory effect of the drugs on the TDI‐induced allergic inflammatory response (ear swelling). After oral and intraperitoneal administration, only tacrolimus induced a distinct inhibition of the TDI‐mediated ear swelling 16 h after challenge. Cilomilast as well as rapamycin failed to do so. After topical administration, cilomilast and tacrolimus, but not rapamycin, inhibited the inflammatory response. Therefore, we compared the combination of topical and systemic administration of cilomilast and tacrolimus in the main experiment. Cilomilast (20 mg/kg) was administered intraperitoneally 16 and 0.5 h before challenge and topically onto mouse ears (3% in 20 μL acetone/DMSO 9:1) 2 h before challenge. Tacrolimus was given via the same routes (systemically 2.5 mg/kg and topically 0.5%) at the same time points as cilomilast. Both substances induced a significant inhibition of the ear swelling measured 16 h after TDI challenge. The mice were sacrificed, draining auricular lymph nodes were weighed, and lymph node cells were counted. Compared to vehicle‐treated mice, both lymph node weight and cell count were significantly reduced in tacrolimus‐treated mice and slightly reduced in cilomilast‐treated mice. Additionally, the dorsal half of the treated ears was cultivated for a skin dendritic cell migration assay. In contrast to a former study in which cilomilast strongly inhibited dendritic cell migration in nonsensitized skin, there was no inhibition of dendritic cell migration by cilomilast or tacrolimus in TDI‐challenged skin. In conclusion, the mixed leucocyte reaction in combination with an in vivo contact dermatitis model is a superior system to predict the efficacy of compounds for the treatment of allergic skin diseases compared to either method alone. Cilomilast and tacrolimus exert anti‐inflammatory effects in this model of allergic contact dermatitis and the mixed leucocyte reaction, but dendritic cell migration through the skin seems to be unaffected. Funding: Self‐funded.