AhR is expressed in different immune cells and was recently shown to be expressed in various murine and human MCs and the RBL-2HR3 MC line.221-224 The studies showed that incubation with 6-formylindolo[3,2-b]carbazole (FICZ), a strong ligand derived from the tryptophan metabolism, induced degranulation, LTC4 release and cytokine production including IL-6 and IL-13.