A histamine H4 receptor agonist (Ki = 50 nM); >100-fold selective for H4 over other histamine receptors; inhibits forskolin-induced CRE-β-galactosidase activity in SK-N-MC cells transfected with the human H4 receptor (EC50 = 39.8 nM); induces a change in eosinophil shape (EC50 = 0.36 μM) and stimulates migration of murine bone marrow mast cells (EC50 = 12 μM); reduces airway resistance and inflammation and increases the number of CD4+CD25+FoxP3+ regulatory T cells in a mouse model of allergic asthma when administered intratracheally at a dose of 10 μg/animal; reduces epidermal hyperplasis, hyperkeratosis, and lymphocyte infiltration and increases the number of CD4+CD25+FoxP3+ regulatory T cells in a mouse model of imiquimod-induced psoriasis