Subgroups of severe asthma patients with marked increases in sputum eosinophils and neutrophils are insensitive to corticosteroids. Exogenous administration of IL-10 negatively regulates both migration of eosinophilic and neutrophilic into tissues. This study evaluated whether intratracheal IL-10 administration suppresses asthmatic responses in a severe model of mice. Ovalbumin (OVA)-sensitized mice were intratracheally challenged with OVA. Dexamethasone (DEX, 1 mg/kg, intraperitoneal) or IL-10 (25 ng/mouse, intratracheal) was administered during the challenges. The number of leukocytes, expressions of adhesion molecules and IL-10 receptor, and development of airway hyperresponsiveness (AHR) were evaluated after the challenges. Although DEX hardly suppressed the development of AHR, the infiltration of eosinophils and neutrophils, and the development of AHR were significantly inhibited by intratracheal IL-10 administration. Moreover, IL-10 administration markedly decreased the numbers of ICAM-1⁺ and VCAM-1⁺ pulmonary vascular endothelial cells, which express IL-10 receptor 1. IL-10 could suppress eosinophil and neutrophil infiltration by inhibiting the proliferation of ICAM-1⁺ and VCAM-1⁺ pulmonary vascular endothelial cells, resulting in inhibition of AHR in severe asthmatic mice.