For juvenile (3–21 days) and adult (2 months to 1 year) mice, skin from abdomen and back was carefully dissected free of other tissue, cut into 2–3 mm3 pieces,washed 3 times in Hanks balanced salt solution (HBSS), and then digested with 0.1% trypsin for 40 min at 37 ºC, followed by 0.1% DNAase for 1 min at room temperature.