May play a protective role in mucosal tissues by preventing exaggerated allergic responses. Expressed in epithelial cells of airways, peripheral bronchioles and alveoli, as well as in the basal cell layer of the epidermis (at protein level). The viability of homozygous knockout embryos is dramatically decreased after 10.0 dpc. Surviving animals have a normal life expectancy, but males are infertile. Ovalbumin sensitization and challenge of heterozygous mice results in a significant increase in pulmonary inflammation, mucous cell metaplasia, airway hyperresponsiveness and ovalbumin-specific IgE compared with wild-type animals. This exacerbation is associated with an increase in CD4(+) IL13(+) T helper cells, as well as an increase IL4, IL5 and IL13 cytokine production in lungs. Sensitized and/or challenged mutant animals show an increased lung epithelial permeability and activation of pro-inflammatory dendritic cells. At 6-7 months of age, about 30% of heterozygous mice develop skin lesions, with significant thickening of the epidermis, including the cornified layer, predominately on the ears and back. Lesions are accompanied by vigorous scratching. In the lesions, IL4, IL5 and IL13 cytokine production is increased and serum IgE levels are up-regulated at the time of appearance of skin lesions.