Our aim was to determine the presence and numbers of immunocompetent cells in the oviduct of laying and moulting hens. Immunocompetent cells were localised by immunocytochemistry throughout the entire length of the oviduct. 2. In laying birds, MHC class II+ cells were observed in the subepithelial and middle part of the stroma of all oviducal segments and the mucosal epithelium of the infundibulum and vagina. CD3+ cells were also localised in subepithelial and middle part of stroma as well as in mucosal epithelium of each oviducal segment. Bu-lb+ and IgG+ cells were also observed in the epithelium and subepithelial and middle part of the stroma of all oviducal segments, though stroma of the magnum, isthmus and uterus contained few Bu-lb+ cells. IgA+ cells were observed only in the mucosal epithelium of the magnum in small numbers. 3. In moulting hens, there were few numbers of immunocompetent cells in the mucosal epithelium of each oviducal segment, although CD3+ cells were observed in the infundibulum and vagina. In the subepithelial stroma, the populations of MHC class II+ cells in the infundibulum, magnum and uterus, CD3+ cells in the infundibulum and vagina, as well as IgG+ cells in each oviducal segment except for isthmus were smaller than in laying hens. In contrast, the number of immunocompetent cells in the middle part of stroma of moulting hens were equal to or greater than in laying hens. 4. These results suggest that the oviducal immune function is active in the surface tissues of the mucosa in laying hens, whereas it is reduced in moulting hens.
