Changes in the localization of MHC class II positive cells in hen ovarian follicles during the processes of follicular growth, postovulatory regression and atresia

The aim of this study was to determine the changes in the population of maj or histocompatibility complex class II positive (MHC-II+) cells in ovarian follicles during the processes of follicular growth, postovulatory regressi on and follicular atresia in hens. Cryostat sections of ovarian stroma cont aining cortical follicles, small white follicles, the largest (F-1) and thi rd largest (F-3) preovulatory follicles, postovulatory and atretic follicle s of laying hens were prepared. The sections were immunostained for MHC-II molecules using mouse anti-chicken MHC-II monoclonal antibody and positive cells were counted using a computer-assisted image analyser under a light m icroscope. MHC-II+ cells were localized in the theca layer of normally grow ing follicles including cortical follicles, small white follicles and F-3 a nd F-1 preovulatory follicles, whereas they were found in both the theca an d granulosa layers in postovulatory and atretic follicles, The frequency of MHC-II+ cells in the theca layer was significantly increased during follic ular growth from cortical follicles to F-3 preovulatory follicles. Although the population of MHC-II+ cells did not differ between F-3 and F-1 preovul atory follicles, it increased significantly in postovulatory follicles (P < 0.01). The population of MHC-II+ cells was significantly greater in the th eca layer of atretic follicles than in non-atretic follicles (P < 0.01). Th ese results indicate that the antigen-presenting function via MHC-II increa ses in association with follicular growth. A marked increase in MHC-II+ cel ls indicates that these cells may be involved in regression of postovulator y and atretic follicular tissues.