Immunohistochemical staining of a fetal ovary specimen, gestation week 22. Hematoxylin-eosin (HE) staining (panels A, G, M) and immunohistochemical staining with mAbs MA454 (panels B, H, N), M3H67 (panels C, I, O), 57B (panels D, J, P), CT7-33 (panels E, K, Q), and ES121 (panels F, L, R) are shown. Ovarian tissue displaying cords of germ cells (oogonia) reaching from the periphery to the central areas are visible (panel G, thick arrows) and large oocytes (panels G, M; thin arrows) in the central parts not yet surrounded completely by follicle epithelia are seen; autolytic changes, i.e. spaces between cells (panels A, G, M), are also visible. Intense immunostaining of focal germ cells is observed with mAbs MA454 (panels B, H, N) and ES121 (panels F, L, R). Cords of oogonia intensely immunopositive for mAbs M3H67 (panels C, I, O), 57B (panels D, J, P), and CT7-33 (panels E, K, Q) are seen. Centrally located negative or weakly positive oocytes are visible (exemplified for mAb M3H67 in panels C, I, O; arrows). Objective magnification: 10x (panels A - F), 20x (panels G - L), 40x (panels M - R).