Calretinin, a
calcium-binding protein, is primarily expressed in certain subtypes of neurons. It has also been found to be present in mesothelial cells and
mesotheliomas but not in many types of
carcinomas. Using a polyclonal anti-
calretinin antibody, we investigated the expression of
calretinin immunohistochemically in nonneoplastic human ovaries and testes and ovarian
sex cord-stromal tumors (SCSTs). In ovaries,
calretinin was expressed in theca interna cells, hilus cells, and scattered individual stromal cells. Oocytes, granulosa cells, theca externa cells, rete ovarii, and most stromal cells were negative. Expression of
calretinin was also seen in the ovarian surface epithelium and in collapsed and flat epithelial inclusion glands (EIGs), but not in round, columnar, and ciliated EIGs. In some glands, a transition from
calretinin-positive to
calretinin-negative epithelium was observed. In postpubertal testes,
calretinin was expressed in Leydig cells, but not in germ cells or most rete testes and Sertoli cells. In ovarian SCSTs, strong
calretinin staining was seen in all hilus cell
tumors (4/4) and the Leydig cell component of
Sertoli-Leydig cell tumors (10/10). The Sertoli cell component showed focal weak positivity in 5/10. Fibrothecomas were completely negative (0/8). In
granulosa cell tumors, the
tumor cells were either completely negative (8/14) or weakly positive at the periphery of the
tumor (6/14) while scattered stromal cell staining was seen in 9/14 cases. The expression of
calretinin in normal Leydig cells, theca interna cells, the Leydig cell component of
Sertoli-Leydig cell tumors, and hilus cell
tumors suggests its functional relationship with
androgen production. Its pattern of expression in ovarian SCSTs is useful in the differential diagnosis of these
tumors. The presence of a transition from
calretinin-positive, flat, nonciliated epithelium to
calretinin-negative, columnar, ciliated epithelium in the same glands provides strong evidence for mullerian
metaplasia.