Relaxin-like factor (RLF): A new specific marker for leydig cells in the ovary

Relaxin-like factor (RLF), also known as the Leydig cell insulin-like facto r (Ley-I-L), is a novel member of the insulin-IGF-relaxin family of hormone s and growth factors that has recently been shown to be strongly expressed in testicular Leydig cells. Expression of the RLF peptide in the human ovar y and in ovarian tumors has not been studied. In the present study, the exp ression of the RLF peptide in the human ovary was investigated by immunohis tochemistry using a specific antibody raised against human RLF. By this met hod, RLF was found to be expressed in hilus (Leydig) cells and theca intern a cells but absent in granulosa cells, ovarian stromal cells, and surface e pithelium. RLF expression was also observed in the corpus luteum, although at a lower level than in theca cells. Thirty-seven sex cord-stromal tumors and five cases of hilar Leydig cell hyperplasia were also investigated for RLF expression. RLF was found to be strongly expressed in hilar Leydig cell hyperplasia and sex cord-stromal tumors with a component of Leydig or lute inized cells. Of the analyzed theca cell tumors, two displayed a diffuse st aining pattern. As expected, RLF was not expressed in granulosa cell tumors . In conclusion, RLF appears to be a useful marker for Leydig cells in the human ovary and may be a diagnostic supplement in hyperplasias and tumors d erived therefrom.