We examined the proteins in serum and peritoneal fluid of women with endometriosis (and of healthy controls) for evidence of an autoimmune response that might account for their impaired fertility. No antibodies against endometrial glycoproteins or against progestin dependent endometrial protein (PEP) were found in any serum or peritoneal fluid sample. Levels of PEP were not different in serum from women with moderate to severe endometriosis (n = 6), with mild endometriosis (n = 21), or from disease-free cycling controls (n = 19). PEP levels in peritoneal fluid from mild endometriosis and from controls did not differ but were elevated ten times in fluid obtained in the secretory phase from women with moderate to severe disease. This suggests that PEP levels in peritoneal fluid reflect the extent of ectopic endometrial growth. The salient finding was a heretofore undescribed protein (mol wt 70,000) in secretory phase peritoneal fluid samples (18/20) and its absence during the proliferative phase (0/35).
Joshi, S. G., Zamah, N. M., Raikar, R. S., Buttram, V. C., Henriques, E. S., & Gordon, M. (1986). Serum and peritoneal fluid proteins in women with and without endometriosis. Fertility and Sterility, 46(6), 1077–1082. https://doi.org/10.1016/S0015-0282(16)49883-3