Production and Secretion of Complement Component 3 by Endometriotic Tissue*

Many investigators have described a variety of immune phenomena associated with endometriosis. Among these are elevated titers of activated macrophages, monokines, and lymphokines in the peritoneal fluid of patients with endometriosis. In 1980, Weed and Arquembourg first described the deposition of complement component C3 in epithelial cells of endometrial glands in patients with endometriosis. In this study our objective was to examine the synthesis and secretion of proteins by endometriotic tissue. Tissues were incubated in Minimal Essential Medium without methionine containing 50 microCi/mL 35Smethionine for 12-16 h at 37 C in 5% CO2-95% air. Twenty thousand trichloroacetic acid-precipitable counts were placed on a 7.5% sodium dodecyl sulfate-polyacrylamide gel, and the radiolabeled proteins were detected by fluorography. We examined the radiolabeled secretory proteins obtained from 17 endometriotic implants and/or endometrioma cyst walls as well as 8 control tissues. A 180 kDa protein was produced in much greater quantities by endometriotic tissue than by control tissues. In the presence of reducing agent this protein dissociated into 113- and 69-kDa subunits. To identify and quantitate this protein we performed immunoprecipitations on the incubated medium using antihuman C3 immunoglobulin G. Up to 16% of the precipitable counts were recovered with this antibody from endometriotic tissue, while a maximum of only 4.6% was recovered from control tissue. In addition, we isolated and incubated the epithelial glandular cells, stromal cells, and remaining cells from two endometriomas. The great majority of the newly synthesized and secreted C3 was found in the glandular epithelial cell incubation. Up to 60% of the total precipitable counts were recovered from the glandular cells using this antibody. Only one protein was immunoprecipitated. The immunoprecipitated protein had a mol wt of 180 kDa under nonreducing conditions and dissociated into two subunits of 113 and 69 kDa in the presence of dithiothreitol. We conclude that the glandular epithelial cells found in endometriotic implants produce and secrete complement component, C3 which could be responsible for many of the immunological phenomena now well described in endometriosis.