P-470: Measurement of activated complement subunit C3: A prospective controlled evaluation of a new test for infertility and implantation failure

Abstract

Uterine receptivity defects and implantation failure have become the black box of infertility diagnosis. Up to 15% of couples with infertility or recurrent pregnancy loss remain unexplained. The endometrium is an active site of innate immunity, including expression of complement and complement regulatory proteins (CRPs). Our objective was to develop a non-invasive blood test for implantation failure based on the observation that many CRPs in human endometrium are aberrantly expressed in some women with infertility. Prospective, controlled trial. The study was approved by the IRB. Plasma samples were obtained from thirty-four women (age range 19 to 42) with infertility (cases) who were actively trying to conceive and 12 controls. Activated C3a des arg was measured by ELISA assay (Quidel Corp, San Diego, CA). Endometrium was evaluated for the complement regulatory proteins decay accelerating factor (DAF), ανβ3 integrin, CD59 and CD46 in a subset of cases. Comparison of overall tissues levels of C3 subunit was also compared in the endometrium of endometriosis and normal individuals. Regulation of C3 was studied using cell line models using ERE luciferase and western blot analysis. Overall, plasma C3a levels were markedly elevated in a subset of cases and none of the controls. Each of those with the highest levels were found to have endometriosis, mostly stage II disease. Based on this, women with laparoscopically proven endometriosis (n = 28) were compared to the controls (Figure; left panel). Based on ROC curves (Figure, right panel), a cut-off value of 203 ng/ml was chosen, yielding a specificity of 92% and a sensitivity of 35.7% and a positive predictive value of 91.6% for the diagnosis of endometriosis. While C3a des arg levels were elevated in only 35% of all patients studied with documented endometriosis, those with elevated C3a des arg levels were highly associated with a lack of CRP expression in the eutopic endometrium (DAF and ανβ3) and an elevation in mid-secretory phase estrogen receptors (ERα; p < 0.05). Results from biochemical studies demonstrated for the first time that complement C3 is regulated by estrogen and epidermal growth factor in a synergistic fashion. Endometriosis has long been shown to exhibit elevated complement C3 levels. For the first time, we document that high plasma levels of activated plasma C3a can be detected, specifically in women with mild (ASRM stage I to II) disease. Based on biochemical studies, we now believe that elevated endometrial estrogen receptors and depressed endometrial CRP expression provides both the stimulus and the means for C3 activation. Like anti-phospholipid syndrome (APS), endometriosis may be an occult cause of early fetal loss or failure of implantation in certain women based on inappropriate activation of the innate immune system. Identification of this subset of patients may establish earlier diagnosis and help target therapy.