The endometria of women with endometriosis exhibit dysfunctional expression of complement regulatory proteins during the mid secretory phase

•Complement regulatory proteins were determined in endometria of women with endometriosis.•Decay accelerating factor (DAF) was reduced during mid secretory phase.•DAF and β3 integrin exhibit molecular interaction.•Paracrine regulation of DAF and β3 integrin is disrupted in endometriosis.•Reduced DAF may boost complement activation risking embryo survival during implantation. The control of complement activation within embryo-endometrium environment is critical for embryo survival. Cell evasion from complement attack requires interaction of complement regulatory proteins (CRPs) with cell adhesion αvβ3 integrin. We aim to compare the expression of CRPs in endometria of women with and without endometriosis and to examine the molecular interaction of decay accelerating factor (DAF) with αvβ3 integrin. Endometrial expression of Membrane cofactor protein (CD46), Decay accelerating factor (DAF), Membrane attack complex inhibitory factor (CD59) and β3 integrin subunit were determined through menstrual cycle by immunohistochemistry. DAF protein quantity was determined by Western blot and mRNA levels measured in epithelial cells isolated by laser capture microdissection (LCM). Using in vitro assay, we examined DAF and β3 integrin expression through paracrine regulation between endometrial compartments. To determine whether β3 integrin and DAF interacts in vivo, endometrial samples were subjected to immunoprecipitation and colocalization using dual immunofluorescence technique. DAF and β3 integrin expression were significantly low in samples from women with endometriosis during mid secretory phase. This observation was supported by decreased DAF protein quantity; faint DAF and β3 integrin interaction and reduced mRNA levels in cells dissected by LCM. Moreover epithelial DAF and β3 integrin expression through paracrine regulation by progesterone from stromal compartment was disrupted in endometriosis. Endometria from women with endometriosis exhibits aberrant expression of complement proteins. The abnormal DAF expression potentially compromises embryo survival, contributing to understand the implantation failure in women with endometriosis.