P450 Side-Chain Cleavage Enzyme (P450-SCC) Is an Ovarian Autoantigen in a Mouse Model for Autoimmune Oophoritis

Steroid-producing cells contain key cytochrome P450 enzymes, such as side-chain cleavage (P450-SCC) and 17α-hydroxylase (17α-OH). They are required for steroid hormone synthesis and considered antigens associated with Addison's disease and autoimmune primary ovarian insufficiency (POI). We studied an animal model for human autoimmune POI in mice with autoimmune oophoritis induced by neonatal thymectomy performed at day 3 (TX3). We previously identified an oocyte-specific protein as a major antigen inciting autoimmune oophoritis in mice. In this study, we characterized ovarian steroid-producing cell antigens. Using indirect immunofluorescence staining, we tested immune reactions in mouse ovarian and adrenal tissue sections with sera from TX3 female mice. More than half of the TX3 mice (8 of 15) produced antibodies reacting with both ovarian and adrenal steroid-producing cells, including some that reacted to oocytes as well. We produced recombinant proteins for the three key steroidogenic enzymes 17α-OH, P450-SSC, and 3β-hydroxysteroid dehydrogenase (3β-HSD) and tested their immune reactions with individual mouse sera. By immunoblotting, all mouse sera that reacted with the steroid-producing cells (n = 8) were shown to react with the P450-SCC, but not with the 17α-OH or 3β-HSD recombinant proteins. The sham-operated mouse sera and TX3 mouse sera negative for steroid-producing cells did not react with the P450-SCC recombinant protein. Our findings indicate that the P450-SCC is a specific and unique major antigen within the ovarian steroid-producing cells. Given their similarity of predicted antigenicity, we assume that P450-SCC acts in human autoimmune POI as it does in mouse autoimmune oophoritis.