A study in mice has found that ovaries undergo a surprising transformation after reproductive decline, becoming infiltrated with immune cells that could fuel low-grade inflammation throughout the body. The findings, presented by researchers at Northwestern University in Illinois, suggest that far from being inert, post-menopausal ovaries may adopt an 'immune-like signature' — a change that could have implications for women's health in later life.
Dr Francesca Duncan, who led the research, said the team had previously assumed the ovaries were largely dormant after reproduction. 'What we found was super surprising,' she said. The study, which has not yet been peer-reviewed, examined the protein composition of ovaries from post-menopausal women aged 50 to 75. The molecular signatures changed markedly over the decades, indicating the organ was still active. To explore further, the team studied mice at different ages — young (2 months), reproductively old (18 months) and post-reproductive (24 months). While mice do not experience menopause in the same way as humans, their egg reserves deplete with age and cycles become irregular, making them a useful model.
The results showed expected changes such as loss of egg-producing follicles and increased scarring. But unexpectedly, genes linked to inflammation and immune activity became more active, and the number of immune cells, including T cells and macrophages, rose with age. 'The ovaries are losing the reproductive signature and taking on an immune signature, but I don't think that's necessarily a good thing,' Dr Duncan said. She suspects the ovaries may contribute to 'inflammaging' — the chronic, low-grade inflammation seen in ageing tissues — by releasing inflammatory signalling molecules.
Dr Diana Laird at the University of California, San Francisco, who was not involved in the study, said she expected similar immune changes occur in humans given the reproductive similarities between mice and women. 'Both organisms cease cycling when their supply of oocytes dips below a critical threshold, and other changes including fibrosis and increased innervation are shared,' she said. The findings add to growing evidence that immune changes in the ovaries may underlie the increased inflammation that drives conditions like rheumatoid arthritis after menopause.
It remains unclear why ageing mice may have evolved this change, but Dr Duncan suggested that if the same applies to humans, it could once have been advantageous to acquire an immune cell reservoir when fewer people lived to old age. However, in modern life, this may lead to inflammation and even autoimmune conditions. The study raises important questions about whether healthy ovaries should be left in place after menopause — they currently are, because they continue to release hormones that help maintain bone density and libido. Further research is needed to determine whether the post-reproductive immune shift has meaningful health consequences.