The Immune System's Role in Endometriosis (It's Bigger Than You Think)

Endometriosis gets talked about almost entirely as a hormonal condition. Hormones are absolutely part of the picture, but they're not the whole story. Your immune system plays a huge role too, and it's rarely part of the conversation.

The surveillance system that's supposed to protect you

In someone without endometriosis, your body has cells whose job is to patrol the peritoneal fluid and clear out anything that shouldn't be there. They're called macrophages, and in a healthy system, they identify and remove stray cells before they can cause a problem.

In endometriosis, that signalling goes wrong. What's strange is that women with endometriosis actually tend to have more of these surveillance cells, not fewer. The problem isn't a shortage. It's that they're dysregulated and unable to do their job properly. Instead of clearing the invading tissue, they end up helping it grow and settle into the body.

Natural killer cells, defective too

You may have heard of NK cells, natural killer cells, another part of the immune system whose role is to identify and destroy foreign or abnormal cells. In endometriosis, these aren't functioning as they should either. The entire clearance cascade, from surveillance to elimination, is compromised.

This is a big part of why endometriosis tissue is able to implant and grow outside the uterus in the first place. It's not just that the tissue is present, it's that the systems meant to remove it aren't working.

The endocannabinoid system

Less well known, but so important, is the endocannabinoid system. It's deeply involved in fertility, implantation, maintaining a pregnancy, and controlling contraction of the uterus when needed. It's especially active during critical windows like ovulation.

In endometriosis, this system is significantly dysregulated. Its receptors are found directly in the lesions and in the surrounding nerve fibres. And notably, it's one of the clearest systems shown to correlate with pain severity in endometriosis, more consistently than the number or size of lesions themselves, which often doesn't track with how much pain someone is actually in.

Why this matters

None of this is meant to be overwhelming, it's meant to explain why endometriosis is so much more complex than "an oestrogen problem," and why treatment that only targets hormones often falls short. Immune dysfunction, impaired clearance mechanisms, and a dysregulated endocannabinoid system are all part of the same picture.

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