Pain is the most common symptom of endometriosis and a new study may help explain why. Using a combination of mice and women with endometriosis, researchers showed that macrophages, a type of immune cell, play a role in how endometriosis generates pain. The study was conducted by scientists from the University of Warwick and University of Edinburgh in the United Kingdom.1,2
What are macrophages?
A macrophage is a type of white blood cell that perform many functions to keep tissue healthy, including detecting and destroying bacteria and other harmful organisms. Macrophages are found throughout the body.3
Studies show that high numbers of macrophages live inside endometrial lesions and the peritoneal fluid of women with endometriosis. The peritoneum is the tissue that lines the abdomen and peritoneal fluid is a liquid that lubricates the surface of this tissue.4 Scientists believe that the macrophages see endometrial lesions as a wound to be repaired, setting off processes that encourage endometriosis growth rather than stopping it.2
How immune cells make endo pain worse
Doctors know that nerves grow into endometriosis lesions and think this is what causes pain.
To test that theory, the scientists created a group of mice with endometriosis. They watched the behavior of the mice for signs of pain. They noticed that the mice were in less pain when lower levels of macrophages were present in their endometrial tissue.
Next, the scientists took macrophages from healthy women and exposed the cells to peritoneal fluid taken from women with endometriosis. Upon exposure, the healthy macrophages produced high levels of insulin-like growth factor-1 (IGF-1), a hormone that encourages tissue and bone growth.5
Tissue samples from women with endometriosis and the study mice were tested and the researchers found lower levels of IGF-1 when levels of macrophages were also low. Women with higher levels of macrophages and IGF-1 also reported more pain.
The study team then looked at the connection between IGF-1 levels and nerve cells in endometrial lesions. They found that macrophage-fueled IGF-1 increased growth of nerve cells into endometrial lesions and increased pain by making the nerves more sensitive. Finally, the scientists went back to their study mice and found that when they lowered levels of IGF-1 the mice experienced less pain.
While this new study does not point to a cure for endometriosis, it does help scientists better understand why pain occurs with the condition.
Treating the pain of endometriosis
Chronic pain and endometriosis seem to go together. To treat the pain, many women try a variety of non-medical treatments for relief, including hot compresses or heating pads, exercise, yoga, diet changes, acupuncture, chiropractic care, and meditation.
If these home remedies do not help, nonsteroidal anti-inflammatory drugs (NSAIDs) are another popular option for pain relief. Over-the-counter NSAIDs include aspirin, ibuprofen, and naproxen. Opioids such as hydrocodone, oxycodone, and codeine are not recommended for endometriosis pain.
Forster R, et al. Macrophage-derived insulin-like growth factor-1 is a key neurotrophic and nerve-sensitizing factor in pain associated with endometriosis. FASEB J. 2019:33:10;11210-11222. doi.org/10.1096/fj.201900797R.
Endometriosis.org. Scientists are now closer to understanding pain mechanisms in endometriosis. Available at: http://endometriosis.org/news/research/scientists-are-now-closer-to-understanding-pain-mechanisms-in-endometriosis. Accessed 10/7/19.
British Society for Immunology. Macrophages. Available at: https://www.immunology.org/public-information/bitesized-immunology/c%C3%A9lulas/macrophages. Accessed 10/7/19.
MedlinePlus. Peritoneal Disorders. Available at: https://medlineplus.gov/peritonealdisorders.html. Accessed 10/7/19.
University of Rochester Medical Center. Insulin-Like Growth Factor. Available at: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=insulin_like_growth_factor. Accessed 10/7/19.