Why Do Some Women Develop Endometriosis While Other Don’t?

A new study may shed light on the reason why only some women develop endometriosis even though many more have retrograde menstruation.

Key Points

Highlights: 

• Both the cytotoxicity and the chemotaxis of natural killer cells are decreased in the peritoneal cavity of women with endometriosis.
• Chemotaxis is particularly decreased during menstruation.

Importance:

• Body natural killer cell alterations may explain why some women develop endometriosis while others do not.
• Natural killer cells may also play a key role in neutralizing antigens that are carried to the peritoneal cavity by retrograde menstrual blood.

What's done here:

• Researchers compared the chemotaxis of body immunocompetent cells (natural killer cells, macrophages, and T lymphocytes) from the peritoneal fluid.
• Samples from 27 women with and 13 without endometriosis were compared for chemotaxis and cytotoxicity.

Key results:

• The chemotaxis of natural killer cells from the peritoneal fluid of women with endometriosis is significantly lower than that of women without the disease. 
• There were no significant differences in the chemotaxis of macrophages and lymphocytes obtained from the peritoneal fluid of women with or without endometriosis.
• The chemotaxis of natural killer cells decreased during menstruation in both groups of women.
• Chemotaxis significantly increased following menstruation in women without endometriosis, while it stayed low in women with endometriosis. 
• There was no correlation between the stage of endometriosis and the chemotaxis of natural killer cells.
• There was no significant difference in the chemotaxis of natural killer cells obtained from peripheral blood in women with or without endometriosis.

Limitations:

• The cause of the decreased chemotaxis in natural killer cells in the peritoneal cavity of women with endometriosis has not been addressed in this study.

Lay Summary

Chemotaxis by natural killer cells as well as cytotoxicity is significantly decreased in the peritoneal cavity of women with endometriosis, according to a new study published in the American Journal of Reproductive Immunology. This means that antigens that enter the peritoneal cavity through retrograde menstruation might be left unprocessed and the repetition of this event each month could lead to the development of endometriosis. This could explain why only some women develop endometriosis even though retrograde menstruation is more common.

It was already known that the function of natural killer cells and macrophages was decreased in women with endometriosis and that the cytotoxicity and chemotaxis, i.e. ability to migrate of natural killer cells were important to keep the disease at bay. 

Even though the cytotoxicity of natural killer cells in endometriosis has been previously examined, their chemotaxis has not.

Here, a team of researchers led by Dr. Nagamasa Maeda from the Department of Obstetrics and Gynecology at Kochi Medical School in Japan compared chemotaxis in natural killer cells, macrophages, and T cells obtained from the peritoneal fluid of 27 women with endometriosis and 13 women without the disease.

They found that chemotaxis in natural killer cells obtained from women with endometriosis was significantly lower than chemotaxis in natural killer cells obtained from women without the disease. However, they were no significant differences in the chemotaxis of macrophages and lymphocytes obtained from the 2 groups of women.

Moreover, the chemotaxis of natural killer cells decreased further during menstruation both in women with and without the disease. 

In women without endometriosis, chemotaxis significantly increased following menstruation while it remained low in women with the disease. 

There was no correlation between the stage of endometriosis and the chemotaxis of natural killer cells with chemotaxis being decreased even in the early stages of the disease. 

There was no significant difference in the chemotaxis of natural killer cells obtained from the peripheral blood of women with endometriosis and those without.

“The combination of a reduced immune response in the peritoneal cavity and frequent retrograde menstruation may lead to the endometrial cells escape from immunological surveillance and their engraftment in the peritoneal cavity,” the researchers concluded. 

Research Source: https://pubmed.ncbi.nlm.nih.gov/35452561/