Mast cells in women may explain osteoarthritis pain differences between sexes

By The Science Advisory Board staff writers

November 14, 2022 -- Researchers from the Hospital for Special Surgery (HSS) have found that an increased level of immune cells -- called mast cells -- in synovial tissue surrounding the knee joint in women may help explain why women with knee osteoarthritis report worse pain than men. Their findings were presented November 14 at the American College of Rheumatology Convergence 2022 meeting.

In their study, the researchers investigated synovial tissue which lines the knee joint and produces fluid that helps the joint move and can become inflamed as osteoarthritis progresses. The team removed synovial tissue at the time of total knee arthroplasty, or replacement, to find a biological reason behind the difference in reported pain between sexes.

Senior author Dr. Dana Orange, assistant professor at the Rockefeller University, and colleagues -- including lead author and HSS rheumatologist Dr. Bella Mehta -- studied joint tissue obtained from 96 women and 61 men who underwent total knee replacement at HSS.

The researchers counted the number of cells for more than a dozen cell types typically found in synovial tissue and examined synovial fluid and blood using a high-powered microscope. They also evaluated patient-reported pain outcomes collected with two validated surveys.

The team discovered that synovial tissue from women had significantly more mast cells, 63 per sample area, compared to 46 in tissue from men, on average. They also found higher levels of a byproduct of mast cells called tryptase in synovial tissue from women than men, providing further evidence of increased mast cell activity. No other differences in synovial tissue between the sexes were observed. Finally, women reported worse pain than men on both surveys.

"We hope our findings encourage other researchers to start thinking about biological factors that may contribute to sex differences in patient-reported pain in knee osteoarthritis," Dr. Orange said in a statement.

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