Mast cell levels may explain the sex difference in osteoarthritis pain

Researchers at the Hospital for Special Surgery (HSS) found that during total knee replacement, women had significantly higher levels of immune cells called mast cells in synovial tissue around the knee than in men
.
Their findings, presented today at the annual meeting of the American College of Rheumatology, ACR Convergence 2022, may help future research to explore why women with knee osteoarthritis have more pain than men
.

Researchers at HSS and other institutions noted that women with knee osteoarthritis reported more pain than men, but the reason for this difference is unclear
.
"Others speculate that women are more inclined than men to delay surgery, but when we looked at our database, this wasn't true," said
Dana Orange, an HSS rheumatologist and MD, M.
M.
S.
, assistant professor at Rockefeller University and senior author of the study.
"We looked at synovial tissue removed during total knee replacement to look for biological reasons to explain the gender differences
in reported pain.
"

Synovial tissue arranges the knee joint and produces fluid to help the joint move
.
As osteoarthritis progresses, it may become inflamed
.
Pathologists at HSS have been collecting data on different types of cells found in synovial tissue, including mast cells, which are also found in many other tissues in the body and often produce inflammatory chemicals
called histamine during allergic reactions and asthma.
Basic studies by other scientists have shown a link
between mast cells and osteoarthritis progression and pain.

Dr.
Orange and his colleagues, including HSS rheumatologist Bella Mehta, MBBS, MS, first author of the study, studied joint tissue
in 96 women and 61 men who underwent total knee replacement from HSS.
They counted the number of cells for more than a dozen cell types commonly found in synovial tissue and examined synovial fluid and blood
using a high-power microscope.
They also evaluated patient-reported pain outcomes
collected through two active surveys.
"At HSS, we are in a unique position to conduct this study because we collected synovial tissue from end-stage osteoarthritis patients and musculoskeletal pathologists who underwent joint replacement who systematically graded
tissue samples based on 13 features," said Dr.
Mehta.

The researchers found that women had significantly more mast cells in synovial tissue, averaging 63 per sample area, compared to an average of 46 mast cells in male tissue
.
They also found higher levels of mast cells in women with higher levels of mast cells called trypsin compared to men, providing further evidence
of increased mast cell activity.
There were no other differences
in synovial tissue between sexes.
Finally, unsurprisingly, in both surveys, women reported more pain than men
.

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