Levels of synovial fluid interleukin-1 receptor antagonist in rheumatoid arthritis and other arthropathies. Potential contribution from synovial fluid neutrophils.
OBJECTIVE
To measure synovial fluid (SF) levels of interleukin-1 receptor antagonist (IL-1ra) and to determine the capacity of SF neutrophils (PMN) to synthesize and release IL-1ra.


METHODS
A sensitive and specific enzyme-linked immunosorbent assay was used to measure SF IL-1ra protein concentrations and IL-1ra production by isolated SF PMN:


RESULTS
SF IL-1ra levels were elevated in 13 of 16 samples from patients with rheumatoid arthritis (RA) (mean 17.1 ng/ml), in 6 of 18 samples from patients with infectious or inflammatory, non-RA arthropathies (mean 10.6 ng/ml), and in none of 11 noninflammatory SF samples. SF IL-1ra levels correlated with SF PMN concentrations (r = 0.680, P < 0.00001). Isolated SF PMN contained preexisting IL-1ra protein in the absence of messenger RNA (mRNA). In addition, both lipopolysaccharide and granulocyte-macrophage colony-stimulating factor induced modest increases in IL-1ra mRNA by cultured SF-PMN.


CONCLUSIONS
IL-1ra levels are increased in > 80% of RA SF samples. SF PMN produce IL-1ra, possibly contributing to the levels of IL-1ra present within the SF.
Division of Rheumatology, University of Colorado Health Sciences Center, Denver 80262.
M
M
Malyak
R E
RE
Swaney
W P
WP
Arend
D001172:Arthritis, Rheumatoid / Q000378:metabolism*; D006801:Humans; D007375:Interleukin-1 / Q000235:genetics / Q000378:metabolism; D007592:Joint Diseases / Q000378:metabolism*; D009504:Neutrophils / Q000737:chemistry; D011506:Proteins / Q000032:analysis / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D017472:Receptors, Interleukin-1 / Q000037:antagonists & inhibitors* / Q000235:genetics; D013582:Synovial Fluid / Q000737:chemistry / Q000166:cytology
D007375:Interleukin-1; D011506:Proteins; D012333:RNA, Messenger; D017472:Receptors, Interleukin-1