The interleukin-1 receptor in normal and osteoarthritic human articular chondrocytes. Identification as the type I receptor and analysis of binding kinetics and biologic function.
OBJECTIVE
To identify and investigate the kinetic binding properties of interleukin-1 receptors (IL-1R), and examine the abilities of the 2 IL-1 isoforms to stimulate metalloprotease synthesis, in normal and osteoarthritic (OA) chondrocytes.


METHODS
Receptor affinity and density were determined using radioligand binding experiments and flow cytometry. Immunocytochemical analysis and affinity cross-linking studies were performed for characterization of IL-1R.


RESULTS
While no difference in receptor affinity between normal and OA chondrocytes was noted in binding studies (Kd approximately 30 pM), a 2-fold increase in receptor density was found in OA chondrocytes as compared with normal chondrocytes (mean 4,069 sites/cell versus 2,315 sites/cell). Flow cytometry experiments also showed a significant increase in receptor density in OA cells, as well as an enhancement in the percentage of positive cells in diseased cartilage compared with normal. Binding data for both IL-1 isoforms revealed a single class of binding sites and receptor specificity. Factors such as IL-2, interferon-gamma, tumor necrosis factor alpha, and bovine insulin did not compete with IL-1 beta. By covalent ligand cross-linking and electrophoretic analysis, only type I IL-1R, a protein of 80 kd, was detected on chondrocytes. By immunocytochemical analysis, IL-1R was identified at the cell membrane level, in both normal and OA chondrocytes. The presence of nuclear staining was also observed, but only in OA chondrocytes. Recombinant human IL-1 (alpha and beta) induced the secretion of stromelysin and collagenase in a dose-dependent manner. The IL-1 concentration required for half-maximal metalloprotease stimulation was 3-4 times lower in OA chondrocytes than in normal cells.


CONCLUSIONS
These results indicate that OA chondrocytes have a higher sensitivity to the stimulation of metalloprotease synthesis by IL-1 than do normal cells. This could be related to the increased levels of IL-1R expressed in the OA cells. The implications of these findings with regard to the possible roles of IL-1 and IL-1R in the pathogenesis of OA are discussed.
Martel-Pelletier
J
J
Rheumatic Disease Unit Research Laboratory, Notre-Dame Hospital Research Center, Montreal, Quebec, Canada.
McCollum
R
R
DiBattista
J
J
Faure
M P
MP
Chin
J A
JA
Fournier
S
S
Sarfati
M
M
Pelletier
J P
JP
D000368:Aged; D002358:Cartilage, Articular / Q000648:ultrastructure*; D005434:Flow Cytometry; D006801:Humans; D007150:Immunohistochemistry; D007700:Kinetics; D008875:Middle Aged; D008970:Molecular Weight; D010003:Osteoarthritis / Q000473:pathology*; D011971:Receptors, Immunologic / Q000032:analysis* / Q000737:chemistry; D017472:Receptors, Interleukin-1
D011971:Receptors, Immunologic; D017472:Receptors, Interleukin-1