The involvement of CD44 and its novel ligand galectin-8 in apoptotic regulation of autoimmune inflammation.
The synovial fluid (SF) cells of rheumatoid arthritis (RA) patients express a specific CD44 variant designated CD44vRA. Using a cellular model of this autoimmune disease, we show in this study that the mammalian lectin, galectin-8 (gal-8), is a novel high-affinity ligand of CD44vRA. By affinity chromatography, flow cytometry, and surface plasmon resonance, we demonstrate that gal-8 interacts with a high affinity (K(d), 6 x 10(-9) M) with CD44vRA. We further demonstrate that SF cells from RA patients express and secrete gal-8, to a concentration of 25-65 nM, well within the concentration of gal-8 required to induce apoptosis of SF cells. We further show that not all gal-8 remains freely soluble in the SF and at least part forms triple complexes with CD44 and fibrinogen that can be detected, after fibrinogen immunoprecipitation, with Abs against fibrinogen, gal-8 and CD44. These triple complexes may therefore increase the inflammatory reaction by sequestering the soluble gal-8, thereby reducing its ability to induce apoptosis in the inflammatory cells. Our findings not only shed light on the receptor-ligand relationships between CD44 and gal-8, but also underline the biological significance of these interactions, which may affect the extent of the autoimmune inflammatory response in the SF of RA patients.
Eshkar Sebban
Lora
L
Lautenberg Center for General and Tumor Immunology, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
Ronen
Denise
D
Levartovsky
David
D
Elkayam
Ori
O
Caspi
Dan
D
Aamar
Suhail
S
Amital
Howard
H
Rubinow
Alan
A
Golan
Ira
I
Naor
David
D
Zick
Yehiel
Y
Golan
Itshak
I
D001172:Arthritis, Rheumatoid / Q000378:metabolism*; D001327:Autoimmune Diseases / Q000378:metabolism; D015153:Blotting, Western; D002846:Chromatography, Affinity; D003001:Cloning, Molecular; D005340:Fibrinogen / Q000378:metabolism; D005434:Flow Cytometry; D037161:Galectins / Q000378:metabolism*; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism*; D047468:Immunoprecipitation; D007249:Inflammation / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000276:immunology*; D020349:Surface Plasmon Resonance; D013582:Synovial Fluid / Q000737:chemistry; D014162:Transfection
D037161:Galectins; D018960:Hyaluronan Receptors; C091991:LGALS8 protein, human; D005340:Fibrinogen