Expression of vascular cell adhesion molecule-1 mRNA and protein in rheumatoid synovium demonstrated by in situ hybridization and immunohistochemistry.
BACKGROUND
Vascular cell adhesion molecule-1 (VCAM-1) is expressed in synovial tissue of patients with rheumatoid arthritis. VCAM-1-protein has been demonstrated in nonvascular cells beside a vascular expression of this molecule. There are conflicting results about the nonvascular cell types expressing VCAM-1.


METHODS
For the evaluation of VCAM-1 expression in rheumatoid synovium, this molecule has been demonstrated by alkaline phosphatase anti-alkaline phosphatase (APAAP) technique. Furthermore, VCAM-1 mRNA has been demonstrated by in situ hybridization to evaluate de novo synthesis of this molecule in vivo. To elucidate the nature of the cell types expressing VCAM-1 mRNA, this molecule has been shown by combined in situ hybridization for VCAM-1 and immunohistochemistry in the same tissue section. Double labeling has been performed with anti-collagen type IV monoclonal antibodies to delineate endothelial cells and pericytes and with anti-CD68 antibodies to elucidate the expression of VCAM-1 mRNA in fibroblast-like (type B) or macrophage-like (type A) synoviocytes.


RESULTS
Although it has been reported that VCAM-1 occurs on endothelial cells after cytokine stimulation, we show that vascular expression of VCAM-1 mRNA and protein was minimal and restricted to small vessels beneath the lining cell layer. Further expression of VCAM-1 mRNA could be demonstrated in pericytes outside the collagen type IV containing vascular basement membrane. With respect to the expression of VCAM-1 in the synovial lining layer, we could clearly demonstrate by combined in situ hybridization and immunohistochemistry that CD68 positive cells of the monocyte/macrophage lineage in the lining layer (type A cells) do not express VCAM-1 mRNA and that the expression of VCAM-1 mRNA in the lining layer was restricted to fibroblast-like synoviocytes (type B cells). Scattered stromal cells revealing VCAM-1 mRNA were also CD68 negative.


CONCLUSIONS
The strong expression of VCAM-1 in the fibroblast-like cells of RA synovium and the lack of expression in the vascular endothelium suggest that the major role of VCAM-1 appears to be associated with the proliferating synovial cells prone to attach and subsequently invade articular cartilage.
Kriegsmann
J
J
Department of Medicine, University of Alabama at Birmingham.
Keyszer
G M
GM
Geiler
T
T
Bräuer
R
R
Gay
R E
RE
Gay
S
S
D015703:Antigens, CD / Q000032:analysis; D015214:Antigens, Differentiation, Myelomonocytic / Q000032:analysis; D001172:Arthritis, Rheumatoid / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002358:Cartilage, Articular / Q000737:chemistry / Q000276:immunology / Q000473:pathology; D015815:Cell Adhesion Molecules / Q000032:analysis* / Q000235:genetics* / Q000378:metabolism; D003094:Collagen / Q000032:analysis; D005347:Fibroblasts / Q000737:chemistry / Q000276:immunology / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008264:Macrophages / Q000737:chemistry / Q000276:immunology / Q000473:pathology; D012333:RNA, Messenger / Q000032:analysis* / Q000235:genetics; D013583:Synovial Membrane / Q000737:chemistry* / Q000378:metabolism / Q000473:pathology; D019010:Vascular Cell Adhesion Molecule-1; D000097382:CD68 Molecule
D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D015815:Cell Adhesion Molecules; D003094:Collagen; D012333:RNA, Messenger; D019010:Vascular Cell Adhesion Molecule-1; C067980:CD68 antigen, human; D000097382:CD68 Molecule