Objective    To investigate whether there exists osteoclasts and differentiation factors in the synovial tissue of patients with ankylosing spondylitis (AS) for the mechanism of destruction of bone and cartilage in AS.     Methods    Enzymohistochemical staining (TRAP staining) was used to detect the expression of osteoclast phenotype

and hybridization in situ to detect the mRNA expressions of TNF-α

VEGF and MMP-3 in synovial membrane samples of 21 AS patients and 21 fracture subjects. Synovial cells isolated from normal group were cultured in presence of TNF-α and VEGF

while those from AS group were cultivated with anti-TNF-α and anti-VEGF antibodies. Gomori method was used to detect alkaline phosphatase (ALP) and radioimmunoassay to detect bone gla protein (BGP) in these cultured cells for the role of differential factors in osteoblast phenotype expression.     Results    The synovial membrane in AS were positive to mRNA expressions of TNF-α

VEGF

and MMP-3

and to TRAP staining

but that of control group were negative. Significant difference was seen in the positive cell numbers between these 2 groups (P0.01). In cultivated synovioblast from AS group

ALP staining was positive

and BGP content was elevated compared with control group. Anti-VEGF and anti-TNF-α inhibited synovioblast to secrete BGP.     Conclusion    An obvious increase of TRAP positive cells in synovium may provide a main source of osteoclastogenesis in AS patients. With induction of TNF-α and VEGF

synovioblast may differentiate into osteoblasts

and express ALP and BGP. In this condition

synovial mononuclear macrophage may differentiate into osteoclasts and express MMP-3

which play important role in bone resorption.