Pentraxin 3 (PTX3) is a locally produced multifunctional protein involved in inflammation, matrix deposition, and immunity. As patients with seropositive rheumatoid arthritis (RA) have a more severe disease course and higher risk of joint destruction than seronegative patients, the aim of the present study was to examine differences in PTX3 in synovial fluid (SF) (and serum) in seropositive compared to seronegative RA, and other local markers of inflammation and destruction.
Ninety-seven RA patients with knee effusion were included. Serum and SF levels of PTX3, as well as serum levels of anti-citrullinated protein antibody and rheumatoid factor of immunoglobulin A and M subclasses, and markers of inflammation and potential destruction in SF: white blood cell counts, tumour necrosis factor, interleukin-6, vascular endothelial growth factor, metalloproteinase 3, and cartilage oligomeric matrix protein, were analysed. In addition, a radiographic knee examination was performed.
Seropositive patients had significantly higher PTX3 levels in SF than seronegative patients, whereas there was no difference for serum levels. SF-PTX3 levels correlated with disease activity and with local inflammatory markers, especially polymorphonuclear cells, and with autoantibody levels. There was no correlation between PTX3 levels in serum and SF.
The correlation of disease activity and autoantibody levels with SF-PTX3 levels in antibody-positive patients suggests a role for PTX3 in the inflammatory process specifically in seropositive RA joints, and supports the hypothesis that seropositive and seronegative RA are different disease entities. Polymorphonuclear granulocytes may be an important source of PTX3 in RA SF.