Objective: Since the early activation antigen CD69 has been implicated in the pathogenesis of some inflammatory diseases, we evaluated the expression of the molecule on peripheral blood (PB) and synovial fluid (SF) neutrophils obtained from RA patients and its possible correlation with PB and SF cytokine concentration.
Methods: CD69 membrane expression (and CD11b as control marker) was assessed by indirect immunofluorescence and flow cytometry analysis on purified PB and SF neutrophils. Cytokine levels (GM-CSF, IFN-gamma, TNF-alpha) in plasma and SF supernatants were measured by ELISA.
Results: CD69 was absent on control neutrophils, while it was expressed on PB neutrophils from RA patients although no detectable GM-CSF, IFN-gamma or TNF-alpha was observed in their plasma. CD69 expression was still more evident on SF neutrophils from RA patients; 59% had detectable levels of INF-gamma in their SF while GM-CSF and TNF-alpha were detectable in SF from 95% and 33% of RA patients, respectively. However, no correlation was observed between cytokine concentrations and CD69 expression on SF neutrophils. SF but not PB neutrophils from RA patients expressed increased amounts of CD11b when compared to control PB neutrophils without any correlation with CD69 membrane expression.
Conclusion: The activation antigen CD69 is significantly expressed on PB and SF neutrophils from RA patients. However, the mechanism(s) of induction and its possible role in the pathogenesis of RA remain to be defined.