BACKGROUND: The interaction of Notch receptors with their transmembrane ligands 
Delta and Jagged plays an important role not only in the organization of a 
variety of tissues but also in several genetic disorders and cancer development. 
The functional involvement of the Notch signaling in rheumatoid arthritis (RA) 
has been reported previously, but the expression profile of Notch-related 
molecules, as well as their relation with clinicopathological parameters, 
remains unclear.
METHODS: In this study, we analyzed the immunohistochemical staining pattern of 
four Notch receptors (Notch1-4) and their ligands (Delta1 and Jagged1) in 14 
synovial tissues obtained from 14 RA patients.
RESULTS: Notch2 and Notch4 were expressed in limited areas in a few samples or 
in small blood vessels, respectively. Notch1, Notch3, Delta1, and Jagged1 were 
overexpressed in the synovial lining and sublining cells on synovial 
hyperplastic lesions in all samples. Notch1 expression was also observed in T 
and B lymphocytes of lymphoid follicles independently. Notch1 and Notch3 
expression overlapped with that of Jagged1, as determined by confocal 
microscopy. Activation of Notch1 signaling in the RA synovium was identified 
using a specific antibody to the cleaved form of Notch1. The expression of these 
molecules did not show any correlation with clinicopathological parameters.
CONCLUSIONS: Our results suggest that Notch signaling is activated in RA 
synovium but does not necessarily reflect the pathological condition of RA.