DLL1 and rheumatoid arthritis: In support of this involvement of NOTCH in RA inflammatory conditions, it has also been demonstrated that in macrophages, IFN-γ, a powerful activator of these cells, determines the increase in the expression of jagged-1 with a simultaneous reduction in expression of the Delta-like family proteins DLL1 and DLL4 [71], resulting in a worsening of the clinical signs of RA.