ULBP1 and rheumatoid arthritis: Notably, we found that the induction of the NKG2DLs ULBP1-3 expression was specific for SLE serum, since serum from patients with Sjogren syndrome, systemic scleroderma or rheumatoid arthritis did not induce the expression of NKG2DLs on Treg cells (Fig. 3A).