Id1 and CXCL16 are linked in RA SF and at the level of transcription in EPCs. An ELISA was developed to detect Id1 in synovial fluids (SFs) taken from rheumatoid arthritis (RA), osteoarthritis (OA) and patients with other arthritic disorders, including gout, seronegative spondyloarthritis and systemic lupus erythematosus. A) The ELISA showed that Id1 was found in SFs of other diseases (n = the number of patients = 4, 13.8 (mean) ± 0.9 (standard error of mean (SEM)) ng/ml) and was significantly higher in RA SFs (n = 13, 19.4 ± 1.3 ng/ml), and OA SF (n = 9, 14.9 ± 1.4 ng/ml), all of which were P <0.05 (n = number of patients). B) CXCL16 was measured in the same samples as Id1, and correlated with Id1 expression in RA SF (r = 0.75 Pearson’s Correlation Coefficient (P <0.05, n = number of patients). C) Total RNA was isolated from human dermal microvascular endothelial cells (HMVECs) and endothelial progenitor cells (EPCs). Following isolation, RNA was quantified and checked for purity using a spectrophotometer and made into cDNA and amplified in a thermocycler (40 cycles). As shown, tumor necrosis factor-alpha (TNF-α) did not affect Id1 mRNA levels in EPCs, and reduced the number of Id1 transcripts in HMVECs. D) CXCL16 stimulation elevated Id1 mRNA expression in EPCs but not HMVECs, indicating that CXCL16 and Id1 are associated at the level of transcription in EPCs but not mature ECs (n = number of independent experimental replicates).
Isozaki et al. Arthritis Research & Therapy 2014 16:R68 doi:10.1186/ar4507