TREM2 and rheumatoid arthritis: This is in line not only with findings in RA showing that TREM-2 is highly upregulated in active but not inactive RA synovium [43], but also with studies in IBD [42,80] that reported high levels of TREM-2 in the inflamed mucosa of patients with IBD and the virtual absence of TREM-2 in colon samples of healthy donors.