IGFBP6 and rheumatoid arthritis: The observation that the number of circulating IGFBP6+ T cells was significantly lower in RA compared to controls, while numerous IGFBP6-expressing T lymphocytes could be detected in RA ST allows us to speculate that T cells coexpressing IGFBP6 are no longer detectable in RA PB as they are migrated in the synovial membrane.