Some of the initial investigations comparing CD5+ B cells in the circulation of RA patients and their nonarthritic first-degree relatives did not show significant differences, whereas other studies found not only significantly elevated CD5+ B-cell levels in the blood of arthritic individuals, but also a correlation between the higher number of CD5+ B cells and higher titers of IgM RF [35-37]. This evidence concerns the gene CD5 and rheumatoid arthritis.