CD4 and rheumatoid arthritis: Plasma levels of soluble OX40L (sOX40L) and the percentages of OX40+CD4+ T cells in PBMCs have been shown to be increased in early RA patients, and sOX40L levels have been shown to be strongly correlated with the levels of anticitrullinated protein antibodies (ACPAs) and IgM-rheumatoid factor (IgM-RF) [29].