CD4 and rheumatoid arthritis: In the non-RA cohort, we also noted increased frequencies of CD4+CD28− T-cells [2.9% (0.1–34) vs. 0.7% (0.1–7.3), p = 0.010, Figure 1A] as well as CD8+CD28− T-cells [38.3% (4.1–82.1) vs. 28.7% (6.6–59.8), p = 0.035, Figure 1B] in patients with reduced bone mass compared to healthy controls.