NFATC1 and rheumatoid arthritis: rIL-9 stimulation can significantly enhance the secretion of nuclear factor and cytoplasmic 1 (NFATc1) by activated T cells; NFATc1 is a master transcriptional regulator of osteoclast is enhanced differentiation in RA patients in whom the bone resorption capacity of osteoclasts and ultimately induces the differentiation of functional osteoclasts.