Frequency of natural killer T (NKT) cells in rheumatoid arthritis (RA) patients and healthy control individuals. NKT cell frequency in freshly isolated peripheral blood (PB) mononuclear cells from 22 healthy control individuals and 23 RA patients, and in synovial fluid (SF) mononuclear cells from seven RA patients was determined by flow cytometry. Cells were stained with anti-Vα24, anti-Vβ11 and anti-CD3 monoclonal antibody. Error bars indicate the standard error of the mean. *P < 0.01.