Natural killer (NK) T cells are significantly decreased in the peripheral blood of patients with rheumatoid arthritis (RA).

The number of NK T cells was measured in relation to the Th1/Th2 imbalance observed in RA. Peripheral blood samples of patients with RA (n = 60) and healthy controls (n = 36) were stained with anti-NK receptor 1A (anti-NKR-P1A), anti-CD56, and anti-CD3 MoAbs, and examined by three-colour flow cytometry. NK T (NKR-P1A+CD3+) cells in the peripheral blood were decreased in RA compared with the controls: 25 +/- 20/microl versus 143 +/- 53/microl (P < 0.0001). CD56+CD3+ cells were also decreased in RA: 60 +/- 46/microl versus 116 +/- 54/microl (P < 0.0001). The decrease was significant when adjusted to the number of total lymphocytes (P < 0.0001) or NK (CD56+CD3-) cells (P < 0.0001), and showed no correlation with age, sex, disease duration, disease activity, functional class, x-ray stage, drug treatment, joint score, grip strength, C-reactive protein, rheumatoid factor or erythrocyte sedimentation rate of the patients. The results show that the levels of NK T cells are depressed in the peripheral blood of patients with RA, suggesting that the measurement of NK T cells in peripheral blood may have clinical importance for a Th1-type autoimmune disease like RA.