In active chronic rheumatoid arthritis, dipeptidyl peptidase IV density is increased on monocytes and CD4(+) T lymphocytes.

The effect of low-dose methotrexate (MTX) treatment on the CD26 density on circulating monocytes and CD4(+) T lymphocytes or levels of soluble CD26 (sCD26) has not yet been described in rheumatoid arthritis (RA). While CD26 in T lymphocytes is involved in the activation and proliferation of T lymphocytes, little is known of the role of CD26 in monocytes as it has only recently been localized to monocytes. We analysed the CD26 density by flow cytometry and levels of sCD26 in plasma before initiation of MTX treatment and 12 weeks later. This was done on 34 RA patients fulfilling the 1987 American College of Rheumatology (ACR) criteria followed for 16 weeks after starting MTX treatment. CD26 density on monocytes was increased in RA patients compared with healthy controls before MTX treatment (P < 0.01). After 12 weeks of MTX treatment, the CD26 density on monocytes decreased significantly in the ACR-50% group (P = 0.03), but not in the ACR-20% and the non-responder group (P = 0.15 and 0.87). The increased CD26 density on CD4(+) T lymphocytes (P < 0.01) was unaffected by the reduction in disease activity in relation to MTX treatment. The percentage of monocytes and CD4(+) T lymphocytes among peripheral blood circulating mononuclear cells did not change during MTX treatment. No effect of MTX treatment was observed on the plasma levels of sCD26. Active chronic RA is characterized by enhanced CD26 density on circulating monocytes and CD4(+) T lymphocytes. MTX treatment decreased CD26 density on monocytes in the ACR-50% responder group and was associated with decreased disease activity. The enhanced CD26 density on CD4(+) T lymphocytes was uninfluenced by MTX treatment.