MHC class II expression on myeloid cells inversely correlates with disease progression in early rheumatoid arthritis

To investigate whether MHC class II expression on myeloid cells of patients with treatment-naive early rheumatoid arthritis (RA) correlates with disease progression.

Monocytes were isolated by negative selection from the peripheral blood of 15 patients with early RA (disease duration < or =12 months), differentiated to macrophages and analysed for MHC class II expression by flowcytometry. The phenotypical data were correlated with clinical disease progression for up to 45 months.

Before treatment was initiated, in vitro differentiated macrophages of 10/15 early RA patients expressed MHC class II comparable with macrophages from healthy controls. In sharp contrast, macrophages of the remaining five patients expressed significantly fewer MHC class II molecules. In contrast to patients with normal levels of myeloid cell MHC class II expression, who developed a smouldering, non-progressive disease, patients with decreased expression of MHC class II on macrophages early in their disease developed a continuously active disease as demonstrated by persistently increased disease activity scores (chi(2) = 4.54, P < 0.02) and progressive bone destructions (chi(2) = 5.66, P < 0.02) despite aggressive therapy.

The level of myeloid cell MHC class II expression in recent onset RA allows a reliable distinction between patients who develop active and destructive RA and patients with a smouldering, slowly progressive disease.