Production of soluble ICAM-1 by mononuclear cells from patients with rheumatoid arthritis patients

The present study was designed to quantify the level of the soluble form of ICAM-1 (sICAM-1) produced by mononuclear cells (MNC) of rheumatoid arthritis (RA) patients, and to correlate these levels with the disease activity and with the amounts of cytokines or rheumatoid factors (RF) produced by MNC. Unstimulated synovial fluid (SF) MNC produced higher amounts of sICAM-1 than peripheral blood (PB) MNC in RA patients (P<0.01). sICAM-1 production by PHA-stimulated MNC was higher in RA SF MNC than RA or normal PB MNC (P<0.01). The amounts of SICAM-1 produced correlated with the amounts of soluble IL-2 receptor produced (P<0.02) but not with IL-1B or the Lansbury activity index in RA PB MNC. sICAM-1 correlated with the amounts of soluble CD23 and IL-4 produced by normal PB MNC (P<0.01). The amounts of sICAM-1 correlated with IgG-RF (P <0.02) and IgM-RF (P<0.01) produced by unstimulated MNC obtained from the bone marrow (BM) of RA patients. ICAM-1 expression of T-lymphocyte subsets, B lymphocytes, and monocytes obtained from RA PB and RA BM assayed by twocolor flow cytometry ranged from 0.1 to 6%, which was not appreciably different from that of normal controls. The monocyte fraction of RA PB MNC produced significantly higher amounts of sICAM-1 than lymphocyte fraction. These results suggest that sICAM-1 produced by MNC may be a marker of cell activation in T and B lymphocytes, in contrast to the transient increase of ICAM-1 expression.