Surface expression of heat shock protein 90 by blood mononuclear cells from patients with systemic lupus erythematosus.

Previous studies have indicated that blood mononuclear cells from 15-20% of patients with systemic lupus erythematosus (SLE) carry elevated levels of hsp90, a heat shock protein associated with steroid receptors in cells. We analysed surface expression of hsp90 on mononuclear cells (lymphocytes and monocytes) from patients with SLE by monoclonal antibody AC88 and flow cytometry. Whilst all blood mononuclear cells have intracellular hsp90, a significant proportion of patients with SLE expressed hsp90 on lymphocyte and monocyte surfaces. This was significantly higher on SLE lymphocytes than in laboratory controls and was positively correlated with disease activity. Comparison of total hsp90 with surface hsp90 in the same SLE patients' blood mononuclear samples indicated a correlation with a subgroup of patients. There was no correlation with expression of surface hsp90 by lymphocytes and activation markers. Patients with Sjögren's syndrome, rheumatoid arthritis, dermatomyositis and scleroderma were studied as disease controls and increased levels of shsp90 were detected in only three of the 53 patients studied. It is concluded that surface hsp90 expression is a feature of about 20% of patients with SLE and is correlated with high disease activity. The exposure of this hsp on the surface of some lymphocytes suggests that it is a candidate autoantigen in SLE.