Relations between surface expression of the interleukin-2 receptor and release of the soluble form of the receptor in cultured mononuclear cells from patients with rheumatoid arthritis or systemic lupus erythematosus.

The relationship between surface expression of the interleukin-2 receptor (IL-2R) and release of the soluble form of the receptor (sIL-2Ralpha or sCD25) was investigated with peripheral blood mononuclear cells (PBMCs) from individuals with rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE). The spontaneous release of sCD25 was significantly increased in PBMCs from RA patients and decreased in cells from SLE patients, compared with normal controls. However, the extent of sCD25 release from phytohaemagglutinin (PHA)-stimulated PBMCs did not differ between RA or SLE patients and normal controls. The serum concentration of sCD25 was significantly increased in SLE or RA patients compared with the normal controls. Whereas the surface expression of CD25 by unstimulated PBMCs did not differ among the three groups of subjects, this parameter was significantly reduced for PHA-stimulated PBMCs from RA patients relative to those from normal controls. The surface expression of CD25 showed a positive correlation with sCD25 release for PBMCs from SLE patients under either basal or stimulated conditions. No such relation was apparent for cells from RA patients. The surface expression of IL-2Rbeta (CD 122) under basal or stimulated conditions was significantly reduced in PBMCs from RA or SLE patients, compared with cells from normal controls. Thus, the increased concentration of sCD25 in the serum of individuals with these autoimmune rheumatic diseases may result from two different mechanisms: an increase in the spontaneous release of sCD25 in RA, and reduced clearance of this protein in SLE.