Interleukin-6 level in systemic lupus erythematosus

ABSTRACT

Systemic lupus erythematosus (SLE) is a disease affecting blood vessels and connective tissue, which are damaged by deposition of pathogenic autoantibodies and immune complexes. Although a complex disease, SLE provides a number of insights into autoimmune pathogenesis. Autoimmune disease, in general, is characterized by B cell hyperactivity which results in hypergammaglobulinemia and production of a variety of autoantibodies reactive to organ-nonspecific antigens such as DNA, RNA, and cell membrane structures. SLE patients usually show a marked increase in the number of activated and immunoglobulin-producing circulating B cells. Recently, cytokines with specific effects on immune regulation have been detected and extensively studied. One of them, Interleukin-6 (IL-6), is an activated monocyte derived factor which stimulates B cell growth and differentiation. We investigated the serum IL-6 levels of SLE patients in an attempt to demonstrate their relationship with the patients' clinical manifestation, and the serum levels of C-reactive protein (CRP), circulating immune complexes (CICs,) and soluble interleukin-2 receptor (sIL-2R). The study subjects consisted of 22 patients with SLE who had visited Severance Hospital from July 1986 to September 1987 and 10 normal controls. The patients' sera were stored at -70degrees C and later analyzed. The serum levels of IL-6 were measured by ELISA method with Inter Test-6X Human IL-6 ELISA kit; the serum CRP levels by fluorescence polarization immunoassay; the serum CIC levels by solid phase Clp binding assay; and the serum sIL-2R levels ELISA method. The results were as follows The mean serum IL-6 level of SLE patients (1,366 pg/ml) was higher that of the controls (98pg/ml) (p<0.05). Among the SLE patients studied. the mean serum IL-6 level was higher in those with vasculitis than those without. ln the SLE patients studied. a linear correlation was present between the measured serum IL-6 and CIC levels; however no correlation was present either between IL-6 and CRP levels, or between IL-6 level and platelet count. The mean sIL-2R level of the SLE patients studied (1,864 U/ml) was higher than that of the controls (300 U/ml). However, in the SLE patients studied, no correlation was present between the serum IL-6 and sIL-2R levels measured. The high serum IL-6 level might play an important role in the pathogenesis of SLE.