Interleukin-6 (IL-6) and acute phase proteins in the disease course of patients with systemic lupus erythematosus.

One of the mediators responsible for the induction of the production of acute phase proteins by hepatocytes is interleukin-6 (IL-6), formally known as hybridoma growth factor (HGF). In a prospective study the biological significance of IL-6, but also the relationship with the acute phase response (C-reactive protein [CRP], alpha 1-antitrypsin and alpha 1-acid glycoprotein) during flare-ups in 12 systemic lupus erythematosus (SLE) patients was investigated. Only 2 SLE patients showed sustained elevated IL-6 levels, and in one of these patients a clear correlation was found between the increases in IL-6 and the acute phase response. In the other SLE patients hardly any response or change in the levels of IL-6, CRP, and/or alpha 1-antitrypsin was found. In contrast to the profiles of alpha 1-acid glycoprotein, in seven of the SLE patients a significant increase in the serum levels took place in the period preceding the exacerbation. This difference between the three acute phase proteins suggests that the regulatory mechanisms are different. Our results are in agreement with the findings that IL-6 might be responsible for the CRP response.