C-reactive protein and systemic lupus erythematosus.

Introduction Although serum levels of the acute-phase reactant C-reactive protein (CRP) usually parallel disease activity in inflammatory states, it is widely believed that systemic lupus erythematosus (SLE) is an exception. It has long been observed that many patients with active SLE display only modestly elevated or even normal CRP levels during periods of intense disease activity (1–3), particularly when compared with patients with rheumatoid arthritis (RA) (4). Indeed, this observation has led to the suggestion that marked CRP elevation in a patient with SLE indicates infection (3,5,6). The explanation for the relatively low levels of CRP in many patients with SLE has remained unclear despite many years of study. In this review, we critically reevaluate this belief and review possible mechanisms that could cause a muted CRP response. In addition, we briefly survey recent evidence raising the possibility that low CRP levels may predispose to or aggravate SLE.