The Pathophysiologic Role of Monocytes and Macrophages in Systemic Lupus Erythematosus: A Reappraisal

Objectives To review current developments, regarding the pathophysiologic role of monocytes and macrophages in systemic lupus erythematosus (SLE). Methods We searched Medline for articles written in the English language using the following terms: monocyte(s) or macrophage(s) and lupus. Although our search spanned the years 1971 to 2008, the majority of the short-listed articles belonged to the period 2000 to 2008. Published literature on phenotypic and functional properties of monocytes/macrophages (Mo/Mφ) in SLE was reviewed. References from identified articles were also selected. Currently available experimental data and their relevance to the pathogenesis of SLE are critically discussed. Results It has traditionally been held that impaired phagocytosis by monocytes and macrophages in SLE allows for the accumulation of apoptotic debris leading to a sequel of autoimmune phenomena. Recent paradigms derived from animal models of systemic autoimmunity, however, has broadened our understanding regarding the possible pathophysiologic roles of Mo/Mφ in SLE. Data derived from studies in patients with SLE show multiple aberrations in activation status and secretory functions of circulating and tissue-infiltrating Mo/Mφ. Such aberrations may be associated with dysregulation of T-cell function and autoantibody production in SLE. Moreover, emerging evidence suggests that phagocytic capacity and antigen-presenting properties of Mo/Mφ are enhanced in some patients with SLE. Conclusions While defective phagocytosis represents a distinctive feature of monocyte function in some patients with SLE, aberrant activation of the Mo/Mφ system may be a more appropriate concept to encompass the broad spectrum of Mo/Mφ disorders in SLE. Aberrant function of lupus Mo/Mφ appears to play a dynamic role in the initiation and perpetuation of the systemic autoimmune response and organ damage. Delineation of the altered biology of lupus Mo/Mφ could provide possible future therapeutic targets for patients with SLE.