[Macrophage activation syndrome secondary to tocilizumab: Myth or reality?]

Some authors have reported macrophage activation syndrome (MAS) secondary to infusion of tocilizumab, a monoclonal antibody that blocks interleukin-6 (IL-6). The pathophysiology of MAS is however linked to uncontrolled activation of innate immunity, mediated in part by IL-6. We conducted a study for macrophage activation biomarkers in a cohort of patients treated with tocilizumab.

Twenty-seven patients were included prospectively in our center. Levels of neutrophils, platelets, CRP and fibrinogen were lower at the end of treatment than at initiation (P<0.05); other biomarkers were stable. There was neither clinical sign of SAM nor hemophagocytosis in myelogram.

Laboratory abnormalities are related to direct blockade of IL-6 by tocilizumab and decrease hepatic protein synthesis. Tocilizumab is not responsible for MAS and associations described are more likely to be related to the autoimmune underlying disease, rather than treatment.