Clinical characteristics of influenza virus infection in juvenile idiopathic arthritis patients treated with tocilizumab

Background: Inhibition of interleukin-6 (IL-6) signaling by tocilizumab is highly effective for treatment of refractory juvenile idiopathic arthritis (JIA). It appears that IL-6 plays an important role in the immune response to the influenza virus, but it is not clear whether treatment with tocilizumab affects the severity of influenza. Methods: We retrospectively collected clinical and laboratory data from JIA patients (n = 33) treated with tocilizumab. Ten patients who developed influenza (tocilizumab group; 10.1 %, 10/99 patient-years) were analyzed. Eleven JIA patients who experienced influenza during conventional treatments, without tocilizumab (control group), were compared with the tocilizumab group. Results: Of the 10 patients in the tocilizumab group, 6 patients did not have high fever (>38 C), and the other 4 febrile patients recovered from fever in 1 day. White blood cell counts and lymphocyte counts were significantly lower at the acute phase of infection compared with data from before influenza infection. The degree of fever and level of C-reactive protein in the tocilizumab group were significantly reduced compared with the control group. Conclusions: IL-6 inhibition by tocilizumab reduced inflammation associated with infection and resulted in mild symptoms during influenza. Leukopenia might be a useful indicator of viral infection, including influenza, during tocilizumab treatment.