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.
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.
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.
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.