In view of age-associated reduction in immune function and the effect of eculizumab on the suppression of the terminal complement pathway (i.e., C5 and subsequent components), one concern is that treatment with eculizumab may elevate the risk of infection in elderly patients (Naylor et al. 2005; Czesnikiewicz-Guzik et al. 2008). Here, C5 is linked to infection.