Increased CD4+IL-17A+ basal levels in filarial-infected (Mansonella perstans and/or Wuchereria bancrofti) patients from Mali (Metenou et al. 2010) and increased IL-17A secretion from PBMCs derived from microfilaria-positive LF patients upon αCD3/αCD28 stimulation (Arndts et al. 2012) imply a critical role of Th17 immune responses during LF infection. Here, CD4 is linked to Lassa fever.