The infection with hMPV promotes a disease associated with an increase in the secretion of pro-inflammatory cytokines, the polarization of CD4+ T cells into a Th2-like profile, an increase in the infiltration of neutrophils into the lung, and an inefficient T and B cell function, which impairs viral clearance (Peiris et al., 2003; Ito et al., 2004; Romagnani, 2006; Hamelin et al., 2006; Fietta and Delsante, 2009). Here, CD4 is linked to infection.