High levels of virus-specific CD4+ T cells predict severe pandemic influenza A virus infection. - Zhao, Y; Zhang, Y; Denney, L; Young, D; Powell, T; Peng, Y; Li, N; Yan, H; Wang, D; Shu, Y; Kendrick, Y; Mcmichael, A; et al. (American journal of respiratory and critical care medicine, 2012)