CD4 and infection: Early seminal work of Mills and Redhead (1993) uncovered the involvement of Th1-polarized CD4+ T cells in elimination of B. pertussis infection and pointed to the difference of Th1 polarization of immune responses elicited by the wP vaccine or experimental infection, as compared to predominant Th2 polarization of immune responses triggered by the aP vaccine in mice [20,21].