Most studies investigating pertussis-specific CD4+ T cell responses use PBMC from vaccinees and whole P.69 Pertactin (P.69 Prn) or Pertussis toxin (Ptx) vaccine antigens, which strictly speaking are not indicative for the breadth and quality of CD4+ T cell response to single epitopes [22]–[25], [29]–[31]. Here, CD4 is linked to pertussis.