In addition, a role of several host genetic loci in the course of B. pertussis infection has been indicated, such as the toll-like receptor 4 (Tlr4) gene [2-5], the interferon gamma receptor gene [6], and three novel loci, B. pertussis susceptibility locus 1, 2, and 3 (Bps1, 2, and 3) [2] that showed linkage with the severity of infection. Here, TLR4 is linked to infection.