To examine the host immune response against infection, the wild-type worms on day 2 of the life-span assay were selected since the numbers of viable worms started to dramatically decrease on day 3 and day 4 (Figure 1) and the major components in the p38 MAPK (tir-1, nsy-1, sek-1, and pmk-1) and DAF/IGF (daf-16 and age-1) pathways, previously identified antimicrobial peptides (lys-7, spp-1, abf-2, clec-85, clec-60, and abf-3), and other reported defense molecules (sod-3, dbl-1, and skn-1) were used as the indicators for the host response and signaling transduction. Here, MAP2K4 is linked to infection.