Il1b is required for the early and late recruitment of neutrophils but not macrophages. PCR amplification of il1b cDNA from the 48 hpf intravenous-infected larvae, which had previously been injected with either scambled morpholino (scramMO) or with a morpholino antisense oligonucleotide that blocked the splicing of intron 2 (il1bMO). (B) The diagram shows the region that is imaged in C (dashed box). (C) Recruitment of neutrophils (green) in Tg(mpx:GFP) larvae at 4 hours and 48 hours following the injection of DsRed-expressing E. coli (red) into the notochord. These larvae had been previously injected with scrambled morpholinos (scramMO) or il1b MO. N, notochord. At 48 hpi, many neutrophils were found in the AGM region, in between the dorsal aorta (DA) and the posterior caudal vein (pcv); arrows indicate the direction of blood flow. (D–G) Plots show the number of total neutrophils at 4 hpi (D) and the number of recruited neutrophils at 4 hpi (E) and 48 hpi (F). (G) The number of recruited macrophages at 48 hpi in similar experiments that were performed using Tg(mpeg1:mCherryF) larvae. Each point represents an individual larva, the bar represents the mean value. **P<0.005, ***P<0.001. (H-J) Bright-field images of control (scramMO) and il1b morphants 3 days after injection of either PBS or E. coli into the notochord. Lateral views of the trunk region are shown in C,H,I,J.