Pathogen recognition and activation of the innate immune response in zebrafish. Danio rerio

We use the zebrafish embryo model to study the similarities and differences in the innate immune response against three different bacterial pathogens. Therefore, we injected E. tarda, Salmonella, or M. marinum into the caudal vein of 28 hours post fertilization (hpf) zebrafish embryos and analysed their gene expression profile at 8 hours or 4 days after infection by microarrays. The results show that infections with the gram-negative bacteria E. tarda and S. typhimurium, which are lethal within 1-2 days, induce a strong early immune response at 8 hours after infection. In contrast, infection with M. marinum leads to a chronic infection that only induces a strong response at 4 days post infection. Overall design: This microarray study was designed to determine the gene expression profile during infection with Salmonella typhimurium, Mycobacterium marinum, and Edwardsiella tarda. RNA was isolated from single embryos and each treatment group consisted of three embryos: (1) Wildtypes injected with PBS 8 hours post infection (hpi), (2) S. typhimurium-infected wildtypes 8hpi, (3) wildtypes injected with PBS/2%PVP 8hpi , (4) M. marinum-infected wildtypes 8hpi, (5) wildtypes injected with PBS/2%PVP 4 days post infection (dpi), (6) M. marinum-infected wildtypes 4dpi, (7) wildtypes injected with PBS 8hpi (E. tarda control), (8) E. tarda-infected wildtypes 8hpi. Embryos were grown at 28.5–30°C in egg water and manually dechorionated at 24 hours post fertilization (hpf). Subsequently, embryos were infected at 28 hpf by micro-injecting 200 colony forming units (CFU) of S. typhimurium SL1027, E. tarda or Mycobacteria marinum M20 bacteria into the caudal vein, or were mock-injected with buffer as a control. After injections embryos were transferred into fresh egg water and incubated for 8 h or 4 days at 28°C. After the incubation period, single embryos were snap-frozen in liquid nitrogen and RNA was isolated for microarray analysis. All treatment groups were analyzed using a common reference approach.