Research

DNA vaccination in fish promotes an early chemokine-related recruitment of B cells to the muscle

Read the article

Abstract

In fish, intramuscular injection of plasmid DNA encoding viral proteins has proved as the most effective vaccination strategy against many viral pathogens. The efficacy of DNA vaccination in teleost fish is based on a high level of viral antigen expression in muscle cells inducing a strong and long-lasting protection. However, the mechanisms through which this protection is conferred in fish are still not understood. Moreover, similarities to mammalian models can not be established since DNA vaccination in mammals induces much lower responses. In this work, we have focused on the characterization of immune cells that infiltrate the muscle at the site of DNA delivery in vaccinated fish and the chemokines that may be involved in their infiltration. It was observed that B lymphocytes, both IgM+ and IgT+, represent a major infiltrating cell type in fish vaccinated with a viral hemorrhagic septicemia virus (VHSV) DNA vaccine, whereas in control fish injected with an oil adjuvant mainly granulocytes were attracted. While IgM+ cells were the major B cell population at early time points post vaccination, IgT+ cells represented the predominant cell type later on. Among twelve chemokine genes studied in the injected muscle tissues, only CXCL10, CK5B and CK6 were more strongly transcribed in DNA vaccinated fish compared to control fish injected with the corresponding vector backbone. In vitro tests performed with recombinant trout CK5B and CK6 revealed that these chemokines have chemotactic capacities which might explain the recruitment of immune cells to the site of DNA injection. Our results suggest that B cells are involved in the initial phase of the immune response to intramuscular DNA vaccination against VHSV. This appears to be a major difference to what we know from mammalian models where T cells play a major role.