The presence of B cells in peripheral tissues in response to infection is known, e.g., IgM+ B cells are recruited to the peritoneum of rainbow trout after injection of bacterium (Escherichia coli), E. coli-derived lipopolysaccharide, or viral hemorrhagic septicemia virus [22], with increased observation of IgM+ and IgT+ cells in the pyloric caeca of orally vaccinated rainbow trout [23] and in the skeletal muscle of rainbow trout [24] and Atlantic salmon [25,26] after DNA vaccination. The gene discussed is CD40LG; the disease is infection.