Mammalian granulocyte-macrophage colony-stimulating factor and some CpG motifs have an effect on the immunogenicity of DNA and subunit vaccines in fish

A eukaryotic plasmid DNA carrying the AACGTT CpG motif in its ampR gene is a 'danger' signal for mice and caused an increase in the specific antibody titres of fish and mice after immunization with beta-galactosidase (beta-ga l). A second pUC-based plasmid, which is inactive in mice and contains the GACGTC CpG motif in its cytomegalovirus (CMV) promoter, had no effect on an tibody responses to beta-gal in either fish or mice. A synthetic oligonucle otide, which contains the GACGTT motif, potentiated antibody responses to c o-administered beta-gal protein in mice, but not in fish. This is early evi dence that lower and higher vertebrates recognize different unmethylated Cp G motifs as 'danger' signals. In addition, plasmid DNA expressing mouse gra nulocyte-macrophage colony-stimulating factor (GM-CSF) had a marked effect on cytotoxic T-cell-like activity in fish by reducing the average number of myofibres that expressed beta-gal, 28 days after co-injection with plasmid DNA expressing beta-gal. Although the mechanism by which the mouse GM-CSF exerted its biological effects in fish is unknown, this finding might have important implications for fish vaccination, particularly when cytotoxic T cells may play a critical role.