Differential induction of immunoglobulin G subclasses by immunization with DNA vectors containing or lacking a signal sequence.

The route and method used to immunize mice with antigen-expressing DNA plasmids have an impact on the resulting T-helper cell response and IgG subclass distribution. Previous findings further indicate that the intracellular targeting of expressed antigens influences the differentiation of naive T-cells into either a Th1 or a Th2 type of response. In the present study, we analyzed the levels of IgG1 and IgG2a antibodies, as correlates of Th2 and Th1 responses, respectively, after intramuscular injection of mice with plasmids encoding a chimeric protein containing a Plasmodium falciparum blood stage antigen expressed in two different forms. One plasmid expresses the antigen in a secreted form as it is preceded by a signal sequence while expression from the other plasmid, lacking this sequence, results in cytoplasmic localization of the antigen. Mice immunized with the plasmid encoding secreted antigen responded with predominantly IgG1 antibodies. In contrast, sera from mice immunized with the plasmid expressing cytosolic protein displayed a mixed IgG1/IgG2a profile. In line with previous findings, our results suggest that the intracellular targeting of proteins expressed by DNA plasmids is an important factor for the differentiation of Th cells and the resulting subclass pattern of IgG responses.