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Coadministration of interleukin 2(IL-2) plasmid DNA with combined DNA vaccines enhanced Th1-type cellular responses by producing higher amounts of IFN-γ with a higher ratio of antigen-specific IgG2a/IgG1. The IFN-γ specific for Ag85B, MPT64, and MPT83 in this group was 415, 267, and 255U/ml, respectively, and was 1.6-, 1.8-, and 2.5-fold higher than that of the same vaccine without adding IL-2. The IgG2a/IgG1 ratio for Ag85B, MPT64, and MPT83 was 4, 8, and 4, respectively, upon addition of the genetic adjuvant in the DNA vaccine, which was four times higher for every antigen when IL-2 was not included. Fluorescenceactivated cell sorter (FACS) analysis showed that, in the presence of IL-2, CD8⁺ and CD4⁺ T cells increased significantly, whereas in the absence of the genetic adjuvant, only a mild increase was observed for CD8⁺ T cells compared to the vector DNA-treated group. Bacterial CFU was reduced to less than 1/100 in the lung and to about 1/10 in the spleen relative to the same combined DNA vaccine without IL-2. The lungs of this group of mice showed much less damage due to an influx of epithelioid macrophages and less lymphocytes. RT-PCR showed that antigen genes could be detected in more organs and for a longer period of time when treated with combined DNA vaccine formulated in IL-2. We suggest that IL-2 enhanced the immunigencity and protective efficacy in immunized mice by improving the Th1-type response and also by prolonging the antigen gene expression in different organs.