Cellular cooperation in the humoral immune response to DNA vaccination

The cellular interactions responsible for developing the humoral immune response to intracellularly expressed DNA vaccine constructs have not been well characterized. We used a novel mammalian ubiquitin promoter-containing DNA plasmid construct, pTEJ-8, to express mycobacterial heat shock protein 65 (hsp65). To identify specific cell populations involved in the development of the anti-hsp65 humoral immune response, we vaccinated a series of C57BL/6 knock out mice. Using specific anti-hsp65 antibody isotypes as an indication of the in vivo cellular interactions, we observed that wildtype C57BL/6 and γ/δ TcR^-/- have similar anti-hsp isotype antibody production that is predominantly IgG2b. CD8^-/-, TAP^-/- and β2^-/- have significantly decreased IgG3 production as compared with wildtype C57BL/6 mice. Mice deficient in α/β TcR-bearing T cells have an almost undetectable anti-hsp65 response which is predominantly IgM and a small amount of IgG3. Interestingly, MHC Class II^-/- mice have a weak anti-hsp65 response that contains IgG2b, IgG3, as well as IgM. In vitro studies have shown that isotype class switching results from exposure to specific cytokines. Our results suggest that the T cell type which provides the cytokine help for the humoral response in pTEJ-8/hsp65 vaccinated mice is an α/β TcR-bearing cell and that both the CD4⁺, and surprisingly, CD8⁺ T cell compartments play a role in the determination of the anti-hsp65 antibody response.