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The skin accommodates multiple dendritic cell (DC) subsets with remarkable functional diversity. Immune reactions are initiated and modulated by the triggering of DC by pathogen-associated or endogenous danger signals. In contrast to these processes, the influence of intrinsic features of protein antigens on the strength and type of immune responses is much less understood. Therefore, we investigated the involvement of distinct DC subsets in immune reactions against two structurally different model antigens, E. coli beta-galactosidase (betaGal) and chicken ovalbumin (OVA) under otherwise identical conditions. After epicutaneous administration of the respective DNA vaccines with a gene gun, wild type mice induced robust immune responses against both antigens. However, ablation of langerin+ DC almost abolished IgG1 and cytotoxic T lymphocytes against betaGal but enhanced T cell and antibody responses against OVA. We identified epidermal Langerhans cells (LC) as the subset responsible for the suppression of anti-OVA reactions and found regulatory T cells critically involved in this process. In contrast, reactions against betaGal were not affected by the selective elimination of LC, indicating that this antigen required a different langerin+ DC subset. The opposing findings obtained with OVA and betaGal vaccines were not due to immune-modulating activities of either the plasmid DNA or the antigen gene products, nor did the differential cellular localization, size or dose of the two proteins account for the opposite effects. Thus, skin-borne protein antigens may be differentially handled by distinct DC subsets, and, in this way, intrinsic features of the antigen can participate in immune modulation. [ABSTRACT FROM AUTHOR]

The type of immune response is critical for successful protection and typically determined by pathogen-associated danger molecules. In contrast, protein antigens are usually regarded as passive target structures. Here, we provide evidence that the structure of the antigen can profoundly influence the type of response that is elicited under else identical conditions. In mice, gene gun vaccines induce predominantly Th2-biased immune reactions against most antigens. One exception is E. coli beta-galactosidase (βGal) that induces a balanced Th1/Th2 response. Because both, the delivered material (plasmid DNA-coated gold particles) as well as the procedure (biolistic delivery to the skin surface) is the same as for other antigens we hypothesized that Th1 induction could be a function of βGal protein expressed in transfected cells. To test this we examined gene gun vaccines encoding structural or functional variants of the antigen. Employing a series of gene gun vaccines encoding individual structural domains of βGal, we found that neither of them induced IgG2a antibodies. Even disruption of the homo-tetramer association of the native protein by deletion of a few N-terminal amino acids was sufficient to abrogate IgG2a production. However, enzymatically inactive βGal with only one point mutation in the catalytic center retained the ability to induce Th1 reactions. Thus, structural but not functional integrity of the antigen must be retained for Th1 induction. βGal is not a Th1 adjuvant in the classical sense because neither were βGal-transgenic ROSA26 mice particularly Th1-biased nor did co-administration of a βGal-encoding plasmid induce IgG2a against other antigens. Despite this, gene gun vaccines elicited Th1 reactions to antigens fused to the open reading frame of βGal. We interpret these findings as evidence that different skin-borne antigens may be differentially handled by the immune system and that the three-dimensional structure of an antigen is an important determinant for this. [ABSTRACT FROM AUTHOR]

In a BALB/c mouse model, we have previously identified a ras oncogene peptide that contained both CD8+ and CD4+ T cell epitopes in a nested configuration. In this study, we developed several plasmid DNA minigene vectors encoding these determinants and examined whether they could induce antigen (Ag)-specific CD8+ cytotoxic and CD4+ lymphoproliferative responses. Furthermore, we compared two different immunization procedures, epidermal gene gun inoculation and intradermal (i.d.) injection of saline plasmid DNA, along with several approaches addressing different aspects of immune modulation. We demonstrated that each DNA plasmid induced the relevant Ag-specific cellular immune response. Gene gun inoculation was superior to that of needle injection for induction of the CTL response. Moreover, DNA plasmids containing both ras epitopes induced the highest CTL response, as compared with vector preparations containing only the CD8+ epitope. These results suggested that a DNA plasmid expressing nested mutant ras epitope-specific CD4+ and CD8+ T cell epitopes can be processed in vivo to induce both subset-specific T cell responses, and that the addition of the helper epitope quantitatively improved the development of the CTL response, which may have implications for DNA-based anti-tumor immunotherapies. [Copyright &y& Elsevier]