Presentation of immunodominant epitopes from mixture of protein antigens is hierarchial (100.21)

Abstract

Immunodominance is defined as restricted responsiveness of T cells to a few selected epitopes from complex antigens. We have established a reductionist cell-free antigen-processing system for MHC class II that constitutes five purified components: HLA-DR1, HLA-DM, and three cathepsins. This system successfully identified the physiologically selected epitopes from two model antigens. When applied for de novo epitope identification to LSA-NRC of malaria, or HA1-H5N1 (Avian Flu), the system selected epitopes that were confirmed to be immunodominant by their capacity to activate CD4+ T cells in HLA-DR1 positive human volunteers or transgenic mice (Hartman/Kim, et al. Nat Med 16, pp1333-1340 (2010). To evaluate our system to a mixture of the above antigens, the system identified the epitopes from both antigens. We tested the immunogenicity of epitopes and the parent proteins in HLA-DR1 transgenic mice immunized with the mixture of both HA1 and LSA-NRC in a recall T cell proliferation assay. T cells responded only to the HA1 and its immunodominant epitope, while little, if any stimulation against LSA-NRC and its dominant epitope were measured. These observations did not change even when the ratio of LSA-NRC:HA1was 2:1. These findings show a hierarchy for the selection of immunodominant epitopes of different proteins during antigen processing, which can be important in design of combination vaccines.