To enable detection of antibodies against tetrameric M2e, the peptide M2eN-GCN4 was designed (Table 1 ). M2e is linked to a GCN4, a coiled coil whose oligomerization state can be determined by the identity of amino acid residues in key a and d positions of the coiled coil. In this case, the tetrameric version of GCN4 was used [30] . By affixing M2e to a tetrameric protein, we can constrain it in its tetrameric conformation. The effect is similar to that experienced by the ends of the tetrameric coiled coil from tetrabrachion of the Tetra-M2e nanoparticle. However, the coiled coil sequence is different. This guarantees that any antibodies bound to M2e-GCN4 are specific for the tetrameric version of M2e and not against the coiled coil or other parts of the nanoparticle.