Schematic representation of the mechanism by which peptide liposomes can induce TI IgG responses. The peptide antigen is presented in an aggregated repetitive β-sheet conformation which allows crosslinking of several BCRs. Presentation of peptide antigen and TLR ligand (in this case MPLA) in close proximity, for example on liposomes, allows costimulation of BCR and TLR4 via TRIF on the same B lymphocyte. Activation of TRIF in B lymphocytes permits B-cell activation and class switching to IgG. T cells, MHC-II, CD40/CD40L, CD28/CD80, CD28/CD86, CD14, and MyD88 (all marked in gray) are not required for the induction of TI IgG responses by peptide liposomes.