The present invention provides novel artificial oligopeptides capable of binding HLA Class II molecules encoded by several alleles. The oligopeptides include the sequence AX1FVAAX2TLX3AX4A (SEQ ID NO:1), wherein X1 is selected from the group consisting of W, F, Y, H, D, E, N, Q, I and K; X2 is selected from the group consisting of F, N, Y and W; X3 is selected from the group consisting of H and K, and X4 is selected from the group consisting of A, D and E, with the proviso that the oligopeptide sequence is not AKFVAAWTLKAAA. The invention also relates to larger peptides comprising the oligopeptides, polynucleotides encoding the oligopeptides and larger peptides, as well as to compositions comprising the oligopeptides, peptides or polynucleotides. Also disclosed are methods for inducing immune responses.