The tremendous progress in the field of basic immunology and immunochemistr
y made in the last decade has significantly advanced our understanding of a
ntigen processing and presentation by MHC class I and II proteins. In this
review different techniques to study peptide interaction with MHC class II
molecules are summarized and their impact on the elucidation of quantitativ
e parameters, like affinities or kinetic data, is discussed. A recently int
roduced method based on synthetic combinatorial peptide libraries allows to
quantify the binding contribution of each amino acid residue ina class II
ligand and is presented in more detail. As this knowledge is fundamental fo
r current investigations in modern medicine, e.g. for novel immune system b
ased therapy concepts, further aspects like the design of new high affinity
MHC class II ligands and the prediction of peptide antigens are discussed.