Abstract
The major histocompatibility complex (MHC) class II molecule displays peptide fragments of foreign proteins to trigger a defensive reaction from the immune system. Before insertion of the foreign peptides into the class II binding groove, a place-holding peptide CLIP must be removed. This is accomplished by the molecule DM, which is shown to increase the dissociation rate of a small class II-associated Ii peptide (CLIP) from class II (see report by Weber et al ., p. 618 ). Roche explains how DM can tell the difference between the class II-CLIP and foreign peptide-CLIP complexes.