CLIP or Class II-associated invariant chain peptide is the part of the invariant chain (li) that binds MHC class II

MHC class II

MHC Class II molecules are found only on a few specialized cell types, including macrophages, dendritic cells and B cells, all of which are professional antigen-presenting cells ....

 groove and remains there until the MHC

MHC

-Biology:*Myosin heavy chain - part of the motor protein myosin's quaternary protein structure*Major histocompatibility complex - a highly polymorphic region on chromosome 6 with genes particularly involved in immune functions-Colleges:...

 receptor is fully assembled. The purpose of CLIP is to prevent the binding of self-peptide fragments prior to MHC II localization within the endo/lysosome

Lysosome

thumb|350px|Schematic of typical animal cell, showing subcellular components. [[Organelle]]s: [[nucleoli]] [[cell nucleus|nucleus]] [[ribosomes]] [[vesicle |vesicle]] rough [[endoplasmic reticulum]]...

.

During MHC II assembly, invariant chain complexes with the MHC II complex. In a special endosome called the MHC II compartment, cathepsin S

Cathepsin S

Cathepsin S, also known as CTSS, is a protein which in humans is encoded by the CTSS gene.The protein encoded by this gene, a member of the peptidase C1 family, is a lysosomal cysteine protease that may participate in the degradation of antigenic proteins to peptides for presentation on MHC class...

 cleaves the invariant chain, leaving CLIP bound to the MHC II complex. In presence of antigen peptide fragments, HLA-DM

HLA-DM

HLA-DM is an intracellular protein involved in peptide presentation by MHC class II. It is encoded by the genes and .In the endosomes, HLA-DM functions by promoting the dissociation of the CLIP peptide from MHC class II which allows endosomal peptides to bind...

then binds to the MHC II molecule, releasing CLIP and allowing peptides to bind. MHC II with bound antigen is then transported to the cell membrane for presentation.