The segment of invariant chain that is critical for association with major histocompatibility complex class II molecules contains the sequence of a peptide eluted from class II polypeptides.

Abstract

Major histocompatiblity complex class II molecules present peptides from an extracellular source of antigens to CD4+ T lymphocytes. The class 11-associated invariant chain affects this role of a and (3 polypeptides by restriction of peptide loading to endocytic vesicles. Up to now no specific portion of the invariant chain has been defined as the class II binding site. We constructed recombinant invariant chain genes and inspected association of the mutant invariant chains with class II polypeptides. Here we demonstrate that an extracytoplasmic sequence of the invariant chain (aa 81-109) that is only 23 residues away from the transmembrane region is essential for contact with class II polypeptides, whereas the remaining C-terminal part is dispensable for binding. The sequence ofinvariantchain-derived peptides that were eluted from class II molecules is contained in this segment and may derme the class II binding site of the invariant chain. The membrane-proximal position of this region suggests that the invariant chain and invariant-chainderived peptides isolated from class II molecules bind to a domain distinct from the class II pocket.Recently, it has been demonstrated that expression of the invariant chain (Ii) facilitates the presentation of various antigens by major histocompatibility complex (MHC) class II molecules (1-5). Ii is a type II membrane protein with the C-terminal domain expressed at the luminal side of the endoplasmic reticulum membrane (6). The following support for two roles of Ii was found. (i) Ii carries a signal sequence on its cytoplasmic domain that is responsible for sorting Ii and associated MHC class II molecules from the secretory to the endocytic route (7-9). (ii) Ii impedes loading of peptides to the MHC class II groove, a process that is postponed until MHC class II molecules enter an endocytic compartment and Ii is degraded (10)(11)(12). Additionally, assembly of Ii with MHC class II polypeptides modulates the shape of a and f3 dimers, which can promote the recognition of the a,3 peptide complex by T cells (13, 14).A soluble 18-kDa fragment of Ii that consists of most of the C-terminal part was found to bind to MHC class II molecules, indicating that association is not mediated by the membranespanning region or the cytoplasmic N terminus (15). Accordingly, a hybrid ofthe luminal domains ofclass II molecules and the transmembrane and cytoplasmic regions of MHC class I molecules associates with Ii (16). In this report we show that a membrane-proximal sequence of the luminal part of Ii is responsible for association with MHC class II molecules. MATERIALS AND METHODSPlasmid Constructions. A 9.4-kb fragment containing the murine Ii gene was subcloned into the plasmid pUC9 (1).The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.Deletions of coding regions of the Ii gene were obtained by restriction enzyme digestion and reli...

MHC Class II Antigen Presentation by Dendritic Cells Regulated through Endosomal Sorting

“…Premature peptide loading is prevented by the invariant chain (Ii, also called CD74) (Teyton et al 1990;Busch et al 1996). Ii binds the MHCII peptide-binding groove with a region in its luminal domain that is called CLIP (for class-II-associated invariant chain peptide) (Rudensky et al 1991;Chicz et al 1992;Riberdy et al 1992;Sette et al 1992;Freisewinkel et al 1993). Normally, Ii is synthesized in excess over MHCII, ensuring Ii rather than peptide binding to MHCII (Kvist et al 1982;Sekaly et al 1986;Marks et al 1990;Pieters et al 1991).…”

C-terminal extension of the MHC class II-associated invariant chain by an antigenic sequence triggers activation of naive T cells

“…1 Ii contains several functional domains, such as the class II binding site and a sorting signal that directs the class II/Ii complex to endocytic compartments and its delivery to MIIC vesicles. [28][29][30] At this location antigen loading to class II dimers takes place.…”

“…This cDNA is under the control of the SV40 promoter and has been described previously. 28 The oligonucleotides were inserted beyond the last coding triplet into a unique DraIII site of Ii31 cDNA. The coding region of the Ii31 cDNA is maintained.…”

Characterization of the T-cell repertoire in autologous graft-versus-host disease (GVHD): evidence for the involvement of antigen-driven T-cell response in the development of autologous GVHD

“…17,18 CLIP is a peptide associated with MHC class II ␤ chain and occupies the MHC class II groove. 35,36 Certain TCR BV elements, including BV15, interact directly with the superantigen SEB. 37,38 It is thought that HLA-DR-bound CLIP stimulates autologous GVHD T cells through the SEB binding site in a superantigen-like fashion, resulting in the induction of T-cell cytotoxicity against MHC class II-positive cells.…”