CDw78 Defines MHC Class II-Peptide Complexes That Require Ii Chain-Dependent Lysosomal Trafficking, Not Localization to a Specific Tetraspanin Membrane Microdomain

Abstract

MHC class II molecules (MHC-II) associate with detergent-resistant membrane microdomains, termed lipid rafts, which affects the function of these molecules during Ag presentation to CD4+ T cells. Recently, it has been proposed that MHC-II also associates with another type of membrane microdomain, termed tetraspan microdomains. These microdomains are defined by association of molecules to a family of proteins that contain four-transmembrane regions, called tetraspanins. It has been suggested that MHC-II associated with tetraspanins are selectively identified by a mAb to a MHC-II determinant, CDw78. In this report, we have re-examined this issue of CDw78 expression and MHC-II-association with tetraspanins in human dendritic cells, a variety of human B cell lines, and MHC-II-expressing HeLa cells. We find no correlation between the expression of CDw78 and the expression of tetraspanins CD81, CD82, CD53, CD9, and CD37. Furthermore, we find that the relative amount of tetraspanins bound to CDw78-reactive MHC-II is indistinguishable from the amount bound to peptide-loaded MHC-II. We found that expression of CDw78 required coexpression of MHC-II together with its chaperone Ii chain. In addition, analysis of a panel of MHC-II-expressing B cell lines revealed that different alleles of HLA-DR express different amounts of CDw78 reactivity. We conclude that CDw78 defines a conformation of MHC-II bound to peptides that are acquired through trafficking to lysosomal Ag-processing compartments and not MHC-II-associated with tetraspanins.

The Tetraspanin CD82 Is Specifically Recruited to Fungal and Bacterial Phagosomes prior to Acidification

“…Unlike CD63, whose appearance on the phagosome is strictly dependent on prior acidification, the addition of bafilomycin to DCs had no bearing on CD82 recruitment. Furthermore, careful examination of recruitment kinetics revealed that CD82 arrives at the phagosome before CD63, indicating that if CD82 and CD63 assemble into tetraspanin microdomains to associate with class II MHC molecules, as suggested by other studies (10,20,29), this association must come about following arrival at the phagosome. Once there, these tetraspanins may serve to escort peptide-loaded class II MHC to the cell surface, a hypothesis supported by the presence of both CD82 and CD63 in endocytic tubules of LPS-stimulated primary dendritic cells (37).…”

“…CD82, along with several other tetraspanins, can also be found in cells of the immune system (23,33). In dendritic cells (DCs), CD82 associates with class II major histocompatibility complex (MHC) and the tetraspanin CD63 (20), as well as with other components of the antigen-processing and presentation pathway, including the peptide-editing/loading mediators HLA-DM and HLA-DO (14,29). CD82 and CD63 are enriched in class II MHC-positive compartments and exosomes (7,11,31), both compartments of central importance to antigen presentation and initiation of an effective immune response (46).…”

CD9 Regulates Major Histocompatibility Complex Class II Trafficking in Monocyte-Derived Dendritic Cells

“…Upon DC maturation, recruitment of the peptide-MHC-II complex to membrane microdomains, such as lipid rafts (64) and TEMs (65), was suggested to be important for Ag presentation and subsequent T cell activation (66). TEMs include Ii-associated MHC-II molecules, HLA-DR, HLA-DM, and MHC-II loaded with restricted antigenic peptide repertoires (65,67). Previous work also suggested that CD9 regulates MHC-II clustering at the DC surface, enhancing the T cell-stimulatory capacity of APCs (51); however, others could not detect differences in the formation of I-A/I-E multimers in CD9 KO BMDCs (52).…”

Major Histocompatibility Complex Class II-Peptide Complexes Internalize Using a Clathrin- and Dynamin-independent Endocytosis Pathway

“…Cells and Reagents-HeLa cells (ATCC, Manassas, VA), JY B cells, HeLa cells expressing CIITA, and the KG-1 DC line (both gifts from Dr. Peter Cresswell, Yale University School of Medicine) were maintained as described previously (60,61). Human DCs were generated from elutriated human monocytes obtained from the NIH Blood bank.…”