Reconstitution of an operational MHC class II compartment in nonantigen-presenting cells

We quantitated the amounts of peptides from hen egg-white lysozyme presented by I-Ak molecules in APC lines. The large chemical gradient of presentation of the four hen egg-white lysozyme epitopes observed in cell lines expressing HLA-DM or H-2DM (referred to in this study as DM) was significantly diminished in the T2.Ak line lacking DM. Differences in levels of presentation between wild-type and DM-deficient APC were observed for all four epitopes, but differences were most evident for the highest affinity epitope. As a result of these quantitative differences in display, presentation of all four epitopes to T cells was impaired in the line lacking DM. The binding affinity of the pool of naturally processed peptides from DM-expressing lines was higher than that from the DM-deficient line. Thus, using a direct biochemical approach in APC, we demonstrate that DM influences the selection of peptides bound to MHC class II by favoring high affinity peptides.

Section: Resultssupporting

confidence: 83%

Cutting Edge: H-2DM Is Responsible for the Large Differences in Presentation Among Peptides Selected by I-Ak During Antigen Processing

Lovitch

Petzold

Unanue

2003

“…In addition, p110␦ mutant B cells showed similar levels of Ag colocalization with H2M (Fig. 6D), a resident of the lysosome/late endosome (MIIC) compartments that catalyze loading of antigenic peptide onto the MHC class II (41)(42)(43)(44). These results suggest that p110␦ mutant B cells are not defective in Ag-BCR internalization or targeting to the MIIC.…”

Section: Ag-bcr Complexes Are Internalized and Targeted To Late Endosmentioning

confidence: 71%

Requirement for Phosphoinositide 3-Kinase p110δ Signaling in B Cell Antigen Receptor-Mediated Antigen Presentation

Al‐Alwan

Okkenhaug

Vanhaesebroeck

et al. 2007

The BCR serves to both signal cellular activation and enhance uptake and presentation of Ags by B cells; however, the intracellular signaling mechanisms linking the BCR to Ag presentation functions have been controversial. PI3Ks are critical signaling enzymes controlling many cellular processes, with the p110δ isoform playing a critical role in BCR signaling. In this study, we used pharmacological and genetic approaches to evaluate the role of p110δ signaling in Ag presentation by primary B lymphocytes. It was found that activation of allogeneic T cells is significantly reduced when B cells are pretreated with global PI3K inhibitors, but was intact when p110δ signaling was specifically inactivated. In contrast, inactivation of p110δ significantly impaired the ability of B cells to activate T cells in a BCR-mediated Ag uptake and presentation model. Prestimulation of p110δ-inactivated B cells with anti-CD40 or LPS could not rescue their BCR-mediated Ag presentation ability to normal levels. p110δ signaling was required for efficient presentation of either anti-Ig or protein Ag via a lysozyme-specific BCR. p110δ-inactivated B cells were able to internalize Ag normally, and no defects in association of Ag with lysosome-associated membrane protein 1+ late endosomes were observed; however, these cells were less effective in forming polarized conjugates with Ag-specific T cells. Our data demonstrate a role for p110δ signaling in B cell Ag presentation function, implicating 3-phosphoinositides and their targets in the latter stages of this process.

“…As for conventional class II complexes, transient Ii chain/DM associations were previously described in pulse-chase experiments (38,40). Recent studies demonstrate that Ii chain-deficient mice express less DM at steady state (80).…”

Section: Discussionmentioning

confidence: 99%

Dissecting MHC Class II Export, B Cell Maturation, and DM Stability Defects in Invariant Chain Mutant Mice

Koonce

Bikoff

2004

Invariant (Ii) chain loss causes defective class II export, B cell maturation, and reduced DM stability. In this study, we compare Ii chain and class II mutant mouse phenotypes to dissect these disturbances. The present results demonstrate that ER retention of αβ complexes, and not β-chain aggregates, disrupts B cell development. In contrast, we fail to detect class II aggregates in Ii chain mutant thymi. Ii chain loss in NOD mice leads to defective class II export and formation of αβ aggregates, but in this background, downstream signals are misregulated and mature B cells develop normally. Finally, Ii chain mutant strains all display reduced levels of DM, but mice expressing either p31 or p41 alone, and class II single chain mutants, are indistinguishable from wild type. We conclude that Ii chain contributions as a DM chaperone are independent of its role during class II export. This Ii chain/DM partnership favors class II peptide loading via conventional pathway(s).