HLA-DO is a lysosomal resident which requires association with HLA-DM for efficient intracellular transport.

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.

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

confidence: 86%

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

Al‐Alwan

Okkenhaug

Vanhaesebroeck

et al. 2007

“…However, the association between the two subunits was suggested in studies examining DO localization in human B lymphoma cells. DO was shown to accumulate in lysosomes in a DM-dependent fashion, and accumulation depended upon both DN␣ and DO␤ (13). Association between DN␣ and DO␤ also has been demonstrated directly by copurification of baculovirus-expressed proteins (14) and by coimmunoprecipitation of endogenous proteins in PGF B cell lysates (15).…”

mentioning

confidence: 84%

Identification of Class II Transcriptional Activator-Induced Genes by Representational Difference Analysis: Discoordinate Regulation of the DNα/DOβ Heterodimer

Taxman

Cressman

Ting

2000

Class II transcriptional activator (CIITA) is a master regulator of MHC class II genes, including DR, DP, and DQ, and MHC class II-associated genes DM and invariant chain. To determine the repertoire of genes that is regulated by CIITA and to identify uncharacterized CIITA-inducible genes, we used representational difference analysis. Representational difference analysis screens for differentially expressed transcripts. All CIITA-induced genes were MHC class II related. We have identified the α subunit, DNα, of the class II processing factor DO as an additional CIITA-inducible gene. Northern analysis confirmed that DNα is induced by IFN-γ in 2fTGH fibrosarcoma cells, and CIITA is necessary for high-level expression in B cells. The β subunit, DOβ, is not inducible in fibrosarcoma cells by IFN-γ or exogenous CIITA expression. Moreover, in contrast to other class II genes, DOβ expression remains high in the absence of CIITA in B cells. The promoters for DNα and DOβ contain the highly conserved WXY motifs, and, like other class II genes, expression of both DNα and DOβ requires RFX. These findings demonstrate that both DNα and DOβ are regulated by RFX. However, DNα is defined for the first time as a CIITA-inducible gene, and DOβ as a MHC class II gene whose expression is independent of CIITA.

“…Because many laboratories have demonstrated that DM and DO are tightly associated within B lymphocytes (17)(18)(19)(20), we were surprised by this finding. To further investigate the distribution of DM and DO within the endocytic pathway of the B lymphocyte, we analyzed the distribution of DM and DO within the A20 murine B cell line.…”

Section: Trafficking Of Ag-bcr Complexes Through Dm-and Docontaining mentioning

confidence: 94%

Prolonged Antigen Persistence Within Nonterminal Late Endocytic Compartments of Antigen-Specific B Lymphocytes

Gondré-Lewis

Moquin

Drake

2001

Although Ag-specific B lymphocytes can process Ag and express peptide-class II complexes as little as 1 h after Ag exposure, it requires 3–5 days for the immune system to develop a population of Ag-specific effector CD4 T lymphocytes to interact with these complexes. Presently, it is unclear how B cells maintain the expression of cell surface antigenic peptide-class II complexes until effector CD4 T lymphocytes become available. Therefore, we investigated B cell receptor (BCR)-mediated Ag processing and presentation by normal B lymphocytes to determine whether these cells have a mechanism to prolong the cell surface expression of peptide-class II complexes derived from the processing of cognate Ag. Interestingly, after transit of early endocytic compartments, internalized Ag-BCR complexes are delivered to nonterminal late endosomes where they persist for a prolonged period of time. In contrast, Ags internalized via fluid phase endocytosis are rapidly delivered to terminal lysosomes and degraded. Moreover, persisting Ag-BCR complexes within nonterminal late endosomes exhibit a higher degree of colocalization with the class II chaperone HLA-DM/H2-M than with the HLA-DM/H2-M regulator HLA-DO/H2-O. Finally, B cells harboring persistent Ag-BCR complexes exhibit prolonged cell surface expression of antigenic peptide-class II complexes. These results demonstrate that B lymphocytes possess a mechanism for prolonging the intracellular persistence of Ag-BCR complexes within nonterminal late endosomes and suggest that this intracellular Ag persistence allows for the prolonged cell surface expression of peptide-class II complexes derived from the processing of specific Ag.