MHC Class II-Peptide Complexes and APC Lipid Rafts Accumulate at the Immunological Synapse

The influence of the pathway of Ag uptake and processing on MHC class II (CII)-mediated B cell function is unknown. In this study, we investigate in resting and activated (via the BCR or CD40) B cells the biological properties of CII-peptide complexes (CII-peptide) generated by either the BCR-mediated Ag processing (type I complex) or fluid phase Ag processing (type II complex). Compared with type I complex, ligation of type II complex by either specific Ab or the TCR in Ag-presenting assay results in significant decreases in B cell survival rate (50–100%) and expression levels of CII, CD86, and CD54. Loss of B cells following ligation of type II complex occurs in the presence of a comparatively good level of specific CD4+ T cell division, indicating that B cell loss is a late event following T cell stimulation. Comparative analysis of T and B cell conjugates after Ab ligation of type I or II complex reveals decreased efficiency of the latter in forming conjugates. Neither initial differential levels of CII and other studied surface markers, B cell type inherent differences, BCR signaling, T cell proliferation, nor initial density of CII-peptide complexes could explain the T cell-induced B cell loss. We propose that the context in which CII-peptide complexes are present in the membrane following BCR uptake and processing leads to B cell survival. Thus, appropriate targeting of Ag ensures generation of relevant immune responses.

Section: Discussionsupporting

confidence: 93%

“…The formation of B and T cell conjugates was measured using a method previously described (15), with some modifications. Briefly, CD43 Ϫ pure B cells were isolated from HEL-specific BCR transgenic mice and nontransgenic littermates.…”

Section: Quantification Of B:t Cell Conjugates By Flow Cytometrymentioning

confidence: 99%

The Pathway of Antigen Uptake and Processing Dictates MHC Class II-Mediated B Cell Survival and Activation

Nashar

Drake

2005

“…rafts and tetraspanin-containing microdomains. Despite the controversy regarding the relationship between cholesterol dependent detergent-insoluble membranes and lipid rafts in intact cells (47), a number of groups have found that the association of MHC-II with plasma membrane lipid rafts is important for the ability of APCs to stimulate CD4 T cells (3)(4)(5)48). By contrast, there is only limited data regarding the importance of MHC-II association with tetraspanins and/or tetraspanin microdomains.…”

Section: Discussionmentioning

confidence: 99%

“…It is now well established that one mechanism that leads to the local concentration of specific pMHC-II is their association with plasma membrane microdomains (1,2). One such microdomain, lipid rafts, has been shown to be important in the presentation of pMHC-II to CD4 ϩ T cells when such complexes are limiting (1,(3)(4)(5).…”

mentioning

confidence: 99%

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

Poloso

Denzin

Roche

2006

Self Cite

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.

“…MHC class II molecules have been detected by means of confocal microscopy in discrete plasma membrane domains in a variety of cell lines (11)(12)(13). Where tested, these domains have been shown to depend on cholesterol for their integrity, suggesting that they are formed by lipid rafts.…”

Section: T He Interaction Between Cognate Peptide-mhc (Pmhc)mentioning

confidence: 99%

Cognate Peptide–MHC Complexes Are Expressed as Tightly Apposed Nanoclusters in Virus-Infected Cells To Allow TCR Crosslinking

Ferez

Castro

Alarcón

et al. 2014

Antigenic T cell stimulation requires interaction between the TCR of the T cell and cognate peptide–MHC molecules presented by the APC. Although studies with TCR-specific Abs and soluble peptide–MHC ligands have shown that the TCR needs to be crosslinked by two or more ligands to induce T cell stimulation, it is not understood how several MHC molecules loaded with the cognate antigenic peptide can produce crosslinking under physiological conditions. We show at the molecular level that large clusters of cognate peptide–MHC are formed at the surface of murine professional and nonprofessional APCs upon virus infection and that these clusters impinge on the stimulatory capacity of the APC. These clusters are formed by tight apposition of cognate peptide–MHC complexes in a configuration that is compatible with simultaneous engagement of two or more TCRs. This suggests that physiological expression of Ag allows formation of multivalent ligands for the TCR that permit TCR crosslinking and T cell activation.