Endogenous viral antigen processing generates peptide-specific MHC class I cell-surface clusters

Abstract

Sensitivity is essential in CD8+ T-cell killing of virus-infected cells and tumor cells. Although the affinity of the T-cell receptor (TCR) for antigen is relatively low, the avidity of T cell-antigen-presenting cell interactions is greatly enhanced by increasing the valence of the interaction. It is known that TCRs cluster into protein islands after engaging their cognate antigen (peptides bound to MHC molecules). Here, we show that mouse K b class I molecules segregate into preformed, long-lasting (hours) clusters on the antigen-presenting cell surface based on their bound viral peptide. Peptide-specific K b clustering occurs when source antigens are expressed by vaccinia or vesicular stomatitis virus, either as proteasome-liberated precursors or free intracellular peptides. By contrast, K b -peptide complexes generated by incubating cells with synthetic peptides are extensively intermingled on the cell surface. Peptide-specific complex sorting is first detected in the Golgi complex, and compromised by removing the K b cytoplasmic tail. Peptide-specific clustering is associated with increased T-cell sensitivity: on a per-complex basis, endogenous SIINFEKL activates T cells more efficiently than synthetic SIINFEKL, and wild-type K b presents endogenous SIINFEKL more efficiently than tailless K b . We propose that endogenous processing generates peptide-specific clusters of class I molecules to maximize the sensitivity and speed of T-cell immunosurveillance.MHC class I clustering | CD8 T cell recognition | dual-color TIRF imaging | antigen processing/presentation | intracellular trafficking

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

“…4D) (33). Our data are in agreement with a recently published paper (34) in which it was shown by optical microscopy that infection of fibroblasts with vaccinia virus also leads to the accumulation of cognate pMHC complexes in patches at the plasma membrane and that this distribution correlated with increased stimulatory capacity. Our data expand these finding by showing that pMHC patching also occurs in physiologically relevant APCs, that is, primary bone marrow-derived dendritic cells, and, more importantly, by showing that cognate pMHC complexes are indeed contacting each other, forming a supramolecular structure or cluster.…”

“…The more important implication is that delivery of this already K b OVAp-enriched composition at the cell surface is indicative of intracellular enrichment. In agreement with this, Lu et al (34) could indeed detect cognate pMHC clusters as far down the secretory pathway as the cis-Golgi. The exact mechanism causing the cognate pMHC enrichment remains unclear but it may result from the burst of viral protein expression that peaks a few hours postinfection.…”

BRAFV600E Co-opts a Conserved MHC Class I Internalization Pathway to Diminish Antigen Presentation and CD8+ T-cell Recognition of Melanoma

“…This region has also been shown to control the rate of surface MHC-I internalization in dendritic cells (DC), in which recycling of MHC-I is known to play a critical role in antigen cross-presentation (12,19,20,23). Moreover, the MHC-I cytoplasmic tail has been shown to mediate surface clustering of MHC-I, which can significantly impact CD8 + T-cell recognition (24). Interestingly, while Tyrosine-320 was required for transit of MHC-I into LAMP-1-positive endocytic compartments of DCs (12,19), these studies suggest that Serine-335 may play a more dominant role in controlling endocytic trafficking in melanoma cells.…”

Preparation of Peptide–MHC and T-cell Receptor Dextramers by Biotinylated Dextran Doping

“…For example, a previous study described a phenomenon of segregated clustering of class I pMHC molecules bearing different peptides on the surfaces of target cells (29). Peptide-specific pMHC clustering required endogenous expression (i.e., it was not observed following exogenous peptide pulsing), and it preceded export to the cell surface (i.e., it was detectable in the Golgi apparatus).…”