Clonal anergy induced in a CD8+ hapten-specific cytotoxic T-cell clone by an altered hapten-peptide ligand

The important role of non-covalent drug-protein interactions in drug hypersensitivity reactions

Drug hypersensitivity reactions (DHR) are heterogeneous and unusual immune reactions with rather unique clinical presentations. Accumulating evidence indicates that certain non-covalent drug-protein interactions are able to elicit exclusively effector functions of antibody reactions or complete T-cell reactions which contribute substantially to DHR. Here, we discuss three key interactions; (a) mimicry: whereby soluble, non-covalent drug-protein complexes ("fake antigens") mimic covalent drug-protein adducts; (b) increased antibody affinity: for example, in quinine-type immune thrombocytopenia where the drug gets trapped between antibody and membrane-bound glycoprotein; and (c) p-i-stimulation: where naïve and memory T cells are activated by direct binding of drugs to the human leukocyte antigen and/or T-cell receptors. This transient drug-immune receptor interaction initiates a polyclonal T-cell response with mild-to-severe DHR symptoms. Notable complications arising from p-i DHR can include viral reactivations, autoimmunity, and multiple drug hypersensitivity. In conclusion, DHR is characterized by abnormal immune stimulation driven by non-covalent drug-protein interactions. This contrasts DHR from "normal" immunity, which relies on antigen-formation by covalent hapten-protein adducts and predominantly results in asymptomatic immunity.

On Peptides and Altered Peptide Ligands: From Origin, Mode of Action and Design to Clinical Application (Immunotherapy)

T lymphocytes equipped with clonotypic T cell antigen receptors (TCR) recognize immunogenic peptides only when presented in the context of their own major histocompatibility complex (MHC) molecules. Peptide loading to MHC molecules occurs in intracellular compartments (ER for class I and MIIC for class II molecules) and relies on the interaction of the respective peptides and peptide binding pockets on MHC molecules. Those peptide residues not engaged in MHC binding point towards the TCR screening for possible peptide MHC complex binding partners. Natural or intentional modification of both MHC binding registers and TCR interacting residues of peptides - leading to the formation of altered peptide ligands (APLs) - might alter the way peptides interact with TCRs and hence influence subsequent T cell activation events, and consequently T cell effector functions. This review article summarizes how APLs were detected and first described, current concepts of how APLs modify T cellular signaling, which biological mechanisms might force the generation of APLs in vivo, and how peptides and APLs might be used for the benefit of patients suffering from allergic or autoimmune diseases.

The molecular signature of CD8+ T cells undergoing deletional tolerance

Peripheral tolerance induction is critical for the maintenance of self-tolerance and can be mediated by immunoregulatory T cells or by direct induction of T-cell anergy or deletion. Although the molecular processes underlying anergy have been extensively studied, little is known about the molecular basis for peripheral T-cell deletion. Here, we determined the gene expression signature of peripheral CD8(+) T cells undergoing deletional tolerance, relative to those undergoing immunogenic priming or lymphopenia-induced proliferation. From these data, we report the first detailed molecular signature of cells undergoing deletion. Consistent with defective cytolysis, these cells exhibited deficiencies in granzyme up-regulation. Furthermore, they showed antigen-driven Bcl-2 down-regulation and early up-regulation of the proapoptotic protein Bim, consistent with the requirement of this BH3-only protein for peripheral T-cell deletion. Bim up-regulation was paralleled by defective interleukin-7 receptor alpha (IL-7Ralpha) chain reexpression, suggesting that Bim-dependent death may be triggered by loss of IL-7/IL-7R signaling. Finally, we observed parallels in molecular signatures between deletion and anergy, suggesting that these tolerance pathways may not be as molecularly distinct as previously surmised.

Derivation and fluidity of acutely induced dysfunctional CD8+ T cells

Dysfunctional CD8(+) T (T(CD8(+))) cells lacking cytokine production have been identified in many viral infections, but their genesis is not well understood. Established results indicate that such cells could be either high avidity that enter a refractory state due to overstimulation or low avidity that are only partially stimulated. Using an acute, resolving infection model that results in rapid production of dysfunctional cells, we show that this IL2 unresponsive phenotype emerges from the low end of the avidity spectrum and is characterized by broad TCR usage and a reduced proliferation rate. Furthermore, the dysfunctional population is extremely fluid, being sustained by high Ag dose but virtually eliminated following low dose boosting. Together, these results suggest that persistence of dysfunctional cells generated in this manner depends upon continual exposure to high Ag levels and that such cells may ultimately predominate if functional cells become exhausted.

Enhanced levels of costimulation lead to reduced effector/memory CD8+ T cell functionality

The role of different levels of costimulation in conjunction with signal 1 in the activation of memory CD8+ T cells remains elusive. In this study, we demonstrate, in a mouse model with the influenza nucleoprotein epitope NP68, that mouse early memory (effector/memory) CD8+ T cells that were generated with high levels of costimulation have reduced CTL functionality compared with those that were generated with low levels of costimulation. This reduction is associated with increased phosphorylation of the negative regulatory site 292 on Zap70 and a decrease in granzyme B levels. Furthermore, we show that enhanced costimulation reduces proliferation and cytokine production of effector/memory CD8+ T cells in response to intermediate and weak TCR stimulation, in contrast to previously described positive effects of costimulation on naive CD8+ T cells. This effect is associated with the expression of ICAM-1 on APCs. Together, our results indicate that enhanced costimulation can lead to reduced functionality in effector/memory CD8+ T cells. This compromised effector function of effector/memory CD8+ T cells in response to high levels of costimulation can have important implications for designing immunotherapeutic strategies to enhance immune responses.

Differences in pairing and cluster formation of T cell receptor α- and β-chains in T cell clones and fusion hybridomas

The questions of T cell receptor (TCR) clustering and preferential pairing of TCR alpha- and beta-chains are discussed controversially. We here describe the rare case of a non-pairing TCR alpha-TCR beta combination detected in the murine T cell hybridoma Hy-E6. Of its two TCR alpha-chains (Valpha3.2, Vbeta17) and one Vbeta16-chain only the Valpha17/Vbeta16 TCR is exposed on the surface, despite intracellular expression of Valpha3.2 protein. The lack of Valpha3.2/Vbeta16 pairing was confirmed by TCR transfections. Surprisingly, however, the parental T cell clone CTL-E6 expressed both alpha-chains on its plasma membrane. Different size distribution of TCR clusters in CTL-E6 versus Hy-E6 and transfectants as determined by Blue-Native gel electrophoresis indicated differences in the supra-molecular TCR assembly as one possible reason for this phenomenon. Our data further reveal that the nominal specificity of CTL-E6 for the fully agonistic trinitrophenyl (TNP) modified peptide M4L-TNP was specifically mediated by the trimeric Valpha3.2/Valpha17/Vbeta16 TCR of CTL-E6. In contrast, the Valpha17/Vbeta16 combination in Hy-E6 only conferred specificity for the cross-reactive partial agonist O4-TNP. Both specificities are H-2Kb-restricted and, hence, appear to be positively selected. The differences in TCR clustering in CTL and hybridoma might indicate differences in the reception and transmission of TCR-signals between these two cell types.

T Lymphocyte-Mediated Immune Responses to Chemical Haptens and Metal Ions: Implications for Allergic and Autoimmune Disease

Chemical haptens and metal ions interact with proteins and thereby become recognizable by T and B lymphocytes. They induce the production of proinflammatory cytokines and chemokines by various cell types due to triggering of innate immune responses. This is an important prerequisite for the activation of the adaptive immune system and the development of diseases like allergic contact dermatitis and adverse drug and autoimmune reactions. Our increasing knowledge about the molecular basis of hapten and metal ion recognition by T cells and about the pathomechanisms of contact hypersensitivity and chemical-induced autoimmune reactions allows concomitant progress in the development of modern strategies for immunotherapy and will hopefully enable more specific intervention in hapten- and metal ion-induced human diseases in the future.