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BACKGROUND: It has been shown that drugs comprise a group of non-peptide antigens that can be recognized by human T cells in the context of HLA class II and that this recognition is involved in allergic reactions. Recent studies have demonstrated a MHC-restricted but processing- and metabolism-independent pathway for the presentation of allergenic drugs such as lidocaine and sulfamethoxazole (SMX) to drug-specific T cells. However, there is little information so far on the precise molecular mechanisms of this non-covalent drug presentation. OBJECTIVE: The aim of this study was to evaluate the requirements for a specific peptide occupying the groove of the MHC class II molecule for the efficient presentation of non-covalently bound drugs to CD4+ T cells. METHODS: We analysed the effect of coincubation or prepulse of antigen presenting cells (APC) with different peptides on the proliferative responses of SMX-specific CD4+ T cell clones. In a second series of experiments, we eluted HLA-bound peptides from the surface of antigen presenting cells by mild acid treatment. Successful removal of peptides was tested directly using labelled peptides and functionally by monitoring activation and proliferation of peptide-specific T cell clones. Finally, the presentation of SMX to SMX-specific T cell clones before and after elution of MHC class II bound peptides was tested. RESULTS: We found that neither peptide coincubation nor peptide prepulse of APC altered the proliferative response of SMX-specific T cells. APC treated with the acid for a short time retained cell viability, MHC class II expression and antigen presenting cell function. However, defined peptides could be eluted from surface MHC class II molecules nearly quantitatively. Nevertheless, the chemically non-reactive drug SMX could still be presented to specific T cells independent of the presence of distinct self-peptides. CONCLUSION: Our data suggest that small molecules like drugs can bind to a multitude of HLA-bound peptides or that, similar to superantigens, they might bind directly to HLA.

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BACKGROUND: The most frequent side-effects of drug therapy are skin eruptions. Their pathomechanism is rather unclear. OBJECTIVE: In this prospective study we investigated the T cell activation and drug specificity in different forms of drug-induced exanthemas from 22 patients. METHODS: During acute drug allergy, liver parameters and T cell subset activation in the circulation (up-regulation of CD25 and HLA-DR) were evaluated and skin biopsies of the acute lesion performed. After recovery, the causative drug was identified by lymphocyte transformation (LTT) and scratch-patch tests. RESULTS: Seventeen of 22 (17/22) patients had maculo-papular exanthema, 4/22 bullous exanthema and 1/22 urticaria. The causative drugs were mainly antibiotics, anti-epileptics and anti-hypertensives. Up-regulation of HLA-DR on circulating CD4(+) and/or CD8(+) T cells was detected in 17 patients, being most marked in patients with bullous reactions or hepatic involvement. The LTT was positive in 14/21 analysed and the patch test in 7/15. All patients showed lymphocytic infiltration in the skin biopsy of the acute lesion. Generally CD4(+) T cells dominated; a higher percentage of circulating CD8(+) T cells was found in patients with bullous skin reactions or hepatic involvement. CONCLUSION: Our data demonstrate activation and drug specificity of T cells in drug-induced skin eruptions. A predominant CD8(+) T cell activation leads to more severe (bullous) skin symptoms or liver involvement, while predominant activation of CD4(+) cells elicits mainly maculo-papular reactions.

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It has been well established that T cells can recognize small mol. wt compounds such as drugs. Results from previous studies revealing a high heterogeneity and cross-reactivity of drug-specific T cell clones (TCC) in individual patients prompted us to analyze the degeneracy of drug-reactive TCR in detail. Hence, we analyzed the MHC restriction pattern of a panel of 100 drug-specific TCC isolated from different drug-allergic donors. We found that 28 of the tested clones showed an MHC allele-unrestricted drug recognition. Most of these clones were at the same time highly drug specific, i.e. they could only be stimulated by the original drug and not by any drug derivatives. In contrast, TCC with the ability to interact with different drug derivatives displayed a clearly MHC allele-restricted drug recognition. Therefore, we concluded that the TCR of these clones is mainly interacting with side chains of the appropriate drug molecules and hence able to tolerate alterations in the MHC molecule. Moreover, we tested all clones for additional alloreactivity and found that 27 clones could be stimulated by a self-MHC--peptide--drug complex as well as by a non-self-MHC--peptide complex. This cross-reactivity with allogeneic MHC molecules was substantially higher in drug-specific TCC compared to tetanus toxoid-specific clones from the same donors. This suggests that from the point of view of drug-specific TCR, non-self-MHC--peptide complexes have a higher incidence to mimic the 'original' self-MHC--peptide-drug complex and this may occur for TCR recognizing self-MHC--pathogen-derived peptide complexes. Finally, the biological functions of bispecific TCC were not influenced by the nature of the stimulating ligand. Both drug as well as allogeneic stimulation led to similar reaction patterns in the analyzed TCC.

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1. Hypersensitivity to the drug sulfamethoxazole (SMX) is thought to be a consequence of bioactivation to the hydroxylamine metabolite (SMX-NHOH) and further oxidation to the ultimate reactive metabolite, nitroso-sulfamethoxazole (SMX-NO). SMX-NO covalently modifies self proteins which in turn might be recognized as neo-antigens by T-cells. The antioxidant glutathione (GSH) is known to protect cells from reactive metabolites by conjugation and subsequent dissociation to SMX-NHOH and/or SMX. 2. To study the reactivity of T-cells to SMX metabolites and their respective role in the generation of drug-specific T-cells, we analysed the effect of GSH on the response of PBMC to SMX and its metabolites SMX-NHOH and SMX-NO. Furthermore, we monitored the proliferative response of drug-specific T-cell clones in the presence or absence of GSH. 3. We found that addition of GSH to peripheral blood mononuclear cells had no effect on the SMX-specific response but enhanced the proliferation to SMX-metabolites. The response of SMX-NO-specific T-cell clones was abrogated when GSH was present during the covalent haptenation of antigen presenting cells (APC). Conversely, SMX-specific T-cell clones gained reactivity through the conversion of SMX-NO to the parent drug by GSH. While GSH had no effect on the initial activation of T-cell clones, it prevented covalent binding to APCs, reduced toxicity and thereby led to proliferation of drug-specific T-cells to non-reactive drug metabolites. 4. Our data support the concept that in allergic individuals T-cells recognize the non-covalently bound parent drug rather than APC covalently modified by SMX-NO.

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The recognition of the antibiotic sulfamethoxazole (SMX) by T cells is usually explained with the hapten-carrier model. However, recent investigations have revealed a MHC-restricted but processing- and metabolism-independent pathway of drug presentation. This suggested a labile, low-affinity binding of SMX to MHC-peptide complexes on APC. To study the role of covalent vs noncovalent drug presentation in SMX allergy, we analyzed the proliferative response of PBMC and T cell clones from patients with SMX allergy to SMX and its reactive oxidative metabolites SMX-hydroxylamine and nitroso-SMX. Although the great majority of T cell clones were specific for noncovalently bound SMX, PBMC and a small fraction of clones responded to nitroso-SMX-modified cells or were cross-reactive. Rapid down-regulation of TCR expression in T cell clones upon stimulation indicated a processing-independent activation irrespective of specificity for covalently or noncovalently presented Ag. In conclusion, our data show that recognition of SMX presented in covalent and noncovalent bound form is possible by the same TCR but that the former is the exception rather than the rule. The scarcity of cross-reactivity between covalently and noncovalently bound SMX suggests that the primary stimulation may be directed to the noncovalently bound SMX.

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In recent years the involvement of T cells in allergic reactions to drugs has been well established. However, several molecular aspects of drug recognition by specific T cells remain still unclear. This review will discuss the known pathways of drug presentations by antigen presenting cells, the recognition of MHC/peptide/drug complexes by specific T-cell receptors, and the activation mechanism of drug-specific T cells.

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Patients with drug allergy show a specific immune response to drugs. Chemically nonreactive drugs like, for example, local anesthetics are directly recognized by alphabeta+ T cells in an HLA-DR restricted way, as neither drug metabolism nor protein processing is required for T cell stimulation. In this study we identified some of the structural requirements that determine cross-reactivity of T cells to local anesthetics, with the aim to improve the molecular basis for the selection of alternatives in individuals sensitized to a certain local anesthetic and to better understand presentation and T cell recognition of these drugs. Fifty-five clones (52 lidocaine specific, three mepivacaine specific from two allergic donors) were analyzed. Stimulatory compounds induced a down-regulation of the T cell receptor, demonstrating that these non-peptide antigens are recognized by the T cell receptor itself. A consistent cross-reactivity between lidocaine and mepivacaine was found, as all except one lidocaine specific clone proliferated to both drugs tested. Sixteen chemically related local anesthetics (including ester local anesthetics, OH- and desalkylated metabolites) were used to identify structural requirements for T cell recognition. Each of the four clones examined in detail was uniquely sensitive to changes in the structures of the local anesthetic: clone SFT24, i.e., did not recognize any of the tested OH- or desalkylated metabolites, while the clone OFB2 proliferated to all OH-metabolites and other differently modified molecules. The broadly reactive clone OFB2 allowed us to propose a model, suggesting that the structure of the amine side chain of local anesthetics is essential for recognition by the T cell receptor.

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Drugs like sulfamethoxazole (SMX) or lidocaine can be presented to specific human alphabeta+ T cell clones (TCC) by undergoing a noncovalent association with MHC-peptide complexes on HLA-matched APCs. For a better understanding of the molecular basis of the recognition of such drugs by specific TCC, we investigated 1) the fine specificity of the recognizing TCR, 2) the dose-response relationship for the induction of proliferation or cytokine production, and 3) the mechanism of TCR triggering. For that purpose, we tested the reactivity of 11 SMX-specific CD4+ TCC and 2 SMX-specific CD8+ TCC to a panel of 13 different sulfonamide derivatives bearing the same core structure. Five of 13 clones recognized only SMX, while all other clones were responding to as many as 6 different compounds. Some of the compounds needed up to two orders of magnitude higher concentrations than SMX to stimulate TCC, thereby displaying features of weak agonists. Different clones showed clear differences in the minimal drug concentration required for the induction of a proliferative response. Therefore, weaker or stronger agonistic properties were not a characteristic of a given sulfonamide derivative but rather an intrinsic property of the reacting TCR. Finally, the number of down-regulated TCRs was a logarithmic function of the ligand concentration, implicating that specific T cells were activated by serial TCR engagement. Our data demonstrate that, despite the special way of presentation, nonpeptide Ag like drugs appear to interact with the TCR of specific T cells in a similar way as peptide Ags.

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The activation of CD4+ T lymphocytes upon Ag stimulation plays a critical role in adverse immune responses including drug-specific hypersensitivity reactions. We examined the modulation of T cell phenotype induced by hapten-specific stimulation using the model of beta-lactam antibiotics such as penicillin G (Pen G), Pen V, and ampicillin (Amp). When PBMC of donors suffering from hypersensitivity reactions against beta-lactams were stimulated in vitro with different doses of Pen G, a preferential expansion of IL-4-producing TCR alphabeta+ cells was detected. A panel of T cell clones was then prepared from Pen G-specific lines after two cycles of restimulation with the hapten. For the majority of these clones, we found that high doses of Pen G induced optimal IL-4 secretion, whereas the amount of IFN-gamma secreted was inversely correlated with the dose of Pen G, thus leading to a hapten-inducible shift of the functional phenotypes for some of the clones. Finally, Pen V and Amp were used to modulate different Ag-induced immune responses. We found that Amp had no influence on the cytokine pattern induced by specific Ag or mitogens. In contrast, Pen V inhibited the secretion of IFN-gamma, but not IL-4, most likely by Ag-independent mechanisms. This last finding may open new applications for immune intervention in those diseases in which polarized Th1 responses are involved in the development of the pathology.

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Drugs are non-peptide antigens that can be recognized by specific T cells. It has been thought for many years that small molecular compounds can only be stimulating for T cells after covalent binding to MHC-embedded peptides. As most drug-specific T cell clones can react to glutaraldehyde fixed antigen presenting cells (APC), recognition of drugs by specific T cells does not require prior uptake and processing of haptenated proteins by APC. In fact, activated T cell clones can recognize drugs associated with the MHC-peptide complex in a non-covalent way. Such a binding is reminiscent of superantigen stimulations of T cells.

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T cell recognition of drugs is explained by the hapten-carrier model, implying covalent binding of chemically reactive drugs to carrier proteins. However, most drugs are nonreactive and their recognition by T cells is unclear. We generated T cell clones from allergic individuals specific to sulfamethoxazole, lidocaine (nonreactive drugs), and cef-triaxone (per se reactive beta-lactam antibiotic) and compared the increase of intracellular free calcium concentration ([Ca2+]i) and the kinetics of T cell receptor (TCR) downregulation of these clones by drug-specific stimulations. All drugs tested induced an MHC-restricted, dose- and antigen-presenting cell (APC)-dependent TCR downregulation on specific CD4(+) and CD8(+) T cell clones. Chemically nonreactive drugs elicited an immediate and sustained [Ca2+]i increase and a rapid TCR downregulation, but only when these drugs were added in solution to APC and clone. In contrast, the chemically reactive hapten ceftriaxone added in solution needed > 6 h to induce TCR downregulation. When APC were preincubated with ceftriaxone, a rapid downregulation of the TCR and cytokine secretion was observed, suggesting a stable presentation of a covalently modified peptide. Our data demonstrate two distinct pathways of drug presentation to activated specific T cells. The per se reactive ceftriaxone is presented after covalent binding to carrier peptides. Nonreactive drugs can be recognized by specific alphabeta+ T cells via a nonconventional presentation pathway based on a labile binding of the drug to MHC-peptide complexes.

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T cells recognize peptide and non-peptide antigens. Drugs represent typical examples of non-peptide antigens. The majority of drug-specific T cells are alphabeta+ TCR T cells and are MHC class I or II restricted. Here we show the existence of drug (lidocaine)-specific T cell clones which proliferate in the presence of antigen-presenting cells (APC) with different HLA alleles. Two clones (SFT24 and E20) were analyzed in detail. They show a narrow dose-dependent proliferation to lidocaine, but not to procaine. With the use of a panel of HLA-typed allogeneic APC, we observed that certain allogeneic APC plus lidocaine lead to a similar, others to partial and some to no proliferation of the lidocaine-specific T cell clones. An APC-independent proliferation could be excluded since both clones proliferated only marginally without APC and increasing the number of APC resulted in a higher proliferation. Blocking experiments with anti-DP, -DQ and -DR antibodies showed that lidocaine is presented in a HLA-DR-restricted way both with autologous or allogeneic APC. Mouse fibroblasts transfected with an allogeneic HLA-DRB1*01 but not HLA-DR-negative mouse fibroblasts could serve as presenting cells. Fixation of APC did not hamper drug presentation, but pulsing of APC with the drug was not possible, indicating that processing is not required and that lidocaine binds in an unstable way to the MHC-peptide complex. This degenerate drug recognition has certain features of superantigen recognition, such as the ability of drugs to bind from the outside to multiple HLA-DR alleles. Such features of drug recognition may open new therapeutic possibilities to intervene with TCR-MHC interactions in a selective way.

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To analyze whether and how T cells are involved in drug allergies, we analyzed the drug-induced activation of T cell subsets, T cell receptor V-beta usage and cytokine secretion of T cells from the peripheral blood of drug-allergic individuals. The specificity of the T cells was demonstrated by specific restimulation of drug specific clones. We found that drugs which do not need to be metabolized to become immunogenic (haptens like penicillin G) can stimulate CD4+ and CD8+ T cells in vitro. The T cell response to penicillin can be oligoclonal (use of a certain T cell receptor Vbeta only) or polyclonal. Only polyclonal T cell lines were cross-reactive with other beta-lactam antibiotics. Sulfamethoxazole and lidocaine are thought to gain their ability to bind to proteins by intracellular drug metabolism. They were found to stimulate CD4+ and CD8+ T cells in vitro, and some reactive T cell lines were oligoclonal. The majority of lidocaine-specific clones secreted rather high amounts of IL-5 and IL-4 after PMA/ionomycin stimulations (Th2-like), but some CD4+ and all CD8+ clones had a Th1-like phenotype (high INF-gamma and TNF-alpha). The data clearly demonstrate the existence of drug-specific alphabeta+ T cells in the circulation of drug-allergic individuals and reveal a great heterogeneity of T-cell-mediated responses. Further studies are needed to correlate the type of T cell response to the clinical picture, which can be quite heterogeneous.

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To investigate the cellular immune response to the drug lidocaine, we generated T cell lines and clones from the peripheral blood of four patients with proven allergy to lidocaine. The patients had contact dermatitis after topical application of lidocaine, and local swelling or generalized erythema exudativum multiforme after submucosal/subcutaneous injection of lidocaine. Two of three lidocaine-specific T cell lines were oligoclonal and one even became monoclonal, while the simultaneously analyzed immune response to tetanus toxoid was polyclonal. The lidocaine-specific T cell lines cross-reacted to mepivacaine, but not to other local anesthetics (bupivacaine, procaine, oxybuprocaine, and tetracaine). The majority of reactive T cells belonged to the CD4 cell lineage and were MHC class II restricted, but cloning also revealed some MHC class I-restricted CD8+ clones. A total of 2 of 56 lidocaine-specific T cell clones were CD4-CD8- and expressed TCR-gammadelta. The majority of 13 analyzed CD4 clones produced a rather polarized cytokine pattern, with a dominance of Th2-like cytokines showing a high IL-5 production. In addition, three CD4+ and all CD8+ (n = 7) clones secreted high IFN-gamma and low levels of IL-5/IL-4 (Th1-like). The data illustrate that a drug that sensitizes via the skin elicits a heterogeneous T cell response. The high IL-5 production and the participation of specific CD4+CD8+ and even gammadelta+ T cells appear to be distinguishing features of this hapten-specific immune response.

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OBJECTIVE AND DESIGN: To better understand how T cells react to small compounds, we investigated the in vitro T cell reactivity to drugs from drug allergic patients. MATERIAL AND SUBJECTS: Peripheral blood mononuclear cells (PBMC) of three drug allergic individuals were stimulated in vitro by different drugs. METHODS: Proliferation was assayed by 3H-thymidine incorporation. Upregulation of activation parameter on T cells was done by immunofluorescence and cytokine release determined via standard ELISA. RESULTS: Drugs can stimulate both CD4 and CD8 T-cell subsets. PenG-stimulated PBMC showed a heterogenous cytokine pattern and clones secreted high amounts of INF gamma. In contrast, sulfamethoxazole and lidocaine-stimulated PBMC secreted high levels of IL-5 and lidocaine-specific clones can be Th1 or Th2-like. CONCLUSION: Drug specific T cells play a pivotal role in drug hypersensitivity reactions, both by regulating the immune response and probably also as specific effector cells with different patterns of cytokine release.

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