Direct, MHC-dependent presentation of the drug sulfamethoxazole to human alphabeta T cell clones

T cells can recognize small molecular compounds like drugs. It is thought that covalent binding to MHC bound peptides is required for such a hapten stimulation. Sulfamethoxazole, like most drugs, is not chemically reactive per se, but is thought to gain the ability to covalently bind to proteins after intracellular drug metabolism. The purpose of this study was to investigate how sulfamethoxazole is presented in an immunogenic form to sulfamethoxazole-specific T cell clones. The stimulation of four CD4(+) and two CD8(+) sulfamethoxazole-specific T cell clones by different antigen-presenting cells (APC) was measured both by proliferation and cytolytic assays. The MHC restriction was evaluated, first, by inhibition using anti-class I and anti-class II mAb, and second, by the degree of sulfamethoxazole-induced stimulation by partially matched APC. Fixation of APC was performed with glutaraldehyde 0.05%. The clones were specific for sulfamethoxazole without cross-reaction to other sulfonamides. The continuous presence of sulfamethoxazole was required during the assay period since pulsing of the APC was not sufficient to induce proliferation or cytotoxicity. Stimulation of clones required the addition of MHC compatible APC. The APC could be fixed without impairing their ability to present sulfamethoxazole. Sulfamethoxazole can be presented in an unstable, but MHC-restricted fashion, which is independent of processing. These features are best explained by a direct, noncovalent binding of sulfamethoxazole to the MHC-peptide complex.

HLA-restricted, processing- and metabolism-independent pathway of drug recognition by human alpha beta T lymphocytes

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.

Recognition of sulfamethoxazole and its reactive metabolites by drug-specific CD4+ T cells from allergic individuals

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.

Diagnosis of sulfonamide hypersensitivity reactions by in-vitro "rechallenge" with hydroxylamine metabolites

STUDY OBJECTIVE

To determine whether differences in in-vitro detoxification of sulfonamide-reactive metabolites can be detected among the lymphocytes from controls, patients with sulfonamide hypersensitivity reactions, and patients with nonhypersensitivity reactions to the sulfonamide agents.

DESIGN

In-vitro toxicity assay on lymphocytes.

SETTING

Clinics for adverse drug reactions in an adult and pediatric tertiary care center.

PATIENTS

Peripheral blood lymphocytes were obtained from 46 normal volunteers and 76 patients referred to the clinic for assessment of adverse drug reactions to sulfonamide agents. Thirty-one patients had clinical histories consistent with a diagnosis of hypersensitivity reaction, whereas 45 patients had clinical histories felt to be inconsistent with a diagnosis of hypersensitivity reaction.

INTERVENTIONS

Lymphocytes were assayed with tetrazolium to determine toxicity from the hydroxylamine of sulfamethoxazole.

MEASUREMENTS AND MAIN RESULTS

The lymphocytes from patients with a history of hypersensitivity reactions showed markedly increased toxicity across a tenfold-concentration toxicity-concentration curve compared with those from controls and patients with a history of nonhypersensitivity reactions. These differences were highly significant (P less than 0.01). No difference was found between the toxicity shown by the lymphocytes from controls and that shown by the lymphocytes from patients with a history of nonhypersensitivity reactions.

CONCLUSIONS

Metabolic differences in the production and detoxification of reactive metabolites of sulfonamide agents are important determinants of hypersensitivity reactions to these agents. These results suggest that the hydroxylamine derivative of sulfamethoxazole may be a reactive metabolite mediating these reactions. Sulfonamide hydroxylamines are useful in the diagnosis and study of the pathogenesis of hypersensitivity reactions to sulfonamide agents.

Antigenicity and immunogenicity of sulphamethoxazole: demonstration of metabolism-dependent haptenation and T-cell proliferation in vivo

Sulphamethoxazole has been associated with the occurrence of hypersensitivity reactions. There is controversy as to whether the immune response is metabolism-dependent or -independent. We have therefore investigated the site of antigen formation and the nature of the drug signal presented to the immune system in vivo. Male Wistar rats were dosed with sulphamethoxazole, sulphamethoxazole hydroxylamine or nitroso sulphamethoxazole. Antigen formation on cell surfaces was determined by flow cytometry using a specific anti-sulphamethoxazole antibody. Immunogenicity was determined by assessment of ex vivo T-cell proliferation. Administration of nitroso sulphamethoxazole, but not sulphamethoxazole or sulphamethoxazole hydroxylamine, resulted in antigen formation on the surface of lymphocytes, splenocytes and epidermal keratinocytes, and a strong proliferative response of splenocytes on re-stimulation with nitroso sulphamethoxazole. Rats dosed with sulphamethoxazole or sulphamethoxazole hydroxylamine did not respond to any of the test compounds. CD4+ or CD8+ depleted cells responded equally to nitroso sulphamethoxazole. The proliferative response to nitroso sulphamethoxazole was seen even after pulsing for only 5 min, and was not inhibited by glutathione. Responding cells produced IFN-gamma, but not IL-4. Haptenation of cells by sulphamethoxazole hydroxylamine was seen after depletion of glutathione by pre-treating the rats with diethyl maleate. Splenocytes from the glutathione-depleted sulphamethoxazole hydroxylamine-treated rats responded weakly to nitroso sulphamethoxazole, but not to sulphamethoxazole or sulphamethoxazole hydroxylamine. Dosing of rats with sulphamethoxazole produced a cellular response to nitroso sulphamethoxazole (but not to sulphamethoxazole or its hydroxylamine) when the animals were primed with complete Freund's adjuvant. These studies demonstrate the antigenicity of nitroso sulphamethoxazole in vivo and provide evidence for the role of drug metabolism and cell surface haptenation in the induction of a cellular immune response in the rat.

The danger hypothesis--potential role in idiosyncratic drug reactions

Idiosyncratic or type B reactions are characterised by their unpredictability and lack of simple dose-dependency. They occur in a small proportion of patients, and usually the predisposing factors are unknown. A proportion of, but not all, idiosyncratic reactions are immune-mediated. Our understanding of immune-mediated reactions is based on the hapten hypothesis, which requires drug bioactivation, covalent binding to proteins, followed by uptake, antigen processing and a polyclonal immune response. The recently proposed 'danger hypothesis' can be considered to be additive to the hapten hypothesis. The hypothesis states that the immune system only responds when it detects danger. If no danger is detected, tolerance results. Thus, stimulation of an immune response to a drug-protein conjugate (signal 1) requires the presence of co-stimulatory signals and cytokines (signals 2 and 3), which propagate and determine the type of immune response. The nature of the danger signal is poorly defined, and has been proposed to include different forms of stress including chemical, physical and viral. Indeed, there are several examples where the frequency of drug hypersensitivity is increased in the presence of a viral infection, most notably in HIV disease. Nevertheless, this clinical evidence has to be regarded as being circumstantial and more direct experimental evidence is required to understand the role of 'danger' in the overall pathogenesis of drug hypersensitivity reactions.

Sulfamethoxazole and its metabolite nitroso sulfamethoxazole stimulate dendritic cell costimulatory signaling

Different signals in addition to the antigenic signal are required to initiate an immunological reaction. In the context of sulfamethoxazole allergy, the Ag is thought to be derived from its toxic nitroso metabolite, but little is known about the costimulatory signals, including those associated with dendritic cell maturation. In this study, we demonstrate increased CD40 expression, but not CD80, CD83, or CD86, with dendritic cell surfaces exposed to sulfamethoxazole (250-500 microM) and the protein-reactive metabolite nitroso sulfamethoxazole (1-10 microM). Increased CD40 expression was not associated with apoptosis or necrosis, or glutathione depletion. Covalently modified intracellular proteins were detected when sulfamethoxazole was incubated with dendritic cells. Importantly, the enzyme inhibitor 1-aminobenzotriazole prevented the increase in CD40 expression with sulfamethoxazole, but not with nitroso sulfamethoxazole or LPS. The enzymes CYP2C9, CYP2C8, and myeloperoxidase catalyzed the conversion of sulfamethoxazole to sulfamethoxazole hydroxylamine. Myeloperoxidase was expressed at high levels in dendritic cells. Nitroso sulfamethoxazole immunogenicity was inhibited in mice with a blocking anti-CD40L Ab. In addition, when a primary nitroso sulfamethoxazole-specific T cell response using drug-naive human cells was generated, the magnitude of the response was enhanced when cultures were exposed to a stimulatory anti-CD40 Ab. Finally, increased CD40 expression was 5-fold higher on nitroso sulfamethoxazole-treated dendritic cells from an HIV-positive allergic patient compared with volunteers. These data provide evidence of a link between localized metabolism, dendritic cell activation, and drug immunogenicity.

In vitro cytotoxicity as a marker of hypersensitivity to sulphamethoxazole in patients with HIV

Hypersensitivity to trimethoprim-sulphamethoxazole (TMP-SMX) in patients with HIV infection may be a result of either immune dysregulation, a direct cytotoxicity of the SMX-hydroxylamine metabolite (SMX-HA) (rather than SMX per se), or glutathione deficiency. We evaluated the in vitro cytotoxicity of SMX and SMX-HA to peripheral blood mononuclear cells (PBMC) of HIV-infected subjects to determine if the degree of in vitro cytotoxicity is associated with hypersensitivity, whether glutathione inhibits cytotoxicity, and whether in vitro cytotoxicity is predictive for the development of hypersensitivity. Given that fever is often a prominent feature of hypersensitivity, we also assessed whether SMX or SMX-HA could induce the in vitro production of IL-1 beta, IL-6 or tumour necrosis factor-alpha (TNF-alpha) by PBMC. The cytotoxicities of SMX and SMX-HA to PBMC were assessed in 45 HIV-infected patients with prior TMP-SMX therapy, and in eight HIV- controls. Twelve HIV-infected subjects were studied prospectively before primary Pneumocystis carinii pneumonia (PCP) therapy or rechallenge with TMP-SMX in previously hypersensitive subjects. Cytokine production was measured in four hypersensitive and two non-hypersensitive HIV-infected subjects, and three HIV-uninfected controls. The cytotoxicity of SMX-HA to PBMC was significantly greater in the 22 HIV-infected patients with prior hypersensitivity than both the 23 HIV-infected patients without hypersensitivity and the control group. Cytotoxicity was significantly reduced by glutathione only in the hypersensitive group. SMX did not induce cytotoxicity in any group. In 12 subjects studied prospectively, SMX-HA cytotoxicity was also significantly greater in those with subsequent hypersensitivity. Exposure of PBMC to SMX-HA resulted in a modest increase in the production of IL-6, IL-1 beta and TNF-alpha, although no major difference was detected between subjects with or without hypersensitivity. These data suggest that SMX-HA and glutathione deficiency are involved in the pathogenesis of hypersensitivity to TMP-SMX in HIV-infected patients, and that in vitro cytotoxicity could be useful in the diagnosis of hypersensitivity and predicting its likelihood.

Immunochemical analysis of sulfonamide drug allergy: identification of sulfamethoxazole-substituted human serum proteins

BACKGROUND

Sulfonamides undergo oxidative metabolism to yield reactive metabolites that haptenate proteins readily. Although it has been shown that sulfonamide metabolites bind covalently to murine microsomes, sulfonamide-conjugated serum proteins have not been analyzed in the peripheral blood of treated individuals.

OBJECTIVE

We hypothesized that during treatment with sulfamethoxazole, intracellular proteins are haptenated by drug metabolites, and some of these are destined for secretion into the serum.

METHODS

Using antibodies specific for sulfamethoxazole and an alkaline phosphatase immunoblotting technique, we attempted to demonstrate the presence of sulfamethoxazole-substituted proteins in the serum of individuals during a course of treatment.

RESULTS

Five days into therapy, serum protein haptenation by sulfamethoxazole was demonstrated in two of the three individuals studied. In addition, Western blot analysis revealed that haptenation is not indiscriminate, but highly selective. A single 30 kd protein is the target of haptenation in all instances. A kinetic analysis revealed that substituted proteins can be detected early, within hours of administration. Moreover, haptenated proteins remain detectable in the serum 48 hours after discontinuation of the drug.

CONCLUSION

The results presented here constitute the first direct evidence that sulfonamides, on being metabolized, covalently haptenate human serum proteins during a course of therapy.

Metabolite-specific (IgG) and drug-specific antibodies (IgG, IgM) in two cases of trimethoprim-sulfamethoxazole-induced immune thrombocytopenia

Two cases of trimethoprim-sulfamethoxazole (TMP-SMX)-induced immune thrombocytopenia are reported in which unusual drug-dependent platelet antibodies were demonstrated by immunofluorescence and enzyme-linked immunosorbent assay. Whereas two distinct sulfamethoxazole-dependent antibodies of the IgG and IgM class were detectable in the serum of one patient, the serum of the other patient contained a platelet antibody exclusively reactive with N-4-acetyl-sulfamethoxazole, a metabolite of sulfamethoxazole. Urine from a healthy volunteer collected after administration of therapeutic doses of TMP-SMX proved to be an appropriate source of ex vivo metabolites for antibody testing. The results of this study stress the role of metabolite-specific antibodies in drug-dependent immune thrombocytopenia and underscore the necessity of including metabolite preparations of drugs in serologic analyses.

Detection of human IgE to sulfamethoxazole by skin testing with sulfamethoxazoyl-poly-L-tyrosine

Adverse reactions to sulfamethoxazole (SMX) occur in 4% to 6% of normal individuals. Many of these reactions resemble immunopathologic reactions, but skin test or in vitro evidence of a role for IgE is limited. Earlier RAST studies in our laboratory provided evidence that the N4-SMX hapten was a major determinant in immediate hypersensitivity reactions to SMX. We tested the hypothesis that IgE to this hapten is present on the mast cells of patients who have experienced immediate hypersensitivity reactions temporally related to exposure to SMX. A multivalent skin test reagent, SMX168-poly-L-tyrosine, and a univalent hapten, SMX-tyrosine, were synthesized. Forty-four patients with histories of allergic reactions to SMX and six subjects who had been exposed to the drug, but who had not reacted, were skin tested. Twenty-seven percent of the history-positive patients were skin test positive. None of the control individuals was positive. The immunologic responses to SMX in three patients who had experienced allergic reactions during SMX/trimethoprim therapy were analyzed in serial skin test and RAST assessments. One to three years after the clinical reactions, IgE to SMX could be demonstrated by skin testing in all three patients with a SMX-poly-L-tyrosine skin test reagent. Skin test reactions were inhibited by the monovalent reagent, SMX-tyrosine, in a dose-dependent manner. SMX-specific IgE antibodies could also be detected by RAST in serum obtained within days of the reactions from two of the three individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug interaction with T-cell receptors: T-cell receptor density determines degree of cross-reactivity

BACKGROUND

Immune-mediated adverse reactions to drugs are often due to T-cell reactivity, and cross-reactivity is an important problem in pharmacotherapy.

OBJECTIVE

We investigated whether chemical inert drugs can stimulate T cells through their T-cell receptor (TCR) and analyzed the cross-reactivities to related compounds.

METHODS

We transfected human TCRs isolated from two drug-reactive T-cell clones (TCCs) by PCR into a TCR-negative mouse T-cell hybridoma. The TCCs were isolated from a patient with drug hypersensitivity to the antibacterial sulfonamide sulfamethoxazole (SMX).

RESULTS

The transfectants reacted to SMX only in the presence of antigen-presenting cells (APCs). Glutaraldehyde-fixed APCs, however, were sufficient to elicit T-cell stimulation, indicating a processing-independent direct interaction of the drug with the TCR and MHC molecule. The transfected hybridomas secreted IL-2 in a drug dose-dependent manner, whereas the degree of reactivity was dependent on the level of TCR expression. One transfectant reacted not only to SMX but also to related sulfonamide compounds. Interestingly, high TCR expression increased cross-reactivity to other structurally related compounds. In addition, SMX-specific TCR cross-reacted only with sulfonamides bearing a sulfanilamide core structure but not with sulfonamides such as celecoxib, furosemide, or glibenclamide.

CONCLUSIONS

These results demonstrate that the T-cell reactivity to drugs is solely determined by the TCR. Moreover, these results show that cross-reactivity of structurally similar compounds correlates with the density of the TCR. Stably transfected T-cell hybridomas may represent a powerful screening tool for cross-reactivity of newly generated sulfonamide-containing compounds such as celecoxib.

Lymphocyte transformation test in drug-induced toxic epidermal necrolysis

Lymphocyte transformation tests (LTT) to drugs remain widely used in drug reactions, despite controversies about their real usefulness. We tested the lymphocytes of 12 patients recovering from a drug-induced Toxic epidermal necrolysis (TEN). There was no difference between the amounts of thymidine incorporated when patients' lymphocytes were cultivated with culprit or innocent drugs. In both situations the lymphocytes from patients reacted like the lymphocytes from controls cultivated with the same panel of drugs. These negative results do not exclude that a hypersensitivity reaction may play a role in the physiopathology of TEN. Anyhow, they clearly indicate that testing lymphocyte transformation to drugs has no practical value in the diagnosis of TEN.

Drugs as allergens: detection and combining site specificities of IgE antibodies to sulfamethoxazole

An immunoassay was developed for the detection of sulfamethoxazole reactive IgE antibodies in the sera of patients who experienced life threatening anaphylactic reactions following the ingestion of co-trimoxazole (trimethoprim and sulfamethoxazole). Patients who had significant levels of sulfamethoxazole reactive IgE antibodies in their sera did not have IgE antibodies that reacted with trimethoprim-Sepharose. Inhibition experiments with a number of sulfonamides to determine the fine structural specificities of the sulfamethoxazole reactive IgE antibodies in three patients revealed that sulfamethoxazole and, depending on the serum, sulfamerazine and sulfamethizole, were the most potent inhibitors of IgE binding, whereas the parent sulfonamide, sulfanilamide, was a very poor inhibitor. From a detailed examination of structure-activity relationships, we concluded that the 5-methyl-3-isoxazolyl group on the sulfamethoxazole molecule was the allergenic determinant for all three patients with the 5-methyl group being particularly important for IgE antibody recognition. The assays for the detection of IgE antibodies to sulfamethoxazole and trimethoprim should prove useful for the diagnosis of immediate hypersensitivity to co-trimoxazole and perhaps for monitoring drug therapy in AIDS patients where a high incidence of adverse reactions to co-trimoxazole has been reported.

High IL-5 production by human drug-specific T cell clones

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.

Negative regulation by PD-L1 during drug-specific priming of IL-22-secreting T cells and the influence of PD-1 on effector T cell function

Activation of PD-1 on T cells is thought to inhibit Ag-specific T cell priming and regulate T cell differentiation. Thus, we sought to measure the drug-specific activation of naive T cells after perturbation of PD-L1/2/PD-1 binding and investigate whether PD-1 signaling influences the differentiation of T cells. Priming of naive CD4(+) and CD8(+) T cells against drug Ags was found to be more effective when PD-L1 signaling was blocked. Upon restimulation, T cells proliferated more vigorously and secreted increased levels of IFN-γ, IL-13, and IL-22 but not IL-17. Naive T cells expressed low levels of PD-1; however, a transient increase in PD-1 expression was observed during drug-specific T cell priming. Next, drug-specific responses from in vitro primed T cell clones and clones from hypersensitive patients were measured and correlated with PD-1 expression. All clones were found to secrete IFN-γ, IL-5, and IL-13. More detailed analysis revealed two different cytokine signatures. Clones secreted either FasL/IL-22 or granzyme B. The FasL/IL-22-secreting clones expressed the skin-homing receptors CCR4, CCR10, and CLA and migrated in response to CCL17/CCL27. PD-1 was stably expressed at different levels on clones; however, PD-1 expression did not correlate with the strength of the Ag-specific proliferative response or the secretion of cytokines/cytolytic molecules. This study shows that PD-L1/PD-1 binding negatively regulates the priming of drug-specific T cells. ELISPOT analysis uncovered an Ag-specific FasL/IL-22-secreting T cell subset with skin-homing properties.

Drug antigenicity, immunogenicity, and costimulatory signaling: evidence for formation of a functional antigen through immune cell metabolism

Recognition of drugs by immune cells is usually explained by the hapten model, which states that endogenous metabolites bind irreversibly to protein to stimulate immune cells. Synthetic metabolites interact directly with protein-generating antigenic determinants for T cells; however, experimental evidence relating intracellular metabolism in immune cells and the generation of physiologically relevant Ags to functional immune responses is lacking. The aim of this study was to develop an integrated approach using animal and human experimental systems to characterize sulfamethoxazole (SMX) metabolism-derived antigenic protein adduct formation in immune cells and define the relationship among adduct formation, cell death, costimulatory signaling, and stimulation of a T cell response. Formation of SMX-derived adducts in APCs was dose and time dependent, detectable at nontoxic concentrations, and dependent on drug-metabolizing enzyme activity. Adduct formation above a threshold induced necrotic cell death, dendritic cell costimulatory molecule expression, and cytokine secretion. APCs cultured with SMX for 16 h, the time needed for drug metabolism, stimulated T cells from sensitized mice and lymphocytes and T cell clones from allergic patients. Enzyme inhibition decreased SMX-derived protein adduct formation and the T cell response. Dendritic cells cultured with SMX and adoptively transferred to recipient mice initiated an immune response; however, T cells were stimulated with adducts derived from SMX metabolism in APCs, not the parent drug. This study shows that APCs metabolize SMX; subsequent protein binding generates a functional T cell Ag. Adduct formation above a threshold stimulates cell death, which provides a maturation signal for dendritic cells.

Non-covalent presentation of sulfamethoxazole to human CD4+ T cells is independent of distinct human leucocyte antigen-bound peptides

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.

Sulfonamide-induced reactions in desensitized patients with AIDS--the role of covalent protein haptenation by sulfamethoxazole

BACKGROUND

Adverse reactions to sulfonamides cause significant morbidity in patients with AIDS. We have demonstrated previously a approximately 40 kd sulfamethoxazole (SMX)-substituted protein in the serum of some individuals treated with SMX.

OBJECTIVE

The purpose of this study was to examine patients with AIDS who had undergone SMX desensitization because of a prior history of SMX allergy for the presence of SMX-haptenated serum proteins and to determine whether these proteins, SMX-specific IgG antibodies, or both predict the development of subsequent clinical reactivity.

METHODS

Four patients with no history of allergy and in whom SMX prophylaxis was initiated and eight patients with AIDS who had undergone SMX desensitization because of prior allergy were evaluated. SMX-conjugated serum proteins were identified with an immunoblotting assay, and SMX-specific IgG antibodies were identified by ELISA inhibition.

RESULTS

One of the four patients receiving SMX prophylactic treatment demonstrated SMX-protein haptenation, none had detectable SMX-specific IgG antibodies, and none developed an SMX-associated reaction during the time in which they were followed. Of the eight patients who underwent SMX desensitization, six (75%) demonstrated SMX-protein haptenation, and three of these six (50%) subsequently developed SMX-induced cutaneous reactions. Only one of these six patients had detectable SMX-specific IgG antibodies. The two individuals who did not demonstrate SMX-protein haptenation have not developed a clinical reaction.

CONCLUSION

These preliminary data suggest that SMX haptenation, but not SMX-specific antibodies, may be important in the development of clinical sensitivity in patients with AIDS who have undergone SMX desensitization.

"Danger" conditions increase sulfamethoxazole-protein adduct formation in human antigen-presenting cells

Antigen-presenting cells (APC) are thought to play an important role in the pathogenesis of drug-induced immune reactions. Various pathological factors can activate APC and therefore influence the immune equilibrium. It is interesting that several diseases have been associated with an increased rate of drug allergy. The aim of this project was to evaluate the impact of such "danger signals" on sulfamethoxazole (SMX) metabolism in human APC (peripheral blood mononuclear cells, Epstein-Barr virus-modified B lymphocytes, monocyte-derived dendritic cells, and two cell lines). APC were incubated with SMX (100 microM-2 mM; 5 min-24 h), in the presence of pathological factors: bacterial endotoxins (lipopolysaccharide and staphylococcal enterotoxin B), flu viral proteins, cytokines [interleukin (IL)-1beta, IL-6, IL-10; tumor necrosis factor-alpha; interferon-gamma; and transforming growth factor-beta], inflammatory molecules (prostaglandin E2, human serum complement, and activated protein C), oxidants (buthionine sulfoximine and H(2)O(2)), and hyperthermia (37.5-39.5 degrees C). Adduct formation was evaluated by enzyme-linked immunosorbent assay and confocal microscopy. SMX-protein adduct formation was time- and concentration-dependent for each cell type tested, in both physiological and danger conditions. A danger environment significantly increased the formation of SMX-protein adducts and significantly shortened the delay for their detection. An additive effect was observed with a combination of danger signals. Dimedone (chemical selectively binding cysteine sulfenic acid) and antioxidants decreased both baseline and danger-enhanced SMX-adduct formation. Various enzyme inhibitors were associated with a significant decrease in SMX-adduct levels, with a pattern varying depending on the cell type and the culture conditions. These results illustrate that danger signals enhance the formation of intracellular SMX-protein adducts in human APC. These findings might be relevant to the increased frequency of drug allergy in certain disease states.

Oral desensitization to trimethoprim-sulfamethoxazole in a patient with acquired immunodeficiency syndrome

Intravenous administration of trimethoprim-sulfamethoxazole (TMS) on three occasions resulted in fever, rash, and wheezing in a 30-year-old man with acquired immunodeficiency syndrome with Pneumocytis carinii pneumonia. Pentamidine administration produced fever, severe myositis, and clinical deterioration, and therefore, desensitization to TMS was attempted. This was done with low doses of oral suspension and then intravenous administration during a period of 60 hours. The patient reacted with fevers, arthralgia, and erythema that cleared 4 days after the desensitization was completed. This single case of successful desensitization to TMS in a patient with acquired immunodeficiency syndrome suggests that the oral route may be useful in similar situations when this drug is urgently needed.

Novel non-labile covalent binding of sulfamethoxazole reactive metabolites to cultured human lymphoid cells

Sulfamethoxazole (SMX) causes rare hypersensitivity syndrome reactions characterized by fever and multi-organ toxicity. Covalent binding of SMX reactive metabolites to cellular proteins has been demonstrated but the link between cytotoxicity and targets of covalent binding has not been explored. We therefore investigated the relationship between covalent binding of the reactive SMX-hydroxylamine (SMX-HA) metabolite, and its cytotoxicity to a hystiocytic lymphoma (U937) cell line. Incubation of U937 cells with 0-1 mM SMX-HA for 3 h resulted in dose-dependent cytotoxicity, as assessed by tetrazolium dye conversion at 24 h. SMX-HA caused dose-dependent covalent binding to cellular proteins as assessed by immunoblotting with SMX antisera at 3 and 24 h. Covalent binding was predominantly to proteins of approximately 45, 59 and 75 kDa, but other targets were also observed. The relative extent of binding to proteins was significantly different from the relative cytotoxicity at 24 h. Further, cells surviving at 24 h also had extensive covalent binding. Covalent binding was observed under reducing (beta-mercaptoethanol) and non-reducing conditions to plasma membrane and microsomal but not cytosolic proteins. This non-labile covalent binding has not been previously reported. These observations suggest that extensive covalent binding does not necessarily lead to cell death, allowing the accumulation of potentially immunogenic drug-protein conjugates. These observations in whole cells may be relevant to the immunopathogenesis of SMX hypersensitivity syndrome reactions.

Sequential assessment of an antidrug antibody response in a patient with a systemic delayed-onset sulphonamide hypersensitivity syndrome reaction

A 19-year-old man was treated with trimethoprim-sulphamethoxazole intermittently over 4 weeks. He developed a rash and fever. Despite treatment with low-dose methylprednisolone, his condition worsened. He developed a confluent erythematous macular eruption, elevated liver enzymes, lymphadenopathy, polyserositis and eosinophilia. A tentative diagnosis of sulphonamide hypersensitivity syndrome reaction (SHSR) was made and a serum sample (acute) was obtained to screen for antibodies associated with SHSR. Intravenous methylprednisolone sodium succinate (250 mg every 6 h for 48 h) was administered. The patient's condition improved, and he was discharged with oral prednisone. A convalescent serum sample was obtained 14 weeks later. By Western blotting and enzyme-linked immunosorbent assay (ELISA), antisulphamethoxazole IgG antibodies were detected in the acute serum sample, supporting the clinical diagnosis of SHSR. Contrary to expectations, antibodies were not detected in the convalescent serum sample by immunoblotting. Antisulphamethoxazole antibodies were detected by ELISA in the convalescent serum, but the titre was decreased approximately 45-fold. One possible explanation for the decrease in antibody concentration in the convalescent sample was the administration of high-dose glucocorticoids to the patient following collection of the acute serum sample.

An immunoassay for the detection of IgE antibodies to trimethoprim in the sera of allergic patients

An immunoassay was developed to detect IgE antibodies to the widely used antibacterial drug trimethoprim. Significant levels of trimethoprim-reactive IgE antibodies were found in the sera of two patients who had experienced life-threatening allergic reactions following administration of a combination of trimethoprim and sulphamethoxazole. No IgE antibodies reactive with sulphamethoxazole were found in the sera of either patient. Inhibition experiments revealed that a high degree of cross-reactivity occurs between the drug-reactive IgE antibodies and two structural analogues of trimethoprim, 6-hydroxy- and 6-chlorotrimethoprim. These experiments also indicated that the combining sites of the trimethoprim-reactive IgE antibodies in the two sera were probably complementary to different parts of the trimethoprim molecule. The assay should supplement skin testing in determining the offending drug in patients with suspected allergic sensitivity to trimethoprim-sulphamethoxazole complex.