Role of T cells in nonimmediate allergic drug reactions

In vitro diagnostics of drug allergies

In vitro diagnostics for drug hypersensitivity reactions distinguish between serological and cellular-based tests. A serological test used for the diagnosis of immediate type reactions is the detection of specific IgE antibodies. The cellular tests include the basophil activation test for immediate type reactions and the lymphocyte transformation test, which is mainly used to detect delayed type hypersensitivity reactions. Further cellular-based tests are the CAST-ELISA and the mast cell activation test. None of the above-mentioned tests can definitively exclude an allergy if the result is negative. In addition, it is important to note that even a positive test result is not necessarily associated with an allergy but has to be interpreted in the clinical context.

Exploring recent advances in drugs severe cutaneous adverse reactions immunopathology

Severe cutaneous adverse reactions to drugs (SCARs) are rare but life-threatening delayed allergies. While they primarily affect the skin, they can also affect internal organs. Accordingly, they present with diverse clinical symptoms that vary not only between SCARs subtypes but also among patients. Despite the availability of topical and systemic treatments, these only address the symptoms and not the cause. To develop more effective therapies, it is necessary to elucidate the complexity of the pathophysiology of SCARs in relation to their severity. In line with the new type IV hypersensitivity reactions nomenclature proposed by the European Academy of Allergy and Clinical Immunology (EAACI), this review highlights the current insights into the intricate immune mechanisms engaged, the interplay between the culprit drug and genetic predisposition in drug presentation mechanisms, but also how external factors, such as viruses, are implicated in SCARs. Their relevance to the development of targeted medicine is also discussed.

Immunological Mechanisms in Cutaneous Adverse Drug Reactions

Adverse drug reactions (ADRs) are an inherent aspect of drug use. While approximately 80% of ADRs are predictable, immune system-mediated ADRs, often unpredictable, are a noteworthy subset. Skin-related ADRs, in particular, are frequently unpredictable. However, the wide spectrum of skin manifestations poses a formidable diagnostic challenge. Comprehending the pathomechanisms underlying ADRs is essential for accurate diagnosis and effective management. The skin, being an active immune organ, plays a pivotal role in ADRs, although the precise cutaneous immunological mechanisms remain elusive. Fortunately, clinical manifestations of skin-related ADRs, irrespective of their severity, are frequently rooted in immunological processes. A comprehensive grasp of ADR morphology can aid in diagnosis. With the continuous development of new pharmaceuticals, it is noteworthy that certain drugs including immune checkpoint inhibitors have gained notoriety for their association with ADRs. This paper offers an overview of immunological mechanisms involved in cutaneous ADRs with a focus on clinical features and frequently implicated drugs.

Diagnostic Value of Oral Provocation Tests in Drug Hypersensitivity Reactions Induced by Nonsteroidal Anti-Inflammatory Drugs and Paracetamol

Oral drug provocation tests (DPT) are the basic diagnostic tool for the detection of hypersensitivity to non-opioid analgesics and for selecting a safe alternative for a patient. They are of great practical importance due to their common use, but the data on the follow-up of patients after negative DPT are still very scarce. We examined the further fate of 164 such adult patients after negative NSAID or paracetamol tests and analyzed which excipients in the studied drugs they could be exposed to after the diagnostic workup. A structured medical interview was performed 32.9 months (mean) after the provocation tests. Of the 164 patients, 131 (79.9%) retook the tested drug and 12 developed another hypersensitivity reaction, giving the estimated negative predictive value of 90.8%. These reactions were induced by acetylsalicylic acid, paracetamol, meloxicam, and diclofenac, and were clinically similar to the initial ones (most commonly urticaria and angioedema). There are 93 generics of these drugs on the local market, containing a total of 33 excipients for which hypersensitivity reactions have been reported. All available generics contain such excipients. Thirty-one patients (20.1%) did not take the previously tested drug again, most often because it was not needed or because they were afraid of another reaction. DPT with analgesics has a high diagnostic performance. A minority of patients had relapsed after reexposure. One of the underestimated reasons for this may be drug excipients provoking a reaction, so it is advisable to use exactly the same medical product that has been negatively tested. Many patients avoid reexposure to a given drug, despite negative tests, therefore very reliable patient education in connection with DPT is highly needed.

Hypersensitivity reactions to small molecule drugs

Drug hypersensitivity reactions induced by small molecule drugs encompass a broad spectrum of adverse drug reactions with heterogeneous clinical presentations and mechanisms. These reactions are classified into allergic drug hypersensitivity reactions and non-allergic drug hypersensitivity reactions. At present, the hapten theory, pharmacological interaction with immune receptors (p-i) concept, altered peptide repertoire model, and altered T-cell receptor (TCR) repertoire model have been proposed to explain how small molecule drugs or their metabolites induce allergic drug hypersensitivity reactions. Meanwhile, direct activation of mast cells, provoking the complement system, stimulating or inhibiting inflammatory reaction-related enzymes, accumulating bradykinin, and/or triggering vascular hyperpermeability are considered as the main factors causing non-allergic drug hypersensitivity reactions. To date, many investigations have been performed to explore the underlying mechanisms involved in drug hypersensitivity reactions and to search for predictive and preventive methods in both clinical and non-clinical trials. However, validated methods for predicting and diagnosing hypersensitivity reactions to small molecule drugs and deeper insight into the relevant underlying mechanisms are still limited.

Advances and highlights in T and B cell responses to drug antigens

The immunological mechanisms involved in drug hypersensitivity reactions (DHRs) are complex, and despite important advances, multiple aspects remain poorly understood. These not fully known aspects are mainly related to the factors that drive towards either a tolerant or a hypersensitivity response and specifically regarding the role of B and T cells. In this review, we focus on recent findings on this knowledge area within the last 2 years. We highlight new evidences of covalent and non-covalent interactions of drug antigen with proteins, as well as the very first characterization of naturally processed flucloxacillin-haptenated human leukocyte antigen (HLA) ligands. Moreover, we have analysed new insights into the identification of risk factors associated with the development of DHRs, such as the role of oxidative metabolism of drugs in the activation of the immune system and the discovery of new associations between DHRs and HLA variants. Finally, evidence of IgG-mediated anaphylaxis in humans and the involvement of specific subpopulations of effector cells associated with different clinical entities are also topics explored in this review. All these recent findings are relevant for the underlying pathology mechanisms and advance the field towards a more precise diagnosis, management and treatment approach for DHRs.

A review of hypersensitivity methods to detect immune responses to SARS-CoV-2

The investigation of the immune response after SARS-CoV-2 infection has been the goal of many researchers worldwide. The study of humoral immune responses and in vitro T cell production after infection requires the obtaining of individualized blood samples to test the presence of antibodies or activated T cells specific for the virus. In vitro T cell studies are especially troublesome due to the need for more specialized resources often outside the daily routine of clinical laboratories. For this reason the development of a simple and objective method to achieve these T cell studies is needed. In this manuscript we reviewed the hypersensitivity reactions, the theoretical basis and the historical background of delayed type hypersensitivity (DTH) which uses the principles of use of this test in the clinical setting for the past century. In the second part of the review, we focus on COVID adaptive immune responses, to understand the differences and challenges offered by this new application of DTH to investigate immune responses elicited after infection. In the last part of the review a vision provided for the use of this test to investigate the immunogenicity elicited by the vaccines. In our opinion, the clinical guidelines of immune assessment of SARS-CoV-2-infected or vaccinated individuals should include this simple and low-cost test to measure T-cell immunity. Rationale and improved vaccination schemes could be obtained after its implementation in the routine assessment of immunity in this pandemic situation.

Exanthematous Drug Eruption to Intravenous Iron: A Case Report

The authors present a rare case of an exanthematous drug reaction to intravenous iron. Exanthematous drug eruptions, also called morbilliform or maculopapular drug rashes, can occur in first-time drug exposures and represent a subtype of delayed-type IV hypersensitivity reactions. 

This patient is a 49-year-old female with a history of iron deficiency anemia and hypothyroidism who presented to the emergency department after experiencing a diffuse whole-body maculopapular rash following ferumoxytol 510 mg intravenously received once two days prior to her presentation. A clinical examination was suspicious of an exanthematous drug eruption. The patient was treated with methylprednisolone 40 mg intravenously twice a day for three days, followed by prednisone 40 mg orally twice a day for two days with a steroid taper upon discharge. The patient’s rash resolved within five days of steroid treatment.

There is a high global prevalence of iron deficiency anemia for which intravenous iron replacement may be required. However, there is limited research addressing its adverse effects, particularly those that include delayed hypersensitivity reactions. This paper aims to alert healthcare professionals of a rare type of delayed hypersensitivity reaction to intravenous iron to better guide management in the clinical setting. 

Lymphocyte transformation test and cytokine detection assays: Determination of read out parameters for delayed-type drug hypersensitivity reactions

Drug hypersensitivity reactions (DHRs) occur in certain people and are often not predictable. DHRs can be classified as immediate and delayed reactions regarding to onset of clinical manifestations. Both reactions are considered to be an important public health problem because they can lead to life-threatening conditions; however, this review article will focus on delayed DHRs. The most important points for diagnosis of delayed DHRs are the recognition of drug hypersensitivity characteristics and culprit drug identification. While it is usually difficult to identify a culprit drug; clinical evaluation using the causality assessment method, a non-invasive process, can identify the culprit drug without the need for intensive investigation. Delayed DHRs can cause life-threatening conditions; therefore, in vivo skin tests, as well as drug provocation tests, have to be cautiously performed by a drug allergist and have not been recommended in uncontrolled conditions. ENDA/EAACI has recommended that in vitro tests (if available) be performed prior to any in vivo tests. Therefore, in vitro diagnostic tests can be alternative methods to identify a culprit drug for delayed DHR diagnosis as there is no or very low risk for patients under investigation. There are many testing approaches to identify causative agents for delayed DHRs such as: the lymphocyte transformation test (LTT), cytokine/mediator detection assays (i.e. ELISA and flow cytometry-based bead assays), multiplex bead-based immunoassay and ELISpot. The LTT is the most standardized method whereas it has been available in medical schools affiliated with university hospitals. Other in vitro tests, like cytokine detection assays, have also been used, even though they are still being evaluated. They could supplement LTT results that would provide drug allergist's with documentary evidence and prevent risk to patients by avoiding in vivo or drug provocation testing. Hence, the in vitro tests have been promising tests contributing to the management of the delayed DHR work-up process in clinical practice.

Drug and Chemical Allergy: A Role for a Specific Naive T-Cell Repertoire?

Allergic reactions to drugs and chemicals are mediated by an adaptive immune response involving specific T cells. During thymic selection, T cells that have not yet encountered their cognate antigen are considered naive T cells. Due to the artificial nature of drug/chemical-T-cell epitopes, it is not clear whether thymic selection of drug/chemical-specific T cells is a common phenomenon or remains limited to few donors or simply does not exist, suggesting T-cell receptor (TCR) cross-reactivity with other antigens. Selection of drug/chemical-specific T cells could be a relatively rare event accounting for the low occurrence of drug allergy. On the other hand, a large T-cell repertoire found in multiple donors would underline the potential of a drug/chemical to be recognized by many donors. Recent observations raise the hypothesis that not only the drug/chemical, but also parts of the haptenated protein or peptides may constitute the important structural determinants for antigen recognition by the TCR. These observations may also suggest that in the case of drug/chemical allergy, the T-cell repertoire results from particular properties of certain TCR to recognize hapten-modified peptides without need for previous thymic selection. The aim of this review is to address the existence and the role of a naive T-cell repertoire in drug and chemical allergy. Understanding this role has the potential to reveal efficient strategies not only for allergy diagnosis but also for prediction of the immunogenic potential of new chemicals.

Histopathologic and immunophenotypic features of cutaneous solid organ transplant-associated graft-vs-host disease: Comparison with acute hematopoietic cell transplant-associated graft-vs-host disease and cutaneous drug eruption

BACKGROUND

Although it is relatively common after hematopoietic cell transplant (HCT), graft-vs-host disease (GVHD) is a rare complication following solid organ transplantation (SOT).

METHODS

This study evaluated skin biopsy specimens from five cases of SOT GVHD, 15 cases of HCT GVHD, and 15 cases of cutaneous drug eruption. Immunohistochemical staining for CD3, CD4, CD8, T-bet, and GATA-3 was performed to examine the density and immune phenotype of skin-infiltrating lymphocytes.

RESULTS

Similar to HCT GVHD, the predominant histopathologic findings in skin biopsy specimens of SOT GVHD were widespread vacuolar interface dermatitis with scattered necrotic keratinocytes. However, the density of dermal inflammation was considerably higher in SOT GVHD. Features that were more predictive of a cutaneous drug eruption over GVHD included spongiosis, confluent parakeratosis, and many eosinophils. Involvement of the hair follicle epithelium was seen in all three disorders. Both forms of cutaneous GVHD showed a predominance of Th1 (CD3+/T-bet+) lymphocytes within the inflammatory infiltrates. This shift was more pronounced in SOT GVHD, particularly among intraepidermal T-cells.

CONCLUSIONS

SOT GVHD shares many histopathologic features with HCT GVHD. However, SOT GVHD has a greater tendency to develop brisk lichenoid inflammation.

Drug hypersensitivity in HIV infection

PURPOSE OF REVIEW

Immune-mediated adverse drug reactions (IM-ADRs) are many times more common in HIV-infected patients. Usual offending drugs include antiretroviral and antiinfectives, but the burden of specific drug IM-ADRs is population-specific; changing as new and fixed dose combinations enter the market, and drug-resistance patterns demand. This review considers recent literature on epidemiology, mechanisms, clinical management and prevention of IM-ADRs amongst persons living with HIV/AIDS.

RECENT FINDINGS

Epidemiological studies continue to describe high rates of delayed hypersensitivity to known offenders, as well as similar reactions in preexposure prophylaxis. IM-ADRs to oral and injectable integrase strand transfer inhibitors are reported with expanding use. The clinical spectrum and management of IM-ADRs occurring in HIV-infected populations is similar to uninfected; with exceptions such as a recently described severe delayed efavirenz DILI with high mortality. Furthermore, the context can be unique, such as the lower than expected mortality in a Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS/TEN) cohort from a HIV/TB high burden setting. Programmatic data showing the near complete elimination of Abacavir drug hypersensitivity syndrome following implementation of HLA-B57:01 screening is a stellar example of how prevention is possible with mechanistic insight.

SUMMARY

IM-ADRs remain a challenge in persons living with HIV. The complexities posed by polypharmacy, overlapping drug toxicities, drug interactions, overlap of IM-ADRs with other diseases, limited alternative drugs, and vulnerable patients with advanced immunosuppression with high mortality, necessitate increased use of drug provocation testing, treat-through and desensitization strategies. There is an urgent need for improved diagnostics and predictive biomarkers for prevention, or to guide treat-through, rechallenge and desensitization approaches.

The Value of In Vitro Tests to DiminishDrug Challenges

Drug hypersensitivity reactions have multiple implications for patient safety and health system costs, thus it is important to perform an accurate diagnosis. The diagnostic procedure includes a detailed clinical history, often unreliable; followed by skin tests, sometimes with low sensitivity or unavailable; and drug provocation testing, which is not risk-free for the patient, especially in severe reactions. In vitro tests could help to identify correctly the responsible agent, thus improving the diagnosis of these reactions, helping the physician to find safe alternatives, and reducing the need to perform drug provocation testing. However, it is necessary to confirm the sensitivity, specificity, negative and positive predictive values for these in vitro tests to enable their implementation in clinical practice. In this review, we have analyzed these parameters from different studies that have used in vitro test for evaluating drug hypersensitivity reactions and estimated the added value of these tests to the in vivo diagnosis.

Hypersensitivity reactions due to black henna tattoos and their components: are the clinical pictures related to the immune pathomechanism?

Hypersensitivity to para-phenylenediamine (PPD) and related compounds induced by temporary black henna tattoos has become a serious health problem worldwide. Different patterns of sensitization with various clinical aspects are described in literature due to PPD associated to henna tattoo and these manifestations are likely correlated with the immunological and dermatological pathomechanisms involved. Henna is the Persian name of the plant Lawsonia inermis, Fam. Lythraceae. It is a woody shrub that grow in regions of North Africa, South Asia, India and Sri Lanka. Nowadays it is rather frequent to see temporary "tattoos" performed with henna. To make tattoos darker and long-lasting PPD has been associated to henna in tattoo drawings mixtures, so obtaining "black henna". In these years there has been a rise of contact sensitization to PPD and in medical literature an increased number of cases have been reported on temporary henna tattoo application. Here we review the various clinical patterns related to PPD and henna tattoo, to investigate the possible link between clinic-morphological pictures and the immunological response to PPD and henna. The literature underlines that different clinical manifestations are related to black henna containing PPD, and its derivative products may cause delayed-type as well as immediate-type reactions. Further studies are needed to investigate the relationship between clinical and morphological aspects of PPD contact dermatitis and the T cell subsets predominance.

Disorders characterized by predominant or exclusive dermal inflammation

Some cutaneous inflammatory disorders are typified by a predominant or exclusive localization in the dermis. They can be further subdivided by the principal cell types into lymphocytic, neutrophilic, and eosinophilic infiltrates, and mixtures of them are also seen in a proportion of cases. This review considers such conditions. Included among the lymphoid lesions are viral exanthems, pigmented purpuras, gyrate erythemas, polymorphous light eruption, lupus tumidus, and cutaneous lymphoid hyperplasia. Neutrophilic infiltrates are represented by infections, Sweet syndrome, pyoderma gangrenosum, and hidradenitis suppurativa, as well as a group of so-called "autoinflammatory" dermatitides comprising polymorphonuclear leukocytes. Eosinophil-dominated lesions include arthropod bite reactions, cutaneous parasitic infestations, the urticarial phase of bullous pemphigoid, Wells syndrome (eosinophilic cellulitis), hypereosinophilic syndrome, and Churg-Strauss disease. In other conditions, eosinophils are admixed with neutrophils in the corium, with or without small-vessel vasculitis. Exemplary disorders with those patterns include drug eruptions, chronic idiopathic urticaria, urticarial vasculitis, granuloma faciale, and Schnitzler syndrome (chronic urticarial with a monoclonal gammopathy).

An exploratory factor analysis of the spontaneous reporting of severe cutaneous adverse reactions

BACKGROUND

Severe cutaneous adverse reactions (SCARs) are prominent in pharmacovigilance (PhV). They have some commonalities such as nonimmediate nature and T-cell mediation and rare overlap syndromes have been documented, most commonly involving acute generalized exanthematous pustulosis (AGEP) and drug rash with eosinophilia and systemic symptoms (DRESS), and DRESS and toxic epidermal necrolysis (TEN). However, they display diverse clinical phenotypes and variations in specific T-cell immune response profiles, plus some specific genotype-phenotype associations. A question is whether causation of a given SCAR by a given drug supports causality of the same drug for other SCARs. If so, we might expect significant intercorrelations between SCARs with respect to overall drug-reporting patterns. SCARs with significant intercorrelations may reflect a unified underlying concept.

METHODS

We used exploratory factor analysis (EFA) on data from the United States Food and Drug Administration Adverse Event Reporting System (FAERS) to assess reporting intercorrelations between six SCARs [AGEP, DRESS, erythema multiforme (EM), Stevens-Johnson syndrome (SJS), TEN, exfoliative dermatitis (ExfolDerm)]. We screened the data using visual inspection of scatterplot matrices for problematic data patterns. We assessed factorability via Bartlett's test of sphericity, Kaiser-Myer-Olkin (KMO) statistic, initial estimates of communality and the anti-image correlation matrix. We extracted factors via principle axis factoring (PAF). The number of factors was determined by scree plot/Kaiser's rule. We also examined solutions with an additional factor. We applied various oblique rotations. We assessed the strength of the solution by percentage of variance explained, minimum number of factors loading per major factor, the magnitude of the communalities, loadings and crossloadings, and reproduced- and residual correlations.

RESULTS

The data were generally adequate for factor analysis but the amount of variance explained, shared variance, and communalities were low, suggesting caution in general against extrapolating causality between SCARs. SJS and TEN displayed most shared variance. AGEP and DRESS, the other SCAR pair most often observed in overlap syndromes, demonstrated modest shared variance, along with maculopapular rash (MPR). DRESS and TEN, another of the more commonly diagnosed pairs in overlap syndromes, did not. EM was uncorrelated with SJS and TEN.

CONCLUSIONS

The notion that causality of a drug for one SCAR bolsters support for causality of the same drug with other SCARs was generally not supported.

DRESS Syndrome in the ICU: When a Patient Is Treated with Multiple Drugs

The Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) syndrome is life-threatening. It associates a skin condition with hematological and visceral disorders. The DRESS syndrome diagnosis in the intensive care unit (ICU) is difficult as clinical features are nonspecific. Furthermore, the need to treat patients with multiple drugs usually prevents the identification of the causative drug. We report the case of a patient who developed two bouts of DRESS caused by piperacillin-tazobactam, the first being complicated with a distributive shock. Cases of DRESS occurring inside ICU are seldom reported. However, any intensivist may encounter this situation during his career and should be aware of its diagnostic and management specific aspects.

Dermatomyositis and Paclitaxel-Induced Cutaneous Drug Eruption Associated with Metastatic Breast Cancer

Dermatomyositis (DM) is an idiopathic autoimmune connective disease characterized by muscles and skin inflammation of and a well-recognized association with several human malignancies, especially breast cancer. Paclitaxel is a taxane antineoplastic agent with therapeutic effects against a wide range of cancers including breast cancer. This drug is well known for neurotoxicity and hypersensitivity reactions. However, cutaneous drug eruptions, especially those of grade III or higher, are not frequent. Here, we describe the case of a 55-year-old woman with metastatic breast cancer who developed paraneoplastic DM and a paclitaxel-induced exanthematous drug eruption. This case report emphasizes the importance of evaluating internal malignancies, such as advanced breast cancer, in newly developed DM patients. In addition, it presents a rare case of paclitaxel-induced exanthematous drug eruption. The purpose of this case report highlights the immunological pathogenic mechanism of DM and drug eruption in underlying advanced breast cancer.

[Delayed-type cutaneous drug reactions. Pathogenesis, clinical features and histology]

BACKGROUND

Cutaneous reactions to drugs can be subdivided in different ways. In addition to the standard classification according to the etiopathogenesis there are also classifications based predominantly on morphological criteria. The majority of drug-related cutaneous adverse reactions are immunological reactions which are collectively classified under the term hypersensitivity. These reactions are based on drug-specific immunoglobulin E (IgE) or cell-mediated mechanisms, not on the mechanism of action of the drug and are unpredictable. Delayed type reactions to drugs are forms of type IV T-cell mediated hypersensitivity. A prerequisite is a stable association of a pharmaceutical substance with a protein so that hapten-protein conjugates can be produced. The most common clinical symptom is maculopapular (morbilliform) drug-related exanthema. This article also examines lichen planus like drug reaction and drug-induced (hematogenic) allergic contact dermatitis in more detail.

DIAGNOSTICS

The diagnostics are never trivial but also include the differentiation from viral exanthema and initial phases of severe cutaneous adverse reactions, such as toxic epidermal necrolysis. In addition to the morphological classification, the final diagnosis encompasses the interpretation of histopathological alterations in the skin biopsy, analysis of patient medication history, laboratory results and inclusion of data from the literature. Patch tests can also have additional diagnostic benefits. In vitro tests which involve the cellular incubation of the drug responsible should be reserved for specialized laboratories. A prerequisite for successful treatment is immediate termination of the drug responsible.

THERAPY AND PROGNOSIS

Therapy is symptomatic with topical and also short-term systemic steroids and antihistamines. The prognosis is very good.

Seven steps to the diagnosis of NSAIDs hypersensitivity: how to apply a new classification in real practice?

Frequent use of non-steroidal anti-inflammatory drugs (NSAIDs) has been paralleled by increasing occurrence of adverse reactions, which vary from mild local skin rashes or gastric irritation to severe, generalized symptoms and even life-threatening anaphylaxis. NSAID-induced hypersensitivity reactions may involve both immunological and non-immunological mechanisms and should be differentiated from type A adverse reactions. Clinical diagnosis and effective management of a hypersensitive patient cannot be achieved without identifying the underlying mechanism. In this review, we discuss the current classification of NSAID-induced adverse reactions and propose a practical diagnostic algorithm that involves 7 steps leading to the determination of the type of NSAID-induced hypersensitivity and allows for proper patient management.

Cellular in vitro diagnosis of adverse drug reactions

Adverse drug reactions can manifest clinically in a variety of ways. Whilst the majority can be explained by dose-dependent side effects, there is group of unpredictable immunological or non-immunological intolerances that represent a particular diagnostic challenge. Skin tests are frequently negative, whilst challenge tests are time-consuming and often hazardous. Against this backdrop, cellular in vitro tests play a particularly important role in the identification of the causative drug. Whilst basophil tests can be used in the case of immunoglobulin E (IgE)- as well as non-IgE-mediated hypersensitivity reactions, T-cellular test methods assist in the diagnosis of drug eruptions. The reliability of individual tests can be affected by a variety of parameters, such as the pathomechanism underlying the drug reaction, the causative medication, or the point in time of testing. Not only is a sound knowledge of the basic principles of the individual assays an essential prerequisite for correctly indicating and interpreting this test method, but also an awareness of these additional factors.

Hypersensitivity reactions to beta-lactams

Beta-lactam antibiotics (BLs) are the most frequent cause of hypersensitivity reactions mediated by specific immunological mechanisms, with two main types, IgE reactions or T-cell-dependent responses. From a practical point of view, these reactions can be classified into immediate, for those appearing within 1 h after drug intake, and non-immediate, for those appearing at least 1 h after and usually within 24 h of BL administration. The clinical symptoms differ according to this classification. Urticaria and anaphylaxis are the most frequently recorded symptoms in immediate reactions and maculopapular exanthema and delayed urticaria in non-immediate reactions. Although the exact diagnostic approach differs depending on the underlying mechanism, it is based on the performance of skin testing, laboratory tests, and drug provocation tests.T cells are a key factor in all types of hypersensitivity reactions to BLs, regulating both IgE production or acting as effector cells, with a different profile of cytokine production. A Th1 pattern is observed in both CD4(+) and CD8(+) peripheral T cells in non-immediate reactions, whereas a Th2 pattern is expressed in CD4(+) T cells in immediate reactions.

T cell responses to drugs and drug metabolites

Understanding the chemical mechanisms by which drugs and drug metabolites interact with cells of the immune system is pivotal to our knowledge of drug hypersensitivity as a whole.In this chapter, we will discuss the currently accepted mechanisms where there is scientific and clinical evidence to support the ways in which drugs and their metabolites interact with T cells. We will also discuss bioanalytical platforms, such as mass spectrometry, and in vitro test assays such as the lymphocyte transformation test that can be used to study drug hypersensitivity; the combination of such techniques can be used to relate the chemistry of drug antigen formation to immune function. Ab initio T cell priming assays are also discussed with respect to predicting the potential of a drug to cause hypersensitivity reactions in humans in relation to the chemistry of the drug and its ability to form haptens, antigens and immunogens in patients.

Classification and practical approach to the diagnosis and management of hypersensitivity to nonsteroidal anti-inflammatory drugs

Hypersensitivity reactions to aspirin (acetylsalicylic acid) and other nonsteroidal anti-inflammatory drugs (NSAIDs) constitute only a subset of all adverse reactions to these drugs, but due to their severity pose a significant burden to patients and are a challenge to the allergist. In susceptible individuals, NSAIDs induce a wide spectrum of hypersensitivity reactions with various timing, organ manifestations, and severity, involving either immunological (allergic) or nonimmunological mechanisms. Proper classification of reactions based on clinical manifestations and suspected mechanism is a prerequisite for the implementation of rational diagnostic procedures and adequate patient management. This document, prepared by a panel of experts from the European Academy of Allergy and Clinical Immunology Task Force on NSAIDs Hypersensitivity, aims at reviewing the current knowledge in the field and proposes uniform definitions and clinically useful classification of hypersensitivity reactions to NSAIDs. The document proposes also practical algorithms for the diagnosis of specific types of NSAIDs hypersensitivity (which include drug provocations, skin testing and in vitro testing) and provides, when data are available, evidence-based recommendations for the management of hypersensitive patients, including drug avoidance and drug desensitization.

Contact dermatitis: from pathomechanisms to immunotoxicology

Contact allergens are small reactive chemicals. They cause allergic contact dermatitis (ACD) by activating the innate and adaptive immune system. Contact allergens are very peculiar because of their built-in autoadjuvanticity that allows them to trigger sterile inflammation following skin penetration. The innate inflammatory response involves the triggering of pattern recognition receptors either by direct chemical interaction with such receptors or by induction of endogenous activators. I discuss here the recent findings regarding prevalence and predisposition, the identification of innate immune and stress response mechanisms relevant for sensitization and the orchestration of the innate and adaptive immune response to contact allergens. Despite still significant gaps of knowledge, recent advances in our understanding of the immunopathogenesis of ACD can now be used for the development of causative treatment strategies and of in vitro alternatives to animal testing for the identification of contact allergens in immunotoxicology.

Immunologic evaluation of drug allergy

Hypersensitivity drug reactions (HDR) consist of an individual abnormal response with the involvement of the immunological system. In addition to specific immunological mechanisms where specific antibodies or sensitised T cells participate, release of inflammatory mediators by non-specific immunological recognition may also occur. Within this category are one of the most common groups of drugs, the non-steroidal anti-inflammatory drugs. In addition to chemical drugs new emerging ones with an increasing protagonism are biological agents like humanised antibodies and others. For IgE dependent reactions both in vivo and in vitro tests can be used for the immunological evaluation. Sensitivity of these is not optimal and very often a drug provocation test must be considered for knowing the mechanism involved and/or establishing the diagnosis. For non-immediate reactions also both in vivo and in vitro tests can be used. Sensitivity for in vivo tests is generally low and in vitro tests may be needed for the immunological evaluation. Immunohistochemical studies of the affected tissue enable a more precise classification of non-immediate reactions. The monitorization of the acute response of the reactions has given clues for understanding these reactions and has promising results for the future of the immunological evaluation of HDR.

Immunological mechanisms underlying delayed-type hypersensitivity reactions to glatiramer acetate

BACKGROUND

Delayed-type hypersensitivity to glatiramer acetate is rare, and the underlying immunological mechanisms are not completely understood.

OBJECTIVE

To study the immunologic response in 2 patients with multiple sclerosis who developed maculopapular exanthema related with the administration of glatiramer acetate.

METHODS

The allergologic study included general blood tests, viral serologic tests, and skin tests (patch and intradermal tests). The immunologic study was performed in skin biopsy specimens by immunohistochemistry and in the peripheral blood by flow cytometry and the lymphocyte transformation test.

RESULTS

Skin test results were negative in both patients, and the diagnosis was confirmed by a drug provocation test. The evaluation of the acute phase showed an increase in the percentage of CD8 T lymphocytes (>50%) and the percentage of cells expressing skin-homing receptor (cutaneous lymphocyte-associated antigen) (>70%) and chemokine receptors (CCR4 and CXCR3) at T1. A positive proliferative response was observed in T lymphocytes (stimulation index [SI] = 3.5 in patient 1 and 3.59 in patient 2), especially the CD8(+) subpopulation (SI = 5.5 and 4.6 in patients 1 and 2, respectively), and NK lymphocytes (SI = 3.9 and 8.5 in patients 1 and 2, respectively) after glatiramer acetate stimulation.

CONCLUSION

This study demonstrates the important role of T(H)1 cells expressing skin-homing receptors in delayed-type hypersensitivity reactions to glatiramer acetate. A lymphocyte transformation test revealed a specific glatiramer acetate recognition by T lymphocytes and NK lymphocytes.

The development of in vitro culture methods to characterize primary T-cell responses to drugs

Adverse drug reactions represent a major stumbling block to drug development and those with an immune etiology are the most difficult to predict. We have developed an in vitro T-cell priming culture method using peripheral blood from healthy volunteers to assess the allergenic potential of drugs. The drug metabolite nitroso sulfamethoxazole (SMX-NO) was used as a model drug allergen to establish optimum assay conditions. Naive T cells were cocultured with monocyte-derived dendritic cells at a ratio of 25:1 in the presence of the drug for a period of 8 days, to expand the number of drug-responsive T cells. The T cells were then incubated with fresh dendritic cells, and drug and their antigen responsiveness analyzed using readouts for proliferation, cytokine secretion, and cell phenotype. All five volunteers showed dose-dependent proliferation as measured by 5-(and 6)-carboxyfluorescein diacetate succinimidyl ester content and by (3)H-thymidine uptake. CD4 T cells that had divided in the presence of SMX-NO had changed from a naive phenotype (CD45RA+) to a memory phenotype (CD45RO+). These memory T cells expressed the chemokine receptors CCR2, CCR4, and CXCR3 suggesting a mixture of T(H)1 and T(H)2 cells in the responding population, with a propensity for homing to the skin. Drug stimulation was also associated with the secretion of a mixture of T(H)1 cytokines (interferon γ) and T(H)2 cytokines (interleukin [IL]-5 and IL-13) as detected by ELISpot. We are currently developing this approach to investigate the allergenic potential of other drugs, including those where an association between specific human leucocyte antigen alleles and susceptibility to an immunological reaction has been established.

Pityriasis rosea-like Drug Eruption Induced by Imatinib Mesylate (Gleevec™)

Imatinib mesylate (Gleevec™, STI571), a selective inhibitor of BCR-ABL, c-Kit, and platelet-derived factor receptor, has been used to treat chronic myelogenous leukemia (CML) and gastrointestinal stromal tumors. Although its use has been associated with various adverse cutaneous reactions, pityriasis rosea-like drug eruptions are rare. Here, we report a case of pityriasis rosea-like drug eruption that developed following the administration of imatinib mesylate to treat CML.

Vancomycin hypersensitivity diagnosed by lymphocyte blast transformation

A 15-year-old male admitted for Pott's puffy tumor developed recurrent episodes of fever, diffuse morbilliform rash, eosinophilia, and tubulointerstitial nephritis while on multiple antibiotics. Lymphocyte blast transformation (LBT), a method of detecting cellular immune response by measuring levels of interferon-γ (IFN-γ), was used to diagnose vancomycin hypersensitivity and guide antibiotic selection.

The in vitro diagnosis of drug allergy: status and perspectives

Adverse drug reactions (ADR) can result from immune-mediated (drug allergy) and nonimmune-mediated mechanisms. In both types of reaction, conclusive diagnosis and appropriate management remain major problems in daily clinical practice. This review summarizes the potentials and shortcomings of the currently available in vitro tests in the diagnosis of immediate (mostly IgE mediated) and nonimmediate (mostly T-cell mediated) drug allergy, particularly quantification of specific IgE, flow-assisted analysis of in vitro activated lymphocytes and basophils and the enzyme-linked immunosorbent spot.

Enhanced antigenicity leads to altered immunogenicity in sulfamethoxazole-hypersensitive patients with cystic fibrosis

BACKGROUND

Exposure of patients with cystic fibrosis to sulfonamides is associated with a high incidence of hypersensitivity reactions.

OBJECTIVE

To compare mechanisms of antigen presentation and characterize the phenotype and function of T cells from sulfamethoxazole-hypersensitive patients with and without cystic fibrosis.

METHODS

T cells were cloned from 6 patients and characterized in terms of phenotype and function. Antigen specificity and mechanisms of antigen presentation to specific clones were then explored. Antigen-presenting cell metabolism of sulfamethoxazole was quantified by ELISA. The involvement of metabolism in antigen presentation was evaluated by using enzyme inhibitors.

RESULTS

Enzyme inhibitable sulfamethoxazole-derived protein adducts were detected in antigen-presenting cells from patients with and without cystic fibrosis. A significantly higher quantity of adducts were detected with cells from patients with cystic fibrosis. Over 500 CD4(+) or CD8(+) T-cell clones were generated and shown to proliferate and kill target cells. Three patterns of MHC-restricted reactivity (sulfamethoxazole-responsive, sulfamethoxazole metabolite-responsive, and cross-reactive) were observed with clones from patients without cystic fibrosis. From patients with cystic fibrosis, sulfamethoxazole metabolite-responsive and cross-reactive, but not sulfamethoxazole-responsive, clones were observed. The response of the cross-reactive clones to sulfamethoxazole was dependent on adduct formation and was blocked by glutathione and enzyme inhibitors. Antigen-stimulated clones from patients with cystic fibrosis secreted higher levels of IFN-γ, IL-6, and IL-10, but lower levels of IL-17.

CONCLUSION

Sulfamethoxazole metabolism and protein adduct formation is critical for the stimulation of T cells from patients with cystic fibrosis. T cells from patients with cystic fibrosis secrete high levels of IFN-γ, IL-6, and IL-10.

Progression of toxic epidermal necrolysis after tanning bed exposure

BACKGROUND

In addition to recreational tanning bed use, UV radiation exposures are sometimes sought to self-treat skin conditions. The ability of tanning bed radiation exposure to trigger toxic epidermal necrolysis has not been reported.

OBSERVATIONS

A young woman attempted to treat a self-limiting drug hypersensitivity reaction via tanning bed radiation exposure, which resulted in a systemic toxic epidermal necrolysis-like reaction. Studies with cultured keratinocytes and an epithelial cell line reveal that UV-A radiation can synergize with other stimuli such as phorbol esters or interleukin 1 to produce large amounts of tumor necrosis factor, providing a potential mechanism for this exaggerated reaction.

CONCLUSION

In addition to inducing photodamage and skin cancer, tanning bed radiation exposure can trigger a toxic epidermal necrolysis-like reaction, possibly via the exaggerated production of keratinocyte cytokines such as tumor necrosis factor.

Plasmacytoid dendritic cells: an overview of their presence and distribution in different inflammatory skin diseases, with special emphasis on Jessner's lymphocytic infiltrate of the skin and cutaneous lupus erythematosus

BACKGROUND

Plasmacytoid dendritic cells (PDC) play a pivotal role in the induction of autoimmune diseases and other skin diseases. The present study focuses on the distribution patterns of PDC in patients with cutaneous lupus erythematosus (LE) and Jessner's lymphocytic infiltrate (LI) of the skin and compares them with other skin diseases. The goal was to scrutinize the involvement of PDC in LI, and to show that PDC present a specific pattern of distribution in various cutaneous disorders.

METHODS

353 skin biopsies of LE (various subtypes), LI, and other inflammatory skin diseases as well as two halo melanocytic nevi and 10 epithelial tumors were immunohistochemically investigated for the presence of PDC by employing antibodies against CD123 and CD2AP.

RESULTS

PDC were constantly detected as distinct perivascular and periadnexal clusters in LE and LI. In other forms of dermatitis, PDC could be found as single cells or scattered throughout the infiltrate or beneath the epidermis.

CONCLUSIONS

Our data suggest that the distribution of PDC in tumid LE and LI is identical, and this observation suggests that both designations signify one disease. The distinct PDC arrangement in LE represents as useful diagnostic tool in the differential diagnosis with other forms of dermatitis.

CD8+ T cells mediate skin allergy to amoxicillin in a mouse model

BACKGROUND

Delayed allergic skin reactions to drugs are common iatrogenic diseases mediated by activation of specific T cells in the skin.

METHODS

To better understand the role of T cells in these diseases, we developed a mouse model of drug allergy induced by skin sensitization to amoxicillin (amox), a penicillin antibiotic frequently involved in delayed drug allergy.

RESULTS

Whereas wild-type mice could not be sensitized to amox, CD4+ T-cell-deficient mice developed an amox-specific allergic skin response, mediated by IFN-gamma-producing CD8+ T cells. Amox-specific CD8+ T cells, induced in lymphoid organs at a high frequency during sensitization, were recruited in the skin upon challenge. CD8+ T cells were effectors of the allergic skin reaction to amox as in vivo treatment with depleting anti-CD8 mAbs abrogated the skin inflammatory reaction and as purified CD8+ T cells could adoptively transfer the allergic response to naive recipients.

CONCLUSION

CD8+ T cells mediate penicillin skin allergy.

The complex clinical picture of beta-lactam hypersensitivity: penicillins, cephalosporins, monobactams, carbapenems, and clavams

Beta-lactam antibiotics are the drugs most frequently involved in drug hypersensitivity reactions that are mediated by specific immunologic mechanisms. In addition to benzylpenicillin, several chemical structures belonging to 5 major subgroups can induce reactions. The most relevant structure is that of the amoxicillin molecule. Reactions belong to the 4 major mechanisms described by Coombs and Gell, whereby type IV reactions have recently been further subclassified. The most frequent reactions are type I, which are IgE mediated, and type IV, which are nonimmediate and T-cell dependent. IgE-specific antibodies may recognize the benzylpenicilloyl structure or another part of the molecule, such as the side chain, as antigenic determinants. Depending on specific recognition, subjects can be either cross-reactors or selective responders. A variety of entities exist in T-cell reactions, ranging from mild exanthema to life-threatening, severe reactions, such as Stevens-Johnson syndrome or toxic epidermal necrolysis. Diagnostic tests for IgE-mediated reactions can be done in vivo by testing skin with different penicillin determinants or in vitro by quantitating specific IgE antibodies. For nonimmediate reactions, there are also in vitro and in vivo tests, with variable degrees of sensitivity and specificity. The natural history of IgE-mediated reactions indicates that the count of specific IgE antibodies decreases over time and that results of diagnostic tests can become negative.