Expression of α-defensin 1-3 in T cells from severe cutaneous drug-induced hypersensitivity reactions

Delabeling Delayed Drug Hypersensitivity: How Far Can You Safely Go?

Delayed immune-mediated adverse drug reactions (IM-ADRs) are defined as reactions occurring more than 6 hours after dosing. They include heterogeneous clinical phenotypes that are typically T-cell-mediated reactions with distinct mechanisms across a wide spectrum of severity from benign exanthems through to life-threatening cutaneous or organ-specific diseases. For mild reactions such as benign exanthem, considerations for delabeling are similar to immediate reactions and may include a graded or single-dose drug challenge with or without preceding skin or patch testing. Evaluation of challenging cases such as the patient who is on multiple drugs at the time a severe delayed IM-ADR occurs should prioritize clinical ascertainment of the most likely phenotype and implicated drug(s). Although not widely available and validated, procedures such as patch testing, delayed intradermal skin testing, and laboratory-based functional drug assays or genetic (human leukocyte antigen) testing may provide valuable information to further help risk stratify patients and identify the likely implicated and/or cross-reactive drug(s). The decision to use a drug challenge as a diagnostic or delabeling tool in a patient with a severe delayed IM-ADR should weigh the risk-benefit ratio, balancing the severity and priority for the treatment of the underlying, and the availability of alternative efficacious and safe treatments.

Mechanisms of Severe Cutaneous Adverse Reactions: Recent Advances

Cutaneous adverse drug reactions are unpredictable and include various different skin conditions of varying degrees of severity. The most concerning are usually referred to as severe cutaneous adverse reactions (SCARs) and include acute generalized exanthematous pustulosis (AGEP), drug reaction with eosinophilia and systemic symptoms (DRESS), also known as drug-induced hypersensitivity syndrome (DiHS) or hypersensitivity syndrome (HSS), Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). All are delayed type IV hypersensitivity reactions in which a T-cell-mediated drug-specific immune response is responsible for causing the disease. Nonetheless, specific T-cell subpopulations develop in response to certain environmental conditions and produce cytokines that orchestrate the various phenotypes. Cytotoxic T lymphocytes (CTLs), T-helper type 1 (Th1), Th2, Th17, and regulatory T cells (Treg), among other T-cell subpopulations, participate in the development of SCAR phenotypes. Cell subpopulations belonging to the innate immune system, comprising natural killer cells, innate lymphoid cells, monocytes, macrophages and dendritic cells, can also participate in shaping specific immune responses in various clinical conditions. Additionally, tissue-resident cells, including keratinocytes, can contribute to epidermal damage by secreting chemokines that attract pro-inflammatory immunocytes. The final phenotypes in each clinical entity result from the complex interactions between a variety of cell lineages, their products, soluble mediators and genetic and environmental factors. Although the pathophysiology of these reactions is not fully understood, intensive research in recent years has led to major progress in our understanding of the contribution of certain cell types and soluble mediators to the variability of SCAR phenotypes.

Management of adverse reactions to first-line tuberculosis antibiotics

PURPOSE OF REVIEW

Tuberculosis (TB) is the commonest infectious cause of death globally. Adverse reactions to first-line tuberculosis antibiotics are common and have a major impact on the outcomes of patients as second-line antibiotics are less effective and more toxic. The present review addresses the most recent literature regarding epidemiology, investigating reactions, and reintroducing treatment in patients who have had their treatment interrupted.

RECENT FINDINGS

Studies have demonstrated that up to 60% of patients experience adverse reactions to TB treatment; around a third of these are idiosyncratic and may relate to immune sensitization. There is an increased risk in patients with HIV. For patients with severe cutaneous reactions patch testing has an important role; however, systemic reactions to patch testing are common in patients with HIV. In-vitro testing remains limited to specialist centers but studies have identified drug-specific lymphocyte responses in patients with cutaneous and liver reactions. Desensitization of patients with severe cutaneous reactions have been demonstrated to be possible, albeit at high risk.

SUMMARY

Management of these patients remains suboptimal. Better identification of predisposing factors, such as HLA alleles, are needed to identify patients at risk. Improved in-vitro diagnostics will reduce the need to re-expose the patient to the drug and optimized desensitization regimens will improve patient safety when drugs have to be re-introduced.

Commensal Bacteria-Dependent CD8αβ+ T Cells in the Intestinal Epithelium Produce Antimicrobial Peptides

The epithelium of the intestine functions as the primary “frontline” physical barrier for protection from enteric microbiota. Intraepithelial lymphocytes (IELs) distributed along the intestinal epithelium are predominantly CD8⁺ T cells, among which CD8αβ⁺ IELs are a large population. In this investigation, the proportion and absolute number of CD8αβ⁺ IELs decreased significantly in antibiotic-treated and germ-free mice. Moreover, the number of CD8αβ⁺ IELs was correlated closely with the load of commensal microbes, and induced by specific members of commensal bacteria. Microarray analysis revealed that CD8αβ⁺ IELs expressed a series of genes encoding potent antimicrobial peptides (AMPs), whereas CD8αβ⁺ splenocytes did not. The antimicrobial activity of CD8αβ⁺ IELs was confirmed by an antimicrobial-activity assay. In conclusion, microbicidal CD8αβ⁺ IELs are regulated by commensal bacteria which, in turn, secrete AMPs that have a vital role in maintaining the homeostasis of the small intestine.

Association between HLA-B*15:02 and oxcarbazepine-induced cutaneous adverse reaction: a meta-analysis

Aim: HLA-B*15:02 has been demonstrated as a key risk factor for carbamazepine-induced severe cutaneous adverse reaction (sCAR), especially in Asian population. Oxcarbazepine (OXC) is a drug that has a similar structure of carbamazepine. However, the relationship between HLA-B*15:02 and induced cutaneous adverse reaction (cADR) remains unknown. This study aims to analyze this association in the published literature. Method: After filtering studies, eight studies were finally included for meta-analysis, including 32 sCAR cases, 112 mild cutaneous adverse reaction (mcADR) cases, 281 OXC tolerant control and 946 population control cases. Result: In the tolerant control group, an association was found between HLA-B*15:02 genotype and OXC-induced sCAR (odds ratio [OR]: 18.13; 95% CI: 6.77–48.56), but not in mcADR (OR: 1.43; 95% CI: 0.56–3.64). In population control group, an association was found between HLA-B*15:02 genotype and OXC-induced sCAR, (OR: 8.22; 95% CI: 3.03–22.34), but not in mcADR (OR: 2.06; 95% CI: 0.91–4.67). Discussion: Our study demonstrates that the genetic risk factor HLA-B*15:02 may be a factor in OXC-induced sCAR.

Severe cutaneous adverse reactions to drugs

During the past decade, major advances have been made in the accurate diagnosis of severe cutaneous adverse reactions (SCARs) to drugs, management of their manifestations, and identification of their pathogenetic mechanisms and at-risk populations. Early recognition and diagnosis of SCARs are key in the identification of culprit drugs. SCARS are potentially life threatening, and associated with various clinical patterns and morbidity during the acute stage of Stevens-Johnson syndrome and toxic epidermal necrolysis, drug reactions with eosinophilia and systemic symptoms, and acute generalised exanthematous pustulosis. Early drug withdrawal is mandatory in all SCARs. Physicians' knowledge is essential to the improvement of diagnosis and management, and in the limitation and prevention of long-term sequelae. This Seminar provides the tools to help physicians in their clinical approach and investigations of SCARs.

Recent advances in the understanding of severe cutaneous adverse reactions

Severe cutaneous adverse reactions (SCARs) encompass a heterogeneous group of delayed hypersensitivity reactions, which are most frequently caused by drugs. Our understanding of several aspects of SCAR syndromes has evolved considerably over the last decade. This review explores evolving knowledge of the immunopathogenic mechanisms, pharmacogenomic associations, in vivo and ex vivo diagnostics for causality assessment, and medication cross-reactivity data related to SCAR syndromes. Given the rarity and severity of these diseases, multidisciplinary collaboration through large international, national and/or multicentre networks to collect prospective data on patients with SCAR syndromes should be prioritized. This will further enhance a systematized framework for translating epidemiological, clinical and immunopathogenetic advances into preventive efforts and improved outcomes for patients.

A Review of the Pathogenesis of Toxic Epidermal Necrolysis

Toxic epidermal necrolysis (TEN) is a rare skin condition, most often drug-induced, known for its skin detachment and high mortality. In general, acute TEN is considered a T-cell mediated, type IV hypersensitivity disorder. It mostly results from a cumulative effect of risks from the drug structure, drug metabolism, HLA alleles and T cell clonotypes. However, the precise mechanism of TEN is still unknown. Apoptosis or necroptosis causes keratinocytes to lose their shape and adhesion, and necrosis predominates within a few days. Total epidermal necrosis separates the epidermis from the dermis. TEN is regarded as an immune reaction with predominantly CD8+ T lymphocytes, monocytes/macrophages, and natural killer cells. Impaired regulatory T-cells, T-helper 17 cells, cytotoxic granules such as perforin-granzyme and granulysin, tumor necrosis factor α, annexin, microRNA-18a-5p, and drug metabolites are all thought to be involved. From what is known, it can be assumed their mechanism is complex, and there is still much to be investigated. New findings will contribute to the identification of effective active methods of intervention.

Drug induced exfoliative dermatitis: state of the art

Drug induced exfoliative dermatitis (ED) are a group of rare and severe drug hypersensitivity reactions (DHR) involving skin and usually occurring from days to several weeks after drug exposure. Erythema multiforme (EM), Stevens–Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are the main clinical presentations of drug induced ED. Overall, T cells are the central player of these immune-mediated drug reactions. Here we provide a systematic review on frequency, risk factors, pathogenesis, clinical features and management of patients with drug induced ED.

Aberrant Expression of Bacterial Pattern Recognition Receptor NOD2 of Basophils and Microbicidal Peptides in Atopic Dermatitis

Atopic dermatitis (AD) is a chronically relapsing inflammatory skin disease, associated with basophil infiltration into skin lesions and Staphylococcus aureus (S.aureus)-induced inflammation. Pattern recognition receptors (PRRs), including microbicidal peptide human neutrophil α-defensins (HNP) and dermcidin, can exert immunomodulating activity in innate immunity and skin inflammation. We investigated the plasma concentration of HNP and dermcidin, the expression of bacterial toll-like receptor (TLR) and nucleotide-binding oligomerization domain (NOD)-like receptors of basophils and plasma concentration and ex vivo induction of AD-related inflammatory cytokines and chemokines using ELISA and flow cytometry, in AD patients and control subjects. Plasma concentrations of HNP, dermcidin and AD-related Th2 chemokines CCL17, CCL22 and CCL27 were significantly elevated in AD patients compared with controls (all p < 0.05). Plasma concentrations of CCL27 and CCL22 were found to correlate positively with SCORing atopic dermatitis (SCORAD), objective SCORAD, % area affected, lichenification and disease intensity, and CCL27 also correlated positively with pruritus in AD patients (all p < 0.05). Protein expressions of NOD2 but not TLR2 of basophils were significantly down-regulated in AD patients compared with controls (p = 0.001). Correspondingly, there were lower ex vivo % inductions of allergic inflammatory tumor necrosis factor-α, IL-6 and CXCL8 from peripheral blood mononuclear cells upon NOD2 ligand S. aureus derived muramyl dipeptide stimulation in AD patients comparing with controls. The aberrant activation of bacterial PRRs of basophils and anti-bacterial innate immune response should be related with the allergic inflammation of AD.

Towards the development of mechanism-based biomarkers to diagnose drug hypersensitivity

T-cells are activated by different mechanisms in the presence of drugs, metabolites or haptens, and they release several molecules that can be used in the diagnosis of drug hypersensitivity.

Immunological response in Stevens-Johnson syndrome and toxic epidermal necrolysis

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are life-threatening cutaneous adverse drug reactions that induce widespread epidermal necrosis. Recent advances in pharmacogenomic studies have provided evidence of genetic predispositions to SJS/TEN. Several concepts have been proposed to explain the pathogenesis of severe cutaneous adverse drug reactions. In the hapten concept, small molecules called haptens elicit an immune response only when attached to proteins. The "p-i" concept postulates that the causative drugs can stimulate cells by binding directly and reversibly to immune receptors. In addition, there is the idea that drugs alter the antigen by binding to the human leukocyte antigen pocket. With regard to keratinocyte death, several cell death mediators, such as FasL, granulysin and annexin A1, have been proposed as playing a role in SJS/TEN pathogenesis. A subset of T lymphocytes, including regulatory T cells, also may play a role in SJS/TEN.

Erythema multiforme, Stevens-Johnson syndrome and toxic epidermal necrolysis: a comparative review

BACKGROUND

Human erythema multiforme (EM) and Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) are separate conditions. There is no consensus on classification criteria for the eponymous diseases in animals.

RESULTS

Animal EM is very different from 90% of human EM, which is herpes virus associated (HAEM). Animals lack acrally distributed, typical raised targets. Unlike canine parvovirus 'EM', HAEM is not an active infection. Animal EM is often attributed to drugs, but this is rarely proved. Conversely, human and animal SJS/TEN are almost identical, life-threatening disorders of epidermal necrosis and detachment, typically triggered by drugs (occasionally by infectious agents). Both EM and SJS/TEN are mediated by cytotoxic lymphocyte responses against altered keratinocytes (infectious agents or drugs). Apoptosis results from direct cytotoxicity or through soluble mediators, namely Fas ligand, granzymes, perforin and granulysin. Diagnosis in humans is clinicopathological, with emphasis on clinical lesions; histopathology confirms the pathological process as interface (cytotoxic) dermatitis. Human EM is self-limiting; only recurrent and rare persistent cases require antiviral/immunosuppressive therapies. Drug-induced EM responds to drug withdrawal. Idiopathic canine EM (>40%) is usually chronic, refractory to treatment and may represent heterogeneous conditions. Early identification and removal of the causative drug and high-quality supportive care are critical in SJS/TEN. Mortality rate is nevertheless high.

CONCLUSIONS AND CLINICAL IMPORTANCE

(1) Histopathological lesions do not reliably differentiate EM, SJS and TEN. (2) A multicentre study to develop a consensus set of clinical criteria for EM and SJS/TEN in animals is overdue. (3) No adjunctive therapies, including intravenous immunoglobulin and ciclosporin, have met evidence-based standards.

Toxic epidermal necrolysis: the year in review

PURPOSE OF REVIEW

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are life-threatening severe adverse drug reactions. Once thought to be idiosyncratic and unpredictable, there has been significant progress made in the understanding of the pathomechanism and pharmacogenetics of such reactions. These advances together with their clinical implications will be elaborated in this review.

RECENT FINDINGS

It is now known that the human leukocyte antigen (HLA) association in SJS/TEN is more than just a genetic marker and has a functional role as well. This reaction is mediated by cytotoxic T lymphocytes (CTLs) in an HLA-restricted fashion. Certain drugs may bind directly to the HLA complex and facilitate the development of self-reactivity due to drug-modified HLA-peptide repertoire. The role of the drug-specific T cells and their T-cell receptors has also been clarified. Downstream cytotoxic signals have been elucidated with granulysin, a cytotoxic protein produced by CTLs or natural killer cells deemed to be the key mediator in the reaction.

SUMMARY

Pharmacogenetic screening of HLA alleles prior to drug initiation has already been shown useful in the prevention of such reactions. The other advances in the disease mechanism will form the basis for better preventive and therapeutic strategies.

Toxic epidermal necrolysis: Part II. Prognosis, sequelae, diagnosis, differential diagnosis, prevention, and treatment

Toxic epidermal necrolysis (TEN) is a life-threatening, typically drug-induced, mucocutaneous disease. TEN has a high mortality rate, making early diagnosis and treatment of paramount importance. New but experimental diagnostic tools that measure serum granulysin and high-mobility group protein B1 (HMGB1) offer the potential to differentiate early TEN from other, less serious drug reactions, but these tests have not been validated and are not readily available. The mainstay of treatment for TEN involves discontinuation of the offending drug, specialized care in an intensive care unit or burn center, and supportive therapy. Pharmacogenetic studies have clearly established a link between human leukocyte antigen allotype and TEN. Human leukocyte antigen testing should be performed on patients of East Asian descent before the initiation of carbamezapine and on all patients before the initiation of abacavir. The effectiveness of systemic steroids, intravenous immunoglobulins, plasmapheresis, cyclosporine, biologics, and other agents is uncertain.

Immunological mechanisms of epidermal damage in toxic epidermal necrolysis

PURPOSE OF REVIEW

The purpose of the present review is to introduce recent findings on the pathomechanisms of toxic epidermal necrolysis (TEN), which is characterized by widespread epidermal detachment due to keratinocyte apoptosis.

RECENT FINDINGS

In the mechanism of epidermal damage, the roles of drug metabolites, cytotoxic lymphocytes, and apoptosis-inducing factors have been noted. In addition, recent studies have focused on monocytes/macrophages, which may participate in epidermal damage through the production of apoptosis-inducing factors and the expression of costimulatory factors with the ability to activate CD8 T cells.

SUMMARY

Epidermal keratinocyte death is a hallmark of TEN. In a very high proportion of cases, drugs are responsible for TEN. It has been suggested that toxic drug metabolites produced by keratinocytes act like electrophilic agents to induce apoptosis and inflammation. Next, cytotoxic lymphocytes and monocytes function in the development of widespread epidermal damage through direct or indirect cytotoxic pathways. In addition, T-cell activation may be strengthened by the impairment of regulatory T-cell function and activated monocytes. The development of epidermal damage in TEN may require the coordinated action of these factors.

Stevens-Johnson syndrome/toxic epidermal necrolysis mouse model generated by using PBMCs and the skin of patients

BACKGROUND

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are life-threatening cutaneous reactions caused by drugs or infections and exhibiting widespread epidermal necrosis. Currently, there is no animal model that reproduces SJS/TEN symptoms.

OBJECTIVE

We sought to develop a novel mouse model of SJS/TEN by using PBMCs and skin from patients who had recovered from SJS/TEN.

METHODS

For our mouse model, patients' PBMCs were injected intravenously into immunocompromised NOD/Shi-scid, IL-2Rγ(null) (NOG) mice, followed by oral administration of a causative drug. Subsequently, to replace human skin, unaffected skin specimens obtained from patients who had recovered from SJS/TEN were grafted onto NOG mice, after which patient-derived PBMCs and the causative drug were applied.

RESULTS

Mice injected with PBMCs from patients with SJS/TEN and given the causative drug showed marked conjunctival congestion and numerous cell death of conjunctival epithelium, whereas there were no symptoms in mice injected with PBMCs from patients with ordinary drug skin reactions. CD8(+) T lymphocyte-depleted PBMCs from patients with SJS/TEN did not elicit these symptoms. In addition, skin-grafted mice showed darkening of the skin-grafted areas. Cleaved caspase-3 staining showed that dead keratinocytes were more numerous in the skin-grafted mice than in the healthy control animals.

CONCLUSION

We have established a novel human-oriented SJS/TEN mouse model and proved the importance of CD8(+) T lymphocytes in SJS/TEN pathogenesis. The mouse model promises to promote diagnostic and therapeutic approaches.

Cutaneous adverse drug reactions to anti-tuberculosis drugs: state of the art and into the future

First- and second-line anti-tuberculosis drugs are associated with a diverse presentation of cutaneous adverse drug reactions (CADR), ranging from mild to life threatening. An individual drug can cause multiple types of CADR, and a specific type of CADR can be due to any anti-tuberculosis drug, which can make the management of tuberculosis (TB) following CADR challenging. The higher incidence of TB and CADR in HIV-infected persons makes TB-associated CADR a burgeoning problem for clinicians, particularly in high HIV-prevalence settings. This review discusses the pathogenesis, epidemiology, clinical presentation, diagnosis and management of TB-associated CADR. Clinical controversies including its impact on treatment outcomes, challenges in restarting optimal anti-tuberculosis therapy and the timing of highly active antiretroviral therapy initiation in those with HIV coinfection are also discussed. Finally, gaps in the current knowledge of TB-associated CADR have been identified and a research agenda has been proposed.

α-Defensins in human innate immunity

Defensins are small, multifunctional cationic peptides. They typically contain six conserved cysteines whose three intramolecular disulfides stabilize a largely β-sheet structure. This review of human α-defensins begins by describing their evolution, including their likely relationship to the Big Defensins of invertebrates, and their kinship to the β-defensin peptides of many if not all vertebrates, and the θ-defensins found in certain non-human primates. We provide a short history of the search for leukocyte-derived microbicidal molecules, emphasizing the roles played by luck (good), preconceived notions (mostly bad), and proper timing (essential). The antimicrobial, antiviral, antitoxic, and binding properties of human α-defensins are summarized. The structural features of α-defensins are described extensively and their functional contributions are assessed. The properties of HD6, an enigmatic Paneth cell α-defensin, are contrasted with those of the four myeloid α-defensins (HNP1-4) and of HD5, the other α-defensin of human Paneth cells. The review ends with a decalogue that may assist researchers or students interested in α-defensins and related aspects of neutrophil function.

The innate immune system in delayed cutaneous allergic reactions to medications

PURPOSE OF REVIEW

Innate immune responses are attracting increasing interest from researchers in the field of drug allergy. This review discusses recent advances in the understanding of several innate immune components in delayed cutaneous hypersensitivity reactions to medications, with special attention on severe reactions.

RECENT FINDINGS

The mechanism of activation of dendritic cells in response to drugs is being unravelled. Activated monocytes and macrophages have been found in affected skin of bullous diseases. Increased gene expression of monomyeloid cell products including several 'alarmins' or endogenous damage-associated molecular patterns has been described in Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN). Natural killer (NK) cells from patients respond to drugs in vitro. In-vivo, NK cells may contribute to severe diseases through the secretion of effector molecules such as granulysin. The innate receptor CD94/NKG2C is expressed by NK cells and cytotoxic T lymphocytes in SJS/TEN and triggers degranulation in response to human leukocyte antigen-E-expressing keratinocytes. T cells with innate activities have been detected in patients during severe acute reactions.

SUMMARY

Humoral and cellular components of the innate immune response have been identified in association with delayed drug hypersensitivity reactions. Their participation in certain diseases may explain the variability of phenotypes in hypersensitivity reactions to medications.