Pathophysiology of fixed drug eruption: the role of skin-resident T cells

Fixed drug eruption after pentavalent diphtheria, tetanus, acellular pertussis, inactivated poliovirus and Haemophilus influenzae type b combined vaccine in an infant

In Turkey, diphtheria-tetanus-acellular pertussis-inactivated poliovirus and Haemophilus influenzae type b (DTaP-IPV-Hib) vaccine has been administered to all children in the second, fourth, sixth and 18th months within the scope of the national vaccination programme. Here we present a rare case of fixed drug eruption (FDE) that occurred as a result of the administration of a pentavalent DTaP-IPV-Hib combined vaccine in a 4-month-old girl. There was no history of taking any other medication before or when the lesion appeared. The lesion responded well to 1 week of topical methylprednisolone aceponate cream application and regressed within 1 week, leaving mild hyperpigmentation. Few cases of FDE have been reported occurring after administration of various vaccines and it is extremely rare in children. To our knowledge, this is the first reported case of FDE developing in an infant after the combined pentavalent DTaP-IPV-Hib vaccine.

A Fixed-Dose Combination of Ofloxacin-Ornidazole Induced Fixed Drug Eruption: A Case Report

Cutaneous drug eruptions are commonly occurring adverse drug reactions. Food and Drug Association does not recommend a fixed dose combination of ofloxacin-ornidazole; still, it is commonly practised in developing countries. Many patients take this combination of drugs for episodes of gastro-enteritis, often as self-medication. We are reporting a 25 years old male patient presenting with repeated episodes of adverse drug reaction to a fixed dose combination of ofloxacin-ornidazole.

Role of tissue-resident memory T cells in the pathophysiology of allergic contact dermatitis

PURPOSE OF REVIEW

We bring updated knowledge on tissue-resident memory T cells (TRM), underlining their major role in the recurrence and the severity of allergic contact dermatitis (ACD).

RECENT FINDINGS

ACD is a frequently encountered skin disease. It is defined as a delayed-type hypersensitivity reaction initiated by the recruitment of antigen-specific T cells into the skin of sensitized patients. ACD lesions tend to develop on already-exposed areas and worsen over time. That clinical observation has raised questions on the contribution of TRM to ACD recurrence and severity. TRM are memory T cells that persist in peripheral tissues, such as the skin, without recirculating through the blood. These cells provide effective immune memory against pathogens, but they may also participate in the development or exacerbation of numerous inflammatory diseases, including skin allergies. Recent works have demonstrated a major role for TRM in ACD pathophysiology.

SUMMARY

In ACD, TRM accumulate preferentially at the allergen contact site during the sensitization phase. Thereafter, these cells cause a rapid and intense response to any new allergen exposure. They also play a key role in flare-ups of ACD and the chronicity and severity of the disease. These aspects suggest that TRM may have an interest as therapeutic targets.

Resident Memory T Cells in Autoimmune Skin Diseases

Tissue resident memory T cells (TRM) are a critical component of the immune system, providing the body with an immediate and highly specific response against pathogens re-infecting peripheral tissues. More recently, however, it has been demonstrated that TRM cells also form during autoimmunity. TRM mediated autoimmune diseases are particularly destructive, because unlike foreign antigens, the self-antigens are never cleared, continuously activating self-reactive TRM T cells. In this article, we will focus on how TRMs mediate disease in autoimmune skin conditions, specifically vitiligo, psoriasis, cutaneous lupus erythematosus, alopecia areata and frontal fibrosing alopecia.

Discipline in Stages: Regulating CD8+ Resident Memory T Cells

Resident memory CD8⁺ T (T_RM) cells are a lymphocyte lineage distinct from circulating memory CD8⁺ T cells. T_RM lodge within peripheral tissues and secondary lymphoid organs where they provide rapid, local protection from pathogens and control tumor growth. However, dysregulation of CD8⁺ T_RM formation and/or activation may contribute to the pathogenesis of autoimmune diseases. Intrinsic mechanisms, including transcriptional networks and inhibitory checkpoint receptors control T_RM differentiation and response. Additionally, extrinsic stimuli such as cytokines, cognate antigen, fatty acids, and damage signals regulate T_RM formation, maintenance, and expansion. In this review, we will summarize knowledge of CD8⁺ T_RM generation and highlight mechanisms that regulate the persistence and responses of heterogeneous T_RM populations in different tissues and distinct microenvironments.

Tissue-resident memory T cells in the skin

PURPOSE

Tissue-resident memory T (T_RM) cells are a newly described subset of memory T cells. The best characterized T_RM cells are CD8+ and express CD103 and CD69. These cells are non-recirculating and persist long term in tissues, providing immediate protection against invading pathogens. However, their inappropriate activation might contribute to the pathogenesis of autoimmune and inflammatory disorders. In the skin, these cells have been described in psoriasis, vitiligo, and melanoma among other diseases.

METHODS

Literature review was done to highlight what is currently known on the phenotype and function of T_RM cells and summarizes the available data describing their role in various cutaneous conditions.

RESULTS

Resolved psoriatic skin and disease-naïve non-lesional skin contain a population of IL-17-producing T_RM cells with shared receptor sequences that recognize common antigens and likely contribute to disease recurrence after cessation of therapy. In vitiligo, T_RM cells produce perforin, granzyme B, and interferon-γ following stimulation by interleukin-15 and collaborate with recirculating memory T cells to maintain disease. In melanoma, increased accumulation of T_RM cells was recently shown to correlate with improved survival in patients undergoing therapy with immune checkpoint inhibitors.

Tissue-resident memory T cells and their biological characteristics in the recurrence of inflammatory skin disorders

The skin is the largest organ of the body. The establishment of immunological memory in the skin is a crucial component of the adaptive immune response. Once naive T cells are activated by antigen-presenting cells, a small fraction of them differentiate into precursor memory T cells. These precursor cells ultimately develop into several subsets of memory T cells, including central memory T (T_CM) cells, effector memory T (T_EM) cells, and tissue resident memory T (T_RM) cells. T_RM cells have a unique transcriptional profile, and their most striking characteristics are their long-term survival (longevity) and low migration in peripheral tissues, including the skin. Under physiological conditions, T_RM cells that reside in the skin can respond rapidly to pathogenic challenges. However, there is emerging evidence to support the vital role of T_RM cells in the recurrence of chronic inflammatory skin disorders, including psoriasis, vitiligo, and fixed drug eruption, under pathological or uncontrolled conditions. Clarifying and characterizing the mechanisms that are involved in skin T_RM cells will help provide promising strategies for reducing the frequency and magnitude of skin inflammation recurrence. Here, we discuss recent insights into the generation, homing, retention, and survival of T_RM cells and share our perspectives on the biological characteristics of T_RM cells in the recurrence of inflammatory skin disorders.

Ciprofloxacin-Induced Bullae of the Lower Extremity: A Case of a Fixed Drug Reaction

Cutaneous adverse drug reactions make up 1% to 2% of all adverse drug reactions. From these adverse cutaneous drug reactions, 16% to 21% can be categorized as fixed drug reactions (FDR). Fixed drug reactions may show diverse morphology including but not limited to the following: dermatitis, Stevens-Johnson syndrome, urticaria, morbilliform exanthema, hypersensitivity syndrome, pigmentary changes, acute generalized exanthematous pustulosis, photosensitivity, and vasculitis. An FDR will occur at the same site because of repeated exposure to the offending agent, causing a corresponding immune reaction. There are many drugs that can cause an FDR, such as analgesics, antibiotics, muscle relaxants, and anticonvulsants. The antibiotic ciprofloxacin has been shown to be a cause of cutaneous adverse drug reactions; however, the fixed drug reaction bullous variant is rare. This case study was published to demonstrate a rare adverse side effect to a commonly used antibiotic in podiatric medicine.

Dapsone-associated fixed drug eruption

INTRODUCTION

Dapsone is a sulfone drug used to treat infectious conditions and also numerous dermatologic diseases. Fixed drug eruption is a distinctive adverse cutaneous reaction associated with the initial administration and subsequent delivery of a specific agent. Areas covered: The authors preformed a literature search using the following keywords: dapsone, fixed drug eruption, and adverse cutaneous drug reaction. Bibliographies were also reviewed for pertinent articles. The results were combed for relevant papers and reviewed. Articles pertaining to dapsone-associated fixed drug eruption were included. Expert commentary: The majority of cases of dapsone-associated fixed drug eruption in the literature come from Africa or India where there is a high prevalence of patients treated for leprosy. Characteristics of these cases are similar to fixed drug eruption described in the western literature, with differences in frequency of multiple versus solitary lesions. Dapsone-associated fixed drug eruption should be considered when reviewing the drug history of a patient with fixed drug eruption. In the case of darker pigmented individuals, multiple fixed drug eruption lesions may be more common. Multiple lesions may mimic Kaposi's sarcoma in human immunodeficiency virus positive patients. Dapsone-associated fixed drug eruption should be considered in the differential diagnosis of multiple hyperpigmented lesions.

Fixed Food Eruption Caused by Actinidia arguta (Hardy Kiwi): A Case Report and Literature Review

Fixed drug eruption (FDE) is a common hypersensitivity reaction characterized by recurrent, well-circumscribed, erythematous patches that arise at the same site as a result of systemic drug exposure. However, fixed food eruption (FFE), a lesion triggered by food ingestion, is a rare allergy that was first defined in 1996. Based on their anti-inflammatory and anti-oxidant properties, the fruit and leaves of Actinidia arguta, the hardy kiwi, are widely consumed across Korea, Japan, and China. This report describes the first case of FFE caused by hardy kiwi leaves, known as Daraesun in Korean, confirmed by oral provocation tests and skin biopsy.

Tissue-Resident Memory T Cells and Fixed Immune Surveillance in Nonlymphoid Organs

T cell immunity is often defined in terms of memory lymphocytes that use the blood to access a range of organs. T cells are involved in two patterns of recirculation. In one, the cells shuttle back and forth between blood and secondary lymphoid organs, whereas in the second, memory cells recirculate between blood and nonlymphoid tissues. The latter is a means by which blood T cells control peripheral infection. It is now clear that there exists a distinct memory T cell subset that is absent from blood but found within nonlymphoid tissues. These nonrecirculating tissue-resident memory T (TRM) cells develop within peripheral compartments and never spread beyond their point of lodgement. This review examines fixed immune surveillance by TRM cells, highlighting features that make them potent controllers of infection in nonlymphoid tissues. These features provide clues about TRM cell specialization, such as their ability to deal with sequestered, persisting infections confined to peripheral compartments.

Ciprofloxacin induced bullous fixed drug reaction: three case reports

Cutaneous adverse drug reactions (ADRs) are seen in about 1–2% cases. Fixed drug reaction (FDR) is responsible for about 10% of all ADRs. It is a delayed type of hypersensitivity reaction that occurs as lesions recurs at the same skin site due to repeated intake of an offending drug. The most common drugs causing fixed drug eruption (FDE) are analgesics, antibiotics, muscle relaxants and anticonvulsants. FDE due to ciprofloxacin has been reported earlier also, but bullous variant of FDR is rare. We hereby report three case reports of bullous FDR caused due to ciprofloxacin.

Fixed Drug Eruption to Propofol

We present a case of fixed drug eruption to propofol following a series of sedations of a patient for a number of day case procedures. The patient experienced oedema and blistering of his penis, increasing in severity and duration following each subsequent exposure. The diagnosis was confirmed by punch biopsy following an intravenous challenge test with propofol. Whilst reports of fixed drug eruptions to anaesthetic induction agents are uncommon, a number of drugs used commonly by anaesthetists are known triggers. We discuss fixed drug eruptions in relation to anaesthetic practice, aiming to raise awareness of this adverse drug reaction.

Peripheral tissue surveillance and residency by memory T cells

T cell immunity has long been described in terms of two circulating memory populations. Central memory T (T(CM)) cells migrate between the secondary lymphoid organs and are capable of mounting a recall proliferative response on pathogen re-encounter, whereas effector memory T (T(EM)) cells traffic between blood and extralymphoid compartments for effective peripheral immune surveillance. It is now clear that there exists a third category of memory cells that never returns to the circulation. These tissue-resident memory T (T(RM)) cells are phenotypically distinct from T(EM) cells, persist in elevated numbers in areas involved in prior infection and have been implicated in various immune phenomena, such as the control of persisting infections and immune disorders in fixed regions of the body.

Maximal Points of Head's Zone in Fixed Drug Eruption

The principles determining the primary localization of lesions in fixed drug eruption (FDE) are still unknown. Studies investigating the predilection areas in FDE have indicated drug-related, trauma-related, or inflammation-related specific site involvement, as well as visceracutaneous reflex-related specific site involvement. The importance of viscerocutaneous reflexes for the location of dermatoses was first recognized in the 1960s. Head's zones are viscerocutaneous reflex projection fields on the skin that extend over certain dermatomes and possess a reflex-associated maximal point. Recently, in a Turkish collective of patients, three women with the primary location of FDE lesions on the maximal points of Head's zones were presented. We also experienced 3 cases with FDE where the lesions were located at specific sites (buttocks), the so-called maximal points of Head's zones, which are known to be the most active dermatomal areas of an underlying visceral pathology. An underlying internal disturbance (ureter stone, pyelonephritis and chronic pelvic inflammatory disease) was found in all 3 patients, corresponding to the organ-related maximal point of Head's zones in each case. In conclusion, the primary location of FDE lesions on the maximal points of Head's zones revealed relevant organ disorders with corresponding projection fields.

Fixed drug eruption: pathogenesis and diagnostic tests

PURPOSE OF REVIEW

Fixed drug eruption is a simplified disease model for elucidating the mechanism(s) of how skin inflammation is induced by skin-resident T cells. In this review, we focus on how the presence of intraepidermal CD8+T cells resident in the fixed drug eruption lesions can provide exciting new clues to our understanding of pathomechanisms of inflammatory skin diseases.

RECENT FINDINGS

Intraepidermal CD8+T cells with an effector-memory phenotype resident in fixed drug eruption lesions have a major contributing role in the development of localized tissue damage. Activation of these CD8+T cells is sufficient for triggering the lesion, however, but not sufficient to cause extensive tissue damage observed in the fully evolved lesions; additional recruitment of CD4+ and CD8+T cells to a specific tissue site would also contribute to the late stage of lesion development. The influx of regulatory T cells into the epidermis observed in fully evolved lesions would serve to limit harmful immune reactions. Consistent with this, positive patch test reactions are only observed at the site of previous lesions harboring significant numbers of intraepidermal CD8+T cells.

SUMMARY

Intraepidermal CD8+T cells may represent double-edged swords of the skin immune system with protective and destructive capacity.

Role of T cells in nonimmediate allergic drug reactions

PURPOSE OF REVIEW

This review presents the current knowledge of the role of T cells in drug allergy manifesting as exanthematous, pustular and bullous skin diseases, collectively referred to as nonimmediate allergic drug reactions.

RECENT FINDINGS

Both CD4+ and CD8+ T cells producing type 1 and type 2 cytokines and endowed with cytotoxic properties are involved in nonimmediate allergic drug reactions. Recent studies have confirmed that CD8+ T cells play a major role in the pathophysiology of nonimmediate allergic drug reactions, and have characterized new cytotoxic molecular pathways responsible for the severity of the bullous forms of nonimmediate allergic drug reactions.

SUMMARY

Nonimmediate allergic drug reactions are mediated by T cells and mostly affect the skin. Nonimmediate allergic drug reactions comprise several diseases ranging from the frequent and benign maculo-papular exanthema to the severe and rare toxic epidermal necrolysis. Progress in the knowledge of the pathophysiology of nonimmediate allergic drug reactions comes from a better understanding of the mechanisms of drug recognition by T cells and from a careful analysis of the phenotype and functions of CD4+ and CD8+ T cells infiltrating the skin lesions. Recent studies have confirmed that the different clinical forms of nonimmediate allergic drug reactions are associated with distinct types of T cell-mediated skin inflammation. However, CD8+ T cells appear as major effector T cells in most of the nonimmediate allergic drug reactions. Future studies to analyze the early cellular and molecular events leading to the development of the allergic skin reaction will be helpful in order to define diagnostic and therapeutic targets.

Fixed drug eruption: a prototypic disorder mediated by effector memory T cells

Effector memory T cells are uniquely specialized to mediate protective immunity. However, their excessive activation may result in the development of organ-specific inflammatory diseases, which have not been extensively studied. Fixed drug eruption (FDE), a localized variant of drug-induced dermatoses characterized by relapse in the same location, is a prototypic disorder mediated by excessive activation of effector memory T cells, which are resident in the lesional epidermis. A variety of clinical and pathologic features uniquely observed in FDE lesions can be explained by the presence of CD8(+) intraepidermal T cells with the effector memory phenotype in the FDE lesion. This review focuses on how these T cells are generated, retained in the epidermis, and activated to cause epidermal damage.

Skin immune surveillance by T cells--a new order?

Although studies of the skin have provided fundamental models for innate and adaptive immune surveillance of body surfaces, there remains relatively little understanding of the role that epithelial cells play in sensing infection and/or organ dysfunction, and the pathways available to them to communicate with local and systemic immune cells. In particular, evidence is emerging for a novel stress response initiated by local lymphocytes, rather than dendritic cells, and based on their recognition of epithelial stress-induced antigens. Its consequences are to sustain tissue integrity by providing immunoprotection and novel modes of immunoregulation, whereas its dysregulation may promote body surface immunopathologies.

Differential diagnosis of chronic urticaria

OBJECTIVES

To review diseases that can present with cutaneous signs and symptoms that mimic those observed in chronic urticaria and to discuss the workup necessary to distinguish these diseases from chronic urticaria.

DATA SOURCES

We performed a PubMed search using the following keywords: urticaria, cryopyrin, Sweet syndrome, subacute cutaneous lupus, urticarial vasculitis, urticaria pigmentosa, angioedema, fixed drug eruption, bullous pemphigoid, and reticular erythematous mucinosis. Appropriate chapters in general dermatology textbooks were also reviewed.

STUDY SELECTION

Articles that related to disease states, which present with persistent urticarial lesions, were catalogued for use in this review.

RESULTS

Besides acute, chronic, and physical urticarias, there are 2 categories of diseases that have urticarial lesions. The first group includes those in which the skin lesions are almost indistinguishable from those seen in patients with chronic idiopathic urticaria. Thus, the diagnosis relies on a careful history and physical examination, and in some cases laboratory studies are required. The second group are ones that have skin lesions that at one point in their development have an urticaria-like appearance or on rare occasion may have such lesions. These latter diseases are numerous, and we have tried to highlight the ones that most mimic chronic idiopathic urticaria or are more common.

CONCLUSIONS

A working knowledge of the diseases that can present with urticarial lesions is essential to accurately diagnose and effectively treat these symptomatic and sometimes serious conditions.

In vivo dynamics of intraepidermal CD8+ T cells and CD4+ T cells during the evolution of fixed drug eruption

BACKGROUND

Although a severe form of fixed drug eruption (FDE) clinically and histologically mimics toxic epidermal necrolysis (TEN), subsequent evolution of the two conditions is quite different. It remains unknown, however, which factors determine whether these lesions resolve spontaneously or subsequently progress to TEN.

OBJECTIVES

Because epidermal injury in TEN can be locally reproduced in the evolving FDE lesions, we sought to investigate how epidermal damage can be induced in the evolving FDE lesions and how disease progression to TEN can be prevented, by analysing the FDE lesions induced by clinical challenge with the causative drug.

METHODS

We immunohistochemically investigated in vivo dynamics of T-cell trafficking and activation that occur in the evolving FDE lesions using sequential biopsy specimens obtained at multiple time points from the FDE lesions.

RESULTS

Intraepidermal CD8+ T cells, which are resident in the lesional epidermis as a stable homogeneous population of memory T cells, transiently acquire a natural killer-like phenotype and express cytotoxic granules upon activation. The influx into the epidermis of CD4+ T cells including Foxp3+ regulatory T cells (Tregs) during the evolution serves to ameliorate epidermal damage induced by activation of the intraepidermal CD8+ T cells. Interleukin-15 derived from the lesional epidermis could maintain the survival of the intraepidermal CD8+ T cells even in the absence of antigenic stimulus over a prolonged period of time (> 4 years).

CONCLUSIONS

Whether Tregs could migrate to the lesions upon activation of intraepidermal CD8+ T cells would determine whether the inflammation becomes resolved spontaneously or progresses to TEN.

Nonimmediate reactions to betalactams

PURPOSE OF REVIEW

Nonimmediate reactions to beta-lactams include several clinical entities, from maculopapular rash to severe reactions such as Steven-Johnson syndrome. Toxic epidermal necrolysis and organ-specific reactions may also occur.

RECENT FINDINGS

Progress has been made in understanding the role of the immunological system in nonimmediate reactions to beta-lactams. Different T-cell subsets recognize beta-lactams after haptenation of serum or cell proteins in the context of major histocompatibility complex. Studies using T-cell lines and clones have shown that a heterogeneous response is generated, with the expression of different cytokine profiles. Betalactams also act on dendritic cells, inducing changes that enable them to interact with naïve lymphocytes, becoming memory T cells. Tissue-activated CD4 and CD8 cells express perforin and other cytotoxic mediators that elicit the lesions. Studies on the clinical course of these entities indicate that cells migrate, establishing a recirculation with homing to the skin and back to the circulation. These cells thus participate not only in skin lesions but probably also in the repair process.

SUMMARY

Understanding the immunological mechanisms involved in nonimmediate reactions to beta-lactams has improved over the last few years, with better definition of the different T-cell subpopulations involved. Experimental studies and monitoring of the response support the implication of different cell subsets.

Targeting leukocyte trafficking to inflamed skin - still an attractive therapeutic approach?

Research into leukocyte trafficking and its therapeutic exploitation appears to be a multistep process, just like the trafficking cascade itself. The initial euphoria evoked by an early understanding of the trafficking steps was followed by considerable disappointment following the clinical failure of the first selectin antagonist Cylexin (CY-1503), a sialyl Lewis(X) mimetic. The research area recovered and identified additional attractive pharmacological targets such as chemokine receptors and integrins. However, after lack of efficacy in anti-chemokine trials and the fatalities associated with anti VLA-4 therapy (Tysabri), the question arose again whether targeting leukocyte trafficking is really promising or whether such a complex, multistep process with many redundant and/or functionally overlapping molecules is simply too challenging to deal with. In this article, we delineate some pros and cons of this approach followed by a brief update on where we stand in the field and where we might move in the future.

Fixed drug eruption induced by an iodinated non-ionic X-ray contrast medium: a practical approach to identify the causative agent and to prevent its recurrence

We describe the case of a 61-year-old physician who developed a fixed drug eruption (FDE) after i.v. administration of a non-ionic monomeric iodinated X-ray contrast medium (CM) (iopromide). During CM injection, a sensation of heat occurred, which was most intense in the right inguinal region. Four hours later, the FDE arose with a red macule of approximately 2 cm in diameter covering a dermal infiltration in the right inguinal region, and enlarged up to a final size of 15 x 8 cm, accompanied by a burning sensation. The patient's history revealed a similar reaction in the same localization and of the same clinical appearance after CM injection 1 year before. Patch testing 4 months later revealed positive reactions to iomeprol and iohexol. Iopamidol injection for another CT examination 23 months later was well tolerated. Based on these results, we suggest patch testing after CM-induced FDE, which could help to select a CM for future CT examinations. Late onset of adverse CM reactions may manifest as FDE. Patch testing within the previous skin reaction area is the diagnostic tool that should be used to confirm the suspected agent, possible cross-reacting agents and well-tolerated agents.

Possible role of Fas/Fas ligand-mediated apoptosis in the pathogenesis of fixed drug eruption

BACKGROUND

Although epidermal and dermal T cells play roles in the pathogenesis of fixed drug eruption (FDE), not much is known about keratinocyte death and its precise mechanism in FDE.

OBJECTIVES

Our aim is to elucidate the mechanism that underlies keratinocyte death in FDE, that is, the role of apoptosis and its signalling pathway.

METHODS

We first examined the involvement of apoptosis in the active FDE lesions by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labelling (TUNEL) assay and immunohistochemical analysis of caspase-3. We then examined the expressions of Fas and Fas ligand (FasL) to deduce the possible upstream signalling pathway of apoptosis, if apoptosis were involved. We finally characterized the infiltrated T-cell subpopulations in the active FDE lesions.

RESULTS

In the active FDE lesions, TUNEL positivity was strongly observed in the basal keratinocytes, and also weakly observed in the upper dermal infiltrates as well as in a few keratinocytes in the granular layer. The distribution of TUNEL-positive cells was similar to that of the strong staining of active capase-3. Fas was found mainly in the keratinocytes and some infiltrated dermal cells, whereas FasL was identified predominantly in the intraepidermal and dermal infiltrated cells and in some basal keratinocytes. Overlapping expression of Fas and FasL was accompanied by apoptosis in the FDE lesions. Many of the infiltrated mononuclear cells were CD8+. Perforin was rarely observed in the FDE lesions.

CONCLUSIONS

These findings suggest that apoptosis of the keratinocyte is highly likely to be involved in the pathogenesis of FDE, and this cytotoxicity might be predominantly mediated by the FasL of the infiltrating CD8+ T cells, possibly also playing an inflammatory role.