Association of toxic shock syndrome toxin-secreting and exfoliative toxin-secreting Staphylococcus aureus with Kawasaki syndrome complicated by coronary artery disease

Immune and non-immune mechanisms that determine vasculitis and coronary artery aneurysm topography in Kawasaki disease and MIS-C

The overlap between multisystem inflammatory syndrome in children (MIS-C) and Kawasaki disease (KD) including coronary artery aneurysms (CAA) and broadly shared gastrointestinal and mucocutaneous disease is poorly defined. In this perspective, we highlight common age-related extravascular epicardial microanatomical and immunological factors that might culminate in CAA expression in both MIS-C and KD. Specifically, the coronary vasa vasorum originates outside the major coronary arteries. Widespread inflammation in the epicardial interstitial compartment in shared between KD and MIS-C. Age-related changes in the neonatal and immature coronary vasculature including the impact of coronary artery biomechanical factors including coronary vessel calibre, age-related vessel distensibility, flow, and vessel neurovascular innervation may explain the decreasing CAA frequency from neonates to older children and the virtual absence of CAA in young adults with the MIS-C phenotype. Other KD and MIS-C features including mucocutaneous disease with keratinocyte-related immunopathology corroborate that disease phenotypes are centrally influenced by inflammation originating outside vessel walls but a potential role for primary coronary artery vascular wall inflammation cannot be excluded. Hence, common extravascular originating tissue-specific responses to aetiologically diverse triggers including superantigens may lead to widespread interstitial tissue inflammation characteristically manifesting as CAA development, especially in younger subjects. Given that CAA is virtually absent in adults, further studies are needed to ascertain whether epicardial interstitial inflammation may impact on both coronary artery physiology and cardiac conduction tissue and contribute to cardiovascular disease- a hitherto unappreciated consideration.

Antibodies and Immunity During Kawasaki Disease

The cause of Kawasaki disease (KD), the leading cause of acquired heart disease in children, is currently unknown. Epidemiology studies support that an infectious disease is involved in at least starting the inflammatory cascade set off during KD. Clues from epidemiology support that humoral immunity can have a protective effect. However, the role of the immune system, particularly of B cells and antibodies, in pathogenesis of KD is still unclear. Intravenous immunoglobulin (IVIG) and other therapies targeted at modulating inflammation can prevent development of coronary aneurysms. A number of autoantibody responses have been reported in children with KD and antibodies have been generated from aneurysmal plasma cell infiltrates. Recent reports show that children with KD have similar plasmablast responses as other children with infectious diseases, further supporting an infectious starting point. As ongoing studies are attempting to identify the etiology of KD through study of antibody responses, we sought to review the role of humoral immunity in KD pathogenesis, treatment, and recovery.

Case report of an unusual presentation of Staphylococcus aureus induced toxic shock syndrome/hyperimmunoglobulinemia E syndrome

RATIONALE

Toxic shock syndrome (TSS) typically is an acute onset multi-organ infection caused by TSS toxin-1 producing Staphylococcus aureus. Herein we describe a highly unusual case report.

PATIENT CONCERNS

A male patient self-referred to the University of Minnesota Hospital with a chronic history of S aureus infection with accompanying fever, hypotension, and nonhealing, football-sized lesion on his leg.

DIAGNOSIS

An unusual case presentation of TSS/hyperimmunoglobulin E syndrome is described. The patient had a leg wound from which TSS toxin-1 S aureus was isolated. The patient exhibited characteristic skewing of T cells to those with variable region, β-chain T cell receptor-2. Other patients have been seen with related presentations.

INTERVENTIONS

The following therapeutic regimen was instituted: vigorous antibacterial scrubs several times daily plus intravenous Ancef 3 days each month; intravenous infusions of immunoglobulin G infusions (28 gm) every 3 weeks; and weekly subcutaneous injections of recombinant granulocyte colony-stimulating factor.

OUTCOME

Improvement was obvious within 3 months: no further cellulitic episodes occurred; the patient regained 95 pounds in 9 months; blanching and cyanosis of fingers disappeared within 3 months as did intractable pain although mild hypesthesias continued for 2 years; erythroderma resolved, and repeat skin biopsies performed after 2 years no longer demonstrated T cell receptor skewing. Although IgE levels have not completely returned to normal, the patient remains in excellent health.

LESSONS

We propose that staphylococcal TSST-1 was responsible for the serious problems suffered by this patient as suggested by the following features: rapid onset of chronic, life-threatening, disorder that began with an episode of staphylococcal sepsis; the extraordinary elevation of IgE levels in this previously non-atopic individual; the acquired severe granulocyte chemotactic defect that accompanied this hyperimmunoglobulinemia ("Job Syndrome") with its accompanying wound-healing defect; and the striking diffuse erythroderma, including palmar erythema ("Red Man Syndrome") with hypotension and fever that also characterizes TSS.

B Cells and Antibodies in Kawasaki Disease

The etiology of Kawasaki disease (KD), the leading cause of acquired heart disease in children, is currently unknown. Epidemiology supports a relationship of KD to an infectious disease. Several pathological mechanisms are being considered, including a superantigen response, direct invasion by an infectious etiology or an autoimmune phenomenon. Treating affected patients with intravenous immunoglobulin is effective at reducing the rates of coronary aneurysms. However, the role of B cells and antibodies in KD pathogenesis remains unclear. Murine models are not clear on the role for B cells and antibodies in pathogenesis. Studies on rare aneurysm specimens reveal plasma cell infiltrates. Antibodies generated from these aneurysmal plasma cell infiltrates showed cross-reaction to intracellular inclusions in the bronchial epithelium of a number of pathologic specimens from children with KD. These antibodies have not defined an etiology. Notably, a number of autoantibody responses have been reported in children with KD. Recent studies show acute B cell responses are similar in children with KD compared to children with infections, lending further support of an infectious disease cause of KD. Here, we will review and discuss the inconsistencies in the literature in relation to B cell responses, specific antibodies, and a potential role for humoral immunity in KD pathogenesis or diagnosis.

Update on association between Kawasaki disease and infection

The relationship between infection and Kawasaki disease (KD) remains unclear. Infection has long been considered a key predisposing factor for KD. Bacterial and viral agents may be related to the onset of KD because of superantigen and cytokine production. Various bacterial and viral infections have been reported to be associated with KD, but the actual mechanism remains unknown. The higher association between KD and enterovirus has been well documented by using Taiwan National Health Insurance Research Database. However, no evidence has been obtained that various bacterial and viral infections induce KD. Comprehensive research, including infectious agents, should be conducted to elucidate the pathogenesis of KD.

Staphylococcal and streptococcal superantigen exotoxins

SUMMARY This review begins with a discussion of the large family of Staphylococcus aureus and beta-hemolytic streptococcal pyrogenic toxin T lymphocyte superantigens from structural and immunobiological perspectives. With this as background, the review then discusses the major known and possible human disease associations with superantigens, including associations with toxic shock syndromes, atopic dermatitis, pneumonia, infective endocarditis, and autoimmune sequelae to streptococcal illnesses. Finally, the review addresses current and possible novel strategies to prevent superantigen production and passive and active immunization strategies.

The role of superantigens of group A Streptococcus and Staphylococcus aureus in Kawasaki disease

PURPOSE OF REVIEW

Since the first suggestion of a superantigen hypothesis for Kawasaki disease over a decade ago, debate on the aetiology remains inconclusive. This article reviews recent publications that address the role of superantigens of group A Streptococcus and Staphylococcus aureus in the pathogenesis of Kawasaki disease.

RECENT FINDINGS

Over the past few years, new superantigens produced by group A Streptococcus and S. aureus have been increasingly identified, bringing the total known number to more than 30. Several studies on T-cell Vbeta repertoires and seroloepidemiology have demonstrated evidence for the involvement of single or multiple superantigens produced by the two pathogens. The associated superantigens differed in those studies, including streptococcal pyrogenic toxins A and C, staphylococcal enterotoxins A-C, and toxic shock syndrome toxin 1. These disparate findings suggest that the inflammation of Kawasaki disease does not result from a single agent but rather a final common inflammatory pathway in genetically susceptible individuals after numerous infectious agents.

SUMMARY

Certain staphylococcal and streptococcal superantigens are suggested to be responsible for the development of Kawasaki disease. A better understanding of the precise role of the causative agents will lead to accurate diagnosis, more targeted therapy and an improvement of coronary outcomes.

Epidemiology and etiology of Kawasaki disease

Kawasaki disease was first reported in Japan in 1967 by Dr. Tomisaku Kawasaki. It has since been recognized worldwide, and in at the United States and Japan is the most important cause of acquired heart disease in children, surpassing other more recognized conditions such as rheumatic fever, endocarditis and myocarditis. It is primarily a disease of children less than 5 years of age but has been reported in older children and adults. Risk factors for the illness include Asian ancestry, male gender and certain familial predispositions. Observations such as similarity to certain exanthematous infectious diseases, temporal-geographic clustering of cases and seasonality in incidence favors an infectious etiology. Pathology and pathogenesis of the disease indicate that it is a medium-sized artery vasculitis that results from a dramatic immune activation that in most cases reversed by immune modulating agents such as intravenous immunoglobulin. Unfortunately, the etiology of the illness remains obscure, although recent studies favor a possible viral etiology.

Kawasaki disease and toxic shock syndrome--at last the etiology is clear?

A decade after the superantigen hypothesis for KD was first suggested, it has still not been either proven or refuted conclusively. Although initial optimism for the hypothesis was quashed by a series of published papers apparently refuting the idea, in the last few years there have been a number of good studies providing evidence in support of the superantigen hypothesis. Whether this renewed enthusiasm is justified will hopefully become clear in the near future. Ultimately, accurate diagnosis, more targeted treatment, and preventative strategies depend on the unraveling of the immunopathogenesis of this disease.

Antibodies to highly conserved peptide sequence of staphylococcal and streptococcal superantigens in Kawasaki disease

Superantigen-mediated disease such as toxic shock syndrome is seen in patients who have a weak antibody response to the antigen toxic shock syndrome toxin 1 (TSST-1). We hypothesized that there may be deficiency in antibody production to staphylococcal and streptococcal toxins in Kawasaki disease (KD) children. A peptide was constructed from the homologous portion of the staphylococcal enterotoxins (SE) and streptococcal pyrogenic enterotoxins (SPE), and antibodies to the peptide were made. The anti-peptide antibody immunoblotted several of the SE toxins and SPE toxins. Presence of the peptide antibodies was investigated via ELISA in the sera of acute KD (n = 30), convalescent KD (n = 12), control adults (n = 10), and children (n = 19). The mean anti-peptide antibodies were indistinguishable between control children and KD before treatment with immunoglobulin (P = 0.7) but rose significantly after therapy (P < 0.01). The adults had significantly higher antibodies than the KD, both acute and late (P < 0.0001) and the control children (P < 0.0001). Thus, KD patients do not have a defective serological response against toxins such as SPE/SE/TSST-1. Normal children have significantly lower antitoxin antibody levels to the toxins compared to the adults.

Staphylococcal superantigens and T cell expansions in Wegener's granulomatosis

In Wegener's granulomatosis (WG), a form of autoimmune systemic vasculitis, chronic carriage of Staphylococcus aureus constitutes a risk factor for the development of exacerbations. Circulating T cells in this disease are persistently activated, suggesting the presence of a chronic stimulus. A causal link between chronic carriage of S. aureus and chronic T cell activation in WG is conceivable, because S. aureus produces superantigens (SAg), which are potent T cell stimulators. Superantigenic stimulation of T cells results in expansion of T cell subsets expressing SAg-binding T cell receptor V-beta (Vbeta) chains. In the present study we hypothesized that in WG the presence of staphylococcal SAg is accompanied by expansion of SAg-reacting T cell subsets. We tested our hypothesis in a cross-sectional and a longitudinal study in which the association between seven staphylococcal SAg genes [typed by poplymerase chain reaction (PCR)], eight SAg-binding Vbeta chains and four SAg-non-binding Vbeta chains (assessed by flow-cytometry) was assessed. Both studies showed that T cell expansions were present at a significantly higher rate in WG patients than in healthy individuals, but were not associated with the presence of either S. aureus or its SAg. Moreover, T cell expansions were generally of small extent, and did not appear simultaneously in both CD4 and CD8 subsets. We conclude that in WG S. aureus effects its supposed pathogenic function by a mechanism other than superantigenic T cell activation.

Pharmacological therapy for patients with Kawasaki disease

Kawasaki disease is a systemic vasculitis of unknown aetiology that has been reported worldwide since its initial description in Japanese children. The most significant sequelae of acute Kawasaki disease are related to the inflammation of small to medium sized arteries and, in particular, the development of coronary artery aneurysms. Because the aetiology is unknown, pharmacological therapy is nonspecific and directed towards modulation of the inflammatory response and inhibition of platelet activation with the aim of preventing coronary artery aneurysms. In the US, the recommended treatment for Kawasaki disease in the acute phase is a single, high dose of intravenous gammaglobulin (2 g/kg) and high dose aspirin (80 to 100 mg/kg/day). Use of this regimen has resulted in a significant decrease in the incidence of coronary artery abnormalities. Although the American Heart Association currently recommends high dose aspirin, moderate doses are used in Japan and the optimal dose of aspirin is not known. There has been renewed interest in the use of corticosteroids in the treatment of acute Kawasaki disease: however, their precise role remains unclear. Newer antiplatelet agents have also shown some promise in the treatment of patients with coronary artery aneurysms. Long term pharmacological therapy consists primarily of anticoagulation in patients with persistent coronary artery abnormalities. In this review, current recommendations for pharmacological therapy in Kawasaki disease are reviewed and some of the controversies in management of this disease, including management of patients who do not respond to initial therapy and the role of corticosteroids in the acute setting, are outlined.

[Staphylococcal toxic syndrome, atypical presentation of Kawasaki syndrome or staphylococcal skin syndrome?]

CASE REPORT

A three-year-old girl was admitted for persistent fever, erythermatous rash with subsequent desquamation, stomatitis, cheleitis and cervical lymphadenopathy following development of a buttock abscess secondary to an insect bite. A TSS-positive Staphylococcus aureus strain was isolated from the abscess.

COMMENTS

Both clinical and bacteriological features led to discuss a "toxic shock syndrome without shock", an atypical form of Kawasaki syndrome without thrombocytosis and coronary arteritis or a staphylococcal skin syndrome. An early treatment with antibiotics could have limited the toxin production explaining both symptomatology and favourable course of the disease.

Staphylococcus aureus and Wegener's granulomatosis

Wegener's granulomatosis (WG) is a form of systemic vasculitis. It is characterized by granulomatous inflammation in the upper and lower airways, vasculitis and necrotizing glomerulonephritis, and is strongly associated with antineutrophil cytoplasmic antibodies against proteinase 3. Since the etiology of the disease is not clear, treatment, consisting of corticosteroids and immunosuppressives, is nonspecific and associated with severe side effects. Pinpointing the trigger(s) of the disease would highly improve treatment. Clinical evidence shows that an infectious agent, the bacterium Staphylococcus aureus, is a risk factor for disease relapse, suggesting its involvement in the pathogenesis of WG. Here we review both clinical and experimental data that either indicate or support a role for S. aureus in WG.

Long-time persistence of superantigen-producing Staphylococcus aureus strains in the intestinal microflora of healthy infants

Staphylococcus aureus has been isolated at an increasing rate from infants' stools during the last decades, but it is not known whether this species can colonize and persist in the intestinal microflora. To investigate this, 49 Swedish infants were followed prospectively from birth until 12 months of age. S. aureus was identified in a rectal swab obtained 3 d after delivery and in quantitative cultures of fecal samples collected at 1, 2, 4, and 8 weeks and at 6 and 12 months of age. A random amplified polymorphic DNA (RAPD) method was developed to distinguish individual S. aureus strains from one another and the strains were tested for production of enterotoxins A-D and TSST-1. By 3 days of age, 16% of infants had S. aureus in their intestines, which increased to 73% by 2-6 months, whereafter it decreased slightly to 53%. At the same time S. aureus population counts in colonized infants declined from an average 10(6.8) CFU/g feces during the first months of life to 10(4.0) CFU/g feces by 12 months. Colonized infants usually harbored one or two S. aureus strains in their microflora for long periods of time. Few strains were transient passengers and the median time of persistence of S. aureus strains in the microflora was several months. Of the 75 S. aureus strains identified, 43% produced one or more toxins: 13% SEA, 7% SEB, 23% SEC, 4% SED, and 11% TSST-1. Altogether, 47% of the investigated infants were colonized by a toxin-producing S. aureus during their first year of life. Despite this they were apparently healthy and did not have more gastrointestinal problems than noncolonized infants. This report is the first to show that S. aureus may be a resident member of the normal intestinal microflora in infancy.

Evidence for the involvement of bacterial superantigens in psoriasis, atopic dermatitis, and Kawasaki syndrome

A growing body of evidence implicates streptococcal and staphylococcal superantigens in the development of psoriasis, atopic dermatitis and Kawasaki syndrome. In each of these illnesses, an abnormal state of immunologic activity is observed. Superantigens, which have a unique ability to activate large numbers of lymphocytes, are likely to contribute to these disorders in a number of ways. The demonstrated activities of bacterial superantigens include increasing the number of circulating lymphocytes, with activation of autoreactive subsets, upregulation of tissue homing receptors on circulating lymphocytes, and local activation of immune cells within affected tissues. Through these and other mechanisms, superantigens have a proven ability to induce high levels of inflammatory cytokines and/or initiate autoimmune responses that contribute to the development of skin and vascular disorders. Though development of the illnesses discussed in this review are highly complex processes, superantigens may well play a critical role in their onset or maintenance. Understanding superantigen function may elucidate potential therapeutic strategies for these disorders.

The many faces of Kawasaki syndrome

The clinical challenge lies in recognizing cases not fully meeting the syndrome's diagnostic criteria and those that strongly resemble a variety of infectious and reactive disorders. Prompt treatment with high-dose intravenous immune globulin in combination with aspirin can significantly reduce the frequency and severity of cardiovascular complications.

Infants colonized with enterotoxin-producing staphylococci at 3 months display a decreased frequency of interferon-gamma-producing CD45RO lymphocytes upon stimulation with staphylococcal enterotoxin A at birth but not at 6 months of age

The aim of the study was to elucidate the relationship between the cytokine response to staphylococcal enterotoxin A (SEA) at birth and subsequent staphylococcal colonization in the first months of life. In a cohort of 45 newborns, cord blood lymphocytes were stimulated with SEA (10 ng/ml) in vitro, re-stimulated with PMA (phorbol myristate acetate) and ionomycin at day 3 and assessed for CD45RO expression and cytokine generation by flow cytometry. The infants were classified into three groups according to nasal staphylococcal colonization and enterotoxin generation at 3 months: There were 16 infants with either no colonization or non-enterotoxin-producing staphylococci, 16 infants with enterotoxins B, C, D and E, and 13 infants colonized with SEA-producing staphylococci. At birth, the group without subsequent colonization displayed a significantly higher frequency of CD45RO-positive interferon-gamma-producing cells (1.7%; range 0.0-9.3%) in comparison to the SEA-positive group (0.1%; range 0.0-0.4%) and also to the group positive for other enterotoxins (0.50%; range 0.0-2.5%). Comparable but less pronounced results were found for interleukin-5 but not for interleukins 2 and 4. At 6 months, no differences in cytokine generation were detected between the three groups. The results provide evidence that a non-specific immunologic immaturity at birth is a risk factor for early bacterial colonization. Furthermore, it is remarkable that this immaturity is similar to that seen in infants destined to be atopic with respect to disequilibrium of interferon-gamma to interleukin-4 generation. Thus the link between early staphylococcal colonization and subsequent atopy requires further investigation.

Staphylococcus aureus isolates from patients with Kawasaki disease express high levels of protein A

Kawasaki disease (KD) is an acute vasculitis of young children that can be complicated by coronary artery abnormalities. Recent findings suggest that a superantigen(s) may play an important role in stimulating the immune activation associated with the disease, although the origin of this superantigen(s) is unclear. Staphylococcus aureus, isolated from the rectum or pharynx of patients with KD, secretes toxic shock syndrome toxin 1 (TSST-1). The KD isolates express low levels of other exoproteins compared to isolates from patients with toxic shock syndrome (TSS). Thus, it was previously suggested that the KD isolates may be defective in the global regulatory locus agr (for accessory gene regulator), which positively regulates these factors (D. Y. M. Leung et al., Lancet 342:1385-1388, 1993). Here we describe another characteristic of KD isolates. When considered collectively, the KD isolates were found to express higher levels of staphylococcal protein A than the TSS isolates, another characteristic of an agr-defective phenotype. This correlated with a higher level of spa mRNA in these isolates. In contrast, the KD and TSS isolates expressed comparable levels of TSST-1, consistent with previous findings (D. Y. M. Leung et al., Lancet 342:1385-1388, 1993). Analysis of RNAIII transcript levels and nucleotide sequence analysis of the RNAIII-coding region suggested that the KD isolates are not defective in RNAIII, the effector molecule of the agr regulatory system. However, induction of RNAIII transcription in the KD isolates did not result in a dramatic decrease in the amount of spa mRNA, as has been reported for other strains (F. Vandenesch, J. Kornblum, and R. P. Novick, J. Bacteriol. 173:6313-6320, 1991).

Anti-Human Cardiac Myosin Autoantibodies in Kawasaki Syndrome

Kawasaki syndrome (KS) is the major cause of acquired heart disease in children. Although acute myocarditis is observed in most patients with KS, its pathogenesis is unknown. Because antimyosin autoantibodies are present in autoimmune myocarditis and rheumatic carditis, the purpose of the current study was to determine whether anticardiac myosin Abs might be present during the acute stage of KS. Sera from KS patients as well as age-matched febrile controls and normal adults were compared for reactivity with human cardiac myosin in ELISAs and Western blot assays. A total of 5 of 13 KS sera, as compared with 5 of 8 acute rheumatic fever sera, contained Ab titers to human cardiac myosin that were significantly higher than those found in control sera. Both cardiac and skeletal myosins were recognized in the ELISA by KS sera, although stronger reactivity was observed to human cardiac myosin. Only IgM antimyosin Abs from KS sera were significantly elevated relative to control sera. KS sera containing antimyosin Abs recognized synthetic peptides from the light meromyosin region of the human cardiac myosin molecule and had a different pattern of reactivity than acute rheumatic fever sera, further supporting the association of antimyosin Ab with KS. These Abs may contribute to the pathogenesis of acute myocarditis found in patients with KS.

The role of superantigens in human diseases: therapeutic implications for the treatment of skin diseases

Although it is well established that immune mechanisms contribute to the pathogenesis of chronic inflammatory skin diseases such as atopic dermatitis (AD) and psoriasis, the actual events that trigger the immunological pathways resulting in these skin diseases are not well understood. Colonization and infection with Staphylococcus aureus and streptococci has been reported to exacerbate AD and psoriasis. Recent studies demonstrating that bacterial toxins can act as superantigens provide mechanism(s) by which S. aureus and streptococci could mediate an inflammatory skin lesion that consists predominantly of activated T-cells and monocytes. This review will explore the diverse mechanisms by which bacterial superantigens can induce skin inflammation following systemic or local infection. These observations provide a new direction for the development of novel approaches for the treatment of skin inflammation.

Endothelial cells expressing an inflammatory phenotype are lysed by superantigen-targeted cytotoxic T cells

The objective of this study was to investigate whether the superantigen staphylococcal enterotoxin A (SEA), which binds to HLA class II and T-cell receptor Vbeta chains, can direct cytotoxic T cells to lyse cytokine-stimulated endothelial cells (EC). In addition, we wanted to determine whether SEA-primed cytotoxic T cells could be targeted to EC surface molecules as a means of a novel cancer immunotherapy. Human umbilical vein EC (HUVEC), dermal microvascular EC (HMVEC), or the EC line EA.hy926 stimulated with gamma interferon (IFN-gamma) or tumor necrosis factor alpha (TNF-alpha) displayed upregulated HLA class II and adhesion molecule (CD54 and CD106) expression, respectively. SEA-primed T cells induced a strong cytotoxicity against IFN-gamma- and TNF-alpha-activated EA.hy926 which had been preincubated with SEA. Blocking of CD54 completely abrogated the T-cell attack. SEA-D227A, which has a mutated class II binding site, did not promote any cytotoxicity. A strong lysis was observed when a fusion protein consisting of protein A and SEA-D227A was added together with T cells to TNF-alpha-induced EA.hy926 and HUVEC precoated with monoclonal antibodies (MAb) directed against HLA class I, CD54, or CD106 molecules. Finally, an scFv antibody fragment reactive with an unknown EC antigen was fused with SEA-D227A. Both EA.hy926 and HMVEC were efficiently lysed by scFv-SEA-D227A-triggered cytotoxic T cells. Taken together, superantigen-activated T-cell-dependent EC killing was induced when EC expressed an inflammatory phenotype. Moreover, specific MAb targeting of the superantigen to surface antigens induced EC lysis. Our data suggest that directed T-cell-mediated lysis of unwanted proliferating EC, such as those in the tumor microvasculature, can be clinically useful.