Updates in SJS/TEN: collaboration, innovation, and community

Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis (SJS/TEN) is a predominantly drug-induced disease, with a mortality rate of 15-20%, that engages the expertise of multiple disciplines: dermatology, allergy, immunology, clinical pharmacology, burn surgery, ophthalmology, urogynecology, and psychiatry. SJS/TEN has an incidence of 1-5/million persons per year in the United States, with even higher rates globally. One of the challenges of SJS/TEN has been developing the research infrastructure and coordination to answer questions capable of transforming clinical care and leading to improved patient outcomes. SJS/TEN 2021, the third research meeting of its kind, was held as a virtual meeting on August 28-29, 2021. The meeting brought together 428 international scientists, in addition to a community of 140 SJS/TEN survivors and family members. The goal of the meeting was to brainstorm strategies to support the continued growth of an international SJS/TEN research network, bridging science and the community. The community workshop section of the meeting focused on eight primary themes: mental health, eye care, SJS/TEN in children, non-drug induced SJS/TEN, long-term health complications, new advances in mechanisms and basic science, managing long-term scarring, considerations for skin of color, and COVID-19 vaccines. The meeting featured several important updates and identified areas of unmet research and clinical need that will be highlighted in this white paper.

Assessment of Need for Improved Identification of a Culprit Drug in Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis

Importance

Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) is a severe hypersensitivity reaction. Identifying a culprit drug is critical for patient care, yet identification is based on clinical judgment. Data are limited on the accuracy in or approach to identifying a culprit drug.

Objective

To evaluate patient allergy list outcomes, current approaches in identifying culprit drugs, and potential methods of improving culprit drug identification.

Design, Setting, and Participants

This retrospective cohort study spanned 18 years (January 2000 to July 2018), was conducted at Brigham and Women's Hospital and Massachusetts General Hospital (Boston), and included patients with clinically and histologically confirmed cases of SJS/TEN overlap and TEN.

Main Outcomes and Measures

This study descriptively analyzed potential culprits to SJS/TEN, patients' allergy lists, and currently used approaches that led to those lists. It then tested the theoretical contribution of incorporating various parameters to allergy list outcomes.

Results

Of 48 patients (29 women [60.4%]; 4 Asian [8.3%], 6 Black [12.5%], 5 Hispanic [10.4%], and 25 White [52.1%] individuals; median age, 40 years [range, 1-82 years]), the mean (SD) number of drugs taken per patient at disease onset was 6.5 (4.7). Physicians labeled 17 patients as allergic to a single culprit drug. Comparatively, 104 drugs were added to allergy lists across all patients. Physicians' approaches relied largely on heuristic identification of high-notoriety drugs and the timing of drug exposure. Use of a vetted database for drug risk improved sensitivity. Algorithm for Drug Causality for Epidermal Necrolysis scoring was discordant in 28 cases, labeling an additional 9 drugs missed by physicians and clearing 43 drugs labeled as allergens by physicians. Human leukocyte antigen testing could have potentially affected 20 cases. Consideration of infection as a culprit was limited.

Conclusions and Relevance

The results of this cohort study suggest that currently used approaches to identify culprit drugs in SJS/TEN are associated with overlabeling patients allergic to likely nonculprit drugs and less commonly missed possible culprit drugs. Incorporation of a systematized unbiased approach could potentially improve culprit drug identification, although ultimately a diagnostic test is necessary.

Peripheral host T cells survive hematopoietic stem cell transplantation and promote graft-versus-host disease

Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality in hematopoietic stem cell transplantation (HSCT). Donor T cells are key mediators in pathogenesis, but a contribution from host T cells has not been explored, as conditioning regimens are believed to deplete host T cells. To evaluate a potential role for host T cells in GVHD, the origin of skin and blood T cells was assessed prospectively in patients after HSCT in the absence of GVHD. While blood contained primarily donor-derived T cells, most T cells in the skin were host derived. We next examined patient skin, colon, and blood during acute GVHD. Host T cells were present in all skin and colon acute GVHD specimens studied, yet were largely absent in blood. We observed acute skin GVHD in the presence of 100% host T cells. Analysis demonstrated that a subset of host T cells in peripheral tissues were proliferating (Ki67+) and producing the proinflammatory cytokines IFN-γ and IL-17 in situ. Comparatively, the majority of antigen-presenting cells (APCs) in tissue in acute GVHD were donor derived, and donor-derived APCs were observed directly adjacent to host T cells. A humanized mouse model demonstrated that host skin-resident T cells could be activated by donor monocytes to generate a GVHD-like dermatitis. Thus, host tissue-resident T cells may play a previously unappreciated pathogenic role in acute GVHD.

High-throughput sequencing of the T cell receptor β gene identifies aggressive early-stage mycosis fungoides

Mycosis fungoides (MF), the most common cutaneous T cell lymphoma (CTCL) is a malignancy of skin-tropic memory T cells. Most MF cases present as early stage (stage I A/B, limited to the skin), and these patients typically have a chronic, indolent clinical course. However, a small subset of early-stage cases develop progressive and fatal disease. Because outcomes can be so different, early identification of this high-risk population is an urgent unmet clinical need. We evaluated the use of next-generation high-throughput DNA sequencing of the T cell receptor β gene (TCRB) in lesional skin biopsies to predict progression and survival in a discovery cohort of 208 patients with CTCL (177 with MF) from a 15-year longitudinal observational clinical study. We compared these data to the results in an independent validation cohort of 101 CTCL patients (87 with MF). The tumor clone frequency (TCF) in lesional skin, measured by high-throughput sequencing of the TCRB gene, was an independent prognostic factor of both progression-free and overall survival in patients with CTCL and MF in particular. In early-stage patients, a TCF of >25% in the skin was a stronger predictor of progression than any other established prognostic factor (stage IB versus IA, presence of plaques, high blood lactate dehydrogenase concentration, large-cell transformation, or age). The TCF therefore may accurately predict disease progression in early-stage MF. Early identification of patients at high risk for progression could help identify candidates who may benefit from allogeneic hematopoietic stem cell transplantation before their disease becomes treatment-refractory.

Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis: Associations, Outcomes, and Pathobiology-Thirty Years of Progress but Still Much to Be Done

Although rare, Stevens-Johnson syndrome and toxic epidermal necrolysis remain among the most devastating of acute conditions involving the skin. In the past 30 years, tremendous progress has been made in understanding the causes and pathobiology of this often life-threatening condition. Su et al demonstrate associations between IL 15 serum levels and the outcome of patients with Stevens-Johnson syndrome and toxic epidermal necrolysis. Their findings provide ideas for further investigations that may help us better understand the role of cytokines in this T-cell mediate disease and provides clues to possible new therapies.

Host skin T cells survive stem cell transplant conditioning and are functional during acute GVHD

Graft-versus-host-disease (GVHD) is a major cause of morbidity and mortality in stem cell transplantation (SCT). Acute GVHD is thought to be mediated by donor T cells that target and destroy host tissues. Studies into the host immune system are limited, as it is assumed that host T cells in peripheral tissues such as skin are depleted by conditioning regimens in parallel to T cells in lymphoid organs and blood. However, it is recently appreciated that a high number of memory T cells reside long-term within the organs most affected by GVHD. We investigated whether host skin T cells survive SCT conditioning and are present during acute GVHD. To do so, excess skin biopsy tissue was obtained from patients with acute skin GVHD who had undergone myeloablative or non-myeloablative conditioning and allogeneic SCT with sex-mismatched donor cells. Tissue was stained for T cell markers via immunofluorescence concurrently with in situ hybridization for the X and Y chromosomes. All seventeen patients studied demonstrated persistence of host T cells in skin, often in equal or greater numbers than donor T cells. Host skin T cells survived regardless of myeloablative or non-myeloablative conditioning, of patient age, and of day post-SCT (samples ranged from 12–213 days post-SCT). Comparatively, blood T cell chimerism was 100% donor in nearly all samples, indicating diverging effects of conditioning on T cell compartments. Skin host T cells demonstrated pro-inflammatory cytokine production. These results provide a novel avenue of research into GVHD pathobiology and suggest that alternative conditioning regimens should be employed if host skin T cells are to be targeted.

Cross-Sectional Study Evaluating Skin, Hair, Nail, and Bone Disease in Patients with Focal Dermal Hypoplasia

Focal dermal hypoplasia (FDH) is an X-linked dominant disease characterized by dermal thinning and fat herniation with other ectodermal and mesodermal abnormalities. There is limited literature regarding the symptomatology and progression of skin, hair, and nail disease. The risk of bone fragility has not been explored either. This cross-sectional survey-based study explored these gaps in knowledge and provides direction for future avenues of research in FDH.

Survival of tissue-resident memory T cells requires exogenous lipid uptake and metabolism

Tissue-resident memory T (T_RM) cells persist indefinitely in epithelial barrier tissues and protect the host against pathogens. However, the biological pathways that enable the long-term survival of T_RM cells are obscure. Here we show that mouse CD8⁺ T_RM cells generated by viral infection of the skin differentially express high levels of several molecules that mediate lipid uptake and intracellular transport, including fatty-acid-binding proteins 4 and 5 (FABP4 and FABP5). We further show that T-cell-specific deficiency of Fabp4 and Fabp5 (Fabp4/Fabp5) impairs exogenous free fatty acid (FFA) uptake by CD8⁺ T_RM cells and greatly reduces their long-term survival in vivo, while having no effect on the survival of central memory T (T_CM) cells in lymph nodes. In vitro, CD8⁺ T_RM cells, but not CD8⁺ T_CM cells, demonstrated increased mitochondrial oxidative metabolism in the presence of exogenous FFAs; this increase was not seen in Fabp4/Fabp5 double-knockout CD8⁺ T_RM cells. The persistence of CD8⁺ T_RM cells in the skin was strongly diminished by inhibition of mitochondrial FFA β-oxidation in vivo. Moreover, skin CD8⁺ T_RM cells that lacked Fabp4/Fabp5 were less effective at protecting mice from cutaneous viral infection, and lung Fabp4/Fabp5 double-knockout CD8⁺ T_RM cells generated by skin vaccinia virus (VACV) infection were less effective at protecting mice from a lethal pulmonary challenge with VACV. Consistent with the mouse data, increased FABP4 and FABP5 expression and enhanced extracellular FFA uptake were also demonstrated in human CD8⁺ T_RM cells in normal and psoriatic skin. These results suggest that FABP4 and FABP5 have a critical role in the maintenance, longevity and function of CD8⁺ T_RM cells, and suggest that CD8⁺ T_RM cells use exogenous FFAs and their oxidative metabolism to persist in tissue and to mediate protective immunity.

Graft-infiltrating host dendritic cells play a key role in organ transplant rejection

Successful engraftment of organ transplants has traditionally relied on preventing the activation of recipient (host) T cells. Once T-cell activation has occurred, however, stalling the rejection process becomes increasingly difficult, leading to graft failure. Here we demonstrate that graft-infiltrating, recipient (host) dendritic cells (DCs) play a key role in driving the rejection of transplanted organs by activated (effector) T cells. We show that donor DCs that accompany heart or kidney grafts are rapidly replaced by recipient DCs. The DCs originate from non-classical monocytes and form stable, cognate interactions with effector T cells in the graft. Eliminating recipient DCs reduces the proliferation and survival of graft-infiltrating T cells and abrogates ongoing rejection or rejection mediated by transferred effector T cells. Therefore, host DCs that infiltrate transplanted organs sustain the alloimmune response after T-cell activation has already occurred. Targeting these cells provides a means for preventing or treating rejection.

Donor dendritic cell-derived exosomes promote allograft-targeting immune response

The immune response against transplanted allografts is one of the most potent reactions mounted by the immune system. The acute rejection response has been attributed to donor dendritic cells (DCs), which migrate to recipient lymphoid tissues and directly activate alloreactive T cells against donor MHC molecules. Here, using a murine heart transplant model, we determined that only a small number of donor DCs reach lymphoid tissues and investigated how this limited population of donor DCs efficiently initiates the alloreactive T cell response that causes acute rejection. In our mouse model, efficient passage of donor MHC molecules to recipient conventional DCs (cDCs) was dependent on the transfer of extracellular vesicles (EVs) from donor DCs that migrated from the graft to lymphoid tissues. These EVs shared characteristics with exosomes and were internalized or remained attached to the recipient cDCs. Recipient cDCs that acquired exosomes became activated and triggered full activation of alloreactive T cells. Depletion of recipient cDCs after cardiac transplantation drastically decreased presentation of donor MHC molecules to directly alloreactive T cells and delayed graft rejection in mice. These findings support a key role for transfer of donor EVs in the generation of allograft-targeting immune responses and suggest that interrupting this process has potential to dampen the immune response to allografts.

Clinical implications of basic science discoveries: nociceptive neurons as targets to control immunity--potential relevance for transplantation

Increasing evidence indicates the existence of a complex cross-regulation between the most important biosensors of the human body: The immune and nervous systems. Cytokines control body temperature and trigger autoimmune disorders in the central nervous system, whereas neuropeptides released in peripheral tissues and lymphoid organs modulate inflammatory (innate) and adaptive immune responses. Surprisingly, the effects of nerve fibers and the antidromic release of its pro-inflammatory neuropeptides on the leukocytes of the immune system that mediate graft rejection are practically unknown. In the transplantation field, such area of research remains practically unexplored. A recent study by Riol-Blanco et al has revealed new details on how nociceptive nerves regulate the pro-inflammatory function of leukocytes in peripheral tissues. Although the mechanism(s) by which neuroinflammation affects the immune response against the allograft remains unknown, recent data suggest that this new area of research is worth exploring for potential development of novel complementary therapies for prevention/treatment of graft rejection.

Pemphigus vulgaris presenting with multiple lesion morphologies

Pemphigus vulgaris is an uncommon intraepidermal blistering disorder that typically presents with flaccid bullae or erosions. We report a patient with pemphigus vulgaris who presented with several unusual clinical features: tense bullae with dependently layered pus, true target lesions coalescing into annular configurations, and diffuse desquamation that initially raised concern for toxic epidermal necrolysis. We discuss the differential diagnosis and implications of these morphological findings.

Chlorhexidine gluconate-impregnated central-line dressings and necrosis in complicated skin disorder patients

Although chlorhexidine gluconate (CHG) disks have been shown to help reduce the incidence of central line-associated blood stream infections, their use can result in local skin necrosis. The effects of CHG disks on patients with complex skin pathology have not been studied. We report 6 cases of dermal necrosis associated with Biopatch (Ethicon Inc, Somerville, NJ) CHG disks in adults with complex skin pathology including those with Stevens-Johnson syndrome, toxic epidermal necrolysis syndrome, graft-versus-host disease, burns, and anasarca. All patients had a CHG disk placed at a central venous catheter insertion site. Age range was from 21 to 84 years. Discovery of the reaction ranged from 4 to 14 days after disk placement. Resultant skin erosions required 2 to 10 weeks to reepithelialize. Complicated skin disorder patients represent a rare subset of the critically ill who appear prone to CHG disk necrosis. Continuous contact of CHG under occlusive dressings is speculated to predispose Stevens-Johnson syndrome, toxic epidermal necrolysis syndrome, graft-versus-host disease, and burn patients to local chemical injury secondary to loss of the epithelial tissue barrier, decreased cohesion of the epidermal-dermal junction, and increased tissue permeability. In these patients, the risk of placing the CHG disk may present more risk than using alternative antimicrobial dressings.

A novel p40-independent function of IL-12p35 is required for progression and maintenance of herpes stromal keratitis

PURPOSE. Interleukin (IL)-12p40 can couple with IL-12p35 or p19 chains to form the molecules IL-12p70 and IL-23, respectively, which promote T(H)1 cytokine responses. IL-12p35 can bind to EBI3 to form the anti-inflammatory molecule IL-35, but a proinflammatory function of IL-12p35 independent of IL-12p40 has not been described. Here such a function in a mouse model of herpes stromal keratitis (HSK), a CD4(+) T(H)1 cell-dependent corneal inflammation, is demonstrated. METHODS. Corneas of wild-type (WT), IL-12p40(-/-), IL-12p35(-/-), and IL-12p35(-/-)p40(-/-) (double knockout) mice were infected with the RE strain of HSV-1, and HSK was monitored based on corneal opacity, neovascularization, leukocytic infiltrate, and cytokine/chemokine levels. RESULTS. All mouse strains developed moderate HSK by 11 days after infection (dpi). However, from 11 to 21 dpi, HSK progressed in WT and IL-12p40(-/-) mice but regressed in IL-12p35(-/-) and IL-12p35(-/-)p40(-/-) mice. HSK regression was characterized by reductions in neutrophils and CD4(+) T cells and attenuation of blood vessels, which was associated with reduced levels of the chemokines KC (CXCL3), Mip-2 (CXCL2), and MCP-1 (CCL2) and the angiogenic factor vascular endothelial growth factor. CONCLUSIONS. HSK development does not require IL-12p40 and is thus independent of IL-12p70 and IL-23. However, late HSK progression does require a previously unrecognized IL-12p40-independent, proinflammatory function of IL-12p35.

An extensive case of dermonecrotic arachnidism

Dermonecrotic arachnidism is the potential cutaneous reaction to spider bite venom. The yellow sac spider, genus Cheiracanthium, is historically considered capable of inducing dermonecrotic lesions. However, recently this belief has been hotly debated. In this article, the authors provide a brief review of dermonecrotic arachnidism and describe a case of a 20-year-old man who developed severe necrosis and edema of the left thigh, buttock, penis, and scrotum following the bite of a yellow sac spider. Notably, the patient wore a tight-fitting garment for multiple hours following the spider bite, thus compressing the envenomated tissue. This is the first case reporting such severe dermonecrosis resulting from a yellow sac spider bite and highlights the potential effects of tissue compression following spider envenomation.

Suppression of autoimmune diabetes by soluble galectin-1

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease that targets the beta-cells of the pancreas. We investigated the ability of soluble galectin-1 (gal-1), an endogenous lectin that promotes T cell apoptosis, to down-regulate the T cell response that destroys the pancreatic beta-cells. We demonstrated that in nonobese diabetic (NOD) mice, gal-1 therapy reduces significantly the amount of Th1 cells, augments the number of T cells secreting IL-4 or IL-10 specific for islet cell Ag, and causes peripheral deletion of beta-cell-reactive T cells. Administration of gal-1 prevented the onset of hyperglycemia in NOD mice at early and subclinical stages of T1D. Preventive gal-1 therapy shifted the composition of the insulitis into an infiltrate that did not invade the islets and that contained a significantly reduced number of Th1 cells and a higher percentage of CD4(+) T cells with content of IL-4, IL-5, or IL-10. The beneficial effects of gal-1 correlated with the ability of the lectin to trigger apoptosis of the T cell subsets that cause beta-cell damage while sparing naive T cells, Th2 lymphocytes, and regulatory T cells in NOD mice. Importantly, gal-1 reversed beta-cell autoimmunity and hyperglycemia in NOD mice with ongoing T1D. Because gal-1 therapy did not cause major side effects or beta-cell toxicity in NOD mice, the use of gal-1 to control beta-cell autoimmunity represents a novel alternative for treatment of subclinical or ongoing T1D.

Dendritic cell (DC)- derived exosomes spread donor allo-antigen between recipient's DC following cardiac transplantation (141.11)

Exosomes are nanovesicles generated in multivesicular endosomes that are released to the extracellular space by different cell types. Since DC-derived exosomes (dexosomes) express MHC-peptide and costimulatory molecules, we investigated the role of dexosomes in elicitation of the anti-donor response in transplantation. Dexosomes were generated from bone marrow-derived DC and labeled with PKH67 for traffic studies. CD4+ TCRtg T cells (Thy1.1+) specific for the IEα52-68 (BALB/c)-IAb (B10) complex were CFSE-labeled and transferred i.v. to host Thy1.2+ B6 mice. Graft infiltrating DC were isolated from BALB/c (CD45.2+) cardiac grafts 3 days after transplantation in B6 (CD45.2+) recipients and genetically-engineered ex vivo to release exosomes expressing the reporter marker eGFP, and then transferred i.v. into host CD45.1+ B6 mice. We demonstrated that although graft-infiltrating leukocytes release exosomes ex vivo, they do not secrete enough exosomes in circulation to stimulate donor-reactive T-cells in lymphoid organs. Instead, migrating DCs (generated in vitro or isolated from allografts), once they home in the spleen, they transfer exosomes expressing eGFP to spleen-resident DCs. Thus, exchange of exosomes between DCs in lymphoid organs constitutes a mechanism by which passenger leukocytes transfer alloAg to recipient's APC and amplify generation of donor-reactive T-cells.

Quiescent recipient splenic dendritic cells (DC) re-process therapeutic DC into alloantigen for presentation to and down-regulation of anti-donor T cells to prolong allograft survival (141.31)

Current dogma in transplantation presumes that therapeutic maturation-resistant dendritic cells (MR-DC) prevent allograft rejection by directly interacting with donor-reactive T-cells in vivo. However, this assumption remains untested. Our study therefore aimed to elucidate the mechanism by which donor MR-DC down-regulate the anti-donor response to prolong allograft survival in mice. We employed as prototypic donor MR-DC, bone marrow-derived DC treated with the active form of vitamin D3, 1α,25(OH)2D3. We demonstrate that donor-derived MR-DC prolonged cardiac allograft survival similarly as donor apoptotic or viable splenocytes, suggesting that different donor-derived cellular therapies share a common mechanism of action. We determined that once injected i.v., MR-DC were short-lived and failed to directly tolerize donor-reactive T-cells. Rather, apoptotic MR-DC were internalized and re-processed by quiescent recipient splenic CD11chiCD8α+ and CD11chiCD8- DC, which in turn induced deletion of effector T-cells and outgrowth of regulatory T-cells via the indirect pathway. Importantly, activated recipient DC induced robust T-cell activation via indirect presentation. Our data suggest that therapeutic DC, like other more practical cellular therapies, serve as a source of alloantigen for recipient quiescent DC that in turn down-regulate the anti-donor response to prolong allograft survival.

Exosomes as a short-range mechanism to spread alloantigen between dendritic cells during T cell allorecognition

Exosomes are nanovesicles released by different cell types including dendritic cells (DCs). The fact that exosomes express surface MHC-peptide complexes suggests that they could function as Ag-presenting vesicles or as vehicles to spread allogeneic Ags for priming of anti-donor T cells during elicitation of graft rejection or induction/maintenance of transplant tolerance. We demonstrate that circulating exosomes transporting alloantigens are captured by splenic DCs of different lineages. Internalization of host-derived exosomes transporting allopeptides by splenic DCs leads to activation of anti-donor CD4 T cells by the indirect pathway of allorecognition, a phenomenon that requires DC-derived, instead of exosome-derived, MHC class II molecules. By contrast, allogeneic exosomes are unable to stimulate direct-pathway T cells in vivo. We demonstrate in mice that although graft-infiltrating leukocytes release exosomes ex vivo, they do not secrete enough concentrations of exosomes into circulation to stimulate donor-reactive T cells in secondary lymphoid organs. Instead, our findings indicate that migrating DCs (generated in vitro or isolated from allografts), once they home in the spleen, they transfer exosomes expressing the reporter marker GFP to spleen-resident DCs. Our results suggest that exchange of exosomes between DCs in lymphoid organs might constitute a potential mechanism by which passenger leukocytes transfer alloantigens to recipient's APCs and amplify generation of donor-reactive T cells following transplantation.

Activated inflammatory infiltrate in HSV-1-infected corneas without herpes stromal keratitis

PURPOSE

To investigate herpes stromal keratitis (HSK) immunopathology by studying HSV-1-infected corneas that fail to develop HSK.

METHODS

Plaque assay quantified HSV-1 in the tear film of infected mice. FACS analysis enumerated corneal leukocytic infiltrate and characterized infiltrate phenotypically after staining for activation and regulatory T cell (Treg) markers and for markers of antigen-presenting cell (APC) maturation. Treg cells were depleted in vivo using anti-CD25 mAb. Luminex analysis quantified the amount of cytokines and chemokines expressed in corneal tissue homogenate.

RESULTS

Infected corneas without HSK exhibited a pronounced leukocytic infiltrate containing a significantly higher proportion and nearly identical absolute number of activated CD4+ T cells 15 days after infection when compared with those with HSK. Moreover, the frequency and absolute number of regulatory CD4+ T cells (Tregs) was lower in nondiseased corneas, and Treg depletion did not influence HSK incidence. The frequency of mature, immunogenic DCs and the ratio of mature DCs to CD4+ T cells were nearly identical in corneas with and without HSK. The authors observed a reduced population of neutrophils and reduced expression of neutrophil chemoattractants MIP-1beta and keratinocyte chemoattractant and the neutrophil-attracting cytokine IL-6 in corneas without HSK.

CONCLUSIONS

These findings demonstrate that HSV-1-infected corneas can retain clarity in the presence of a substantial secondary leukocytic infiltrate, that activated CD4+ T cells, while necessary, are not sufficient for HSK development, that susceptibility to HSK is not determined by Tregs, and that clinical disease correlates with the accumulation of a critical mass of neutrophils through chemoattraction.