Efficacy of Mepliex® Ag Versus Xeroform® As A Split-Thickness Skin Graft Donor Site Dressing: Bad Habits Die Hard.

Autografting with split-thickness skin grafts (STSG) remains an essential procedure in burn and reconstructive surgery. The process of harvesting STSG, however, leaves behind a donor site, an exposed area of partial-thickness dermis left to heal by secondary intention. There has yet to be a consensus amongst surgeons regarding optimal management of the donor site. The ideal donor site dressing is one that allows for expeditious healing while minimizing pain and infection. Despite numerous studies demonstrating the superiority of moist wound healing, many surgeons continue to treat STSG donor sites dry, with petroleum-based gauze. In this study, two burn centers performed a retrospective review of burn patients whose STSG donor sites were treated with either Xeroform® or Mepilex® Ag dressings. Infections were documented and in a subgroup analysis of patients, postoperative pain scores were noted and total opiate usage during hospitalization was calculated. Analysis revealed an overall infection rate of 1.2% in the Mepilex® Ag group and 11.4% in the Xeroform® group (p<0.0001). Patients with Xeroform® donor site dressings had increased odds of donor site infection (OR=10.8, p=0.002). In subgroup analysis, there were no significant differences in maximum pain scores between Mepilex® Ag and Xeroform® groups, nor were there differences in opiate usage. STSG donor sites dressed with silver foam dressings have a lower rate of donor site infection relative to those dressed with petroleum-based gauze. Moist donor site dressings such as foam dressings (including Mepilex® Ag) should be the standard of care in STSG donor site wound care.

La greffes de peau mince (GPM) demeure une procédure essentielle dans la chirurgie de brûlure et de reconstruction. La zone donneuse de greffe (ZDG) représente une perte de substance cutanée superficielle, cicatrisant spontanément. Il n'y a pas de consensus concernant la prise en charge optimale de la ZDG. Le pansement idéal de la ZDG doit promouvoir la cicatrisation et réduire la douleur ainsi que le risque infectieux. Malgré les nombreuses publications montrant l'intérêt d'un environnement humide pour la cicatrisation, de nombreux chirurgiens réalisent des pansements secs vaselinés. Cette étude rétrospective effectuée dans 2 CTB compare les pansements de ZDG réalisés au Xéroform® ou au Mepilex Ag®. Les infections ont été documentées et, dans un sous-groupe, les scores de douleur et la consommation d'opiacés au long de l'hospitalisation ont été notés. Les taux d'infection sont de 1,2% dans le groupe Mepilex Ag® et 11,4% avec Xéroform® (p<0,0001). Le risque d'infection de la ZDG est augmenté (OR 10,8 ; p = 0,002) en cas d'utilisation de Xéroform®. Il n'y avait pas de différence de douleur et de consommation d'opiacés entre les 2 groupes. Les ZDG recouvertes d'un pansement hydrocellulaire imprégné d'argent s'infectent moins que celles traitées avec une gaze imprégnée de vaseline. L'utilisation sur les ZDG d'un pansement humide comme une mousse hydrocellulaire (par exemple Mepilex Ag®) devrait devenir la norme.

Satisfaction with life after burn: A Burn Model System National Database Study.

OBJECTIVES: While mortality rates after burn are low, physical and psychosocial impairments are common. Clinical research is focusing on reducing morbidity and optimizing quality of life. This study examines self-reported Satisfaction With Life Scale scores in a longitudinal, multicenter cohort of survivors of major burns. Risk factors associated with Satisfaction With Life Scale scores are identified. METHODS: Data from the National Institute on Disability, Independent Living, and Rehabilitation Research (NIDILRR) Burn Model System (BMS) database for burn survivors greater than 9 years of age, from 1994 to 2014, were analyzed. Demographic and medical data were collected on each subject. The primary outcome measures were the individual items and total Satisfaction With Life Scale (SWLS) scores at time of hospital discharge (pre-burn recall period) and 6, 12, and 24 months after burn. The SWLS is a validated 5-item instrument with items rated on a 1-7 Likert scale. The differences in scores over time were determined and scores for burn survivors were also compared to a non-burn, healthy population. Step-wise regression analysis was performed to determine predictors of SWLS scores at different time intervals. RESULTS: The SWLS was completed at time of discharge (1129 patients), 6 months after burn (1231 patients), 12 months after burn (1123 patients), and 24 months after burn (959 patients). There were no statistically significant differences between these groups in terms of medical or injury demographics. The majority of the population was Caucasian (62.9%) and male (72.6%), with a mean TBSA burned of 22.3%. Mean total SWLS scores for burn survivors were unchanged and significantly below that of a non-burn population at all examined time points after burn. Although the mean SWLS score was unchanged over time, a large number of subjects demonstrated improvement or decrement of at least one SWLS category. Gender, TBSA burned, LOS, and school status were associated with SWLS scores at 6 months; scores at 12 months were associated with LOS, school status, and amputation; scores at 24 months were associated with LOS, school status, and drug abuse. CONCLUSIONS: In this large, longitudinal, multicenter cohort of burn survivors, satisfaction with life after burn was consistently lower than that of non-burn norms. Furthermore mean SWLS scores did not improve over the two-year follow-up period. This study demonstrates the need for continued efforts to improve patient-centered long term satisfaction with life after burn.

Microsurgery in the burn population - a review of the literature.

The management of patients suffering from burn injury poses unique challenges for the reconstructive surgeon, both in the acute and delayed settings. Once resuscitative measures are optimized and hemodynamic stability is achieved, early burn debridement and coverage is performed. Traditionally, this consists of excision of devitalized tissue and subsequent coverage using split thickness skin grafts. However, in certain instances, and depending on the extent and nature of the burn injury, skin grafting (or even local tissue rearrangement) may not be a reasonable option. in these cases, free tissue transfer may provide a viable reconstructive alternative. While free flap reconstruction is rare in burn surgery, particularly in the acute setting, burn injuries that expose vital structures, such as tendon, nerve, bone, or deep vessels, require robust flap coverage. in the delayed setting, unsightly scar formation and contracture often occurs secondary to skin graft coverage. These significant patient morbidities are often amenable to free tissue transfer as well. This review article discusses the indications, applications, and problems with free flap surgery for burn injuries in both the acute and delayed setting, and summarizes the available literature on microsurgical free tissue transfer for burn management.

La prise en charge des patients atteints de brûlures pose des défis uniques pour le chirurgien de reconstruction, à la fois dans les cadres aigus et retardés. Une fois les mesures de réanimation sont optimisés et la stabilité hémodynamique est obtenue, il faut faire le débridement précoce et la couverture de la brûlure. Traditionnellement, il s'agit de l'excision des tissus dévitalisés et la couverture par division ultérieure en utilisant des greffes de peau partielle épaisse. Cependant, dans certains cas, et en fonction des dimensions et la nature de la brûlure, une greffe de peau n'est pas toujours une option raisonnable. Dans ces cas, le transfert de tissu libre peut fournir une alternative viable. Alors que la reconstruction de lambeau libre est rare dans la chirurgie des brûlures, en particulier dans le cadre aiguë, les brûlures qui exposent les structures vitales, telles que les tendons, nerfs, os, ou les vaisseaux profonds, nécessitent une couverture robuste. Dans le cadre retardé, la formation de cicatrices inesthétiques et de contractures se produit fréquemment secondaire à une couverture de greffe de peau. Souvent ces morbidités importantes sont aussi prêtent au transfert de tissu libre. Cet article de revue discute les indications, les applications, et des problèmes avec la chirurgie de lambeau libre pour des brûlures dans les cadres aigus et retardés. Cet article résume aussi la littérature disponible sur la microchirurgie du transfert de tissu libre pour la prise en charge des brûlures.

Sulfur mustard gas exposure: case report and review of the literature.

This report describes a case of burn injury following exposure to sulfur mustard, a chemical agent used in war. A review of the diagnostic characteristics, clinical manifestations, and therapeutic measures used to treat this uncommon, yet extremely toxic, entity is presented. The aim of this report is to highlight the importance of considering this diagnosis in any war victim, especially during these unfortunate times of rising terrorist activities.

Ce rapport décrit un cas de brûlure suite à une exposition au gaz moutarde, un agent chimique utilisé dans la guerre. On présente un examen des caractéristiques de diagnostic, les manifestations cliniques et les mesures thérapeutiques utilisés pour traiter ce phénomène rare, mais extrêmement toxique. L'objectif de ce rapport est de mettre en évidence l'importance de considérer ce diagnostic dans toute victime de la guerre, surtout en ces temps malheureux de la hausse des activités terroristes.

Renal dysfunction in burns: a review.

Acute kidney injury (AKI), although rare, is a major complication of burn injury that commonly leads to mortality. It results from a complex interplay of various cellular and neuro-humoral changes affecting burn patients. Guidelines for the treatment of this entity are still not well defined; therefore, prevention and early diagnosis are key to avoid the unfavorable prognosis of AKI. These entail a comprehensive understanding of the global physiologic changes underlying the condition of burn patients and a judicious interpretation of their continuous homeostatic alterations. The aim of this review is to present the salient features in burn patient physiology that contribute to AKI. Strategies for identifying early AKI are presented. Finally, the different treatment modalities are revisited.

Les lésions rénales aiguës (LRA) sont rares, mais elles constituent une complication majeure des brûlures qui mène souvent à la mortalité. Ces lésions sont provoquées par une interaction complexe de divers changements cellulaires et neurohumoraux qui affectent les patients brûlés. Les directives pour le traitement de ces patients ne sont pas encore bien définies et, par conséquent, la prévention et le diagnostic précoce sont essentiels pour éviter le pronostic défavorable des LRA. Cela nécessite une compréhension complète des changements physiologiques présents dans ces patients et une interprétation judicieuse de leurs continuelles altérations homéostatiques. Les Auteurs se sont proposé de présenter les principales caractéristiques de la physiologie du patient brûlé qui contribuent à ce type de lésion. Apres avoir discuté les stratégies pour identifier ces lésions en phase précoce, ils concluent avec une description des différentes modalités de traitement.

The role of a dedicated staff psychiatrist in modern burn centers.

Psychiatric disorders may be more common in burn-injured subjects than in the general population, and oftentimes contribute to the injury itself. Even in the absence of underlying psychiatric illnesses, burn patients may still benefit from a psychiatric evaluation during and after their hospitalization. In this regard, we included a dedicated psychiatry service in our multidisciplinary burn team. We review herein the course of burn patients that were offered psychiatric evaluation and highlight the benefits of such a program. We conducted an IRB-approved retrospective chart review of burn subjects admitted to our institution between June 15, 2009 and April 30, 2010 and identified 83 patients that were examined by our psychiatrist. Indications for consultation, history of psychiatric illness and substance abuse, as well as administered drugs, were recorded. Among the 83 evaluated patients, 48 (57.8%) had a preexisting psychiatric disorder and 36 (43.4%) suffered from substance abuse. The most common indications for consultation were pain (28.1%), alcohol dependence (25.8%), anxiety (24.7%), illicit drug abuse (16.8%), depression (15.7%), post-traumatic stress disorder (8.9%), and sleep disturbances (8.9%). Pharmacotherapy was initiated in 75 patients (90.3%). 31 (37.3%) had neither a psychiatric disorder nor a history of substance abuse, although 26 of them (83.9%) still received drugs for psychiatric conditions. The inclusion of a dedicated psychiatrist as part of our burn team has improved our comprehensive burn care. In the overwhelming majority of cases, even in the absence of preexisting psychiatric illnesses, consultation resulted in pharmacologic intervention and enhanced patient care.

Les troubles psychiatriques peuvent être plus fréquents chez les patients brûlés que dans la population générale, et contribuent souvent à la blessure elle-même. Même en l'absence de maladies psychiatriques sous-jacents, les patients brûlés peuvent encore bénéficier d'une évaluation psychiatrique pendant et après leur hospitalisation. À cet égard, nous avons inclus un service de psychiatrie dédié à notre équipe multidisciplinaire pour la gestion des brûlures. Nous examinons ici les cours de patients brûlés à qui une évaluation psychiatrique a été proposée et nous mettons en évidence les avantages d'un tel programme. Nous avons effectué un examen rétrospectif - approuvé par les CPP - des patients brûlés admis dans notre institution entre le 15 Juin 2009 et le 30 Avril, 2010, à partir de lequel nous avons identifié 83 patients qui ont été examinés par notre psychiatre. Nous avons enregistré les indications pour la consultation, les antécédents de maladie psychiatrique et la toxicomanie, ainsi que les médicaments administrés. Parmi les 83 patients évalués, 48 (57,8 %) avaient un trouble psychiatrique préexistante et 36 (43,4%) a souffert de l'abus de substances. Les indications les plus fréquentes de consultation étaient la douleur (28,1%), la dépendance à l'alcool (25,8%), l'anxiété (24,7%), l'abus de drogues illicites (16,8%), la dépression (15,7%), les troubles de stress post-traumatique (8,9%), et troubles du sommeil (8,9%). La pharmacothérapie a été instaurée dans 75 patients (90,3%). 31 (37,3%) ne présentaient pas de troubles psychiatriques ni une histoire d'abus de substance mais quand même 26 d'entre eux (83,9 %) ont reçu des médicaments pour des troubles psychiatriques. L'inclusion d'un psychiatre spécialisé dans le cadre de notre équipe a amélioré notre système complet de soins aux brulés. Dans l'écrasante majorité des cas, même en l'absence des maladies psychiatriques préexistantes, la consultation a donné lieu à une intervention pharmacologique et a amélioré les soins aux patients.

A pathogenic role for myelin-specific CD8(+) T cells in a model for multiple sclerosis.

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system (CNS) characterized by plaques of infiltrating CD4(+) and CD8(+) T cells. Studies of MS and experimental autoimmune encephalomyelitis (EAE), an animal model of MS, focus on the contribution of CD4(+) myelin-specific T cells. The role of CD8(+) myelin-specific T cells in mediating EAE or MS has not been described previously. Here, we demonstrate that myelin-specific CD8(+) T cells induce severe CNS autoimmunity in mice. The pathology and clinical symptoms in CD8(+) T cell-mediated CNS autoimmunity demonstrate similarities to MS not seen in myelin-specific CD4(+) T cell-mediated EAE. These data suggest that myelin-specific CD8(+) T cells could function as effector cells in the pathogenesis of MS.

Rag-1-dependent cells are necessary for 1,25-dihydroxyvitamin D(3) prevention of experimental autoimmune encephalomyelitis.

Multiple sclerosis (MS) is a demyelinating disease involving genetic and environmental risk factors. Geographic, genetic, and biological evidence suggests that one environmental risk factor may be lack of vitamin D. Here, we investigated how 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) inhibits experimental autoimmune encephalomyelitis (EAE), an MS model. The experiments used adoptive transfer of TCR-transgenic (TCR1) cells specific for myelin basic protein (MBP) peptide into unprimed recipients. When unprimed TCR1 splenocytes were transferred, and the recipients were immunized with peptide, the mock-treated mice developed EAE, but the 1,25-(OH)(2)D(3)-treated recipients remained disease-free. Both groups had TCR1 T cells that proliferated in response to MBP Ac1-11 and produced IFN-gamma but not IL-4 in the lymph node. In the central nervous system (CNS), the mock-treated mice had activated TCR1 T cells that produced IFN-gamma but not IL-4, while the 1,25-(OH)(2)D(3)-treated mice had TCR1 T cells with a non-activated phenotype that did not produce IFN-gamma or IL-4. When activated TCR1 T cells producing IFN-gamma were transferred into unprimed mice, the mock-treated and the 1,25-(OH)(2)D(3)-treated recipients developed EAE. Likewise, the 1,25-(OH)(2)D(3) did not inhibit Th1 cell IFN-gamma production or promote Th2 cell genesis or IL-4 production in vitro. Finally, the 1,25-(OH)(2)D(3) inhibited EAE in MBP-specific TCR-transgenic mice that were Rag-1(+), but not in animals that were Rag-1-null. Together, these data refute the hypothesis that the hormone inhibits Th1 cell genesis or function directly or through an action on antigen-presenting cells, or promotes Th2 cell genesis or function. Instead, the evidence supports a model wherein the 1,25-(OH)(2)D(3) acts through a Rag-1-dependent cell to limit the occurrence of activated, autoreactive T cells in the CNS.

Age-dependent T cell tolerance and autoimmunity to myelin basic protein.

Experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis, is induced by activating a subset of myelin basic protein (MBP)-specific T cells that have escaped tolerance induction. Here, we define the tolerance mechanisms that eliminate the majority of MBP-specific T cells from the periphery. We show that MBP-specific T cells undergo central tolerance mediated by bone marrow-derived antigen-presenting cells presenting exogenously derived MBP epitopes. The efficiency of tolerance is age dependent, reflecting the developmentally regulated expression of MBP. Dependence of tolerance on the amount of MBP expressed in vivo results in an age window of susceptibility to EAE in mice that peaks during puberty. These results suggest that factors regulating expression of self-antigens in vivo can influence susceptibility to autoimmunity.

Rapid depletion of peripheral antigen-specific T cells in TCR-transgenic mice after oral administration of myelin basic protein.

In myelin basic protein (MBP)-specific TCR-transgenic (Tg) mice, peripheral T cells express the Valpha2.3/Vbeta8.2-Tg TCR, demonstrate vigorous proliferative responses to MBP in vitro, and can exhibit experimental autoimmune encephalomyelitis (EAE) within 5 days of pertussis toxin injection. We explored the effects of oral administration of MBP on the cellular trafficking of the MBP-specific TCR-Tg cells and the ability of oral MBP to protect Tg mice from EAE. Tg mice were fed MBP, OVA or vehicle and sacrificed at various times after feeding. An immediate and dramatic decrease in Valpha2.3/Vbeta8.2(+)-Tg cells was observed in the periphery within 1 h after feeding. By 3 days after feeding, the percentage of Tg cells increased to near control levels, but decreased again by 10 days. When MBP or vehicle-fed Tg mice were challenged for EAE at this point, disease was severe in the vehicle-fed mice and reduced in the MBP-fed mice over the 40-day observation period. In vitro studies revealed a biphasic pattern of MBP proliferative unresponsiveness and an induction of Th1 cytokines. Immunohistochemical staining showed that the number of Tg cells found in the intestinal lamina propria increased dramatically as the number of Tg cells in the periphery decreased. There was no apparent proliferation of Tg cells in the lamina propria, indicating that Tg cells trafficked there from the periphery. Taken together, these results suggest that T cell trafficking into the site of Ag deposition acts to protect the TCR-Tg mouse from EAE.

In situ tolerance within the central nervous system as a mechanism for preventing autoimmunity.

Multiple sclerosis (MS) is believed to be an autoimmune disease in which autoreactive T cells infiltrate the central nervous system (CNS). Animal models of MS have shown that CNS-specific T cells are present in the peripheral T cell repertoire of healthy mice and cause autoimmune disease only when they are activated by immunization. T cell entry into the CNS is thought to require some form of peripheral activation because the blood-brain barrier prohibits trafficking of this tissue by naive cells. We report here that naive T cells can traffic to the CNS without prior activation. Comparable numbers of T cells are found in the CNS of both healthy recombinase activating gene (Rag)(-/)- T cell receptor (TCR) transgenic mice and nontransgenic mice even when the transgenic TCR is specific for a CNS antigen. Transgenic T cells isolated from the CNS that are specific for non-CNS antigens are phenotypically naive and proliferate robustly to antigenic stimulation in vitro. Strikingly, transgenic T cells isolated from the CNS that are specific for myelin basic protein (MBP) are also primarily phenotypically naive but are unresponsive to antigenic stimulation in vitro. Mononuclear cells from the CNS of MBP TCR transgenic but not nontransgenic mice can suppress the response of peripheral MBP-specific T cells in vitro. These results indicate that naive MBP-specific T cells can traffic to the CNS but do not trigger autoimmunity because they undergo tolerance induction in situ.

Scanning electron microscopy and X-ray diffraction studies in the analysis of medical materials: Gore-Tex versus braided polyester tape for repair of the incompetent cervix.

Cathodoluminescence in the scanning electron microscope and roentgenogram diffraction studies were applied to the analysis of two different medical materials used in cervical cerclage, the treatment of cervical incompetence. Braided polyester tape or Gore-Tex was used as suture material and was analyzed both before and after use in cerclage of the cervix. Results of SEM and X-ray diffraction studies showed distinct differences between the two materials, with the Gore-Tex demonstrating a superior morphological integrity and a decreased likelihood of phagocyte adhesion. These results correlated well with the clinical observations, which also showed Gore-Tex to be a superior medical material.

Transducer user syndrome: an occupational hazard of the ultrasonographer.

Since no study to date has assessed the prevalence of scanning-related disorders amongst sonographers in Obstetrics and Gynecology, we distributed a survey to all trained personnel in our ultrasound division. We evaluated the correlation between injuries sustained in the workplace, and factors such as age, gender, work load and intensity, scanning techniques, previous medical problems, and physical activity. Injuries included one or more of the following: carpal tunnel syndrome; carpal instability; tendinitis; back, shoulder, and neck pain; tingling and/or numbness in the extremities; weakness; and motion restriction. Of the 44 respondents, 29 (65%) have experienced some type of injury or symptom over the course of their scanning career. Five (12%) reported having missed work because of their symptoms, 15 (34%) have received orthopedic treatment (medication or physiotherapy), two (4.5%) have been diagnosed with carpal tunnel syndrome, and one (2.3%) with carpal instability based on electrophysiological examinations. These results demonstrate that ultrasound scanning in Obstetrics and Gynecology may pose an occupational risk for doctors and technicians.

Tolerance and autoimmunity in TCR transgenic mice specific for myelin basic protein.

T-cell receptor (TCR) transgenic mice provide the ability to follow the maturation and fate of T cells specific for self-antigens in vivo. This technology represents a major breakthrough in the study of autoimmune diseases in which specific antigens have been implicated. Proteins expressed within the central nervous system are believed to be important autoantigens in multiple sclerosis. TCR transgenic models specific for myelin basic protein (MBP) allowed us to assess the role of tolerance in providing protection from T cells with this specificity. Our studies demonstrate that T cells specific for the immunodominant epitope of MBP do not undergo tolerance in vivo and that TCR transgenic mice are susceptible to spontaneous autoimmune disease. The susceptibility to spontaneous disease is dependent on exposure to microbial antigens. MBP TCR transgenic models expressing TCRs specific for the same epitope of MBP but utilizing different V alpha genes exhibit differing susceptibilities to spontaneous disease. These data support the idea that genetic and environmental differences play a role in susceptibility to autoimmunity. MBP TCR transgenic models are playing an important role in defining mechanisms by which infectious agents trigger autoimmune disease as well as defining mechanisms by which tolerance is induced to distinct epitopes within self-antigens.

Cutting edge: myelin basic protein-specific cytotoxic T cell tolerance is maintained in vivo by a single dominant epitope in H-2k mice.

Multiple sclerosis (MS) is believed to be an autoimmune disease mediated by T cells specific for CNS Ags. MS lesions contain both CD4+ and CD8+ T lymphocytes. The contribution of CD4+ T cells to CNS autoimmune disease has been extensively studied in an animal model of MS, experimental autoimmune encephalomyelitis. However, little is known about the role of autoreactive CD8+ cytotoxic T cells in MS or experimental autoimmune encephalomyelitis. We demonstrate here that myelin basic protein (MBP) is processed in vivo by the MHC class I pathway leading to a MBP79-87/Kk complex. The recognition of this complex by MBP-specific cytotoxic T cells leads to a high degree of tolerance in vivo. This study is the first to show that the pool of self-reactive lymphocytes specific for MBP contain MHC class I-restricted T cells whose response is regulated in vivo by the induction of tolerance.

Highly cross-reactive T cell responses to myelin basic protein epitopes reveal a nonpredictable form of TCR degeneracy.

We identified two nonoverlapping epitopes in myelin basic protein presented by I-Au that are responsible for mediating tolerance induction to this self-Ag. A large number of T cells expressing diverse TCRs are strongly cross-reactive to both epitopes. Surprisingly, the TCR contact residues in each peptide are highly dissimilar. Furthermore, functional TCR contacts cannot be interchanged between the two epitopes, indicating that the TCR contacts in each peptide can only be recognized within the context of the other amino acids present in that peptide's sequence. This observation indicates that both buried and exposed residues of each peptide contribute to the sculpting of completely distinct antigenic surfaces. We propose that the cross-reactive TCRs adopt mutually exclusive conformations to recognize these dissimilar epitopes, adding a new dimension to TCR degeneracy. This unpredictable TCR plasticity indicates that using just the TCR contacts on a single epitope to define other cross-reactive peptides will identify only a subset of the complete repertoire of cross-reactive epitopes.

Selection of CD8+ T cells with highly focused specificity during viral persistence in the central nervous system.

The relationships between T cell populations during primary viral infection and persistence are poorly understood. Mice infected with the neurotropic JHMV strain of mouse hepatitis virus mount potent regional CTL responses that effectively reduce infectious virus; nevertheless, viral RNA persists in the central nervous system (CNS). To evaluate whether persistence influences Ag-specific CD8+ T cells, functional TCR diversity was studied in spleen and CNS-derived CTL populations based on differential recognition of variant peptides for the dominant nucleocapsid epitope. Increased specificity of peripheral CTL from persistently infected mice for the index epitope compared with immunized mice suggested T cell selection during persistence. This was confirmed with CD8+ T cell clones derived from the CNS of either acutely (CTLac) or persistently (CTLper) infected mice. Whereas CTLac clones recognized a broad diversity of amino acid substitutions, CTLper clones exhibited exquisite specificity for the wild-type sequence. Highly focused specificity was CD8 independent but correlated with longer complementarity-determining regions 3 characteristic of CTLper clonotypes despite limited TCR alpha/beta-chain heterogeneity. Direct ex vivo analysis of CNS-derived mononuclear cells by IFN-gamma enzyme-linked immunospot assay confirmed the selection of T cells with narrow Ag specificity during persistence at the population level. These data suggest that broadly reactive CTL during primary infection are capable of controlling potentially emerging mutations. By contrast, the predominance of CD8+ T cells with dramatically focused specificity during persistence at the site of infection and in the periphery supports selective pressure driven by persisting Ag.

A molecular map of T cell development.

Using a sensitive molecular marker for positive selection, the appearance of a particular functional TCR alpha chain sequence in cells from mice bearing a transgenic beta chain, we address several aspects of intrathymic T cell development. First, by examining specific TCR prior to and after maturation, we demonstrate how a restricted TCR repertoire is positively selected from a highly diverse immature TCR repertoire. Second, since this molecular marker is enriched in cells progressing toward the CD4 lineage and depleted in cells progressing toward the CD8 lineage, a map of the developmental pathway of alphabeta thymocytes can be inferred. Third, the first cells that show clear signs of positive intrathymic selection are identified.