Naive CD4(+) lymphocytes convert to anergic or memory-like cells in T cell-deprived recipients

Recent demonstrations that naive T cells proliferate after transfer to lymphopenic hosts have led to the theory that active homeostatic mechanisms fill the peripheral pool of naive T cells. To extend these data, we injected naive CD4(+) T cells from AND TCR transgenic mice (H-2(b/b) or H-2(k/k)) into CD3 epsilon-deficient mice, and studied the absolute number, phenotype and functional capacities of the transferred lymphocytes, from the first days to a few months after transfer. Proliferation of naive CD4(+) T cells did not fill the peripheral naive T cell pool. Injected naive T cells acquired a memory-like phenotype that was stable with time, despite the absence of foreign antigenic stimulation. Their functional capacities were modified, enhanced or abolished depending on the MHC haplotype. Thus, "homeostatic" proliferation of naive CD4(+) T cells in T cell-deprived recipients does not regenerate the naive CD4(+) T cell pool.

Maternal and child health nutrition training builds leadership skills

For more than 30 years, the Maternal and Child Health Bureau (MCHB) has funded specialized professional training in nutrition with an emphasis on the development of leadership skills. A survey was conducted of individuals who received Maternal and Child Health nutrition training at the Center for Human Development and Disability (CHDD) at the University of Washington. Those surveyed were asked to reflect on the impact of the training on their career pathway and to report on their leadership activities. Of the 91 respondents, 83 (92%) indicated that the training supported a career pathway that emphasized maternal and child health or children with special healthcare needs. Eighty-five former trainees (93% of respondents) reported leadership activities at the local level, 61 (67%) reported leadership activities at the state level, and 46 (51%) reported leadership activities at the national level. The results of the survey indicate that specialized, intensive training in the field of nutrition develops and supports leadership skills.

[Gastroduodenal metastases: an unusual manifestation of lung cancer. Study of two cases and review ot the literature]

INTRODUCTION

Diagnosis of gastroduodenal metastases is rare. Primary tumors are essentially melanomas and breast cancer, and exceptionally lung cancer.

EXEGESIS

We report two patients who have a diagnosis of gastroduodenal metastases as initial manifestation of lung cancer. In one case, the patient died 3 weeks after the diagnosis. In the other case, chemotherapy was performed and complete response was obtained for the gastric metastasis. After a few months, node recurrence was diagnosed and the patient died 8 months after the diagnosis.

CONCLUSION

We review the endoscopic and non-endoscopic literature and discuss the different histological types and therapeutic strategies concerning these unusual manifestations of lung cancer.

Continuous, bilateral Achilles' tendon vibration is not detrimental to human walk

Sensory feedback from the moving limbs contributes to the regulation of animal and human locomotion. However, the question of the specific role of the various modalities is still open. Further, functional loss of leg afferent fibres due to peripheral neuropathy does not always lead to major alteration in the gait pattern. In order to gain further insight on proprioceptive control of human gait, we applied vibratory tendon stimulation, known to recruit spindle primary afferent fibres, to both triceps surae muscles during normal floor walk. This procedure would disturb organisation and execution of walking, especially if spindles fire continuously and subjects are blindfolded. Vibration induced significant, though minor, changes in duration and length of stance and swing phase, and on speed of walking and kinematics of lower limb segments. No effect was induced on angular displacement of the ankle joint or trunk and head kinematics. This paucity of effects was at variance with the perception of the subjects, who reported illusion of leg stiffness and gait imbalance. These findings would speak for a selective gating of Ia input during locomotion and emphasise the notion that the central nervous system can cope with an unusual continuous input along the Ia fibres from a key muscle like the soleus.

Stance control is not affected by paresis and reflex hyperexcitability: the case of spastic patients

OBJECTIVES

Spastic patients were studied to understand whether stance unsteadiness is associated with changes in the control of voluntary force, muscle tone, or reflex excitability, rather than to abnormal posture connected to the motor deficit itself.

METHODS

Twenty four normal subjects, 12 patients affected by amyotrophic lateral sclerosis (ALS), seven by spastic paraparesis, and 14 by hemiparesis were studied. All patients featured various degrees of spasticity and paresis but were free from clinically evident sensory deficits. Body sway during quiet upright stance was assessed through a stabilometric platform under both eyes open (EO) and eyes closed (EC) conditions. The sudden rotation of a supporting platform, in a toe up and toe down direction respectively, evoked short (SLR) and medium latency (MLR) reflex responses to stretch of the soleus or the tibialis anterior (TA) muscle.

RESULTS

No relation was found between clinical findings (tone, muscle strength, tendon reflexes, plantar response, and duration of disease) and body sway. On average, all patient groups exhibited a forward shift of the centre of foot pressure (CFP) with respect to normal subjects; in addition, paraparetic and to a much larger extent hemiparetic patients showed a lateral shift of CFP. Body sway area was significantly increased only in the hemiparetic patients. No relation was found between position of the CFP and sway within any patient group. Soleus SLR was increased in all patients with respect to normal subjects. TA SLR was often seen in both patients with ALS and paraparetic patients, but only rarely in normal subjects and hemiparetic patients. However, no relation was found between amplitude of soleus or TA SLRs and stabilometric variables. The frequency and size of soleus MLR and TA MLR were decreased in all patients. These responses were decreased in size and not modulated by background EMG in the affected leg of hemiparetic patients, suggesting a disturbed control of spinal reflexes fed by spindle group II afferent fibres.

CONCLUSIONS

It is proposed that body posture, paresis, or monosynaptic reflex hyperexcitability do not affect the control of equilibrium during quiet upright stance. In hemiparetic patients, the decreased amplitude of MLRs might be the main cause of the large postural instability. The results are congruent with the hypothesis of a role for group II afferent input in the reflex control of equilibrium.

Implications of multiple phenotypes observed in prolactin receptor knockout mice

The development of a mouse line deficient in the PRL receptor (PRLR) would be an ideal means to better understand the multiple functions of prolactin. We were worried initially that removal of the PRLR from the mouse genome might be lethal and were surprised to find this not to be the case. We identified numerous deficiencies in PRLR knockout (KO) animals. Female homozygous mice are completely infertile and lack normal mammary development, while hemizygotes are unable to lactate following their first pregnancy. PRLR KO males and females have markedly elevated (30- to 100-fold) serum prolactin levels and in some instances pituitary hyperplasia is present. Maternal behavior is severely affected in both hemizygous and heterozygous animals. Bone formation is reduced in young animals and adults (males and females). Recently, we noticed that older KO animals show a slight reduction in body weight which appears to be due to reduced abdominal fat deposition.

Adoptive transfer of CD4+ T cells specific for subunit A of Helicobacter pylori urease reduces H. pylori stomach colonization in mice in the absence of interleukin-4 (IL-4)/IL-13 receptor signaling

Protection in the murine model of Helicobacter pylori infection may be mediated by CD4+ T cells, but the mechanism remains unclear. To better understand how protection occurs in this model, we generated and characterized H. pylori urease-specific CD4+ T cells from BALB/c mice immunized with Salmonella enterica serovar Typhimurium expressing H. pylori urease (subunits A and B). The CD4+ T cells were found to be specific for subunit A (UreA). Upon antigen-specific stimulation, expression of interleukin 4 (IL-4), IL-10, gamma interferon (IFN-gamma), and tumor necrosis factor alpha was induced. Immunocytochemical analysis showed that the majority of cells produced IFN-gamma and IL-10. Adoptive transfer of the UreA-specific CD4+ T cells into naive syngeneic recipients led to a threefold reduction in the number of bacteria in the recipient group when compared to that in the nonrecipient group. Stomach colonization was also reduced significantly after transfer of these cells into patently infected mice. Adoptive transfer of UreA-specific CD4+ T cells into IL-4 receptor alpha chain-deficient BALB/c mice indicated that IL-4 and IL-13 were not critical in the control of bacterial load. In addition, synthetic peptides were used to identify three functional T-cell epitopes present in subunit A which were recognized by the UreA-specific T cells. Analysis of H. pylori-specific cellular immune responses in recipient challenged and nonrecipient infected mice indicated a strong local restriction of the response in infected animals. The implications of these findings for the mechanism of protection and the development of peptide-based vaccination are discussed.

A small molecule designed to bind to the adenine nucleotide pocket of Hsp90 causes Her2 degradation and the growth arrest and differentiation of breast cancer cells

BACKGROUND

The Hsp90s contain a conserved pocket that binds ATP/ADP and plays an important role in the regulation of chaperone function. Occupancy of this pocket by several natural products (geldanamycin (GM) and radicicol) alters Hsp90 function and results in the degradation of a subset of proteins (i.e. steroid receptors, Her2, Raf). We have used the structural features of this pocket to design a small molecule inhibitor of Hsp90.

RESULTS

The designed small molecule PU3 competes with GM for Hsp90 binding with a relative affinity of 15-20 microM. PU3 induces degradation of proteins, including Her2, in a manner similar to GM. Furthermore, PU3 inhibits the growth of breast cancer cells causing retinoblastoma protein hypophosphorylation, G1 arrest and differentiation.

CONCLUSIONS

PU3 is representative of a novel class of synthetic compounds that binds to Hsp90 and inhibits the proliferation of cancer cells. These reagents could provide a new strategy for the treatment of cancers.

Electrical and mechanical H(max)-to-M(max) ratio in power- and endurance-trained athletes

The aim of this study was to compare the mechanical and electromyographic (EMG) characteristics of soleus motor units activated during maximal H reflex and direct M response among subjects with different histories of physical activity. Power-trained athletes produced stronger twitches, with a higher rate of twitch tension buildup and relaxation, than their endurance counterparts for both maximal H-reflex and maximal M-wave responses. The maximal H-reflex-to-maximal M-wave ratios for both force output (twitch) and EMG wave amplitude were significantly lower in power-trained than endurance-trained athletes. However, power-trained athletes exhibited a significantly greater twitch-to-EMG ratio for the reflexly activated motor units with respect to the entire motor pool, whereas endurance-trained athletes had comparable twitch-to-EMG ratios for both reflexly and directly activated units. Power training increases the force output of the whole ensemble of the motor units, thereby compensating for the lower efficacy of the reflex transmission between Ia spindle afferent input and soleus alpha-motoneuron. On the other hand, the lower level of force evoked by the reflexly activated units in endurance-trained athletes is associated with a greater motor pool reflex excitability. Therefore, endurance-trained athletes produce the necessary force by recruitment of more slow-twitch units than do other subjects for comparable levels of force and type of task.

Costs and characteristics of heavy inpatient service users in outer London

"Heavy users" is a new term often used to describe those who occupy a disproportionate number of psychiatric beds. In this study we identified the heaviest 10% (193) inpatient service users in one London borough over a 6 year period and compared these with a control group of 400 ordinary inpatient users. A weighting index was used to combine frequency of admission with duration. Heavy users were diagnostically and demographically similar to ordinary inpatient service users and only differed by their extensive use of services, about 3 times more than ordinary users in terms of health care costs, during the measured year. Their heavy use mainly depended on occupying hospital beds, and their use of outpatient, day patient and community services was relatively light.

[Contribution of magnetic resonance imaging in sclerotic combined degeneration of the spinal cord due to vitamin B12 deficiency]

Subacute combined degeneration (SCD) of the spinal cord is known to present histopathologically degenerative lesions in the spinal cord, but few studies on the neuroradiological findings have so far been reported. We present the interest of initial and follow-up MR findings in three cases of SCD. In the three cases, a causal event precipitated the onset of neurological symptoms: general anesthesia for the first and the third one and folic acid treatment for the second one. Clinical evolution was favorable after specific treatment with nearly total recovery. The initial MR study disclosed lesions predominantly involving the posterior columns of the spinal cord: high intensity on T2 weighted image was seen in the initial MR study and disappeared three months after treatment in correlation with good recovery, but with a delay. The recognition of this MR pattern suggests that MRI may be used in conjunction with clinical assessment to confirm the diagnosis and to monitor the efficacity of treatment in SCD.

How CD4(+) T cells may eliminate extracellular gastric Helicobacter?

Helicobacter pylori is recognised as a causal agent in the pathogenesis of gastritis, gastric and duodenal ulcer disease as well as gastric cancers. Eradication of the bacteria with antibiotics is currently used to treat symptomatic, infected individuals. Theoretically the infection could also be controlled by vaccination. Several immunisation protocols were developed in small animal models and primates in order to validate this approach. Recently making use of mice with defined genetic defects, H. pylori-specific CD4(+) T cells were found to be crucial for protective vaccination. This was unexpected and poses the question of how activation of CD4(+) T cells leads to the elimination of bacteria that reside primarily in the mucin layer behind a barrier of epithelial cells. CD4(+) T cells fulfil their effector function by secreting lymphokines and by engaging specific surface ligands on interacting cells. Here we propose that phagocytes and epithelial cells stimulated either by direct interaction with CD4(+) T cells or by soluble mediators such as cytokines or neuropeptides are the ultimate effector populations in protective immunity induced by vaccination.

TCR signaling for initiation and completion of thymocyte positive selection has distinct requirements for ligand quality and presenting cell type

Thymocyte selection involves signaling by TCR engaging diverse self-peptide:MHC molecule ligands on various cell types in the cortex and medulla. Here we separately analyze early and late stages of selection to better understand how presenting cell type, ligand quality, and the timing of TCR signaling contribute to intrathymic differentiation. TCR transgenic CD4+CD8+ thymocytes (double positive (DP)) from MHC-deficient mice were stimulated using various presenting cells and ligands. The resulting CD69high cells were isolated and evaluated for maturation in reaggregate cultures with wild-type or MHC molecule-deficient thymic stroma with or without added hemopoietic dendritic cells (DC). Production of CD4+ T cells required TCR signaling in the reaggregates, indicating that transient recognition of self-ligands by DP is inadequate for full differentiation. DC bearing a potent agonist ligand could initiate positive selection, producing activated thymocytes that matured into agonist-responsive T cells in reaggregates lacking the same ligand. DC could also support the TCR signaling necessary for late maturation. These results argue that despite the negative role assigned to DC in past studies, neither the peptide:MHC molecule complexes present on DC nor any other signals provided by these cells stimulate only thymocyte death. These findings also indicate that unique epithelial ligands are not necessary for positive selection. They provide additional insight into the role of ligand quality in selection events and support the concept that following initiation of maturation from the DP state, persistent TCR signaling is characteristic of and perhaps required by T cells.

Developmental regulation of TCR efficiency

Unresponsiveness of mature T cells to the same self-peptide/self-MHC molecule complexes with which thymocytes have reacted during positive selection results from an increase of activation thresholds during maturation. The molecular events accounting for this increase are still unknown. In mature cells, a strong correlation between the extent of TCR down-modulation and T cell responses has been demonstrated. Exploiting this relationship, we show that the efficiency with which the TCR mediates full signaling is developmentally regulated. It decreases with thymic maturation and then increases with differentiation of naive T cells into memory lymphocytes. This analysis based on TCR modulation revealed an unexpected characteristic of the T cell receptor: its ability to signal fully is regulated inversely by its level of expression. This latter relationship may apply to other receptors both within and outside the immune system.

Opening a window on thymic positive selection: developmental changes in the influence of cosignaling by integrins and CD28 on selection events induced by TCR engagement

How TCR and non-TCR signals are integrated by thymocytes to generate a decision to undergo either positive or negative selection remains incompletely understood. Recent evidence suggests that TCR signal transduction changes its quality during thymocyte maturation, but whether the contributions of various cosignaling or costimulatory pathways to thymocyte selection also are modified during development is unclear. Questions also remain about the possible selective roles of specific costimulatory pathways in induction of differentiation vs death among thymocytes at any given stage of maturity. To address these issues, a quantitative in vitro analysis of initiation of CD4+CD8+ thymocyte differentiation as measured by CD69 up-regulation/coreceptor down-modulation was conducted in parallel with an analysis of induction of death. Using transfected cells varying in their surface display of ICAM-1 or B7.1 along with antibody blocking experiments, we demonstrate here that ICAM-1 provides a selective boost to signaling for differentiation without substantially affecting induction of death among CD4+CD8+ cells, a property that is lost as thymocytes mature further. In contrast, B7 engagement enhances both cell activation and death in parallel. Based on these data, we propose that the high level of ICAM-1 on cortical epithelial cells plays a special role in opening a window between TCR signaling for differentiation vs death, permitting efficient initiation of positive selection on epithelial ligands. In contrast, late CD28-dependent cosignaling on hemopoietic cells in the medulla would help enforce negative selection by augmenting the effects of TCR engagement by low levels of high affinity ligands.

Continuous spikes and waves during slow sleep (CSWS): outcome in adulthood

We report a longitudinal, electroencephalographic and neuropsychological analysis of epilepsy with continuous spikes and waves during slow sleep (CSWS) in a 19 year-old boy. The clinical course fluctuated, with temporary worsening or improvement of the paroxysmal abnormalities, epilepsy and cognitive functions. At the end of the follow-up period, seizures persisted. Evaluation of the boy's behaviour, language and cognitive function suggested a dysexecutive syndrome. We discuss the relationship between paroxysmal abnormalities and neuropsychological disorders.

[Pyoderma gangrenosum and breast cancer: a new case]

We report here a new case of pyoderma gangrenosum (PG) associated with a breast cancer in a 39-year-old woman. We only found in literature three other reports of this rare entity which seems usually to be associated with monoclonal gammopathy, gastro-intestinal diseases such as Crohn's disease, chronic ulcerative colitis, leukemias or rheumatologic diseases. A commun hapten between of tumor and skin may explain the origin of this inflammatory lesion. In our case, PG could be a paraneoplastic syndrome.

[Specific factors of diabetes in the rehabilitation of coronary patients]

This prospective controlled trial included two groups of subjects with coronary artery disease: one of 33 patients with non-insulin-dependent diabetes mellitus (6 females and 27 males, mean age 57 +/- 9 years, left ventricular ejection fraction of 56 +/- 14%) and the control group of 33 subjects without diabetes (3 females and 33 males, mean age of 57 +/- 11 years, LVEF of 58 +/- 11%). Before training heart rate was faster for patients with diabetes at rest (72 +/- 11 vs 66 +/- 81 bpm, p = 0.03) and at the end of the stress test (127 +/- 15 versus 118 +/- 18 bpm, p = 0.03). After rehabilitation, resting heart rate and peak heart rate were similar. However cardiovascular capacities improvement was better in subjects without diabetes mellitus, especially concerning peak VO2 (28.98 +/- 8.88 versus 22.78 +/- 6.28 mL/min/kg, p < 0.01) and mechanical power (138 +/- 48 versus 118 +/- 23 watts, p < 0.01). Two groups were retrospectively distinguished among diabetic patients: one group of 17 patients showing a VO2 improvement superior to 5% and a second group non improved (VO2 < 5%). For the second group the two selective factors were higher fasting glycemia (1.83 +/- 0.75 versus 1.31 +/- 0.38 g/L, p = 0.01) and higher hemoglobin A1C (8.05 +/- 2.04 vs 6.62 +/- 1.03%, p = 0.02). Heart rate variability was not significantly different for these two groups: changes in autonomic nervous system cannot explain resistance of diabetic subjects to training. On the other hand, principal aim must be the equilibrium of glycemia in the management of diabetes.

Incidence of multiple sclerosis in Dijon, France: a population-based ascertainment

Incidence of multiple sclerosis (MS) was prospectively determined within the population of the city of Dijon (94,000 inhabitants under 60 years old) at 47 degrees northern latitude, in Burgundy, France. All the incident cases were diagnosed according to the criteria of Poser, associated to the study of cerebrospinal fluid, evoked potentials and cerebral magnetic resonance imaging. Diagnosis was assessed in all the cases by a neurologist working either in the University Hospital (four neurologists) or in private offices (seven neurologists). The ascertainment was performed on a full 5-year period, from 1993 to 1997. Twenty-one cases were diagnosed in the population of 94,000 inhabitants, with an incidence of 6.1/100,000/year in women, 3.3/100,000/year in men and 4.3/100,000/year in both sexes. The sex-ratio female/male was 2.5. Our data are similar to those of the literature, in particular in countries around the Burgundy area. Our data allow evaluation of the burden of MS in our area and allow evaluation of the changes of incidence in the future.

Sleep and epilepsy

This review considers the effect of sleep on seizures and interictal electroencephalogram (EEG) paroxysmal activities (PAs), as classified by the International League Against Epilepsy criteria. No type of seizure is, per se, specifically linked with non-rapid eye movement (NREM) or rapid eye movement (REM) sleep. However, in some syndromes, seizures are more frequent in slow wave sleep (SWS) [partial motor or generalized seizure in benign epilepsy with centro-temporal spikes (BECTS), frontal seizures in idiopathic familial or not familial frontal lobe epilepsy and generalized tonic seizure in secondary generalized epilepsy are increased by SWS]. Conversely myoclonia and grand mal seizures are associated with awakening in some forms of generalized idiopathic epilepsy. There is a mean increase in PAs during SWS in generalized and in partial epilepsies on the whole. However, precise analysis shows that in partial cryptogenic or symptomatic epilepsy and, most likely, in the majority of generalized idiopathic epileptic syndromes about 20% of patients have an increase in PA density during SWS, 20% experience an increase in waking, 50% have very few PAs and in 10% there is no significant difference between sleep and waking. BECTS, however, exhibits a definite increase in sleep PA increase and in juvenile myoclonic epilepsy an increase in PAs during the intra-night awakening is reported. There are at least three syndromes, which cause a huge increase in PAs during sleep: the Landau-Kleffner syndrome and the syndromes of continuous focal or generalized spike-waves during SWS. Their physiopathology and neuropsychological consequences are discussed. Neurophysiological animal data are also reported highlighting the relationships between slow sleep oscillations and the generation of spike waves. A biochemical review is also presented.

Nanoindentation studies of titanium single crystals

Titanium single crystal planes of different atomic density have been reported to show different oxidation characteristics. The differences in oxide characteristics have further been demonstrated to lead to differences in osteoblast attachment. Investigations of the preferred crystallographic planes of titanium for osteoblast attachment can be used to optimize the surfaces of single crystal and polycrystalline titanium implants for anchoring various prostheses. Nanoindentation techniques were used to determine mechanical properties of two crystallographic planes of titanium of different atomic density. Modulus of elasticity of 128 +/- 10 GPa was obtained for polycrystalline titanium and 123 +/- 5 and 124 +/- 6 GPa for the basal plane and pyramidal planes, respectively. The variation of modulus with crystal orientation was not greater than the statistical variation in the data. Surface hardness values were 2.1 +/- 0.1 GPa for the polycrystalline sample and 1.6 +/- 0.1 and 1.9 +/- 0.1 GPa, respectively, for the basal and pyramidal planes. Curves of hardness as a function of depth (0-2000 nm) obtained from electrochemically polished surfaces showed a sharp increase at shallow depths and may reflect changes caused by oxidation of the titanium surfaces.

[Fotemustine (Muphoran) in 22 patients with relapses of high-grade cerebral gliomas]

Fotemustine is a third-generation nitrosourea characterized by a phosphoalanine carrier group grafted onto the nitrosourea radical, which gives it a high lipophilicity and a better penetration through the cell membrane. Between September 1988 and December 1997, 22 patients with inoperable or incompletely resected recurrent high-grade gliomas of the brain were treated at the University Hospital in Brest (France). Treatment consisted of three weekly infusions of fotemustine (100 mg/m2 days 1, 8 and 15). If patients responded or were stabilized, fotemustine was continued at the same dose, but every three weeks only. Four patients responded to the treatment (18%), while 6 were stabilized (32%). Main toxicity was haematologic (leucopenia and, above all, thrombocytopenia); treatment was only interrupted in one patient for leucothrombopenia, and there was no toxic death. Medium duration of response and/or stabilisation was 6.5 months, and median survival 9.4 months in responding and/or stabilized patients, while it was only 5.0 months if tumour progressed under chemotherapy (median survival for all patients: 7.5 months). Besides, there was a difference in survival in favour of the young patients (< 50 years-median survival = 11.8 months) in comparison with patients between 50 and 60 years (median survival = 6.8 months; p = 0.0282) or elderly patients (> 60 years-median survival = 5.8 months; p = 0.0634). In our series, we did not found any difference in survival according to the initial performance status of patients before treatment. Therefore, fotemustine seems to represent an interesting well-tolerated treatment possibility in patients with inoperable recurrent malignant gliomas of the brain.

Divergent changes in the sensitivity of maturing T cells to structurally related ligands underlies formation of a useful T cell repertoire

CD4+ CD8+ thymocyte differentiation requires TCR signaling induced by self-peptide/MHC ligands. Nevertheless, the resulting mature T cells are not activated by these self-complexes, whereas foreign ligands can be potent stimuli. Here, we show that the signaling properties of TCR change during thymocyte maturation, differentially affecting responses to related peptide/MHC molecule complexes and contributing to this discrimination. Weak agonists for CD4+ CD8+ thymocytes lose potency during development, accompanied by a change in TCR-associated phosphorylation from an agonist to a partial agonist/antagonist pattern. In contrast, sensitivity to strong agonists is maintained, along with full signaling. This yields a mature T cell pool highly responsive to foreign antigen while possessing a wide margin of safety against activation by self-ligands.