Increased SIRT3 combined with PARP inhibition rescues motor function of SBMA mice

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease with substantial mitochondrial and metabolic dysfunctions. SBMA is caused by polyglutamine (polyQ) expansion in the androgen receptor (AR). Activating or increasing the NAD+-dependent deacetylase, SIRT3, reduced oxidative stress and death of cells modeling SBMA. However, increasing diminished SIRT3 in AR100Q mice failed to reduce acetylation of the SIRT3 target/antioxidant, SOD2, and had no effect on increased total acetylated peptides in quadriceps. Yet, overexpressing SIRT3 resulted in a trend of motor recovery, and corrected TCA cycle activity by decreasing acetylation of SIRT3 target proteins. We sought to boost blunted SIRT3 activity by replenishing diminished NAD+ with PARP inhibition. Although NAD+ was not affected, overexpressing SIRT3 with PARP inhibition fully restored hexokinase activity, correcting the glycolytic pathway in AR100Q quadriceps, and rescued motor endurance of SBMA mice. These data demonstrate that targeting metabolic anomalies can restore motor function downstream of polyQ-expanded AR.

Pleomorphic xanthoastrocytoma of childhood: MR imaging and diffusion MR imaging features

BACKGROUND AND PURPOSE

Pleomorphic xanthoastrocytomas are rare astrocytic neoplasms of childhood and young adulthood. The purpose of this retrospective review was to evaluate MR imaging features of pediatric pleomorphic xanthoastrocytomas with an emphasis on diffusion MR imaging.

MATERIALS AND METHODS

Review of the neuro-oncology data base revealed 11 pediatric patients (range, 4.7-16.1 years) with pleomorphic xanthoastroacytomas with 9 of these patients having preoperative MR imaging available. Six patients had preoperative diffusion MR imaging. Demographics, histopathology slides, conventional imaging characteristics (location, cystic component, hemorrhage, enhancement, vasogenic edema, inner table scalloping), and ADC metrics (mean tumor ADC and tumor to normal brain ADC ratio) were evaluated.

RESULTS

Three pleomorphic xanthoastrocytomas had anaplastic features. Ten tumors were supratentorial. Two-thirds (6 of 9) of all tumors were either predominantly cystic or had cystic components, and three-fourths (6 of 8) of the supratentorial tumors had associated inner table scalloping. Seven of the 9 tumors had marked vasogenic edema (>10 mm). Mean tumoral ADC (n = 7) was 912 ± 219 × 10(-6) mm(2)/s (min-max: 617-1189). The tumor to normal brain ADC ratio was 1.14 ± 0.26 (min-max: 0.75-1.47).

CONCLUSIONS

Pleomorphic xanthoastrocytoma should be entertained in the differential diagnosis of peripheral supratentorial tumors that appear during childhood. Cysts, inner table scalloping, and marked vasogenic edema are relatively frequent features. Relatively low ADC values and ADC ratios are not uncommon in pleomorphic xanthoastrocytoma.

The Type 1 Diabetes PhysioLab Platform: a validated physiologically based mathematical model of pathogenesis in the non-obese diabetic mouse

Type 1 diabetes is an autoimmune disease whose clinical onset signifies a lifelong requirement for insulin therapy and increased risk of medical complications. To increase the efficiency and confidence with which drug candidates advance to human type 1 diabetes clinical trials, we have generated and validated a mathematical model of type 1 diabetes pathophysiology in a well-characterized animal model of spontaneous type 1 diabetes, the non-obese diabetic (NOD) mouse. The model is based on an extensive survey of the public literature and input from an independent scientific advisory board. It reproduces key disease features including activation and expansion of autoreactive lymphocytes in the pancreatic lymph nodes (PLNs), islet infiltration and beta cell loss leading to hyperglycaemia. The model uses ordinary differential and algebraic equations to represent the pancreas and PLN as well as dynamic interactions of multiple cell types (e.g. dendritic cells, macrophages, CD4+ T lymphocytes, CD8+ T lymphocytes, regulatory T cells, beta cells). The simulated features of untreated pathogenesis and disease outcomes for multiple interventions compare favourably with published experimental data. Thus, a mathematical model reproducing type 1 diabetes pathophysiology in the NOD mouse, validated based on accurate reproduction of results from multiple published interventions, is available for in silico hypothesis testing. Predictive biosimulation research evaluating therapeutic strategies and underlying biological mechanisms is intended to deprioritize hypotheses that impact disease outcome weakly and focus experimental research on hypotheses likely to provide insight into the disease and its treatment.

Occult metastatic lung carcinoma presenting as locally advanced uterine carcinosarcoma on positron emission tomography/computed tomography imaging

Increasingly, positron emission tomography/computed tomography (PET/CT) is being used as a tumor surveillance modality for multiple tumor types. A 73-year-old postmenopausal female with stage IV nonsmall cell lung cancer presented after a PET/CT demonstrated focal uptake in the superior and lateral aspects of the uterus. The patient reported a history of intermittent postmenopausal bleeding and an endometrial biopsy documented uterine carcinosarcoma. Postoperative pathologic review and immunohistochemical staining with thyroid transcription factor-1 revealed metastatic adenocarcinoma consistent with her lung primary in her uterus and adnexa. Our case represents a rare occurrence in which lung cancer has metastasized to multiple female pelvic organs. Increasing use of PET/CT may lead to the discovery of occult metastases masquerading as a second primary malignancy.

Le syndrome de Diogène, une approche transnosographique

Diogenes syndrome is a behavioural disorder of the elderly. Symptoms include living in extreme squalor, a neglected physical state and unhygienic conditions. This is accompanied by a self-imposed isolation, the refusal of external help and a tendency to accumulate heteroclite objects. This particular geriatric syndrome has been described for the first time only quite recently, as the 2 primary descriptions by geriatricians and psychiatrists date from 1966 and 1975 respectively. Its rare occurrence contrasts with the fact that it is well-known, partly due to it being named after the Greek philosopher "Diogene de Sinope", who taught cynicism philosophy and a return to a natural way of life, and partly because of its rare characteristics. The Diogenes syndrome is a fascinating object of study for the clinician who takes care of patients living in uncommon conditions, on the edge of society and unaware of the particularity of their lifestyles. Patients suffering from Diogenes syndrome are usually discovered by chance, either because of a somatic illness, or as a result of social intervention related to their behavioural problems. Management of the syndrome is difficult and ethically challenging, as the patient does not seek help. Moreover, 46% of patients have a 5 year mortality rate. Hospitalisation has to be avoided whenever possible and ambulatory treatment and social measures should be favoured. Psychotropic treatment prescription may be necessary, depending on clinical features and the possible underlying psychiatric disease. Although several clinical hypotheses have been suggested, the true ethiopathogeny of the syndrome remains unclear. Most authors agree that this behaviour does not reflect free will and has consequently no theoretical relationship to the Greek philosopher. There is no true consensus about diagnostic criteria. They include the main features of the syndrome and exclude known psychiatric syndromes. Clark and Mankikar, who named this syndrome, reckon it may represent stress-related defence mechanisms of the elderly or may be related to natural ageing process. However, psychiatric pathologies as paranoid and paranoiac psychoses, mood disorders and obsessive and compulsive disorders have been described to be associated with it in the literature. Dementia, in particular temporo-frontal dementia, should be looked for and excluded clinically. Alcohol abuse seems to be an aggravating rather than a precipitating factor. Finally, the link between these pathologies and Diogenes syndrome is not yet determined: are they triggering, co-morbid or etiological factors? Should this syndrome be considered as a true illness or as a symptom? This paper presents Diogenes syndrome as a behavioural disorder and distinguishes 2 types: the "active type"--patients who collect from outside to clutter inside--and the "passive type"--patients who passively become invaded by their rubbish. Active type patients fill their home to fill in the vacuum of their life, as it deteriorates and looses its narcissical appeal. Passive type patients accumulate by default and emptiness. A psychopathological understanding is presented here, referring to psychoanalytical theories of the Moi-peau (ego-skin) described by Anzieu. The Moi-peau represents a structure of the psyche founded on the following principle: any psychic function develops itself according to a bodily function from which it transposes its functioning at a mental level. The skin has three functions: the containing shell, the protective barrier of the psyche, and a medium of exchange. The Moi-peau is organised as a double-wall acting both as a defence mechanism and as a filter between the psyche and the external world. It preserves the relationship and the cohesion "container-content". As a result of a narcissical wound, the Moi-peau is damaged and looses its function of a container. In the case of Diogenes Syndrome, the accumulated items repair the Moi-peau and the home becomes an "exterior-proof", thus playing the role of the Moi-peau. This behaviour therefore plays a repairing role for psychic functioning, allowing psychic survival.

beta-Cell death during progression to diabetes

The hallmark of type 1 diabetes is specific destruction of pancreatic islet beta-cells. Apoptosis of beta-cells may be crucial at several points during disease progression, initiating leukocyte invasion of the islets and terminating the production of insulin in islet cells. beta-Cell apoptosis may also be involved in the occasional evolution of type 2 into type 1 diabetes.

Self-esteem matters: racial & gender differences among rural southern adolescents

Self-esteem does matter! It matters so much that Oprah dedicated an entire issue of "O" magazine to address the subject. "It's a woman's most treasured possession" (Winfrey, 2000a). Self-esteem has a profound influence on adolescent health promotion behaviors. This study contributes to understanding the role self-esteem plays in the behavior of adolescents. Utilizing a secondary data analysis, race and gender self-esteem differences among adolescents were investigated. The sample of 1,237 students (46% African-American and 52% White) from rural southern areas consisted of 744 females and 493 males. Self-esteem was assessed using the Miller Self-esteem Questionnaire (SEQ). The Hendricks Perceptual Health Promoting Determinants Model (HPHD) provided the theoretical framework for the study. The results of the study revealed a statistically significant difference in various aspects of self-esteem according to race and gender. African-Americans and males had a higher self-esteem which is consistent with many prior studies.

Damage control, rather than unresponsiveness, effected by protective DX5+ T cells in autoimmune diabetes

The progression of autoimmune diabetes is regulated. We examined here the cellular controls exerted on disease that developed in the BDC2.5 T cell receptor-transgenic model. We found that all BDC2.5 mice with a monoclonal, beta cell-reactive, T cell repertoire developed diabetes before 4 weeks of age; transfer of splenocytes from young standard NOD (nonobese diabetic) mice into perinatal monoclonal BDC2.5 animals protected them from diabetes. The protective activity was generated by CD4+ alphabeta T cells, which operated for a short time at disease initiation, could be partitioned according to DX5 cell surface marker expression and split into two components. Protection did not involve clonal deletion or anergy of the autoreactive BDC2.5 cells, permitting their full activation and attack of pancreatic islets; rather, it tempered the aggressiveness of the insulitic lesion and the extent of beta cell destruction.

A molecular chart of thymocyte positive selection

As a new slant on T lymphocyte repertoire selection, we have examined batteries of TCR sequences in thymi from transgenic mice engineered to exhibit limited, focussed TCR diversity. We have tracked the fate of differentiating thymocytes expressing a set of particular TCR through the positive selection process. Subtly different TCR sequences can promote different maturation pathways and commitment choices. Two distinct routes are followed by CD8-lineage cells interacting with MHC class I molecules, via TCR(hi) CD4(+)CD8(+) or CD4(+)CD8(int) intermediates, while CD4-lineage cells mature exclusively via a CD4(+)CD8(int) stage. The CD8-lineage routes are partially exclusive, indicating that the latter cell type is not always preceded by the former. The distribution of sequences also indicates that CD4 / CD8-lineage commitment is not strictly correlated with the class of MHC molecule engaged, and that some mechanism prevents mismatched intermediates from achieving full maturity.

Autoimmunity provoked by infection: how good is the case for T cell epitope mimicry?

Autoimmune diseases remain one of the mysteries that perplex immunologists. What makes the immune system, which has evolved to protect an organism from foreign invaders, turn on the organism itself? A popular answer to this question involves the lymphoid network's primordial function: autoimmunity is a by-product of the immune response to microbial infection. For decades there have been tantalizing associations between infectious agents and autoimmunity: beta-hemolytic streptococci and rheumatic fever; B3 Coxsackieviruses and myocarditis; Trypanosoma cruzi and Chagas' disease; diverse viruses and multiple sclerosis; Borrelia burgdorfii and Lyme arthritis; and B4 Coxsackievirus, cytomegalovirus or rubella and type 1 diabetes, to name the most frequently cited examples. In addition, animal models have provided direct evidence that infection with a particular microbe can incite a particular autoimmune disease. Nonetheless, many of the associations appear less than convincing and, even for those that seem to be on solid footing, there is no real understanding of the underlying mechanism(s).

T lymphocytes need IL-7 but not IL-4 or IL-6 to survive in vivo

The role of IL-4, -6 and -7 in the survival of T lymphocytes was studied in vivo. The decay of polyclonal populations of CD4(+) and CD8(+) T cells was monitored in thymectomized anti-cytokine receptor mAb-treated and/or cytokine-deficient mice. The lack of IL-4 or -6 did not have any detectable effect on T cell survival, but IL-7 played an important role in the survival of the naive T cell compartment, especially of naive CD4(+) T cells.

How much TCR does a T cell need?

Kinetic features of TCR:MHC/peptide interactions dictate their outcome in vitro, some important parameters of which include the number of molecules engaged and the duration of engagement. We explored the in vivo significance of these findings in transgenic mice expressing TCRs in a quantitatively and temporally controlled manner. As anticipated, reduced TCR levels resulted in attenuated reactivity, but response thresholds were substantially lower than expected-at as low as 1/20th the normal TCR numbers and with no indication of phenotypic skewing at suboptimal levels. We also studied survival of T lymphocytes stripped of their TCRs. Unlike B cells, T cells lacking antigen receptors did not die precipitously; instead, populations decayed gradually, just as previously reported in the absence of MHC molecules.

The shaping of the T cell repertoire

By combining a TCRbeta transgene with a TCRalpha minilocus comprised of a single V and two J gene segments, we engineered a mouse line exhibiting ample but focused TCR diversity, restricted to CDR3alpha. Using single-cell PCR and high-throughput sequencing, we have exploited this system to scrutinize T cell repertoire selection and evolution. Some striking observations emerged: (1) thymic selection produces a repertoire that is very "bumpy," with marked overrepresentation of a subset of sequences; (2) MHC class I- and class II-restricted TCRs can be distinguished by minute, single-residue changes in CDR3alpha; and (3) homeostatic expansion and survival in the periphery can markedly remold the postselection repertoire, likely reflecting variability in the potential of cells displaying different TCRs to respond to homeostatic cues.

A cassette vector for high-level reporter expression driven by a hybrid invariant chain promoter in transgenic mice

A plasmid cassette vector was designed to generate transgenic mice expressing reporter cDNAs at high levels in antigen-presenting cells under the control of the murine invariant chain (Ii) promoter. Analysis of several transgenic mice harboring a chimeric Ii cDNA placed in this vector showed that it can drive expression of the reporter protein to levels comparable to those of endogenous Ii. Furthermore, its expression pattern overlaps quite well with that of endogenous Ii. This vector should therefore be a convenient and versatile tool for the generation of transgenic mouse lines in which a desired protein may be expressed in Ii-positive cells at levels similar to those of endogenous Ii. Such a vector would be ideal for complementation studies of Ii-deficiency by specific Ii variants.

Pinpointing when T cell costimulatory receptor CTLA-4 must be engaged to dampen diabetogenic T cells

Engagement of the T cell costimulatory receptor CTLA-4 can potently down-regulate an immune response. For example, in a T cell receptor transgenic mouse model of autoimmune diabetes, CTLA-4 interactions keep pancreatic islet-reactive T cells in check, evidenced by the finding that mAb blockade of CTLA-4 rapidly provokes diabetes in animals that would not normally succumb until many months later. Interestingly, this effect is only observed early in the course of disease, before insulitis is stably entrenched. Here, we have exploited a highly synchronous and easily manipulable transfer system to determine precisely when CTLA-4 must be engaged to check the diabetogenicity of islet-reactive T cells. Our results indicate that CTLA-4 interactions during initial priming of the T cells in the pancreatic lymph nodes are not determinant. Rather, the critical interactions occur when the T cells secondarily reencounter their antigen in the target organ, the pancreatic islets. In addition, we made use of CTLA-4-deficient mice to bolster our interpretation that CTLA-4 engagement has a dampening rather than an enhancing influence on diabetes progression.

Role of the forkhead transcription family member, FKHR, in thymocyte differentiation

While performing a large-scale analysis of mRNA transcripts in the murine thymus, our attention was drawn to the forkhead family transcription factor FKHR. Here we demonstrate that FKHR is expressed in thymocytes, most prominently in those that are undergoing positive selection. Interestingly, FKHR transcripts show a highly regionalized pattern of expression, concentrated in the innermost areas of the medulla. We define the FKHR binding site as (G/C)(A/C)N(G/a)T(A/c)AA(T/c) A(T/g)(T/g)(G/c), a sequence found in the regulatory elements of many genes, including certain that encode molecules crucial for thymocyte differentiation. To study the function of FKHR, we engineered mice expressing a dominant-negative mutant specifically in T cells in a tetracycline-regulatable fashion. In these animals, T cell differentiation appeared quite normal; however, total thymocyte numbers were decreased, owing to reductions in all four of the CD4/CD8 subsets, and incorporation of the thymidine analogue bromo-deoxyuridine was increased, again in all four subsets. These data suggest that, in thymocytes, FKHR may be involved in cell survival and/or cycling.

The arthritogenic T cell receptor and its ligand in a model of spontaneous arthritis

OBJECTIVE

Spontaneous arthritis in the KRN transgenic mouse model is due to the autoreactivity of the transgenic T cell receptor (TCR) against Ag7 major histocompatibility complex (MHC) molecules, which leads to strong but incomplete clonal deletion. We sought to determine whether other stimuli triggering this receptor might provoke arthritis, whether the apparently systemic reactivity might have some joint-preferential component explaining the paradoxical arthritic phenotype, and whether the transgenic receptor was the only one required or whether other TCRs might be ferried along in a leaky tolerance process.

METHODS

Crosses and radiation chimeras involving a panel of transgenic and knockout mouse lines were used. The reactivity of the KRN TCR was tested in carboxyfluorescein diacetate succinimidyl ester-transfer experiments and in crosses with transgenic or inbred mice expressing other molecules that stimulate the KRN receptor (the mls-1a superantigen, the Aalpha(k69)Abeta(k) mutant MHC molecule). The arthritogenic capacity of T cells expressing only the KRN TCR was tested by crossing to recombination-activating gene-knockout mice, and constructing bone marrow chimeras with precursors to these strictly monoclonal T cells.

RESULTS

The data show that the KRN TCR itself is the only receptor needed. It needs to be triggered by the Ag7 molecule loaded with self-peptides in order to provoke arthritis, but there is no indication of preferential presentation of joint-derived peptides.

CONCLUSION

Arthritis can be generated by systemic recognition of self-MHC-peptide complexes by autoreactive T cells. This triggers B lymphocytes to produce arthritogenic antibodies, without the involvement of joint-specific T cell targets.

Tetracycline-controllable selection of CD4(+) T cells: half-life and survival signals in the absence of major histocompatibility complex class II molecules

A system that allows the study, in a gentle fashion, of the role of MHC molecules in naive T cell survival is described. Major histocompatibility complex class II-deficient mice were engineered to express Ealpha chains only in thymic epithelial cells in a tetracycline (tet)-controllable manner. This resulted in tet-responsive display of cell surface E complexes, positive selection of CD4(+)8(-) thymocytes, and generation of a CD4(+) T cell compartment in a class II-barren periphery. Using this system, we have addressed two unresolved issues: the half-life of naive CD4(+) T cells in the absence of class II molecules (3-4 wk) and the early signaling events associated with class II molecule engagement by naive CD4(+) T cells (partial CD3 zeta chain phosphorylation and ZAP-70 association).

A revival of the B cell paradigm for rheumatoid arthritis pathogenesis?

Dominant paradigms for the understanding of rheumatoid arthritis (RA) pathogenesis have changed over the years. A predominant role of B lymphocytes, and perhaps of the rheumatoid factor they produced, was initially invoked. In more recent years, recognition of antigens in the joint by T cells sparking an inflammatory cascade has been a more favored interpretation. Here, we re-examine some of the arguments that underpin this proposed role of joint T cells, in light of recent results from transgenic mice in which a self-reactive T-cell receptor provokes disease, but from outside the joint and indirectly via B lymphocytes and immunoglobulins.

The arthritogenic T cell receptor and its ligand in a model of spontaneous arthritis

OBJECTIVE

Spontaneous arthritis in the KRN transgenic mouse model is due to the autoreactivity of the transgenic T cell receptor (TCR) against Ag7 major histocompatibility complex (MHC) molecules, which leads to strong but incomplete clonal deletion. We sought to determine whether other stimuli triggering this receptor might provoke arthritis, whether the apparently systemic reactivity might have some joint-preferential component explaining the paradoxical arthritic phenotype, and whether the transgenic receptor was the only one required or whether other TCRs might be ferried along in a leaky tolerance process.

METHODS

Crosses and radiation chimeras involving a panel of transgenic and knockout mouse lines were used. The reactivity of the KRN TCR was tested in carboxyfluorescein diacetate succinimidyl ester-transfer experiments and in crosses with transgenic or inbred mice expressing other molecules that stimulate the KRN receptor (the mls-1a superantigen, the Aalpha(k69)Abeta(k) mutant MHC molecule). The arthritogenic capacity of T cells expressing only the KRN TCR was tested by crossing to recombination-activating gene-knockout mice, and constructing bone marrow chimeras with precursors to these strictly monoclonal T cells.

RESULTS

The data show that the KRN TCR itself is the only receptor needed. It needs to be triggered by the Ag7 molecule loaded with self-peptides in order to provoke arthritis, but there is no indication of preferential presentation of joint-derived peptides.

CONCLUSION

Arthritis can be generated by systemic recognition of self-MHC-peptide complexes by autoreactive T cells. This triggers B lymphocytes to produce arthritogenic antibodies, without the involvement of joint-specific T cell targets.

Arthritis provoked by linked T and B cell recognition of a glycolytic enzyme

The hallmark of rheumatoid arthritis (RA) is specific destruction of the synovial joints. In a mouse line that spontaneously develops a disorder with many of the features of human RA, disease is initiated by T cell recognition of a ubiquitously expressed self-antigen; once initiated, pathology is driven almost entirely by immunoglobulins. In this study, the target of both the initiating T cells and pathogenic immunoglobulins was identified as glucose-6-phosphate isomerase, a glycolytic enzyme. Thus, some forms of RA or related arthritides may develop by a mechanism fundamentally different from the currently popular paradigm of a joint-specific T cell response.

Amino acids specifying MHC class preference in TCR V alpha 2 regions

Some TCR variable regions are preferentially expressed in CD4+ or CD8+ T cells, reflecting a predilection for interacting with MHC class II or class I molecules. The molecular basis for MHC class bias has been studied previously, in particular for V alpha 3 family members, pointing to a dominant role for two amino acid positions in complementary-determining regions (CDRs) 1 and 2. We have evaluated the generality of these findings by examining the MHC class bias of V alpha 2 family members, an attractive system because it shows more variability within the CDR1 and -2, exhibits variation in the framework regions, and includes a member for which the crystal structure has been determined. We find that preferential recognition of MHC class I or II molecules does not always depend on residues at the same positions of CDR1 and -2; rules for one family may be reversed in another. Instead, there are multiple influences exerted by various CDR1/2 positions as well as the CDR3s of both the TCR alpha- and TCR beta-chains.

Positive selection of thymocytes induced by gene transfer: MHC class II-mediated selection of CD8 lineage cells

Recombinant adenovirus vectors are powerful tools for inducing de novo gene expression in vivo. Here we have exploited them to study the specificity of CD4/CD8 lineage commitment during thymocyte positive selection, transferring MHC class II genes directly into thymi of mice deficient in both class I and II molecules. Expression of class II molecules was induced on cortical stroma, provoking the selection of a large population of mature CD4(+)CD8(-) cells, as expected, but also of a significant number of CD4(-)CD8(+) cells. The latter constituted a diverse population, containing both immature precursors and, though less frequent, cells that were mature according to several criteria. CD4(-)CD8(+) cells appeared with the same kinetics as their CD4(+)CD8(-) counterparts, but tended to be more prevalent at early times or when thymocyte reconstitution was only modest. These observations, derived from a dynamic selection system, indicate that CD4/CD8 lineage commitment is not irredeemably linked to the class of MHC molecule driving positive selection, a conclusion most compatible with selective models of commitment.

An influence of CD5 on the selection of CD4-lineage T cells

Combining CD5-null, MHC-deficient and lineage-specific reporter animals, we have investigated the influence of CD5 on positive selection and the choice of CD4- versus CD8-lineage commitment on broad populations of thymocytes. CD5 has no obvious quantitative effect in wild-type mice. In mice lacking MHC class II molecules, however, increased numbers of transitional, class I-selected CD4+ CD8(int) CD3(hi) cells were positively selected in the absence of CD5. Importantly, they were committed to the CD4 lineage. Our results indicate that CD5 negatively regulates the differentiation of CD4-committed cells in suboptimal conditions, thus perhaps serving to tighten the correlation between restriction of the TCR and lineage choice.

Mice lacking all conventional MHC class II genes

MHC class II (MHC-II) molecules play a central role in the selection of the T cell repertoire, in the establishment and regulation of the adaptive immune response, and in autoimmune deviation. We have generated knockout mice lacking all four of the classical murine MHC-II genes (MHCII(Delta/Delta) mice), via a large (80-kilobase) deletion of the entire class II region that was engineered by homologous recombination and Cre recombinase-mediated excision. These mice feature immune system perturbations like those of Aalpha and Abeta knockout animals, notably a dearth of CD4(+) lymphocytes in the thymus and spleen. No new anatomical or physiological abnormalities were observed in MHCII(Delta/Delta) mice. Because these animals are devoid of all classical MHC-II chains, even unpaired chains, they make excellent recipients for MHC-II transgenes from other species, avoiding the problem of interspecies cross-pairing of MHC-II chains. Therefore, they should be invaluable for engineering "humanized" mouse models of human MHC-II-associated autoimmune disorders.

Different modes of pathogenesis in T-cell-dependent autoimmunity: clues from two TCR transgenic systems

T lymphocytes constantly flirt with reactivity to self peptides, a price they pay for their ability to recognize foreign peptides presented by self-MHC molecules, and autoreactivity in the T compartment occasionally gives rise to autoimmune disease. Pathology from T-cell autoimmunity can manifest itself through radically different strategies, as we have observed recently in two transgenic models. In the BDC2.5 diabetes model, T cells express a transgene-encoded T-cell receptor (TCR) with reactivity against a pancreatic antigen. This leads to a massive, if often controlled, infiltration of the pancreatic islets. Target cell destruction then results from the local consequences of this local immune/inflammatory process. On the other hand, the arthritic manifestations of the KRN transgenic model are indirect: the transgenic TCR confers a broad autoreactivity, through which T cells stimulate B cells to produce arthritogenic immunoglobulins. These molecules are then sufficient to produce the disease, even in the complete absence of any lymphocytes. Although important questions subsist in this model--how the KRN T cells interfere with B-cell tolerance, what the target of arthritogenic IgG is--its implication is that an isolated T-cell dysregulation may manifest itself through an Ig-mediated disease.

From systemic T cell self-reactivity to organ-specific autoimmune disease via immunoglobulins

Rheumatoid arthritis is a common and debilitating autoimmune disease whose cause and mechanism remain a mystery. We recently described a T cell receptor transgenic mouse model that spontaneously develops a disease with most of the clinical, histological, and immunological features of rheumatoid arthritis in humans. Disease development in K/BxN mice is initiated by systemic T cell self-reactivity; it requires T cells, as expected, but B cells are also needed, more surprisingly. Here, we have identified the role of B cells as the secretion of arthritogenic immunoglobulins. We suggest that a similar scenario may unfold in some other arthritis models and in human patients, beginning with pervasive T cell autoreactivity and ending in immunoglobulin-provoked joint destruction.

Inhibition of thymocyte positive selection by natural MHC: peptide ligands

The 3A9 transgenic mouse line carries the rearranged TCR genes from a T cell hybridoma that recognizes hen egg lysozyme peptide 46-61 in the context of MHC class II Ak molecules. As expected, positive selection of immature 3A9 thymocytes to become mature CD4+ 8- T cells was efficient on the "selecting" CBA (H-2k) genetic background but not on the "non-selecting" C57BL/6 (H-2b) background. Surprisingly, positive selection was also inefficient on the CBA x C57BL/6 F1 background (H-2kb). We present evidence that expression of A(beta)b molecules on thymus epithelium (in conjunction with A(alpha)b or A(alpha)k molecules) inhibits the positive selection of 3A9 thymocytes mediated by A(alpha)k:A(beta)k complexes, in a process evocative of peptide antagonism of mature T cells.

T-cell development: a new marker of differentiation state

Differentiation of T cells is a complicated affair and there has been a dearth of markers that faithfully reflect thymocyte phenotype. A new strategy based on T-cell receptor gene sequencing has revealed a marker that can be used to monitor thymocyte differentiation with fidelity and without perturbation.

Initiation of autoimmune diabetes by developmentally regulated presentation of islet cell antigens in the pancreatic lymph nodes

Little is known about the events triggering lymphocyte invasion of the pancreatic islets in prelude to autoimmune diabetes. For example, where islet-reactive T cells first encounter antigen has not been identified. We addressed this issue using BDC2.5 T cell receptor transgenic mice, which express a receptor recognizing a natural islet beta cell antigen. In BDC2.5 animals, activated T cells were found only in the islets and the lymph nodes draining them, and there was a close temporal correlation between lymph node T cell activation and islet infiltration. When naive BDC2.5 T cells were transferred into nontransgenic recipients, proliferating cells were observed only in pancreatic lymph nodes, and this occurred significantly before insulitis was detectable. Surprisingly, proliferation was not seen in 10-day-old recipients. This age-dependent dichotomy was reproduced in a second transfer system based on an unrelated antigen artificially expressed on beta cells. We conclude that beta cell antigens are transported specifically to pancreatic lymph nodes, where they trigger reactive T cells to invade the islets. Systemic or extrapancreatic T cell priming, indicative of activation via molecular mimicry or superantigens, was not seen. Compromised presentation of beta cell antigens in the pancreatic lymph nodes of juvenile animals may be the root of a first "checkpoint" in diabetes progression.

Cellular and molecular changes accompanying the progression from insulitis to diabetes

Insulin-dependent diabetes mellitus (IDDM) is not a disease of unbridled destruction. The autoimmune attack on pancreatic beta cells has two distinct stages - insulitis and diabetes - and progression of the former to the latter appears to be highly regulated. Identifying the factors controlling this transition has been difficult because it is a complex process that occurs non-universally and asynchronously. We have overcome these difficulties by coupling a simplified TCR transgenic (tg) model of IDDM and the immunosuppressive drug cyclophosphamide (CY). Young BDC2.5 TCR tg mice show insulitis but not diabetes; CY treatment provoked diabetes in 100% of animals with rapid, highly reproducible kinetics. This allowed a detailed temporal analysis of changes in cellular organization and cytokine gene expression within the lesion. The monokines IL-18, IL-12 and TNF-alpha were pivotal, their induction occurring almost immediately and their coordinate action being required for the onset of aggression. Other cytokines with direct toxicity for beta cells, including IL-1 -beta, IL-6 and IFN-gamma, were subsequently induced; in contrast, there was no cellular or molecular evidence of cell contact-mediated mechanisms of beta cell death.

Visualization of CD4/CD8 T cell commitment

A system to innocuously visualize T cell lineage commitment is described. Using a "knock-in" approach, we have generated mice expressing a beta-galactosidase reporter in place of CD4; expression of beta-galactosidase in these animals appears to be an accurate and early indicator of CD4 gene transcription. We have exploited this knock-in line to trace CD4/CD8 lineage commitment in the thymus, avoiding important pitfalls of past experimental approaches. Our results argue in favor of a selective model of thymocyte commitment, demonstrating a fundamentally symmetrical process: engagement of either class of major histocompatibility complex (MHC) molecule by a differentiating CD4(+)CD8(+) cell can give rise to T cell antigen receptor (TCR)hi thymocytes of either lineage. Key findings include (a) direct demonstration of a substantial number of CD4-committed, receptor/coreceptor-mismatched cells in MHC class II- deficient mice, a critical prediction of the selective model; (b) highly efficient rescue of such "mismatched" intermediates by forced expression of CD8 in a TCR transgenic line, and an explanation of why previous experiments of this nature were less successful-a major past criticism of the selective model; (c) direct demonstration of an analogous, though smaller, population of CD8-committed mismatched intermediates in class I-deficient animals. Finally, we found no evidence of a CD4 default pathway.

Mice lacking the transcription factor CIITA--a second look

We have generated a second line of mice lacking a transcription factor thought to be a critical regulator of MHC class II gene expression, CIITA (for class II transactivator). Our and the previously published lines differ in the deletion that was engineered and by the fact that we removed the neomycin-resistance promoter and structural gene via the cre-loxP recombination system. Characterization of our line led to two new findings. First, a substantial number of cells can express class II molecules in the absence of CIITA, albeit at 5-fold reduced levels, most notably dendritic cells in s.c. lymph nodes; therefore, the CIITA gene cannot be an absolute 'master gene' controlling the expression of class II molecules, as had been thought. Second, in contrast to recent results on human cell lines, CIITA is not critically involved in the IFN-gamma-induced up-regulation of MHC class I genes.

CD4+ T cell responses in mice lacking MHC class II molecules specifically on B cells

The role of B lymphocytes in initiating and maintaining a CD4+ T cell response has been examined using a variety of strategies, but remains controversial because of weaknesses inherent to each of the approaches. Here, we address this issue by measuring CD4+ T cell priming both in mutant mice devoid of B cells and in chimeric animals lacking major histocompatibility complex class II molecules specifically on B cells. We find that peptide and some protein antigens do not require B cells expressing class II molecules, nor B cells themselves, to efficiently prime. This could be demonstrated by the usual lymph node proliferation assay, a rather indirect in vitro measure of priming, and by a direct ex vivo assay of population expansion and activation marker expression. Interestingly, one protein antigen, conalbumin, could not prime in the absence of B cells, but could in the presence of B cells devoid of class II molecules. This finding constrains the possible mechanisms whereby B lymphocytes contribute to the initiation of a CD4+ T cell response, arguing against the importance of surface immunoglobulin-mediated antigen presentation by B cells.

CD4/CD8 lineage commitment: matching fate with competence

The outcome of positive selection of T lymphocytes is that there is a close match between the lineage adopted by a particular cell (CD4+ or CD8+) and the specificity of the T-cell receptor for the class of Major Histocompatibility Complex molecule recognized. How this match is obtained has been a matter of debate. We review the evidence, from recent and older experiments, that indicates that the process follows a selective logic, rather than an instructive one.

The phenotype of H-2M-deficient mice is dependent on the MHC class II molecules expressed

For a broader view of the role of H-2M as an accessory molecule in antigen presentation, we investigated the degree to which different MHC class II isotypes and alleles depend on H-2M to function in vivo. We generated H-2M-deficient animals expressing Ek/b or Ak molecules in addition to the Ab molecules already present in the mutant strain, and compared the ability of the different MHC class II molecules to present antigen at the cell surface for recognition by T cells, and contribute to positive selection of CD4+ T cells in the thymus. Biochemical analyses were performed to assess MHC class II maturation, and to determine the peptide content of the molecules. In the absence of H-2M, Ek/b molecules contained a more heterogeneous set of class II-associated invariant chain peptides (CLIP) than Ab did, which, unlike Ab-CLIP complexes, were not SDS-stable. Unlike Ab molecules, both Ek/b and Ak efficiently presented exogenously added peptides to T cells in the absence of H-2M. In addition, epitopes from some proteins, especially those known to be invariant chain independent, were presented by Ak molecules in the mutant animals. To our surprise, expression of Ek/b overcame the positive selection defect observed in H-2M-deficient mice expressing Ab alone. In contrast, Ak expression did not augment positive selection of CD4+ T cells in the mutant animals. Some of these findings in vivo contrast significantly with findings from in vitro studies on murine MHC class II molecules in human DM-deficient cell lines.

Interleukin-4 deficiency does not exacerbate disease in NOD mice

To investigate the role of interleukin (IL)-4 in the regulation of autoimmune diabetes, we crossed the IL-4 knock-out mutation onto the NOD genetic background. This experiment was accelerated by typing for microsatellites linked to known diabetes susceptibility (Idd) loci, and included a control backcross of the wild-type 129/SvJ-derived IL-4 gene, the original target locus. We also crossed the mutation into the BDC2.5 transgenic line, a diabetes model that carries the rearranged T-cell receptor genes from a diabetogenic T-cell clone. The IL-4-null mutation did not accelerate or intensify insulitis in regular NOD mice or in the BDC2.5 transgenic model; it also had no effect on the timing or frequency of the transition to overt diabetes. These data indicate that IL-4 plays no required role in controlling the aggressiveness of murine diabetes.

Major histocompatibility complex class II molecules can protect from diabetes by positively selecting T cells with additional specificities

Insulin-dependent diabetes is heavily influenced by genes encoded within the major histocompatibility complex (MHC), positively by some class II alleles and negatively by others. We have explored the mechanism of MHC class II-mediated protection from diabetes using a mouse model carrying the rearranged T cell receptor (TCR) transgenes from a diabetogenic T cell clone derived from a nonobese diabetic mouse. BDC2.5 TCR transgenics with C57Bl/6 background genes and two doses of the H-2(g7) allele exhibited strong insulitis at approximately 3 wk of age and most developed diabetes a few weeks later. When one of the H-2(g7) alleles was replaced by H-2(b), insulitis was still severe and only slightly delayed, but diabetes was markedly inhibited in both its penetrance and time of onset. The protective effect was mediated by the Abetab gene, and did not merely reflect haplozygosity of the Abetag7 gene. The only differences we observed in the T cell compartments of g7/g7 and g7/b mice were a decrease in CD4(+) cells displaying the transgene-encoded TCR and an increase in cells expressing endogenously encoded TCR alpha-chains. When the synthesis of endogenously encoded alpha-chains was prevented, the g7/b animals were no longer protected from diabetes. g7/b mice did not have a general defect in the production of Ag7-restricted T cells, and antigen-presenting cells from g7/b animals were as effective as those from g7/g7 mice in stimulating Ag7-restricted T cell hybridomas. These results argue against mechanisms of protection involving clonal deletion or anergization of diabetogenic T cells, or one depending on capture of potentially pathogenic Ag7-restricted epitopes by Ab molecules. Rather, they support a mechanism based on MHC class II-mediated positive selection of T cells expressing additional specificities.

Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) regulates the unfolding of autoimmune diabetes

Evidence has been accumulating that shows that insulin-dependent diabetes is subject to immunoregulation. To determine whether cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) is involved, we injected anti-CTLA-4 mAb into a TCR transgenic model of diabetes at different stages of disease. When injected into young mice, months before they would normally become diabetic, anti-CTLA-4 induced diabetes rapidly and essentially universally; this was not the result of a global activation of T lymphocytes, but did reflect a much more aggressive T cell infiltrate in the pancreatic islets. These effects were only observed if anti-CTLA-4 was injected during a narrow time window, before the initiation of insulitis. Thus, engagement of CTLA-4 at the time when potentially diabetogenic T cells are first activated is a pivotal event; if engagement is permitted, invasion of the islets occurs, but remains quite innocuous for months, if not, insulitis is much more aggressive, and diabetes quickly ensues.

Interferon-gamma impacts at multiple points during the progression of autoimmune diabetes

The role of interferon-gamma in autoimmune diabetes was assessed by breeding a null mutation of the interferon-gamma receptor alpha chain into the nonobese diabetic mouse strain, as well as into a simplified T cell receptor transgenic model of diabetes. In contrast to a previous report on abrogation of the interferon-gamma gene, mutation of the gene encoding its receptor led to drastic effects on disease in both mouse lines. Nonobese diabetic mice showed a marked inhibition of insulitis-both the kinetics and penetrance-and no signs of diabetes; the transgenic model exhibited near-normal insulitis, but this never evolved into diabetes, either spontaneously or after experimental provocation. This failure could not be explained by perturbations in the ratio of T helper cell phenotypes; rather, it reflected a defect in antigen-presenting cells or in the islet beta cell targets.