Pericarditis as a cardiac manifestation of acute leptospirosis.

Leptospirosis is an infectious disease with an increasing incidence worldwide. The clinical presentation is unspecific and ranges from an asymptomatic clinical course to an acute fulminant disease. The current case report describes a 32-year-old male patient who presented with ST segment elevation in the electrocardiogram about 14 days after cross-country running. Pericarditis was diagnosed and linked to an acute leptospirosis that was serologically confirmed.

The functional role of class II-associated invariant chain peptide (CLIP) in its ability to variably modulate immune responses.

During the process of class II MHC assembly and cell surface expression, the class II-associated invariant chain peptide (CLIP) is removed from the peptide-binding groove of MHC, a task mediated by H-2M. This allows binding and presentation of peptide epitopes. We have previously shown that exogenously added CLIP interferes with this process and down-regulates the cell surface expression of class II molecules. In this study, we explored the effect of exogenously added CLIP on antigen-specific immune responses. In vivo studies with CLIP and various peptide and protein antigens with different affinities for I-A(d) molecules demonstrated that CLIP variably affects the T cell-mediated immune responses. Immunization with CLIP along with the antigen induced a shift from a T(h)1- to T(h)2-like response as determined by the cytokine profile and antibody isotype. These results suggest that the presence of exogenous CLIP can significantly influence the presentation of antigen by class II MHC molecules to CD4 T cells and thereby modulate immune responses. Exogenously added CLIP rapidly localized into the subcellular compartment of antigen-presenting cells where MHC class II molecules are present. We suggest that exogenous CLIP reduces the loading of peptides on the class II molecules, thus down-regulating MHC-peptide complexes on the cell surface. Alternatively, CLIP may bind to cell surface class II molecules and this complex is rapidly internalized resulting in reduced cell surface MHC class II expression. The reduced level of MHC-peptide complexes favors the activation of T(h)2 cells over T(h)1 cells. These results have implications in the regulation of immune responses, particularly the prevention of certain autoimmune diseases where T(h)1-type responses are pathogenic and T(h)2-type responses are protective.

A self MHC class II beta-chain peptide prevents diabetes in nonobese diabetic mice.

We explored T cell responses to the self class II MHC (I-Ag7) beta-chain-derived peptides in diabetic and prediabetic nonobese diabetic (NOD) mice. We found that one of these immunodominant epitopes of the beta-chain of I-Ag7 molecule, peptide 54-76, could regulate autoimmunity leading to diabetes in NOD mice. T cells from prediabetic young NOD mice do not respond to the peptide 54-76, but T cells from diabetic NOD mice proliferated in response to this peptide. T cells from older nondiabetic mice or mice protected from diabetes do not respond to this peptide, suggesting a role for peptide 54-76-specific T cells in pathogenesis of diabetes. We show that this peptide is naturally processed and presented by the NOD APCs to self T cells. However, the peptide-specific T cells generated after immunization of young mice regulate autoimmunity in NOD mice by blocking the diabetogenic cells in adoptive transfer experiments. The NOD mice immunized with this peptide are protected from both spontaneous and cyclophosphamide-induced insulin-dependent diabetes mellitus. Immunization of young NOD mice with this peptide elicited T cell proliferation and production of Th2-type cytokines. In addition, immunization with this peptide induced peptide-specific Abs of IgG1 isotype that recognized native I-Ag7 molecule on the cell surface and inhibited the T cell proliferative responses. These results suggest that I-Abetag7(54-76) peptide-reactive T cells are involved in the pathogenesis of diabetes. However, immunization with this peptide at young age induces regulatory cells and the peptide-specific Abs that can modulate autoimmunity in NOD mice and prevent spontaneous and induced diabetes.

Characterization of a model of hydrocephalus in transgenic mice.

OBJECT: The purpose of this study was to elucidate the pathophysiological characteristics of hydrocephalus in a new transgenic model of mice created to overproduce the cytokine transforming growth factor-beta1 (TGFbeta1) in the central nervous system (CNS). METHODS: Galbreath and colleagues generated transgenic mice that overexpressed TGFbeta1 in the CNS in an effort to examine the role of this cytokine in the response of astrocytes to injury. Unexpectedly, the animals developed severe hydrocephalus and died. The authors have perpetuated this transgenic colony to serve as a model of congenital hydrocephalus, breeding asymptomatic carrier males that are heterozygous for the transgene with wild-type females. One hundred twelve (49.6%) of 226 mice developed clinical manifestations of hydrocephalus, characterized by dorsal doming of the calvaria, spasticity, limb tremors, ataxia, and, ultimately, death. The presence of the TGFbeta1 transgene was determined by performing polymerase chain reaction (PCR) analysis of sample tail slices. Animals with the hydrocephalic phenotype consistently carried the transgene, although some animals with the transgene did not develop hydrocephalus. Animals without the transgene did not develop hydrocephalus. Alterations in brain structure were characterized using magnetic resonance (MR) imaging, gross and light microscopic analysis, and immunocytochemical studies. Magnetic resonance imaging readily distinguished hydrocephalic animals from nonhydrocephalic controls and demonstrated an obstruction at the outlets of the fourth ventricle. Gross and light microscopic examination confirmed the MR findings. The results of immunofluorescent staining of brain tissue slices revealed the presence of the TGFbeta1 cytokine and its receptor preferentially in the meninges and subarachnoid space in both hydrocephalic and control mice. Reverse transcriptase-PCR analysis demonstrated tissue-specific expression of the TGFbeta1, gene in the brains of transgenic mice, and enzyme-linked immunosorbent assay confirmed overexpression of the TGFbeta1 cytokine in brain, cerebrospinal fluid, and plasma. CONCLUSIONS: The transgenic murine model provides a reproducible representation of congenital hydrocephalus. The authors hypothesize that overexpression of TGFbeta1 in the CNS causes hydrocephalus by altering the environment of the extracellular matrix and interfering with the circulation of cerebrospinal fluid. A model of hydrocephalus in which the genetic basis is known should be useful for evaluating hypotheses regarding the pathogenesis of this disorder and should also help in the search for new treatment strategies.

Epitope dominance: evidence for reciprocal determinant spreading to glutamic acid decarboxylase in non-obese diabetic mice.

Autoimmune T-cell responses to peptide determinants of several autoantigens have recently been characterized. These data suggest that, in some autoimmune models, such as experimental autoimmune encephalomyelitis, T-cell responses may diversify from a nested set of peptides to include many other peptide regions. A similar immune phenomenon pertaining to autoimmune diabetes (IDDM) is observed in NOD mice. We have explored a similar pattern of T-cell responses related to age and disease status in NOD mice termed epitope dominance, which describes immune responses toward a pronounced subset of determinants of the autoantigen glutamic acid decarboxylase (GAD). Our studies have identified a total of five GAD epitopes between the 65 and 67 kDa isoforms. The magnitude of T-cell responses to these various determinants was dependent on the stage of disease as well as on whether mice were protected from disease. The T-cell responses of these epitopes in NOD mice correlated with the predicted binding of these peptides to the NOD class II molecule I-Ag7. We therefore propose a model which implicates antigen presenting cells as critical entities in the propagation of dominant responses to the presentation of autoantigens to T cells, particularly in the Th 1 environment of the NOD mouse. This hypothesis presents a new framework for the discussion and interpretation of the kinetics of T-cell responses to different peptide epitopes in autoimmune diseases such as IDDM.

Characterization of novel T-cell epitopes on 65 kDa and 67 kDa glutamic acid decarboxylase relevant in autoimmune responses in NOD mice.

It has recently been shown that the T-cell mediated immune responses to glutamic acid decarboxylase (GAD) play an important role in insulin-dependent diabetes mellitus (IDDM) in NOD mice. However, specific epitopes responsible for eliciting these responses remain unresolved. In this study, the T-cell epitopes involved in GAD-specific immune responses in NOD mice were characterized. By priming NOD mice with GAD65, three new GAD65 epitopes (GAD65 78-97, GAD65 202-221, GAD65 217-236) distinct from those previously reported were found. Furthermore, our investigations into the fine determinant specificity of GAD67 revealed two additional GAD67-specific peptide epitopes (GAD67 28-47, GAD67 42-61). Two of the GAD65 epitopes (GAD65 202-221 and GAD65 217-236) are shared between GAD65 and GAD67. Spontaneous immune responses to these peptides were found in pre-diabetic and diabetic mice and differential patterns of responses to these peptides were observed depending on the age of the mice, disease status, or if the mice were protected from diabetes by adjuvant immunotherapy. Characterization of these new epitopes will help in the elucidation of autoimmune responses to GAD in IDDM.

Modulation of antigen presentation and class II expression by a class II-associated invariant chain peptide.

During the process of MHC class II assembly, the class II-associated invariant chain peptide (CLIP) remains bound within the peptide binding groove until its subsequent removal, which is mediated by H-2 M. We have defined the functional role of CLIP, through saturation of the endosomal compartment with exogenous CLIP-(85-101), resulting in reduced class II MHC on the surface of APCs and an impeded T cell response. Conversely, incubation of the same cells with immunogenic peptides or proteins resulted in an up-regulation of surface class II MHC. T cells from CLIP- plus Ag-immunized mice showed a marked decrease in Ag-specific response over that in mice primed with Ag alone. A B cell hybridoma, TA3 (H-2d,k) incubated with CLIP in vitro showed dramatically reduced MHC class II I-A surface expression. APCs derived from CLIP-immunized mice exhibited down-regulation of surface class II MHC, but not of CD45 (B220). Electrophoretic studies showed that the addition of exogenous CLIP resulted in a relative decrease in SDS-stable MHC class II heterodimers in TA3 cells. Studies with FITC-CLIP and FITC-OVA-(323-339) peptides demonstrated that exogenously added CLIP peptide does not bind to surface class II molecules via the endogenous route, whereas OVA peptide does. This suggests that exogenously added CLIP acts intracellularly, perhaps in the compartment where H-2 M intersects with class II molecules. These findings demonstrate the functional role of CLIP to regulate MHC class II-mediated Ag presentation in CD4+ T cell responses.