Issue published March 15, 2003

A mong infectious agents, measles virus (MV) remains a scourge responsible for 1 million deaths per year and is a leading cause of childhood deaths in developing countries. Although MV infection itself is not commonly lethal, MV-induced suppression of the immune system results in a greatly increased susceptibility to opportunistic bacterial infections that are largely responsible for the morbidity and mortality associated with this disease. Despite its clinical importance, the underlying mechanisms of MV-induced immunosuppression remain unresolved. To begin to understand the basis of increased susceptibility to bacterial infections during MV infection, we inoculated transgenic mice expressing the MV receptor, CD46, with MV and Listeria monocytogenes. We found that MV-infected mice were more susceptible to infection with Listeria and that this corresponded with significantly decreased numbers of macrophages and neutrophils in the spleen and substantial defects in IFN-γ production by CD4⁺ T cells. The reduction in CD11b⁺ macrophages and IFN-γ–producing T cells was due to reduced proliferative expansion and not to enhanced apoptosis or to altered distribution of these cells between spleen, blood, and the lymphatic system. These results document that MV infection can suppress both innate and adaptive immune responses and lead to increased susceptibility to bacterial infection.

T he only curative therapy for sickle cell disease (SCD) is allogeneic hematopoietic stem cell (HSC) transplantation. Gene therapy approaches for autologous HSC transplantation are being developed. Although earlier engraftment is seen when cells from GCSF-mobilized blood are transplanted than when bone marrow is transplanted, administration of GCSF to patients with SCD can cause significant morbidity. We tested whether primitive hematopoietic progenitors are spontaneously mobilized in the blood of patients with SCD during acute crisis (AC-SCD patients). The frequency of myeloid-lymphoid–initiating cells (ML-ICs) and SCID-repopulating cells (SRCs) was significantly higher in blood from AC-SCD patients than in blood from patients with steady-state SCD or from normal donors. The presence of SRCs in peripheral blood was not associated with detection of long-term culture–initiating cells, consistent with the notion that SRCs are more primitive than long-term culture–initiating cells. As ML-ICs and SRCs were both detected in blood of AC-SCD patients only, these assays may both measure primitive progenitors. The frequency of ML-ICs also correlated with increases in stem cell factor, GCSF, and IL-8 levels in AC-SCD compared with steady-state SCD and normal-donor sera. Because significant numbers of ML-ICs and SRCs are mobilized in the blood without exogenous cytokine treatment during acute crisis of SCD, collection of peripheral blood progenitors during crisis may yield a source of autologous HSCs suitable for ex-vivo correction by gene therapy approaches and subsequent transplantation.

P soriatic arthritis (PsA) is an inflammatory joint disease characterized by extensive bone resorption. The mechanisms underlying this matrix loss have not been elucidated. We report here that blood samples from PsA patients, particularly those with bone erosions visible on plain radiographs, exhibit a marked increase in osteoclast precursors (OCPs) compared with those from healthy controls. Moreover, PsA PBMCs readily formed osteoclasts in vitro without exogenous receptor activator of NF-κB ligand (RANKL) or MCSF. Both osteoprotegerin (OPG) and anti-TNF antibodies inhibited osteoclast formation. Additionally, cultured PsA PBMCs spontaneously secreted higher levels of TNF-α than did healthy controls. In vivo, OCP frequency declined substantially in PsA patients following treatment with anti-TNF agents. Immunohistochemical analysis of subchondral bone and synovium revealed RANK-positive perivascular mononuclear cells and osteoclasts in PsA specimens. RANKL expression was dramatically upregulated in the synovial lining layer, while OPG immunostaining was restricted to the endothelium. These results suggest a model for understanding the pathogenesis of aggressive bone erosions in PsA. OCPs arise from TNF-α–activated PBMCs that migrate to the inflamed synovium and subchondral bone, where they are exposed to unopposed RANKL and TNF-α. This leads to osteoclastogenesis at the erosion front and in subchondral bone, resulting in a bidirectional assault on psoriatic bone.

C ardiac hypertrophy is a common response to pressure overload and is associated with increased mortality. Mechanical stress in the heart can result in the integrin-mediated activation of focal adhesion kinase and the subsequent recruitment of the Grb2 adapter molecule. Grb2, in turn, can activate MAPK cascades via an interaction with the Ras guanine nucleotide exchange factor SOS and with other signaling intermediates. We analyzed the role of the Grb2 adapter protein and p38 MAPK in cardiac hypertrophy. Mice with haploinsufficiency of the Grb2 gene (Grb2^+/– mice) appear normal at birth but have defective T cell signaling. In response to pressure overload, cardiac p38 MAPK and JNK activation was inhibited and cardiac hypertrophy and fibrosis was blocked in Grb2^+/– mice. Next, transgenic mice with cardiac-specific expression of dominant negative forms of p38α (DN-p38α) and p38β (DN-p38β) MAPK were examined. DN-p38α and DN-p38β mice developed cardiac hypertrophy but were resistant to cardiac fibrosis in response to pressure overload. These results establish that Grb2 action is essential for cardiac hypertrophy and fibrosis in response to pressure overload, and that different signaling pathways downstream of Grb2 regulate fibrosis, fetal gene induction, and cardiomyocyte growth.

B one marrow harbors cells that have the capacity to differentiate into cells of nonhematopoietic tissues of neuronal, endothelial, epithelial, and muscular phenotype. Here we demonstrate that bone marrow–derived cells populate pancreatic islets of Langerhans. Bone marrow cells from male mice that express, using a CRE-LoxP system, an enhanced green fluorescent protein (EGFP) if the insulin gene is actively transcribed were transplanted into lethally irradiated recipient female mice. Four to six weeks after transplantation, recipient mice revealed Y chromosome and EGFP double-positive cells in their pancreatic islets. Neither bone marrow cells nor circulating peripheral blood nucleated cells of donor or recipient mice had any detectable EGFP. EGFP-positive cells purified from islets express insulin, glucose transporter 2 (GLUT2), and transcription factors typically found in pancreatic β cells. Furthermore, in vitro these bone marrow–derived cells exhibit — as do pancreatic β cells — glucose-dependent and incretin-enhanced insulin secretion. These results indicate that bone marrow harbors cells that have the capacity to differentiate into functionally competent pancreatic endocrine β cells and that represent a source for cell-based treatment of diabetes mellitus. The results generated with the CRE-LoxP system also suggest that in vivo cell fusion is an unlikely explanation for the “transdifferentiation” of bone marrow–derived cells into differentiated cell phenotypes.

A ccumulating evidence favors a role for proinsulin as a key autoantigen in diabetes. In the mouse, two proinsulin isoforms coexist. Most studies point to proinsulin 2 as the major isoform recognized by T cells in the NOD mouse. We studied mice in which a null proinsulin 2 mutation was transferred from proinsulin 2–deficient 129 mice onto the NOD background along with 16 genetic markers (including I-A^g7 MHC molecule) associated with diabetes. Intercross mice from the fourth backcross generation showed that proinsulin 2^–/– mice develop accelerated insulitis and diabetes. The high prevalence of anti-insulin autoantibodies in proinsulin 2^–/– mice indicates that diabetes acceleration relates to altered recognition of proinsulin. The prevalence of anti–glutamic acid decarboxylase autoantibodies and of sialitis is not increased in proinsulin 2^–/– mice. We give evidence that proinsulin 2 expression leads to silencing of T cells specific for an epitope shared by proinsulin 1 and proinsulin 2. In the human, alleles located in the VNTR region flanking the insulin gene control β cell response to glucose and proinsulin expression in the thymus and are key determinants of diabetes susceptibility. Proinsulin 2^–/– NOD mice provide a model to study the role of thymic expression of insulin in susceptibility to diabetes.

C ardiac hypertrophy, either compensated or decompensated, is associated with cardiomyocyte contractile dysfunction from depressed sarcoplasmic reticulum (SR) Ca²⁺ cycling. Normalization of Ca²⁺ cycling by ablation or inhibition of the SR inhibitor phospholamban (PLN) has prevented cardiac failure in experimental dilated cardiomyopathy and is a promising therapeutic approach for human heart failure. However, the potential benefits of restoring SR function on primary cardiac hypertrophy, a common antecedent of human heart failure, are unknown. We therefore tested the efficacy of PLN ablation to correct hypertrophy and contractile dysfunction in two well-characterized and highly relevant genetic mouse models of hypertrophy and cardiac failure, Gαq overexpression and human familial hypertrophic cardiomyopathy mutant myosin binding protein C (MyBP-C_MUT) expression. In both models, PLN ablation normalized the characteristically prolonged cardiomyocyte Ca²⁺ transients and enhanced unloaded fractional shortening with no change in SR Ca²⁺ pump content. However, there was no parallel improvement in in vivo cardiac function or hypertrophy in either model. Likewise, the activation of JNK and calcineurin associated with Gαq overexpression was not affected. Thus, PLN ablation normalized contractility in isolated myocytes, but failed to rescue the cardiomyopathic phenotype elicited by activation of the Gαq pathway or MyBP-C mutations.

I n human disease and experimental animal models, depressed Ca²⁺ handling in failing cardiomyocytes is widely attributed to impaired sarcoplasmic reticulum (SR) function. In mice, disruption of the PLN gene encoding phospholamban (PLN) or expression of dominant-negative PLN mutants enhances SR and cardiac function, but effects of PLN mutations in humans are unknown. Here, a T116G point mutation, substituting a termination codon for Leu-39 (L39stop), was identified in two families with hereditary heart failure. The heterozygous individuals exhibited hypertrophy without diminished contractile performance. Strikingly, both individuals homozygous for L39stop developed dilated cardiomyopathy and heart failure, requiring cardiac transplantation at ages 16 and 27. An over 50% reduction in PLN mRNA and no detectable PLN protein were noted in one explanted heart. The expression of recombinant PLN-L39stop in human embryonic kidney (HEK) 293 cells and adult rat cardiomyocytes showed no PLN inhibition of SR Ca²⁺-ATPase and the virtual absence of stable PLN expression; where PLN was expressed, it was misrouted to the cytosol or plasma membrane. These findings describe a naturally-occurring loss-of-function human PLN mutation (PLN null). In contrast to reported benefits of PLN ablation in mouse heart failure, humans lacking PLN develop lethal dilated cardiomyopathy.

I n response to Ab-complement–mediated injury, podocytes can undergo lysis, apoptosis, or, when exposed to sublytic (<5% lysis) amounts of C5b-9, become activated. Following the insertion of sublytic quantities of C5b-9, there is an increase in signaling pathways and growth factor synthesis and release of proteases, oxidants, and other molecules. Despite an increase in DNA synthesis, however, sublytic C5b-9 is associated with a delay in G₂/M phase progression in podocytes. Here we induced sublytic C5b-9 injury in vitro by exposing cultured rat podocytes or differentiated postmitotic mouse podocytes to Ab and a complement source; we also studied the passive Heymann nephritis model of experimental membranous nephropathy in rats. A major finding was that sublytic C5b-9–induced injury caused an increase in DNA damage in podocytes both in vitro and in vivo. This was associated with an increase in protein levels for p53, the CDK inhibitor p21, growth-arrest DNA damage-45 (GADD45), and the checkpoint kinases-1 and -2. Sublytic C5b-9 increased extracellular signal-regulated kinase-1 and -2 (ERK-1 and -2), and inhibiting ERK-1 and -2 reduced the increase in p21 and GADD45 and augmented the DNA damage response to sublytic C5b-9–induced injury. These results show that sublytic C5b-9 induces DNA damage in vitro and in vivo and may explain why podocyte proliferation is limited following immune-mediated injury.

W e performed a genetic and epigenetic study of the hMLH1 and hMSH2 mismatch repair genes in resected primary tumors from 77 non-small cell lung cancer (NSCLC) patients. The molecular alterations examined included the loss of mRNA and protein expression as well as promoter methylation, and the allelic imbalance of the chromosomal regions that harbor the genes. We found that 78% and 26% of patients showed at least one type of molecular alteration within the hMLH1 and hMSH2 genes, respectively. Promoter methylation of the hMLH1 gene was present in 55.8% of tumors, and was significantly associated with the reduction in mRNA and protein expression (P = 0.001). A 72% concordance of aberrant methylation in sputum samples with matched resected tumors was found. In addition, a 93% consistency between the promoter methylation and the mRNA expression of the hMSH2 gene was found in 14 female NSCLC patients. However, no correlation was found between the expression of hMLH1 and hMSH2 proteins and the allelic imbalance of five microsatellite markers closely linked to the genes. Our results suggest that hMLH1 is the major altered mismatch repair gene involved in NSCLC tumorigenesis, and that promoter methylation is the predominant mechanism in hMLH1 and hMSH2 deregulation. In addition, promoter methylation of the hMLH1 gene may be identified in sputum samples to serve as a potential diagnostic marker of NSCLC.

H uman atherosclerotic lesions overexpress the lysosomal cysteine protease cathepsin S (Cat S), one of the most potent mammalian elastases known. In contrast, atheromata have low levels of the endogenous Cat S inhibitor cystatin C compared with normal arteries, suggesting involvement of this protease in atherogenesis. The present study tested this hypothesis directly by crossing Cat S–deficient (CatS^–/–) mice with LDL receptor–deficient (LDLR^–/–) mice that develop atherosclerosis on a high-cholesterol diet. Compared with LDLR^–/– mice, double-knockout mice (CatS^–/–LDLR^–/–) developed significantly less atherosclerosis, as indicated by plaque size (plaque area and intimal thickening) and stage of development. These mice also had markedly reduced content of intimal macrophages, lipids, smooth muscle cells, collagen, CD4⁺ T lymphocytes, and levels of IFN-γ. CatS^–/–LDLR^–/– monocytes showed impaired subendothelial basement membrane transmigration, and aortas from CatS^–/–LDLR^–/– mice had preserved elastic laminae. These findings establish a pivotal role for Cat S in atherogenesis.

N euronal nicotinic AChRs (nAChRs) are implicated in the pathogenesis of diverse neurological disorders and in the regulation of small-cell lung carcinoma growth. Twelve subunits have been identified in vertebrates, and mutations of one are recognized in a rare form of human epilepsy. Mice with genetically manipulated neuronal nAChR subunits exhibit behavioral or autonomic phenotypes. Here, we report the first model of an acquired neuronal nAChR disorder and evidence for its pertinence to paraneoplastic neurological autoimmunity. Rabbits immunized once with recombinant α3 subunit (residues 1–205) develop profound gastrointestinal hypomotility, dilated pupils with impaired light response, and grossly distended bladders. As in patients with idiopathic and paraneoplastic autoimmune autonomic neuropathy, the severity parallels serum levels of ganglionic nAChR autoantibody. Failure of neurotransmission through abdominal sympathetic ganglia, with retention of neuronal viability, confirms that the disorder is a postsynaptic channelopathy. In addition, we found ganglionic nAChR protein in small-cell carcinoma lines, identifying this cancer as a potential initiator of ganglionic nAChR autoimmunity. The data support our hypothesis that immune responses driven by distinct neuronal nAChR subtypes expressed in small-cell carcinomas account for several lung cancer–related paraneoplastic disorders affecting cholinergic systems, including autoimmune autonomic neuropathy, seizures, dementia, and movement disorders.

S uppressor of cytokine signaling-1 (SOCS-1) is a negative regulator of cytokine signaling. To investigate the role of SOCS-1 in regulating inflammatory and immune responses in disease, acute inflammatory arthritis was induced in mice lacking SOCS-1. Expression of SOCS-1 protein was detected within synovial granulomas and pannus tissue of WT mice by day 7 following induction of acute arthritis. The severity of synovial inflammation and joint destruction at the peak of disease was greater in the absence of SOCS-1, although disease resolution occurred normally. There was an increased percentage of myeloid cells infiltrating the synovium in mice lacking SOCS-1, and SOCS-1 promoter activity was present in synovial macrophages, lymphocytes, and fibroblasts, but not granulocytes. The T cell response in draining LNs was also dysregulated, as popliteal LNs from mice lacking SOCS-1 contained approximately fivefold more cells at the peak of acute arthritis. These cells were hyperproliferative on exposure to antigen in vitro, and purified splenic CD4⁺ T cells from mice lacking SOCS-1 proliferated more strongly in response to stimulation with anti-CD3. Reporter gene expression was detected in CD4⁺ T cells bearing the activation markers CD25, CD44, and CD69. SOCS-1 is therefore expressed in hematopoietic and nonhematopoietic cell types in vivo and is an important regulator of acute inflammatory arthritis and of CD4⁺ T cell activation.