Severe acute respiratory syndrome (SARS) is a life-threatening infectious disease which has been difficult to study and treat because of the lack of a readily available animal model. Intranasal infection of A/J mice with the coronavirus murine hepatitis virus strain 1 (MHV-1) produced pulmonary pathological features of SARS. All MHV-1-infected A/J mice developed progressive interstitial pneumonitis, including dense macrophage infiltrates, giant cells, and hyaline membranes, resulting in death of all animals. In contrast, other mouse strains developed only mild transitory disease. Infected A/J mice had significantly higher cytokine levels, particularly macrophage chemoattractant protein 1 (MCP-1/CCL-2), gamma interferon, and tumor necrosis factor alpha. Furthermore, FGL2/fibroleukin mRNA transcripts and protein and fibrin deposits were markedly increased in the lungs of infected A/J mice. These animals developed a less robust type I interferon response to MHV-1 infection than resistant C57BL/6J mice, and treatment with recombinant beta interferon improved survival. This study describes a potentially useful small animal model of human SARS, defines its pathogenesis, and suggests treatment strategies.

Mice with targeted deletion of fibrinogen‐like protein 2 (fgl2) spontaneously developed autoimmune glomerulonephritis with increasing age, as did wild‐type recipients reconstituted with fgl2−/− bone marrow. These data implicate FGL2 as an important immunoregulatory molecule and led us to identify the underlying mechanisms. Deficiency of FGL2, produced by CD4+CD25+ regulatory T cells (Treg), resulted in increased T cell proliferation to lectins and alloantigens, T helper 1 (Th1) polarization, and increased numbers of antibody‐producing B cells following immunization with T‐independent antigens. Dendritic cells (DC) were more abundant in fgl2−/− mice and had increased expression of CD80 and MHCII following LPS stimulation. Treg cells were also more abundant in fgl2−/− mice, but their suppressive activity was significantly impaired. Antibody to FGL2 completely inhibited Treg cell activity in vitro. FGL2 inhibited DC maturation and induced apoptosis of B cells through binding to the low affinity FcγRIIB receptor. Collectively, these data suggest that FGL2 contributes to Treg cell activity and inhibits the development of autoimmune disease. This work was supported in part by grants from the Heart and Stroke Foundation of Canada and the Canadian Institutes for Health Research.

for the Gene Modifier Study Group C YSTIC FIBROSIS (CF) IS A REcessive monogenic disorder characterizedbymultiorganinvolvement and clinical heterogeneity that is incompletely explained by mutations within the cystic fibrosis transmembraneconductanceregulator(CFTR) gene (OMIM 602421). 1 Patients with CF, including those homozygous for DF508, smallfraction(Ϸ3%-5%)ofpatientswith CF develops severe liver disease characterized by cirrhosis with portal hypertension (CFLD) 1 ; thus, non-CFTR genetic variability may contribute to risk for severe liver disease. [14][15][16][17] To determine the association between non-CFTR genetic polymorphisms and CFLD, we studied 9 functional variants in 5 genes previously See also Patient Page.

contributed equally to this work. Conflict of interest:The authors have declared that no conflict of interest exists. Nonstandard abbreviations used: tissue factor (TF); murine hepatitis virus type 3 (MHV-3); postcoitus (pc); alanine aminotransferase (ALT); hepatitis B surface antigen (HBsAg); hepatitis B e-antigen (HBeAg); hepatitis B viral capsid (HBcAg); severe acute respiratory syndrome (SARS).

contributed equally to this work. Conflict of interest:The authors have declared that no conflict of interest exists. Nonstandard abbreviations used: tissue factor (TF); murine hepatitis virus type 3 (MHV-3); postcoitus (pc); alanine aminotransferase (ALT); hepatitis B surface antigen (HBsAg); hepatitis B e-antigen (HBeAg); hepatitis B viral capsid (HBcAg); severe acute respiratory syndrome (SARS).

In the present studies, we report the cloning and structural characterization of the HFGL2 gene and its functional role in human fulminant hepatitis. The HFGL2 gene is approximately 7 kb in length with 2 exons. The putative promoter contains cis element consensus sequences that strongly suggest the inducibility of its expression. From the nucleotide sequence of the human gene, a 439-amino acid long protein is predicted. The overall identity between the murine fgl2 and hfgl2 coded proteins is over 70%. About 225 amino acids at the carboxyl end of these molecules are almost 90% identical, and correspond to a well-conserved fibrinogen-related domain. Both HFGL2 and FGL2 encode a type II transmembrane protein with a predicted catalytic domain toward the amino terminus of the protein. Transient transfection of Chinese hamster ovary (CHO) cells with a fulllength cDNA of HFGL2 coding region resulted in high levels of prothrombinase activity. Livers from 8 patients transplanted for fulminant viral hepatitis were examined for extent of necrosis, inflammation, fibrin deposition, and HFGL2 induction. In situ hybridization showed positive staining of macrophages in areas of active hepatocellular necrosis. Fibrin stained positively in these areas and was confirmed by electron microscopy. These studies define a unique prothrombinase gene (HFGL2) and implicate its importance in the pathogenesis of fulminant viral hepatitis. The majority of individuals who develop acute viral hepatitis recover completely, and only a small fraction, less than one tenth of 1%, develop fulminant hepatic failure; why this occurs is not known.1 The fulminant form of the disease occurs at all ages of life and is not specific for any one viral type. The hallmark of the condition is the extreme rapidity of the necroinflammatory process resulting in widespread or total hepatocellular necrosis in weeks or even days; any satisfactory explanation must explain this rapid progression.A novel murine cDNA fgl2, encoding a protein with prothrombinase-like activity, was previously cloned in our laboratory.2 The sequence of the cDNA was essentially identical to a previously described sequence corresponding to a gene encoding a mouse fibrinogen-like protein, originally described as a cytotoxic T-cell-specific gene. When the cDNA containing the entire coding region was expressed in RAW 264.7 cells, a prothrombinase activity was detected by both a one-stage clotting assay and cleavage of 125 I-labeled prothrombin. Using a model of fulminant viral hepatitis, we demonstrated a causal relationship between the induction of fgl2 prothrombinase and the mortality of murine hepatitis virus infection (MHV-3). 3 We demonstrated that after MHV-3 infection in susceptible mice, mRNA transcripts of fgl2 were seen in macrophages and endothelial cells in the liver followed by fibrin deposition and liver necrosis. 4 The infusion of high-titered monoclonal antibodies to fgl2 prevented the coagulation disturbance, the hepatic necrosis, and mortality associated with MHV-3 infection. 5H...

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Donor-lymphocyte infusion (DLI) before transplantation can lead to specific tolerance to allografts in mice, nonhuman primates, and humans. We and others have demonstrated a role for regulatory T cells in DLI-induced, donor-specific transplantation tolerance, but it is not known how regulatory T cells are activated and where they execute their function. In this study, we observed, in both transgenic and normal mice, that DLI before transplantation is required for activation of ␣␤-T-cell-receptor-positive, CD3 ؉ CD4 ؊ CD8 ؊ double-negative (DN) regulatory T cells in the periphery of recipient mice. More interestingly, DLI induced DN regulatory T cells to migrate preferentially to donor-specific allogeneic skin grafts and to form a majority of graft-infiltrating T cells in accepted skin allografts. Furthermore, both recipientderived peripheral and graft-infiltrating DN T cells were able to suppress and kill antidonor CD8 ؉ T cells in an antigenspecific manner. These data indicate that DLI may induce donor-specific transplantation tolerance by activating recipient DN regulatory T cells in the periphery and by promoting migration of regulatory T cells to donor-specific allogeneic skin grafts. Our results also show that DN regulatory T cells can eliminate antidonor T cells both systemically and locally, a finding suggesting that graft-infiltrating T cells can be beneficial to graft survival. IntroductionInduction of tolerance to an allogeneic graft without the need for nonspecific immunosuppression is a major goal of transplantation therapy. There are many experimental models in which tolerance can be induced by donor-lymphocyte infusion (DLI) before transplantation, 1-7 and the effects of DLI have also been observed clinically in recipients of renal, cardiac, and bone marrow transplants. [8][9][10][11][12][13][14] Several mechanisms have been postulated to explain DLI-induced tolerance, including mixed allogeneic chimerism, [15][16][17][18] deletion of donor-reactive T cells, [19][20][21][22][23] induction of clonal anergy, 24 immune deviation, [24][25][26] and regulatory T cells. 4,[27][28][29][30][31][32] Regulatory T cells have also been found to play an important role in preventing autoimmune diseases [33][34][35][36][37][38][39][40][41][42][43] and allograft rejection. [27][28][29]32,44,45 We previously showed that pretransplantation infusion of lymphocytes from L d or bm1 donors with a single major histocompatibility complex (MHC) class I locus mismatch led to permanent or significantly prolonged survival of donor-specific but not third-party skin allografts in both transgenic and normal mice. 14,32,46,47 We have also identified and cloned a novel ␣␤-T-cellreceptor (TCR)-positive, CD3 ϩ CD4 Ϫ CD8 Ϫ , double-negative (DN) regulatory T cell from mice that permanently accepted donorspecific skin allografts after one dose of a single class I locusmismatched DLI. 31,32,48 We found that infusion of DN regulatory T-cell clones into syngeneic naive animals led to a significantly prolonged survival of allogeneic skin ...