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R Flavell

Publications and source records attributed to R Flavell.

At least 19 recordsLinked to original sources
PubMed2001

Interleukin-10 targets p38 MAPK to modulate ARE-dependent TNF mRNA translation and limit intestinal pathology.

Interleukin-10 (IL-10) is a key inhibitory signal of inflammatory responses that regulates the production of potentially pathogenic cytokines like tumor necrosis factor (TNF). We show here that the development of chronic intestinal inflammation in IL-10-deficient mice requires the function of TNF, indicating that the IL-10/TNF axis regulates mucosal immunity. We further show that IL-10 targets the 3' AU-rich elements (ARE) of TNF mRNA to inhibit its translation. Moreover, IL-10 does not alter TNF mRNA stability, and its action does not require the presence of the stability-regulating ARE binding factor tristetraprolin, indicating a differential assembly of stability and translation determinants on the TNF ARE. Inhibition of TNF translation by IL-10 is exerted mainly by inhibition of the activating p38/MAPK-activated protein kinase-2 pathway. These results demonstrate a physiologically significant cross-talk between the IL-10 receptor and the stress-activated protein kinase modules targeting TNF mRNA translation. This cross-talk is necessary for optimal TNF production and for the maintenance of immune homeostasis in the gut.

Animals↗
PubMed2000

Local IL-4 expression in the lung reduces pulmonary influenza-virus-specific secondary cytotoxic T cell responses.

We studied the effect of lung-specific IL-4 expression on the T cell response during primary and secondary heterologous infection with influenza virus by using transgenic mice that express IL-4 under a lung-specific promoter. Subsequent to primary infection with a type A/H1N1 influenza virus these transgenic mice exhibited similar local recruitment of CD4(+) and CD8(+) T cells and only slightly decreased virus-specific CTL activity. However, during secondary challenge with a heterologous influenza virus, the local infiltration with virus-specific, MHC class I-restricted CD8(+) T cells was significantly decreased compared to that of nontransgenic littermates. The ability of IL-4 transgenic mice to clear the heterologous infection was delayed but not abrogated. This was associated with a faster virus-neutralizing antibody response in IL-4 transgenic mice and with their ability to mount significant Th1 responses even in the presence of increased local IL-4 expression. Our observations demonstrate a negative regulatory effect of IL-4 on memory Tc1/CD8(+) T cells, but are also consistent with complementary mechanisms important for virus clearance such as virus-neutralizing antibodies. The reduction of memory CTL in the presence of IL-4 might have consequences for understanding the course of influenza infection in situations where T(H)2 immunity is increased.

Animals↗
PubMed2000

In vivo evidence for the contribution of human histocompatibility leukocyte antigen (HLA)-DQ molecules to the development of diabetes.

Although DQA1*0301/DQB1*0302 is the human histocompatibility leukocyte antigen (HLA) class II gene most commonly associated with human type 1 diabetes, direct in vivo experimental evidence for its diabetogenic role is lacking. Therefore, we generated C57BL/6 transgenic mice that bear this molecule and do not express mouse major histocompatibility complex (MHC) class II molecules (DQ8(+)/mII(-)). They did not develop insulitis or spontaneous diabetes. However, when DQ8(+)/mII(-) mice were bred with C57BL/6 mice expressing costimulatory molecule B7-1 on beta cells (which normally do not develop diabetes), 81% of the DQ8(+)/mII(-)/B7-1(+) mice developed spontaneous diabetes. The diabetes was accompanied by severe insulitis composed of both T cells (CD4(+) and CD8(+)) and B cells. T cells from the diabetic mice secreted large amounts of interferon gamma, but not interleukin 4, in response to DQ8(+) islets and the putative islet autoantigens, insulin and glutamic acid decarboxylase (GAD). Diabetes could also be adoptively transferred to irradiated nondiabetic DQ8(+)/mII(-)/B7-1(+) mice. In striking contrast, none of the transgenic mice in which the diabetes protective allele (DQA1*0103/DQB1*0601, DQ6 for short) was substituted for mouse MHC class II molecules but remained for the expression of B7-1 on pancreatic beta cells (DQ6(+)/mII(-)/B7-1(+)) developed diabetes. Only 7% of DQ(-)/mII(-)/B7-1(+) mice developed diabetes at an older age, and none of the DQ(-)/mII(+)/B7-1(+) mice or DQ8(+)/mII(+)/B7-1(+) mice developed diabetes. In conclusion, substitution of HLA-DQA1*0301/DQB1*0302, but not HLA-DQA1*0103/DQB1*0601, for murine MHC class II provokes autoimmune diabetes in non-diabetes-prone rat insulin promoter (RIP).B7-1 C57BL/6 mice. Our data provide direct in vivo evidence for the diabetogenic effect of this human MHC class II molecule and a unique "humanized" animal model of spontaneous diabetes.

Animals↗
PubMed1999

Caspase-1 regulates the inflammatory process leading to autoimmune demyelination.

T cell-mediated inflammation is considered to play a key role in the pathogenic mechanisms sustaining multiple sclerosis (MS). Caspase-1, formerly designated IL-1beta-converting enzyme, is crucially involved in immune-mediated inflammation because of its pivotal role in regulating the cellular export of IL-1beta and IL-18. We studied the role of caspase-1 in experimental autoimmune encephalomyelitis (EAE), the animal model for MS. Caspase-1 is transcriptionally induced during EAE, and its levels correlate with the clinical course and transcription rate of proinflammatory cytokines such as TNF-alpha, IL-1beta, IFN-gamma, and IL-6. A reduction of EAE incidence and severity is observed in caspase-1-deficient mice, depending on the immunogenicity and on the amount of the encephalitogenic myelin oligodendrocyte glycoprotein (MOG) peptide used. In caspase-1-deficient mice, reduced EAE incidence correlates with defective development of anti-MOG IFN-gamma-producing Th1 cells. Finally, pharmacological blockade of caspase-1 in Biozzi AB/H mice, immunized with spinal cord homogenate or MOG35-55 peptide, by the caspase-1-inhibitor Z-Val-Ala-dl -Asp-fluoromethylketone, significantly reduces EAE incidence in a preventive but not in a therapeutic protocol. These results indicate that caspase-1 plays an important role in the early stage of the immune-mediated inflammatory process leading to EAE, thus representing a possible therapeutic target in the acute phase of relapsing remitting MS.

Amino Acid Chloromethyl Ketones↗
PubMed1999

Cutting edge: sustained expansion of CD8+ T cells requires CD154 expression by Th cells in acute graft versus host disease.

Brief treatment with alphaCD154 Ab has been shown to prevent acute graft versus host disease (aGvHD). We extend these data to show that in the absence of CD154 function, donor T cells are unable to expand or generate high level anti-host CTL activity. Using transgenic (Tg) alloreactive CD8+ T cells adoptively transferred into allogeneic recipients, we show that short-term expansion of the CD8+ Tg T cells occurred in the absence of Th cells, and this short-term expansion could be facilitated with an agonistic alphaCD40. While CD40 agonism could enhance short-term expansion, sustained expansion of CD8+ Tg T cells required bona fide CD154-expressing CD4+ alloreactive Th cells. While CD154 was necessary for CD8+ Tg T cell sustained expansion, IL-2 was also implicated as essential. These observations suggest alphaCD154 therapy in GvHD is effective because the treatment causes an abortive CD8 alloresponse leading to the exhaustion or deletion of alloreactive CD8+ clones preventing the development of disease.

Acute Disease↗
PubMed1998

The role of lymphocyte subsets in accelerated diabetes in nonobese diabetic-rat insulin promoter-B7-1 (NOD-RIP-B7-1) mice.

B7-1 transgene expression on the pancreatic islets in nonobese diabetic (NOD) mice leads to accelerated diabetes, with >50% of animals developing diabetes before 12 wk of age. The expression of B7-1 directly on the pancreatic beta cells, which do not normally express costimulator molecules, converts the cells into effective antigen-presenting cells leading to an intensified autoimmune attack. The pancreatic islet infiltrate in diabetic mice consists of CD8 T cells, CD4 T cells, and B cells, similar to diabetic nontransgenic NOD mice. To elucidate the relative importance of each of the subsets of cells, the NOD-rat insulin promoter (RIP)-B7-1 animals were crossed with NOD.beta2microglobulin -/- mice which lack major histocompatibility complex class I molecules and are deficient in peripheral CD8 T cells, NOD.CD4 -/- mice which lack T cells expressing CD4, and NOD.muMT -/- mice which lack B220-positive B cells. These experiments showed that both CD4 and CD8 T cells were necessary for the accelerated onset of diabetes, but that B cells, which are needed for diabetes to occur in normal NOD mice, are not required. It is possible that B lymphocytes play an important role in the provision of costimulation in NOD mice which is unnecessary in the NOD-RIP-B7-1 transgenic mice.

Adoptive Transfer↗
PubMed1998

Requirement of CD40-CD40 ligand interaction for elimination of Cryptosporidium parvum from mice.

Mice with disrupted genes for CD40 and CD40 ligand (CD40L) are unable to clear infection with Cryptosporidium parvum and develop cholangitis. Parasites are present in the gut, gall bladder, and biliary tree, and biliary epithelial cells express CD40 on the cell surface. SCID mice infected with C. parvum for >1 month can clear the infection after reconstitution with spleen cells from CD40, but not CD40L, knockout mice. In an in vitro model, C. parvum-infected HepG2 cells were triggered to apoptosis when incubated with a CD40L-CD8 fusion protein. The requirement for CD40-CD40L interactions for immunity to C. parvum indicated by our results may entail the triggering of apoptosis in infected cells, in addition to the known role of CD40L-CD40 interactions in stimulating cytokine production and promoting T-cell responses.

Animals↗
PubMed1997

In vivo properties of monocyte chemoattractant protein-1.

Monocyte chemoattractant protein-1 (MCP-1) attracts monocytes, memory T lymphocytes, and natural killer (NK) cells in vitro. Its expression has been documented in disorders characterized by mononuclear cell infiltrates, suggesting that it may contribute to the inflammatory component of such diseases as atherosclerosis, multiple sclerosis, or rheumatoid arthritis. To prove a causal association, the in vivo properties of MCP-1 must be understood. Several lines of transgenic mice have been constructed to address this question. A transgenic line in which MCP-1 expression is controlled by the MMTV-LTR expressed high levels of MCP-1 in multiple organs but showed no evidence for monocyte infiltration. Instead, these mice were more susceptible to infection by the intracellular pathogens, Listeria monocytogenes and Mycobacterium tuberculosis. These mice had high serum levels of MCP-1, suggesting that their circulating monocytes may have been desensitized or that MCP-1 stimulated a Th2-dominant response. In contrast, another model in which MCP-1 expression was controlled by the insulin promoter demonstrated a monocytic infiltrate in pancreatic islets. These results indicate that MCP-1 expression at low levels in an anatomically confined area results in monocyte infiltration, suggesting that when properly expressed, MCP-1's in vitro properties are reproduced in vivo. This justifies the examination of MCP-1-deficient mice in disease models in order to explore MCP-1's role in pathogenesis.

Animals↗
PubMed1996

CD40L is important for induction of, but not response to, costimulatory activity. ICAM-1 as the second costimulatory molecule rapidly up-regulated by CD40L.

The CD40 ligand (CD40L):CD40 interaction plays an important role in the activation of both T and B cells. However, the mechanisms by which this interaction is involved in activation of T cells is still unclear. Here we show that CD40L is not essential for T cell response to TCR engagement if the APC have costimulatory activity, although it is essential for T cell-mediated induction of such costimulatory activity. To determine the molecular basis of this activity, we have produced three mAbs that appear to recognize the costimulatory molecules rapidly induced by CD40L. Two of them recognize CD44H, which we showed to have CD28-independent costimulatory activity for T cells. The molecule recognized by the remaining mAb is hereby identified as ICAM-1. Furthermore, ICAM-1-mediated costimulation is likely to serve for a function similar to that mediated by the B7:CD28 interaction, as targeted mutation of CD28 renders T cell responses to Con A more dependent on ICAM-1.

Animals↗
PubMed1996

STAT activation by epidermal growth factor (EGF) and amphiregulin. Requirement for the EGF receptor kinase but not for tyrosine phosphorylation sites or JAK1.

The epidermal growth factor (EGF) receptor activates several signaling cascades in response to the ligands EGF and amphiregulin (AR). One of these signaling events involves the tyrosine phosphorylation of STATs (signal transducers and activators of transcription), a process believed to require the activation of a tyrosine kinase of the JAK family. In this report we demonstrate that EGF- and AR-induced STAT activation requires the intrinsic kinase activity of the receptor but not the presence of Jak1. We show that both wild type (WT) and truncated EGF receptors lacking all autophosphorylation sites activate STAT 1, 3, and 5 in response to either EGF or AR. Furthermore, relative to cells expressing WT receptor, ligand-induced tyrosine phosphorylation of the STATs was enhanced in cells expressing only the truncated receptor. These results provide the first evidence that (i) EGF receptor-mediated STAT activation occurs in a Jak1-independent manner, (ii) the intrinsic tyrosine kinase activity of the receptor is essential for STAT activation, and (iii) tyrosine phosphorylation sites within the EGF receptor are not required for STAT activation.

Amphiregulin↗
PubMed1996

Renal ischemic-reperfusion injury in L-selectin-deficient mice.

L-selectin on leukocyte surfaces mediates cell rolling on endothelium. L-selectin blockade with antibodies attenuated ischemic-reperfusion injury (IRI) in heart and skeletal muscle, but its role in renal IRI is unknown. We evaluated the role of L-selectin in renal IRI using L-selectin-deficient mice. Neutrophil migration to chemically inflamed peritoneum was reduced by 47% (P < 0.01) in L-selectin-deficient mice. Ischemia was induced by bilateral renal pedicle clamping for 30 min. Control and L-selectin groups had similar elevations of serum creatinine (1.8 +/- 0.3 vs. 1.7 +/- 0.2 mg/dl) and blood urea nitrogen (111 +/- 17 vs. 128 +/- 12 mg/dl) 24 h postischemia. Pathological assessment showed comparable degrees of tubular necrosis at 24 h. The postischemic increase in peritubular neutrophils per 10 high-power field was similar in control and L-selectin-deficient groups at 4 (28 +/- 10 vs. 22 +/- 5), 12 (245 +/- 80 vs. 236 +/- 78), and 24 h (130 +/- 12 vs. 156 +/- 18). These data argue against a significant role for L-selectin in renal IRI. Patho-physiological roles of L-selectin in vivo appear to be more complex than in vitro data would suggest.

Animals↗
PubMed1995

Peptide and protein antigens require distinct antigen-presenting cell subsets for the priming of CD4+ T cells.

Priming of naive CD4+ T cells to Ag requires an antigen-presenting cell (APC) that can take up the Ag and present peptide bound to MHC class II molecules. We have used both in vivo and in vitro approaches to demonstrate that the APC used to prime naive CD4+ T cells depends on the initial form in which an Ag is administered. Although Ag delivered as a peptide was presented most efficiently to CD4+ T cells by DC, these APC were poor at priming to a protein form of the same Ag. In contrast, the presence of B cells was a requisite for priming to protein Ag.

Animals↗
PubMed1995

Regulation of transgenic class II major histocompatibility genes in murine Langerhans cells.

I-E is a class II major histocompatibility complex molecule normally expressed by Langerhans cells. A series of transgenic mice were developed previously that carry E alpha d gene constructs with promoter-region deletions that cause expression of I-E by different cell types when maintained on a B6 (I-E[-]) genetic background. To study cis-acting gene sequences that regulate expression of class II proteins by Langerhans cells, we identified transgenic I-E expression by tissue immunoperoxidase staining and by epidermal cell suspension immunofluorescence cytometry. Mice with a transgene containing 1.4 kilobase pairs (kb) of flanking sequence 5' to the E alpha initiation site expressed barely detectable levels of I-E on a tiny percentage of Langerhans cells, indicating that sequences promoting Langerhans cell expression of E alpha exist between 2.0 and 1.4 kb 5' of the E alpha initiation site. Removal of an additional 170 bp of 5' flanking sequence caused near-normal levels of expression by approximately one third of epidermal Langerhans cells, which contrasts with studies that showed minimal transgene expression by splenic dendritic cells in these animals. Thus, sequences between 1.4 and 1.23 kb 5' of the E alpha initiation site decrease expression of I-E by epidermal Langerhans cells, but enable I-E expression by splenic dendritic cells. These studies identify Langerhans cell-specific regulatory sequences and genetic regions controlling major histocompatibility complex class II gene expression in Langerhans cells and splenic dendritic cells. The genetic regions identified may be particularly important because differential regulation of class II major histocompatibility complex protein synthesis by Langerhans cells and dendritic cells may be crucial to immune functions of intact animals.

Animals↗
PubMed1994

Human CD4-major histocompatibility complex class II (DQw6) transgenic mice in an endogenous CD4/CD8-deficient background: reconstitution of phenotype and human-restricted function.

To reconstitute the human immune system in mice, transgenic mice expressing human CD4 and human major histocompatibility complex (MHC) class II (DQw6) molecules in an endogenous CD4- and CD8-deficient background (mCD4/8-/-), after homologous recombination, have been generated. We report that expression of human CD4 molecule in mCD4/8-/- mice rescues thymocyte development and completely restores the T cell compartment in peripheral lymphoid organs. Upon vesicular stomatitis virus (VSV) challenge, the reconstituted mature T cell population effectively provide T help to B cells in immunoglobulin class switching from IgM to specific IgG-neutralizing antibodies. Human CD4+DQw6+ double transgenic mice are tolerant to DQw6 and the DQw6 molecule functions in antigen presentation, effectively generating a human MHC class II-restricted T cell response to streptococcal M6C2 peptide. These data show that both the hCD4 and DQw6 molecules are functional in mCD4/8-/- mice, fully and stably reconstituting this limb of the human immune system in mice. This animal model provides a powerful in vivo tool to dissect the human CD4-human class II MHC interaction, especially its role in human autoimmune diseases, superantigen-mediated diseases, and acquired immunodeficiency syndrome (AIDS).

Animals↗
PubMed1994

The role of the T cell costimulator B7-1 in autoimmunity and the induction and maintenance of tolerance to peripheral antigen.

T cell tolerance to peripheral antigens is believed to result mainly from the inability of parenchymal cells to present antigens in an immunogenic form due to the lack of expression of T cell costimulator. We found, however, that transgenic expression of the T cell costimulator B7-1 on the islets of Langerhans is not sufficient to abolish the in vivo tolerance to islets antigen. Here, we present evidence indicating that the level of major histocompatibility complex (MHC) antigen expressed by islet cells plays a critical role. Mice coexpressing the B7-1 transgene and high levels of the class II MHC antigen I-E on the islets develop an autoimmune destruction of the beta cells of the pancreas. By contrast, expression of the I-E molecule by islets, in the absence of T cell costimulator, leads to specific tolerance of these autoreactive T cells that cannot be reversed by costimulation with B7-1.

Animals↗
PubMed1994

The liver eliminates T cells undergoing antigen-triggered apoptosis in vivo.

Deletion of mature peripheral T cells may result from TCR ligation by bacterial enterotoxins, endogenous provirus-encoded superantigens, and peptide antigens. But the ultimate fate of deleted T cells is not clear. Using a line of T cell receptor transgenic mice injected with antigenic peptide, we have documented that peripheral deletion is accompanied by the induction of abortive T cell activation followed by the disappearance of transgene-positive T cells. As these T cells disappear from the lymph nodes and spleen, they accumulate in the liver, where they undergo apoptosis. This is likely to be a general clearance pathway for T cells that are programmed to undergo apoptosis in vivo, and it may further explain the expansion of the intrahepatic T cell pool in mice with genetic defects in the T cell apoptosis mechanism, such as the lpr mutant.

Animals↗
PubMed1993

Role of dendritic cells in the priming of CD4+ T lymphocytes to peptide antigen in vivo.

The contribution of dendritic cells (DC) in the initial priming of CD4+ T lymphocytes in vivo was examined. To assess the capacity of different APC to prime CD4+ T cells, a series of MHC class II I-E transgenic mice that differentially express I-E on APC were utilized. Transgenic mice that express I-E primarily on DC, on macrophages, and on B cells were primed with an I-E restricted peptide in vivo, and the extent of priming was determined by restimulation of CD4+ T cells in vitro with the same Ag. The results indicate that DC are required for priming of CD4+ T cells, and that the extent of priming correlates with the frequency of I-E+ DC. Moreover, DC alone can serve as APC for the peptide Ag, in that priming can be restored in an I-E negative mouse by the transfer of peptide-pulsed I-E+ DC. The potency of DC, compared with B cells and macrophages, to prime naive CD4+ T cells was confirmed with in vitro studies.

Animals↗