IDH2 and TET2 mutations synergize to modulate T Follicular Helper cell functional interaction with the AITL microenvironment

Angioimmunoblastic T cell lymphoma (AITL) is a peripheral T cell lymphoma that originates from T follicular helper (Tfh) cells and exhibits a prominent tumor microenvironment (TME). IDH2 and TET2 mutations co-occur frequently in AITL, but their contribution to tumorigenesis is poorly understood. We developed an AITL mouse model that is driven by Idh2 and Tet2 mutations. Malignant Tfh cells display aberrant transcriptomic and epigenetic programs that impair TCR signaling. Neoplastic Tfh cells bearing combined Idh2 and Tet2 mutations show altered cross-talk with germinal center B cells that promotes B cell clonal expansion while decreasing Fas-FasL interaction and reducing B cell apoptosis. The plasma cell count and angiogenesis are also increased in the Idh2-mutated tumors, implying a major relationship between Idh2 mutation and the characteristic AITL TME. Our mouse model recapitulates several features of human IDH2-mutated AITL and provides a rationale for exploring therapeutic targeting of Tfh-TME cross-talk for AITL patients.

Cholinergic control of Th17 cell pathogenicity in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a mouse model of multiple sclerosis (MS) in which Th17 cells have a crucial but unclear function. Here we show that choline acetyltransferase (ChAT), which synthesizes acetylcholine (ACh), is a critical driver of pathogenicity in EAE. Mice with ChAT-deficient Th17 cells resist disease progression and show reduced brain-infiltrating immune cells. ChAT expression in Th17 cells is linked to strong TCR signaling, expression of the transcription factor Bhlhe40, and increased Il2, Il17, Il22, and Il23r mRNA levels. ChAT expression in Th17 cells is independent of IL21r signaling but dampened by TGFβ, implicating ChAT in controlling the dichotomous nature of Th17 cells. Our study establishes a cholinergic program in which ACh signaling primes chronic activation of Th17 cells, and thereby constitutes a pathogenic determinant of EAE. Our work may point to novel targets for therapeutic immunomodulation in MS.

Glutathione Restricts Serine Metabolism to Preserve Regulatory T Cell Function

Regulatory T cells (Tregs) maintain immune homeostasis and prevent autoimmunity. Serine stimulates glutathione (GSH) synthesis and feeds into the one-carbon metabolic network (1CMet) essential for effector T cell (Teff) responses. However, serine's functions, linkage to GSH, and role in stress responses in Tregs are unknown. Here, we show, using mice with Treg-specific ablation of the catalytic subunit of glutamate cysteine ligase (Gclc), that GSH loss in Tregs alters serine import and synthesis and that the integrity of this feedback loop is critical for Treg suppressive capacity. Although Gclc ablation does not impair Treg differentiation, mutant mice exhibit severe autoimmunity and enhanced anti-tumor responses. Gclc-deficient Tregs show increased serine metabolism, mTOR activation, and proliferation but downregulated FoxP3. Limitation of cellular serine in vitro and in vivo restores FoxP3 expression and suppressive capacity of Gclc-deficient Tregs. Our work reveals an unexpected role for GSH in restricting serine availability to preserve Treg functionality.

Choline acetyltransferase-expressing T cells are required to control chronic viral infection

Although widely studied as a neurotransmitter, T cell-derived acetylcholine (ACh) has recently been reported to play an important role in regulating immunity. However, the role of lymphocyte-derived ACh in viral infection is unknown. Here, we show that the enzyme choline acetyltransferase (ChAT), which catalyzes the rate-limiting step of ACh production, is robustly induced in both CD4⁺ and CD8⁺ T cells during lymphocytic choriomeningitis virus (LCMV) infection in an IL-21-dependent manner. Deletion of Chat within the T cell compartment in mice ablated vasodilation in response to infection, impaired the migration of antiviral T cells into infected tissues, and ultimately compromised the control of chronic LCMV clone 13 infection. Our results reveal a genetic proof of function for ChAT in T cells during viral infection and identify a pathway of T cell migration that sustains antiviral immunity.

Glutathione Primes T Cell Metabolism for Inflammation

Activated T cells produce reactive oxygen species (ROS), which trigger the antioxidative glutathione (GSH) response necessary to buffer rising ROS and prevent cellular damage. We report that GSH is essential for T cell effector functions through its regulation of metabolic activity. Conditional gene targeting of the catalytic subunit of glutamate cysteine ligase (Gclc) blocked GSH production specifically in murine T cells. Gclc-deficient T cells initially underwent normal activation but could not meet their increased energy and biosynthetic requirements. GSH deficiency compromised the activation of mammalian target of rapamycin-1 (mTOR) and expression of NFAT and Myc transcription factors, abrogating the energy utilization and Myc-dependent metabolic reprogramming that allows activated T cells to switch to glycolysis and glutaminolysis. In vivo, T-cell-specific ablation of murine Gclc prevented autoimmune disease but blocked antiviral defense. The antioxidative GSH pathway thus plays an unexpected role in metabolic integration and reprogramming during inflammatory T cell responses.

K48-linked KLF4 ubiquitination by E3 ligase Mule controls T-cell proliferation and cell cycle progression

T-cell proliferation is regulated by ubiquitination but the underlying molecular mechanism remains obscure. Here we report that Lys-48-linked ubiquitination of the transcription factor KLF4 mediated by the E3 ligase Mule promotes T-cell entry into S phase. Mule is elevated in T cells upon TCR engagement, and Mule deficiency in T cells blocks proliferation because KLF4 accumulates and drives upregulation of its transcriptional targets E2F2 and the cyclin-dependent kinase inhibitors p21 and p27. T-cell-specific Mule knockout (TMKO) mice develop exacerbated experimental autoimmune encephalomyelitis (EAE), show impaired generation of antigen-specific CD8⁺ T cells with reduced cytokine production, and fail to clear LCMV infections. Thus, Mule-mediated ubiquitination of the novel substrate KLF4 regulates T-cell proliferation, autoimmunity and antiviral immune responses in vivo.

The E3 ligase Mule has been previously reported to be essential for B cell development and function by modulating p53 ubiquitination and degradation. Here Hao et al. identify KLF4 as a novel ubiquitination target of Mule and show it controls T cell proliferation and autoimmunity.

The E3 ubiquitin ligase Mule acts through the ATM-p53 axis to maintain B lymphocyte homeostasis

Cellular homeostasis is controlled by pathways that balance cell death with survival. Mcl-1 ubiquitin ligase E3 (Mule) is an E3 ubiquitin ligase that targets the proapoptotic molecule p53 for polyubiquitination and degradation. To elucidate the role of Mule in B lymphocyte homeostasis, B cell-specific Mule knockout (BMKO) mice were generated using the Cre-LoxP recombination system. Analysis of BMKO mice showed that Mule was essential for B cell development, proliferation, homeostasis, and humoral immune responses. p53 transactivation was increased by two- to fourfold in Mule-deficient B cells at steady state. Genetic ablation of p53 in BMKO mice restored B cell development, proliferation, and homeostasis. p53 protein was increased in resting Mule-deficient mouse embryonic fibroblasts (MEFs) and embryonic stem (ES) cells. Loss of Mule in both MEFs and B cells at steady state resulted in increased levels of phospho-ataxia telangiectasia mutated (ATM) and the ATM substrate p53. Under genotoxic stress, BMKO B cells were resistant to apoptosis, and control MEFs exhibited evidence of a physical interaction between Mule and phospho-ATM. Phospho-ATM, phospho-p53, and Brca1 levels were reduced in Mule-deficient B cells and MEFs subjected to genotoxic stress. Thus, Mule regulates the ATM-p53 axis to maintain B cell homeostasis under both steady-state and stress conditions.

Nfil3/E4bp4 is required for the development and maturation of NK cells in vivo

Nuclear factor interleukin-3 (Nfil3; also known as E4-binding protein 4) is a basic region leucine zipper transcription factor that has antiapoptotic activity in vitro under conditions of growth factor withdrawal. To study the role of Nfil3 in vivo, we generated gene-targeted Nfil3-deficient (Nfil3^−/−) mice. Nfil3^−/− mice were born at normal Mendelian frequency and were grossly normal and fertile. Although numbers of T cells, B cells, and natural killer (NK) T cells were normal in Nfil3^−/− mice, a specific disruption in NK cell development resulted in severely reduced numbers of mature NK cells in the periphery. This defect was NK cell intrinsic in nature, leading to a failure to reject MHC class I–deficient cells in vivo and reductions in both interferon γ production and cytolytic activity in vitro. Our results confirm the specific and essential requirement of Nfil3 for the development of cells of the NK lineage.

Fas receptor expression in germinal-center B cells is essential for T and B lymphocyte homeostasis

Fas is highly expressed in activated and germinal center (GC) B cells but can potentially be inactivated by misguided somatic hypermutation. We employed conditional Fas-deficient mice to investigate the physiological functions of Fas in various B cell subsets. B cell-specific Fas-deficient mice developed fatal lymphoproliferation due to activation of B cells and T cells. Ablation of Fas specifically in GC B cells reproduced the phenotype, indicating that the lymphoproliferation initiates in the GC environment. B cell-specific Fas-deficient mice also showed an accumulation of IgG1(+) memory B cells expressing high amounts of CD80 and the expansion of CD28-expressing CD4(+) Th cells. Blocking T cell-B cell interaction and GC formation completely prevented the fatal lymphoproliferation. Thus, Fas-mediated selection of GC B cells and the resulting memory B cell compartment is essential for maintaining the homeostasis of both T and B lymphocytes.

Generation and characterization of B7-H4/B7S1/B7x-deficient mice

Members of the B7 family of cosignaling molecules regulate T-cell proliferation and effector functions by engaging cognate receptors on T cells. In vitro and in vivo blockade experiments indicated that B7-H4 (also known as B7S1 or B7x) inhibits proliferation, cytokine production, and cytotoxicity of T cells. B7-H4 binds to an unknown receptor(s) that is expressed on activated T cells. However, whether B7-H4 plays nonredundant immune regulatory roles in vivo has not been tested. We generated B7-H4-deficient mice to investigate the roles of B7-H4 during various immune reactions. Consistent with its inhibitory function in vitro, B7-H4-deficient mice mounted mildly augmented T-helper 1 (Th1) responses and displayed slightly lowered parasite burdens upon Leishmania major infection compared to the wild-type mice. However, the lack of B7-H4 did not affect hypersensitive inflammatory responses in the airway or skin that are induced by either Th1 or Th2 cells. Likewise, B7-H4-deficient mice developed normal cytotoxic T-lymphocyte reactions against viral infection. Thus, B7-H4 plays a negative regulatory role in vivo but the impact of B7-H4 deficiency is minimal. These results suggest that B7-H4 is one of multiple negative cosignaling molecules that collectively provide a fine-tuning mechanism for T-cell-mediated immune responses.

Lipocalin 2-deficient mice exhibit increased sensitivity to Escherichia coli infection but not to ischemia-reperfusion injury

Diverse functions have been reported for lipocalin 2. To investigate these functions in vivo, we generated gene-targeted lipocalin 2-deficient mice (Lcn2-/- mice). In vitro studies have suggested that lipocalin 2 is important for cellular apoptosis induced by IL-3 withdrawal, and for the induction of kidney differentiation during embryogenesis. Analysis of Lcn2-/- mice showed normal cell death upon IL-3 withdrawal and normal kidney development. However, we found that Lcn2-/- mice exhibited an increased susceptibility to bacterial infections, in keeping with the proposed function of lipocalin 2 in iron sequestration. Neutrophils isolated from Lcn2-/- mice showed significantly less bacteriostatic activity compared with WT controls. The bacteriostatic property of the WT neutrophils was abolished by the addition of exogenous iron, indicating that the main function of lipocalin 2 in the antibacterial innate immune response is to limit this essential element. Another important function ascribed to lipocalin 2 has been its protective role against kidney ischemia-reperfusion injury. We analyzed Lcn2-/- mice using a mouse model for severe renal failure and could not detect any significant differences compared with their WT littermates.

Cutting Edge: Tissue Inhibitor of Metalloproteinase 3 Regulates TNF-Dependent Systemic Inflammation

Host response to infectious agents must be rapid and powerful. One mechanism is the release of presynthesized membrane-bound TNF. TNF shedding is mediated by TNF-alpha converting enzyme, which is selectively inhibited by the tissue inhibitor of metalloproteinase 3 (TIMP3). We show that loss of TIMP3 impacts innate immunity by dysregulating cleavage of TNF and its receptors. Cultured timp3-/- macrophages release more TNF in response to LPS than wild-type macrophages. In timp3-/- mice, LPS causes serum levels of TNF and its receptors to rise more rapidly and remain higher compared with wild-type mice. The altered kinetics of ligand and receptor shedding enhances TNF signaling in timp3-/- mice, indicated by elevated serum IL-6. Physiologically, timp3-/- mice are more susceptible to LPS-induced mortality. Ablation of the TNF receptor gene p55 (Tnfrsf1a) or treatment with a synthetic metalloproteinase inhibitor rescues timp3-/- mice. Thus, TIMP3 is essential for normal innate immune function.

Specific ablation of the apoptotic functions of cytochrome C reveals a differential requirement for cytochrome C and Apaf-1 in apoptosis

As components of the apoptosome, a caspase-activating complex, cytochrome c (Cyt c) and Apaf-1 are thought to play critical roles during apoptosis. Due to the obligate function of Cyt c in electron transport, its requirement for apoptosis in animals has been difficult to establish. We generated "knockin" mice expressing a mutant Cyt c (KA allele), which retains normal electron transfer function but fails to activate Apaf-1. Most KA/KA mice displayed embryonic or perinatal lethality caused by defects in the central nervous system, and surviving mice exhibited impaired lymphocyte homeostasis. Although fibroblasts from the KA/KA mice were resistant to apoptosis, their thymocytes were markedly more sensitive to death stimuli than Apaf-1(-/-) thymocytes. Upon treatment with gamma irradiation, procaspases were efficiently activated in apoptotic KA/KA thymocytes, but Apaf-1 oligomerization was not observed. These studies indicate the existence of a Cyt c- and apoptosome-independent but Apaf-1-dependent mechanism(s) for caspase activation.

Survivin loss in thymocytes triggers p53-mediated growth arrest and p53-independent cell death

Because survivin-null embryos die at an early embryonic stage, the role of survivin in thymocyte development is unknown. We have investigated the role by deleting the survivin gene only in the T lineage and show here that loss of survivin blocks the transition from CD4⁻ CD8⁻ double negative (DN) thymocytes to CD4⁺ CD8⁺ double positive cells. Although the pre–T cell receptor signaling pathway is intact in survivin-deficient thymocytes, the cells cannot respond to its signals. In response to proliferative stimuli, cycling survivin-deficient DN cells exhibit cell cycle arrest, a spindle formation defect, and increased cell death. Strikingly, loss of survivin activates the tumor suppressor p53. However, the developmental defects caused by survivin deficiency cannot be rescued by p53 inactivation or introduction of Bcl-2. These lines of evidence indicate that developing thymocytes depend on the cytoprotective function of survivin and that this function is tightly coupled to cell proliferation but independent of p53 and Bcl-2. Thus, survivin plays a critical role in early thymocyte development.

Enhanced TCR-induced apoptosis in interferon regulatory factor 4-deficient CD4(+) Th cells

Transcription factors of the interferon regulatory factor (IRF) family contribute to the regulation of cell proliferation and apoptosis. Here, we show that CD4⁺ T helper (Th) cells lacking IRF4 (IRF4^−/−) are highly sensitive to apoptosis. After infection of IRF4^−/− mice with the protozoan parasite Leishmania major, the lesion-draining lymph nodes developed the prototypic lymphadenopathy of wild-type mice after 4 wk, but demonstrated almost total loss of cellularity and enhanced apoptosis after 7 wk. In vitro, activation of IRF4^−/− CD4⁺ Th cells led to greatly increased apoptosis compared with wild-type cells. Coculture of IRF4^−/− and IRF4^+/+ CD4⁺ cells did not increase survival of IRF4^−/− CD4⁺ cells, indicating that the enhanced rate of IRF4^−/− Th cell apoptosis was neither transferable nor due to lack of a cytokine. Enhanced CD4⁺ cell apoptosis was also observed after anti-CD95 mAb treatment, despite normal CD95 expression. Removal of endogenous cytokines, notably interleukin (IL)-4, led to increased and equally high levels of IRF4^−/− and IRF4^+/+ cell apoptosis, whereas the protective activity of exogenous IL-4 was reduced in IRF4^−/− CD4⁺ cells despite normal expression of the IL-4 receptor. Therefore, IRF4 is central in protecting CD4⁺ cells against proapoptotic stimuli.

The Inducible Costimulator Plays the Major Costimulatory Role in Humoral Immune Responses in the Absence of CD28

CD28 plays crucial costimulatory roles in T cell proliferation, cytokine production, and germinal center response. Mice that are deficient in the inducible costimulator (ICOS) also have defects in cytokine production and germinal center response. Because the full induction of ICOS in activated T cells depends on CD28 signal, the T cell costimulatory capacity of ICOS in the absence of CD28 has remained unclear. We have clarified this issue by comparing humoral immune responses in wild-type, CD28 knockout (CD28 KO), and CD28-ICOS double-knockout (DKO) mice. DKO mice had profound defects in Ab responses against environmental Ags, T-dependent protein Ags, and vesicular stomatitis virus that extended far beyond those observed in CD28 KO mice. However, DKO mice mounted normal Ab responses against a T-independent Ag, indicating that B cell function itself was normal. Restimulated CD4(+) DKO T cells that had been primed in vivo showed decreased proliferation and reduced IL-4 and IL-10 production compared with restimulated CD4(+) T cells from CD28 KO mice. Thus, in the absence of CD28, ICOS assumes the major T cell costimulatory role for humoral immune responses. Importantly, CD28-mediated ICOS up-regulation is not essential for ICOS function in vivo.

Differential Requirement for Malt1 in T and B Cell Antigen Receptor Signaling

The translocation t(11;18)(q21;q21) involving MALT1 is the most common chromosomal abnormality in lymphomas of mucosa-associated lymphoid tissue. Although the paracaspase MALT1 can bind to BCL10, the physiological function of MALT1 is unknown. Using mouse models, we show that Malt1 is essential for T cell activation, proliferation, and IL-2 production in response to TCR ligation and strictly required for signal-specific NF-kappaB activation induced by the TCR but not TNF-alpha or IL-1 signaling. Malt1 operates downstream of Bcl10, controls the catalytic activity of the canonical IKK complex, and regulates the signaling of Jnk and p38 MAP kinases. In contrast to Bcl10 disruption, however, inactivation of Malt1 has only mild effects on B cell activation and does not cause defects during neurodevelopment. Thus, Malt1 is an essential regulator of Bcl10 signaling that is differentially required depending on cellular context.

Caspase-3 regulates cell cycle in B cells: a consequence of substrate specificity

Caspases are important for apoptosis but are also involved in mammalian cell survival and cell division. Here we report that caspase-3 is a negative regulator of B cell cycling. Mice deficient in caspase-3 (Casp3-/- mice) have increased numbers of splenic B cells that show normal apoptosis but enhanced proliferation in vivo and hyperproliferation after mitogenic stimulation in vitro. Cdkn1a encodes p21 (also called Waf1 or Cip1), a cyclin-dependent kinase (CDK) inhibitor. Although expression of p21 was increased, CDK activities and proliferating cell nuclear antigen (PCNA) were increased in Casp3-/- B cells. Using Casp3-/-Cdkn1a-/- mice, we show that the hyperproliferation of Casp3-/- B cells is abolished when Cdkn1a is also deleted. Our genetic and biochemical data demonstrate that caspase-3 is essential in the regulation of B cell homeostasis.

The B7 family member B7-H3 preferentially down-regulates T helper type 1-mediated immune responses

We investigated the in vivo function of the B7 family member B7-H3 (also known as B7RP-2) by gene targeting. B7-H3 inhibited T cell proliferation mediated by antibody to T cell receptor or allogeneic antigen-presenting cells. B7-H3-deficient mice developed more severe airway inflammation than did wild-type mice in conditions in which T helper cells differentiated toward type 1 (T(H)1) rather than type 2 (T(H)2). B7-H3 expression was consistently enhanced by interferon-gamma but suppressed by interleukin 4 in dendritic cells. B7-H3-deficient mice developed experimental autoimmune encephalomyelitis several days earlier than their wild-type littermates, and accumulated higher concentrations of autoantibodies to DNA. Thus, B7-H3 is a negative regulator that preferentially affects T(H)1 responses.

Dysregulated T helper cell differentiation in the absence of interferon regulatory factor 4

Certain IFN regulatory factor (IRF) transcription factors indirectly influence T helper (Th) cell differentiation by regulating the production of IL-12. Here, we show that IRF4 directly regulates Th cell differentiation in vitro and in vivo during murine leishmaniasis. In the absence of IRF4, IL-12-induced Th1 cell differentiation was compromised, while IL-4 failed to induce Th2 cell differentiation. Instead, IL-4 tended to induce Th1 cells, defined by production of IFN-gamma and TNF. Although early IL-4 signaling was normal in IRF4(-/-) Th cells, the protein GATA-3, a transcription factor critical for Th2 development, was not up-regulated following IL-4 treatment. Retroviral overexpression of GATA-3 rescued Th2 differentiation. Therefore, IRF4 deficiency manifests itself as severely dysregulated Th cell differentiation.

Generation and characterization of Smac/DIABLO-deficient mice

The mitochondrial proapoptotic protein Smac/DIABLO has recently been shown to potentiate apoptosis by counteracting the antiapoptotic function of the inhibitor of apoptosis proteins (IAPs). In response to apoptotic stimuli, Smac is released into the cytosol and promotes caspase activation by binding to IAPs, thereby blocking their function. These observations have suggested that Smac is a new regulator of apoptosis. To better understand the physiological function of Smac in normal cells, we generated Smac-deficient (Smac(-/-)) mice by using homologous recombination in embryonic stem (ES) cells. Smac(-/-) mice were viable, grew, and matured normally and did not show any histological abnormalities. Although the cleavage in vitro of procaspase-3 was inhibited in lysates of Smac(-/-) cells, all types of cultured Smac(-/-) cells tested responded normally to all apoptotic stimuli applied. There were also no detectable differences in Fas-mediated apoptosis in the liver in vivo. Our data strongly suggest the existence of a redundant molecule or molecules capable of compensating for a loss of Smac function.

Severe impairment of interleukin-1 and Toll-like receptor signalling in mice lacking IRAK-4

Toll-like receptors (TLRs), which recognize pathogen-associated molecular patterns, and members of the pro-inflammatory interleukin-1 receptor (IL-1R) family, share homologies in their cytoplasmic domains called Toll/IL-1R/plant R gene homology (TIR) domains. Intracellular signalling mechanisms mediated by TIRs are similar, with MyD88 (refs 5-8) and TRAF6 (refs 9, 10) having critical roles. Signal transduction between MyD88 and TRAF6 is known to involve the serine-threonine kinase IL-1 receptor-associated kinase 1 (IRAK-1) and two homologous proteins, IRAK-2 (ref. 12) and IRAK-M. However, the physiological functions of the IRAK molecules remain unclear, and gene-targeting studies have shown that IRAK-1 is only partially required for IL-1R and TLR signalling. Here we show by gene-targeting that IRAK-4, an IRAK molecule closely related to the Drosophila Pelle protein, is indispensable for the responses of animals and cultured cells to IL-1 and ligands that stimulate various TLRs. IRAK-4-deficient animals are completely resistant to a lethal dose of lipopolysaccharide (LPS). In addition, animals lacking IRAK-4 are severely impaired in their responses to viral and bacterial challenges. Our results indicate that IRAK-4 has an essential role in innate immunity.

Platelet-endothelial cell adhesion molecule-1 (PECAM-1)-deficient mice demonstrate a transient and cytokine-specific role for PECAM-1 in leukocyte migration through the perivascular basement membrane

Studies with neutralizing antibodies have indicated roles for platelet-endothelial cell adhesion molecule-1 (PECAM-1) in leukocyte migration through the endothelium and the perivascular basement membrane. Because some of these findings have been contentious, this study aimed to explore the role of PECAM-1 in leukocyte migration by analyzing leukocyte responses in interleukin 1beta (IL-1beta)- and tumor necrosis factor-alpha (TNFalpha)-activated cremasteric venules of PECAM-1-deficient mice using intravital and electron microscopy. Although no differences in levels of leukocyte rolling flux or firm adhesion were observed, a delay in leukocyte transmigration in response to IL-1beta, but not TNFalpha, was detected in PECAM-1-deficient mice. Electron microscopy indicated that this delay occurred at the level of perivascular basement membrane. To address the cytokine specificity of PECAM-1 dependence, in vitro experiments demonstrated that TNFalpha, but not IL-1beta, could induce rapid adhesion of murine neutrophils to protein-coated surfaces, suggesting that TNFalpha elicited leukocyte transmigration in wild-type mice via direct stimulation of leukocytes. In summary, the results suggest a regulatory role for PECAM-1 in leukocyte migration through the perivascular basement membrane, a role that appears to be cytokine-specific and associated with the ability of the cytokine to stimulate rapid neutrophil adhesion.

Bcl10 is a positive regulator of antigen receptor-induced activation of NF-kappaB and neural tube closure

Bcl10, a CARD-containing protein identified from the t(1;14)(p22;q32) breakpoint in MALT lymphomas, has been shown to induce apoptosis and activate NF-kappaB in vitro. We show that one-third of bcl10-/- embryos developed exencephaly, leading to embryonic lethality. Surprisingly, bcl10-/- cells retained susceptibility to various apoptotic stimuli in vivo and in vitro. However, surviving bcl10-/- mice were severely immunodeficient and bcl10-/- lymphocytes are defective in antigen receptor or PMA/Ionomycin-induced activation. Early tyrosine phosphorylation, MAPK and AP-1 activation, and Ca2+ signaling were normal in mutant lymphocytes, but antigen receptor-induced NF-kappaB activation was absent. Thus, Bcl10 functions as a positive regulator of lymphocyte proliferation that specifically connects antigen receptor signaling in B and T cells to NF-kappaB activation.

Deficiency in the transcription factor interferon regulatory factor (IRF)-2 leads to severely compromised development of natural killer and T helper type 1 cells

Interferon (IFN) regulatory factor (IRF)-2 was originally described as an antagonist of IRF-1-mediated transcriptional regulation of IFN-inducible genes. IRF-1(-/)- mice exhibit defective T helper type 1 (Th1) cell differentiation. We have used experimental leishmaniasis to show that, like IRF-1(-/)- mice, IRF-2(-/)- mice are susceptible to Leishmania major infection due to a defect in Th1 differentiation. Natural killer (NK) cell development is compromised in both IRF-1(-/)- and IRF-2(-/)- mice, but the underlying mechanism differs. NK (but not NK(+) T) cell numbers are decreased in IRF-2(-/)- mice, and the NK cells that are present are immature in phenotype. Therefore, like IRF-1, IRF-2 is required for normal generation of Th1 responses and for NK cell development in vivo. In this particular circumstance the absence of IRF-2 cannot be compensated for by the presence of IRF-1 alone. Mechanistically, IRF-2 may act as a functional agonist rather than antagonist of IRF-1 for some, but not all, IFN-stimulated regulatory element (ISRE)-responsive genes.

Brca1 required for T cell lineage development but not TCR loci rearrangement

Brca1 (breast cancerl, early onset) deficiency results in early embryonic lethality. As Brca1 is highly expressed in the T cell lineage, a T cell-specific disruption of Brca1 was generated to assess the role of Brca1 in relation to T lymphocyte development. We found that thymocyte development in Brca1-/- mice was impaired not as a result of V(D)J T cell receptor (TCR) recombination but because thymocytes had increased expression of tumor protein p53. Chromosomal damage accumulation and abnormal cell death were observed in mutant cells. We found that cell death inhibitor Bcl-2 overexpression, or p53-/- backgrounds, completely restored survival and development of Brca1-/- thymocytes; peripheral T cell numbers were not totally restored in Brcal-/- p53-/- mice; and that a mutant background for p21 (cyclin-dependent kinase inhibitor 1A) did not restore Brca1-/- thymocyte development, but partially restored peripheral T cell development. Thus, the outcome of Brca1 deficiency was dependent on cellular context, with the major defects being increased apoptosis in thymocytes, and defective proliferation in peripheral T cells.

In Vivo Evidence That Caspase-3 Is Required for Fas-Mediated Apoptosis of Hepatocytes

Caspase-3 is essential for Fas-mediated apoptosis in vitro. We investigated the role of caspase-3 in Fas-mediated cell death in vivo by injecting caspase-3-deficient mice with agonistic anti-Fas Ab. Wild-type controls died rapidly of fulminant hepatitis, whereas the survival of caspase-3−/− mice was increased due to a delay in hepatocyte cell death. Bcl-2 expression in the liver was dramatically decreased in wild-type mice following anti-Fas injection, but was unchanged in caspase-3−/− mice. Hepatocytes from anti-Fas-injected wild-type, but not caspase-3−/−, mice released cytochrome c into the cytoplasm. Western blotting confirmed the lack of caspase-3-mediated cleavage of Bcl-2. Presumably the presence of intact Bcl-2 in caspase-3−/− hepatocytes prevents the release of cytochrome c from the mitochondria, a required step for the mitochondrial death pathway. We also show by Western blot that Bcl-xL, caspase-9, caspase-8, and Bid are processed by caspase-3 in injected wild-type mice but that this processing does not occur in caspase-3−/− mice. This study thus provides novel in vivo evidence that caspase-3, conventionally known for its downstream effector function in apoptosis, also modifies Bcl-2 and other upstream proteins involved in the regulation of Fas-mediated apoptosis.

In vivo evidence that caspase-3 is required for Fas-mediated apoptosis of hepatocytes

Caspase-3 is essential for Fas-mediated apoptosis in vitro. We investigated the role of caspase-3 in Fas-mediated cell death in vivo by injecting caspase-3-deficient mice with agonistic anti-Fas Ab. Wild-type controls died rapidly of fulminant hepatitis, whereas the survival of caspase-3-/- mice was increased due to a delay in hepatocyte cell death. Bcl-2 expression in the liver was dramatically decreased in wild-type mice following anti-Fas injection, but was unchanged in caspase-3-/- mice. Hepatocytes from anti-Fas-injected wild-type, but not caspase-3-/-, mice released cytochrome c into the cytoplasm. Western blotting confirmed the lack of caspase-3-mediated cleavage of Bcl-2. Presumably the presence of intact Bcl-2 in caspase-3-/- hepatocytes prevents the release of cytochrome c from the mitochondria, a required step for the mitochondrial death pathway. We also show by Western blot that Bcl-xL, caspase-9, caspase-8, and Bid are processed by caspase-3 in injected wild-type mice but that this processing does not occur in caspase-3-/- mice. This study thus provides novel in vivo evidence that caspase-3, conventionally known for its downstream effector function in apoptosis, also modifies Bcl-2 and other upstream proteins involved in the regulation of Fas-mediated apoptosis.

TRAF2 deficiency results in hyperactivity of certain TNFR1 signals and impairment of CD40-mediated responses

Tumor necrosis factor (TNF) receptor-associated factor 2 (TRAF2) can interact with various members of the TNF receptor family. Previously, we reported that TRAF2-deficient mice die prematurely and have elevated serum TNF levels. In this study, we demonstrate that TRAF2-deficient macrophages produce increased amounts of nitric oxide (NO) and TNF in response to TNF stimulation. Furthermore, we could enhance the survival of TRAF2-deficient mice by eliminating either TNF or TNFR1. Using these double-knockout mice, we show that in the absence of TRAF2, the T helper-dependent antibody response, CD40-mediated proliferation, and NF-kappaB activation are defective. These data demonstrate two important roles of TRAF2, one as a negative regulator of certain TNFR1 signals and the other as a positive mediator of CD40 signaling.

TRAF6 deficiency results in osteopetrosis and defective interleukin-1, CD40, and LPS signaling

Bone resorption and remodeling is an intricately controlled, physiological process that requires the function of osteoclasts. The processes governing both the differentiation and activation of osteoclasts involve signals induced by osteoprotegerin ligand (OPGL), a member of tumor necrosis factor (TNF) superfamily, and its cognate receptor RANK. The molecular mechanisms of the intracellular signal transduction remain to be elucidated. Here we report that mice deficient in TNF receptor-associated factor 6 (TRAF6) are osteopetrotic with defects in bone remodeling and tooth eruption due to impaired osteoclast function. Using in vitro assays, we demonstrate that TRAF6 is crucial not only in IL-1 and CD40 signaling but also, surprisingly, in LPS signaling. Furthermore, like TRAF2 and TRAF3, TRAF6 is essential for perinatal and postnatal survival. These findings establish unexpectedly diverse and critical roles for TRAF6 in perinatal and postnatal survival, bone metabolism, LPS, and cytokine signaling.

Genetic Evidence for Functional Redundancy of Platelet/Endothelial Cell Adhesion Molecule-1 (PECAM-1): CD31-Deficient Mice Reveal PECAM-1-Dependent and PECAM-1-Independent Functions

Platelet/endothelial cell adhesion molecule-1 (PECAM-1; CD31), a member of the Ig superfamily, is expressed strongly at endothelial cell-cell junctions, on platelets, and on most leukocytes. CD31 has been postulated to play a role in vasculogenesis and angiogenesis, and has been implicated as a key mediator of the transendothelial migration of leukocytes. To further define the physiologic role of CD31, we used targeted gene disruption of the CD31 gene in embryonic stem cells to generate CD31-deficient mice. CD31-deficient mice (CD31KO) are viable and born at the expected Mendelian frequency, remain healthy, and exhibit no obvious vascular developmental defects. In response to inflammatory challenge, polymorphonuclear leukocytes of CD31KO mice are arrested between the vascular endothelium and the basement membrane of inflammatory site mesenteric microvessels, confirming a role for CD31 in the migration of neutrophils through the subendothelial extracellular matrix. Normal numbers of leukocytes are recovered from inflammatory sites in CD31KO mice, however, suggesting that the defect in leukocyte migration across basal lamina observed in the absence of CD31 may be compensated for by the use of other adhesion molecules, or possibly an increased rate of migration. Homing of T lymphocytes in vivo is normal, and CD31KO mice are able to mount a cutaneous hypersensitivity response normally. In addition, CD31-mediated homophilic adhesion does not appear to play a role in platelet aggregation in vitro. This study provides genetic evidence that CD31 is involved in transbasement membrane migration, but does not play an obligatory role in either vascular development or leukocyte migration.

Genetic evidence for functional redundancy of Platelet/Endothelial cell adhesion molecule-1 (PECAM-1): CD31-deficient mice reveal PECAM-1-dependent and PECAM-1-independent functions

Platelet/endothelial cell adhesion molecule-1 (PECAM-1; CD31), a member of the Ig superfamily, is expressed strongly at endothelial cell-cell junctions, on platelets, and on most leukocytes. CD31 has been postulated to play a role in vasculogenesis and angiogenesis, and has been implicated as a key mediator of the transendothelial migration of leukocytes. To further define the physiologic role of CD31, we used targeted gene disruption of the CD31 gene in embryonic stem cells to generate CD31-deficient mice. CD31-deficient mice (CD31KO) are viable and born at the expected Mendelian frequency, remain healthy, and exhibit no obvious vascular developmental defects. In response to inflammatory challenge, polymorphonuclear leukocytes of CD31KO mice are arrested between the vascular endothelium and the basement membrane of inflammatory site mesenteric microvessels, confirming a role for CD31 in the migration of neutrophils through the subendothelial extracellular matrix. Normal numbers of leukocytes are recovered from inflammatory sites in CD31KO mice, however, suggesting that the defect in leukocyte migration across basal lamina observed in the absence of CD31 may be compensated for by the use of other adhesion molecules, or possibly an increased rate of migration. Homing of T lymphocytes in vivo is normal, and CD31KO mice are able to mount a cutaneous hypersensitivity response normally. In addition, CD31-mediated homophilic adhesion does not appear to play a role in platelet aggregation in vitro. This study provides genetic evidence that CD31 is involved in transbasement membrane migration, but does not play an obligatory role in either vascular development or leukocyte migration.

Differential requirement for caspase 9 in apoptotic pathways in vivo

Mutation of Caspase 9 (Casp9) results in embryonic lethality and defective brain development associated with decreased apoptosis. Casp9-/- embryonic stem cells and embryonic fibroblasts are resistant to several apoptotic stimuli, including UV and gamma irradiation. Casp9-/- thymocytes are also resistant to dexamethasone- and gamma irradiation-induced apoptosis, but are surprisingly sensitive to apoptosis induced by UV irradiation or anti-CD95. Resistance to apoptosis is accompanied by retention of the mitochondrial membrane potential in mutant cells. In addition, cytochrome c is translocated to the cytosol of Casp9-/- ES cells upon UV stimulation, suggesting that Casp9 acts downstream of cytochrome c. Caspase processing is inhibited in Casp9-/- ES cells but not in thymocytes or splenocytes. Comparison of the requirement for Casp9 and Casp3 in different apoptotic settings indicates the existence of at least four different apoptotic pathways in mammalian cells.

The transcription factor interferon regulatory factor 1 (IRF-1) is important during the maturation of natural killer 1.1+ T cell receptor-alpha/beta+ (NK1+ T) cells, natural killer cells, and intestinal intraepithelial T cells

In contrast to conventional T cells, natural killer (NK) 1.1+ T cell receptor (TCR)-alpha/beta+ (NK1+T) cells, NK cells, and intestinal intraepithelial lymphocytes (IELs) bearing CD8-alpha/alpha chains constitutively express the interleukin (IL)-2 receptor (R)beta/15Rbeta chain. Recent studies have indicated that IL-2Rbeta/15Rbeta chain is required for the development of these lymphocyte subsets, outlining the importance of IL-15. In this study, we investigated the development of these lymphocyte subsets in interferon regulatory factor 1-deficient (IRF-1-/-) mice. Surprisingly, all of these lymphocyte subsets were severely reduced in IRF-1-/- mice. Within CD8-alpha/alpha+ intestinal IEL subset, TCR-gamma/delta+ cells and TCR-alpha/beta+ cells were equally affected by IRF gene disruption. In contrast to intestinal TCR-gamma/delta+ cells, thymic TCR-gamma/delta+ cells developed normally in IRF-1-/- mice. Northern blot analysis further revealed that the induction of IL-15 messenger RNA was impaired in IRF-1-/- bone marrow cells, and the recovery of these lymphocyte subsets was observed when IRF-1-/- cells were cultured with IL-15 in vitro. These data indicate that IRF-1 regulates IL-15 gene expression, which may control the development of NK1+T cells, NK cells, and CD8-alpha/alpha+ IELs.

Essential contribution of caspase 3/CPP32 to apoptosis and its associated nuclear changes

Caspases are fundamental components of the mammalian apoptotic machinery, but the precise contribution of individual caspases is controversial. CPP32 (caspase 3) is a prototypical caspase that becomes activated during apoptosis. In this study, we took a comprehensive approach to examining the role of CPP32 in apoptosis using mice, embryonic stem (ES) cells, and mouse embryonic fibroblasts (MEFs) deficient for CPP32. CPP32(ex3-/-) mice have reduced viability and, consistent with an earlier report, display defective neuronal apoptosis and neurological defects. Inactivation of CPP32 dramatically reduces apoptosis in diverse settings, including activation-induced cell death (AICD) of peripheral T cells, as well as chemotherapy-induced apoptosis of oncogenically transformed CPP32(-/-) MEFs. As well, the requirement for CPP32 can be remarkably stimulus-dependent: In ES cells, CPP32 is necessary for efficient apoptosis following UV- but not gamma-irradiation. Conversely, the same stimulus can show a tissue-specific dependence on CPP32: Hence, TNFalpha treatment induces normal levels of apoptosis in CPP32 deficient thymocytes, but defective apoptosis in oncogenically transformed MEFs. Finally, in some settings, CPP32 is required for certain apoptotic events but not others: Select CPP32(ex3-/-) cell types undergoing cell death are incapable of chromatin condensation and DNA degradation, but display other hallmarks of apoptosis. Together, these results indicate that CPP32 is an essential component in apoptotic events that is remarkably system- and stimulus-dependent. Consequently, drugs that inhibit CPP32 may preferentially disrupt specific forms of cell death.

iNOS expression and nitrotyrosine formation in the myocardium in response to inflammation is controlled by the interferon regulatory transcription factor 1

BACKGROUND

Production of NO by inducible NO synthase (iNOS) has been implicated in the pathology of spontaneous and antigen-induced autoimmune diseases, and iNOS is expressed in the myocardium of patients with heart failure. It is not clear whether inflammatory murine autoimmune heart disease, an experimental model for human postviral heart disease, is characterized by increased iNOS expression within the heart and whether iNOS and NO are essential in the pathogenesis of autoimmune myocarditis.

METHODS AND RESULTS

In the murine model of cardiac myosin-induced myocarditis, we demonstrate that iNOS expression was elicited in inflammatory macrophages and in distinct cardiomyocytes. Autoimmune heart disease was accompanied by formation of the NO reaction product nitrotyrosine in inflammatory macrophages as well as in cardiomyocytes. iNOS expression and nitrotyrosine formation were strictly dependent on myocardial inflammation. Focal myocarditis was sufficient to induce nitrotyrosine formation throughout the whole heart muscle. Mice defective for the interferon regulatory transcription factor-1 (IRF-1(-/-)) after gene targeting failed to induce iNOS expression and nitrotyrosine formation in the heart but developed cardiac myosin-induced myocarditis at prevalence and severity similar to those of heterozygous littermates (IRF-1(+/-)).

CONCLUSIONS

These data provide the first in vivo evidence that iNOS expression and NO synthesis in macrophages and distinct cardiomyocytes are elicited in experimental murine inflammatory heart disease. The transcription factor IRF-1 controls iNOS expression and NO synthesis in disease. Because autoimmune myocarditis can develop in animals lacking IRF-1, these mice will be useful to elucidate the link between iNOS expression in inflammatory heart disease and the development of dilated cardiomyopathy and heart failure.

Interferon regulatory factor-1 is required for a T helper 1 immune response in vivo

The transcription factor interferon regulatory factor-1 (IRF-1) mediates the effects of IFN. No information exists on its role in lymphokine production. Protection against the intracellular pathogen Leishmania major depends on a Th1 response. Here, we show that CD4+ T cells from Leishmania-infected mice lacking one (+/-) or both (-/-) alleles of the IRF-1 gene developed a profound, gene dose-dependent decrease in IFNgamma production. IRF-1(-/-) mice showed dramatically exacerbated Leishmaniasis. They produced increased Leishmania-specific IgG1 and IgE, and their CD4+ T cells produced increased IL-4, characteristics of the non-protective Th2 response. In cell transfer experiments, IRF-1(-/-) CD4+ T cells mounted normal Th1 responses. However, the ability of IRF-1(-/-) mice to produce IL-12 was severely compromised. Thus, IRF-1 is a determining factor for Th1 responses.

Abnormal development of intestinal intraepithelial lymphocytes and peripheral natural killer cells in mice lacking the IL-2 receptor beta chain

The interleukin-2 receptor beta chain (IL-2R beta) is expressed on a variety of hematopoietic cell types, including natural killer (NK) cells and nonconventional T lymphocyte subsets such as intestinal intraepithelial lymphocytes (IEL). However, the importance of IL-2R beta-mediated signaling in the growth and development of these cells has yet to be clearly established. We have investigated IEL and NK cells in mice deficient for IL-2R beta and describe here striking defects in the development of these cells. IL-2R beta-/- mice exhibited an abnormal IEL cell population, characterized by a dramatic reduction in T cell receptor alpha beta CD8 alpha alpha and T cell receptor gamma delta lymphocytes. This selective decrease indicates that IEL can be classified into those whose development and/or differentiation is dependent on IL-2R beta function and those for which IL-2R beta-mediated signaling is not essential. NK cell development was also found to be disrupted in IL-2R beta-deficient mice, characterized by a reduction in NK1.1+CD3- cells in the peripheral circulation and an absence of NK cytotoxic activity in vitro. The dependence of NK cells and certain subclasses of IEL cells on IL-2R beta expression points to an essential role for signaling through this receptor, presumably by IL-2 and/or IL-15, in the development of lymphocyte-subsets of extrathymic origin.

The transcription factor interferon regulatory factor-1 is essential for natural killer cell function in vivo

The activation of natural killer (NK) cells, cytotoxic lymphocytes capable of major histocompatibility complex (MHC)-unrestricted killing and early antiviral defense, is temporally related to the increased interferon (IFN)-alpha/beta production that is seen in the viral infection of mice. Type I IFN (IFN-alpha/beta) are expressed in many cell types early after primary viral infection and have been shown to mediate resistance against a variety of viruses. In this study, the role of the transcriptional activator IFN regulatory factor-1 (IRF-1) in murine NK cell activity was assessed. IRF-1-deficient mice displayed a normal frequency of NK marker-positive cells, but exhibited greatly reduced NK cell-mediated cytotoxicity after both virus infection and stimulation with the IFN inducer polyinosinic:polycytidilic acid in vivo. In vitro, cytolytic activity in IRF-1-deficient NK cells remained defective after stimulation with IFN-beta, IL-2, and IL-12. IRF-1-deficient mice were unable to eliminate syngeneic MHC class I-negative tumor cells in vivo, and had a reduced ability to reject parental semi-allogeneic donor cells from the circulation. Thus, IRF-1 is essential for the induction of NK cell-mediated cytotoxicity and for the in vivo effector functions that are mediated by this activity.

Regulation of T cell receptor signaling by tyrosine phosphatase SYP association with CTLA-4

The absence of CTLA-4 results in uncontrolled T cell proliferation. The T cell receptor-specific kinases FYN, LCK, and ZAP-70 as well as the RAS pathway were found to be activated in T cells of Ctla-4-/- mutant mice. In addition, CTLA-4 specifically associated with the tyrosine phosphatase SYP, an interaction mediated by the SRC homology 2 (SH2) domains of SYP and the phosphotyrosine sequence Tyr-Val-Lys-Met within the CTLA-4 cytoplasmic tail. The CTLA-4-associated SYP had phosphatase activity toward the RAS regulator p52SHC. Thus, the RAS pathway and T cell activation through the T cell receptor are regulated by CTLA-4-associated SYP.

Imaging inflammation with 99Tcm-labeled chemotactic peptides: analogues with reduced neutropenia

Two 99Tcm-labelled analogues of the chemotactic peptide ForMLF were evaluated as potential agents for imaging inflammation and infection, in the hope that they would be simple to use and would give diagnostically useful images shortly after injection. The peptides differed in the chelation site for 99Tcm and the presence of a hydrophilic spacer. The sequences of RP050 and RP056 were ForNleLFNleYK(G)G-C(Acm)-GPic and ForNleLFNleYKK(DG)GC(Acm)SPic respectively, where Pic is picolinic acid. In in vitro tests of binding to the ForMLF receptor on polymorphonuclear neutrophils and potency for release of myeloperoxidase, RP056 was similar in potency to ForMLF, whereas RP050 was 10 times more potent. When administered in 5-nmol doses to rats, RP050 produced less extensive neutropenia than ForMLF, whereas RP056 produced very little neutropenia. Following labelling by ligand exchange from tartrate or glucoheptonate at 100 degrees C and purification using a C-18 solid-phase extraction cartridge, 4-MBq doses were administered to rats bearing infectious (Escherichia coli) or sterile (zymosan) inflammation sites in the thigh. The inflammation-to-normal muscle ratios at 30 min after injection were 3.9 +/- 0.4 for RP050 and 4.7 +/- 0.3 for RP056 (mean +/- S.E.M., n = 4), and the ratios were maintained for up to 3 h. These peptides are promising agents for imaging inflammation and infection.

Endogenous corticosteroids modulate lymphoproliferation and susceptibility to experimental allergic encephalomyelitis in the Brown Norway rat

Successful induction of the experimental autoimmune disease allergic encephalomyelitis (EAE) depends, in part, upon species susceptibility. The Lewis rat is highly susceptible to EAE whereas the Brown Norway (BN) strain is resistant to induction. Endogenous glucocorticoids influence the manifestation of the disease and recovery from neurological deficits. Moreover, abrogation of the curative steroid-mediated effects converts the condition to a terminal state. In the present study treatment of EAE-inoculated BN rats with the steroid antagonist RU486 (Mifepristone) failed to influence the resistance to symptoms. Similarly, adrenalectomy (ADX) prior to sensitisation did not allow the development of clinical EAE but did facilitate neuroperivascular accumulation of inflammatory-type cells. However, RU486 treatment after ADX induced neurological and histological signs of EAE in the majority of animals. Lymphocyte proliferation studies on cells isolated from BN rats treated with RU486 revealed an enhanced responsiveness to mitogenic and antigenic stimulation. These results strongly implicate endogenous steroids in the expansion of immune cell numbers which would be an absolute requirement for the expression of autoimmune-based neurological disease in otherwise resistant rats.

Serum corticosterone, interleukin-1 and tumour necrosis factor in rat experimental endotoxaemia: comparison between Lewis and Wistar strains

1. Circulating corticosterone, interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF alpha) activities in serum of Lewis and Wistar rats were measured following injection of lipopolysaccharide (LPS). IL-1 was measured as 'lymphocyte activation factor' (LAF) activity following precipitation of inhibitory activity with polyethylene glycol. TNF alpha activity was measured as cytotoxic activity. 2. Compared to the Wistar, the Lewis rat had higher circulating LAF and TNF activities following LPS, and release of both cytokines was prolonged in this strain. 3. Corticosterone increases in response to LPS were less in the Lewis than in the Wistar rat following the initial peak at 1 h; basal corticosterone was lower in the Lewis rat. 4. Adrenalectomized Lewis rats had even greater amounts of circulating LAF and TNF activities following LPS than did intact animals; the effect of adrenalectomy was not however mimicked by acute treatment with the steroid receptor antagonist, RU486, suggesting that endogenous corticosteroids did not acutely control cytokine release. 5. Although in vivo administration of anti-murine IL-1 alpha antiserum significantly lowered LAF activity of serum, circulating corticosterone in response to LPS was not affected. Similarly, treatment with anti-murine TNF alpha monoclonal antibody (mAb) abrogated TNF activity without affecting corticosterone, suggesting that other mediators may be responsible for corticosterone release following LPS. 6. This 'overproduction' of inflammatory cytokines together with lower circulating corticosterone may contribute to the susceptibility of the Lewis rat to diseases such as adjuvant arthritis or experimental allergic encephalomyelitis.

Development of specific antibody and in vivo response to antigen in different rat strains: effect of dexamethasone and importance of endogenous corticosteroids

Endogenous glucocorticoids undoubtedly play a role in the control of immune responses: their contribution to inter-strain variation is unknown. The development of specific IgG and IgE was measured following inoculation with ovalbumin in Lewis, Fischer, Wistar and Brown Norway rats. The Lewis gives a smaller IgG and IgE response than the other strains and the response in vivo to antigen injected into the paw correlates with the titre of specific antibody. Treatment with the steroid receptor antagonist RU486 (mifepristone) following inoculation reveals that in the Lewis, and to a lesser extent in the Brown Norway, the development of a specific IgG response is limited by endogenous corticosteroids. The IgG response in different strains is differently sensitive to treatment with the synthetic glucocorticoid dexamethasone, the Lewis being particularly resistant. The importance of control by endogenous corticosteroids should not be overlooked in contributing to strain differences in immune response.

The local anti-inflammatory action of dexamethasone in the rat carrageenin oedema model is reversed by an antiserum to lipocortin 1

1. A local pre-injection of 1 micrograms dexamethasone sodium phosphate strongly inhibited (> 60% inhibition at 3 h; P < 0.001 at all time points) the development of carrageenin-induced paw oedema in the rat induced by a subplantar injection of 0.1 ml, 2% carrageenin. 2. Coinjection of a polyclonal rabbit antiserum raised against human 1-188 recombinant lipocortin 1, which also recognised the rat protein, reversed the inhibitory action of dexamethasone (P < 0.05 at 4 h and 5 h). At the highest volume used (40 microliters) control antisera were without any effect. 3. These data further support the concept that lipocortin 1 is involved in the anti-inflammatory mechanism of action of the glucocorticoids.

Nutrition in podiatric surgery

Although obtaining the preoperative nutritional status of the typical elective podiatric surgical patient is not usually addressed, knowledge of malnutrition towards surgical success and basic parameters to identify malnutrition is imperative. This paper will attempt to provide information to better prepare the patient for essential postoperative healing and minimize possible complications.

Monostotic fibrous dysplasia of the foot

Fibrous dysplasia is a benign, nonfamilial disorder of the skeleton, characterized by expanding fibroosseous lesions occupying single or multiple bones with possible extraskeletal anomalies. Fibrous dysplasia begins in childhood and is not usually recognized until adolescence or adulthood. When fibrous dysplasia affects the foot, it is often the expression of the polystotic form of the disease. This paper will review the pathology of the disease and monostotic involvement of the first metatarsal.

The use of intravenous regional anesthesia in podiatric surgery

Several options become available when choosing between types of anesthesia in foot surgery. Ease in administration, minimal systemic effects, and rapid return of sensation make intravenous regional anesthesia an excellent option. The authors will discuss considerations and concepts along with their experiences with the procedure.