Protein S is inducible by interleukin 4 in T cells and inhibits lymphoid cell procoagulant activity

TAM family kinases as therapeutic targets at the interface of cancer and immunity

Novel treatment approaches are needed to overcome innate and acquired mechanisms of resistance to current anticancer therapies in cancer cells and the tumour immune microenvironment. The TAM (TYRO3, AXL and MERTK) family receptor tyrosine kinases (RTKs) are potential therapeutic targets in a wide range of cancers. In cancer cells, TAM RTKs activate signalling pathways that promote cell survival, metastasis and resistance to a variety of chemotherapeutic agents and targeted therapies. TAM RTKs also function in innate immune cells, contributing to various mechanisms that suppress antitumour immunity and promote resistance to immune-checkpoint inhibitors. Therefore, TAM antagonists provide an unprecedented opportunity for both direct and immune-mediated therapeutic activity provided by inhibition of a single target, and are likely to be particularly effective when used in combination with other cancer therapies. To exploit this potential, a variety of agents have been designed to selectively target TAM RTKs, many of which have now entered clinical testing. This Review provides an essential guide to the TAM RTKs for clinicians, including an overview of the rationale for therapeutic targeting of TAM RTKs in cancer cells and the tumour immune microenvironment, a description of the current preclinical and clinical experience with TAM inhibitors, and a perspective on strategies for continued development of TAM-targeted agents for oncology applications.

Association of Risk of Incident Venous Thromboembolism With Atopic Dermatitis and Treatment With Janus Kinase Inhibitors: A Systematic Review and Meta-analysis

Importance

The risk of venous thromboembolism (VTE) among patients with atopic dermatitis (AD), especially when receiving treatment with Janus kinase (JAK) inhibitors, is unclear.

Objective

To determine the association of AD with incident VTE and evaluate the risk of incident VTE among patients with AD who were receiving treatment with JAK inhibitors.

Data Sources

The MEDLINE, Embase, Cochrane Library, and Web of Science databases were searched with no restrictions on language nor geographic locations from their respective inception to February 5, 2022.

Study Selection

Cohort studies examining the association of AD with incident VTE and randomized clinical trials (RCTs) reporting VTE events in participants with AD receiving JAK inhibitors were included. Around 0.7% of initially identified articles met the selection criteria.

Data Extraction and Synthesis

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline was followed. The risk of bias of included cohort studies and RCTs was assessed by the Newcastle-Ottawa Scale and the Cochrane Risk of Bias Tool 2, respectively. A random-effects model meta-analysis was conducted to calculate the pooled hazard ratio (HR) and risk difference for incident VTE.

Main Outcomes and Measures

The HRs for incident VTE associated with AD and risk difference for incident VTE between participants with AD who were receiving treatment with JAK inhibitors and controls receiving placebo or dupilumab.

Results

Two cohort studies and 15 RCTs with a total of 466 993 participants were included. The meta-analysis found no significant association of AD with incident VTE (HR, 0.95; 95% CI 0.62-1.45; incidence rate of VTE, 0.23 events/100 patient-years). Overall, 3 of 5722 patients with AD (0.05%) who were receiving treatment with JAK inhibitors experienced VTE compared with 1 of 3065 patients with AD (0.03%) receiving placebo or dupilumab (Mantel-Haenszel risk difference, 0; 95% CI, 0-0). The incidence rate of VTE was 0.15 and 0.12 events per 100 patient-years in participants with AD receiving JAK inhibitors and placebo, respectively. The findings were similar in 4 unique JAK inhibitors (abrocitinib, baricitinib, upadacitinib, and SHR0302).

Conclusions and Relevance

The results of this systematic review and meta-analysis suggest that the currently available evidence does not detect an increased risk of VTE associated with AD or treatment with JAK inhibitors. These findings may provide a reference for clinicians in prescribing JAK inhibitors for patients with AD.

Lifting the innate immune barriers to antitumor immunity

The immune system evolved for adequate surveillance and killing of pathogens while minimizing host damage, such as due to chronic or exaggerated inflammation and autoimmunity. This is achieved by negative regulators and checkpoints that limit the magnitude and time course of the immune response. Tumor cells often escape immune surveillance and killing. Therefore, disrupting the brakes built into the immune system should effectively boost the anticancer immune response. The success of anti-CTLA4, anti-PD-1 and anti-PD-L1 have firmly established this proof of concept. Since the response rate of anti-CTLA4, anti-PD-1 and anti-PD-L1 is still limited, there is an intense effort for the identification of new targets and development of approaches that can expand the benefits of immunotherapy to a larger patient pool. Additional T cell checkpoints are obvious targets; however, here we focus on the unusual suspects—cells that function to initiate and guide T cell activity. Innate immunity is both an obligate prerequisite for the initiation of adaptive immune responses and a requirement for the recruitment of activated T cells to the site of action. We discuss some of the molecules present in innate immune cells, including natural killer cells, dendritic cells, macrophages, myeloid-derived suppressor cells, endothelial cells and stromal cells, that can activate or enhance innate immune cell functions, and more importantly, the inhibitors or checkpoints present in these cells that restrain their functions. Boosting innate immunity, either by enhancing activator functions or, preferably, by blocking the inhibitors, may represent a new anticancer treatment modality or at least function as adjuvants to T cell checkpoint inhibitors.

Tyro3, Axl, Mertk receptor-mediated efferocytosis and immune regulation in the tumor environment

Three structurally related tyrosine receptor cell surface kinases, Tyro3, Axl, and Mertk (TAM) have been recognized to modulate immune function, tissue homeostasis, cardiovasculature, and cancer. The TAM receptor family appears to operate in adult mammals across multiple cell types, suggesting both widespread and specific regulation of cell functions and immune niches. TAM family members regulate tissue homeostasis by monitoring the presence of phosphatidylserine expressed on stressed or apoptotic cells. The detection of phosphatidylserine on apoptotic cells requires intermediary molecules that opsonize the dying cells and tether them to TAM receptors on phagocytes. This complex promotes the engulfment of apoptotic cells, also known as efferocytosis, that leads to the resolution of inflammation and tissue healing. The immune mechanisms dictating these processes appear to fall upon specific family members or may involve a complex of different receptors acting cooperatively to resolve and repair damaged tissues. Here, we focus on the role of TAM receptors in triggering efferocytosis and its consequences in the regulation of immune responses in the context of inflammation and cancer.

Role of Vitamin K-Dependent Factors Protein S and GAS6 and TAM Receptors in SARS-CoV-2 Infection and COVID-19-Associated Immunothrombosis

The vitamin K-dependent factors protein S (PROS1) and growth-arrest-specific gene 6 (GAS6) and their tyrosine kinase receptors TYRO3, AXL, and MERTK, the TAM subfamily of receptor tyrosine kinases (RTK), are key regulators of inflammation and vascular response to damage. TAM signaling, which has largely studied in the immune system and in cancer, has been involved in coagulation-related pathologies. Because of these established biological functions, the GAS6-PROS1/TAM system is postulated to play an important role in SARS-CoV-2 infection and progression complications. The participation of the TAM system in vascular function and pathology has been previously reported. However, in the context of COVID-19, the role of TAMs could provide new clues in virus-host interplay with important consequences in the way that we understand this pathology. From the viral mimicry used by SARS-CoV-2 to infect cells, to the immunothrombosis that is associated with respiratory failure in COVID-19 patients, TAM signaling seems to be involved at different stages of the disease. TAM targeting is becoming an interesting biomedical strategy, which is useful for COVID-19 treatment now, but also for other viral and inflammatory diseases in the future.

TAM-ing T cells in the tumor microenvironment: implications for TAM receptor targeting

The TAM receptors-TYRO3, AXL, MERTK-are pleiotropically expressed receptors in both healthy and diseased tissue. A complex of the ligands Protein S (PROS1) or Growth Arrest-Specific 6 (GAS6) with apoptotic phosphatidylserine activates the TAM receptors. Hence, this receptor family is essential for the efferocytosis of apoptotic material by antigen-presenting cells. In addition, TAM receptors are expressed by virtually all cells of the tumor microenvironment. They are also potent oncogenes, frequently overexpressed in cancer and involved in survival and therapy resistance. Due to their pro-oncogenic and immune-inhibitory traits, TAM receptors have emerged as promising targets for cancer therapy. Recently, TAM receptors have been described to function as costimulatory molecules on human T cells. TAM receptors' ambivalent functions on many different cell types therefore make therapeutic targeting not straight-forward. In this review we summarize our current knowledge of the function of TAM receptors in the tumor microenvironment. We place particular focus on TAM receptors and the recently unraveled role of MERTK in activated T cells and potential consequences for anti-tumor immunity.

MERTK Acts as a Costimulatory Receptor on Human CD8+ T Cells

The TAM family of receptor tyrosine kinases (TYRO3, AXL, and MERTK) is known to be expressed on antigen-presenting cells and function as oncogenic drivers and as inhibitors of inflammatory responses. Both human and mouse CD8⁺ T cells are thought to be negative for TAM receptor expression. In this study, we show that T-cell receptor (TCR)-activated human primary CD8⁺ T cells expressed MERTK and the ligand PROS1 from day 2 postactivation. PROS1-mediated MERTK signaling served as a late costimulatory signal, increasing proliferation and secretion of effector and memory-associated cytokines. Knockdown and inhibition studies confirmed that this costimulatory effect was mediated through MERTK. Transcriptomic and metabolic analyses of PROS1-blocked CD8⁺ T cells demonstrated a role of the PROS1-MERTK axis in differentiation of memory CD8⁺ T cells. Finally, using tumor-infiltrating lymphocytes (TIL) from melanoma patients, we show that MERTK signaling on T cells improved TIL expansion and TIL-mediated autologous cancer cell killing. We conclude that MERTK serves as a late costimulatory signal for CD8⁺ T cells. Identification of this costimulatory function of MERTK on human CD8⁺ T cells suggests caution in the development of MERTK inhibitors for hematologic or solid cancer treatment.

Coagulopathies and inflammatory diseases: '…glimpse of a Snark'

Coagulopathies and inflammatory diseases, ostensibly, have distinct underlying molecular bases. Notwithstanding, both are host defense mechanisms to physical injury. In invertebrates, clotting can function directly in anti-pathogen defense. Molecules of the vertebrate clotting cascade have also been directly linked to the regulation of inflammation. We posit that thrombophilia may provide resistance against pathogens in vertebrates. The selective pressure of improved anti-pathogen defense may have retained mutations associated with a thrombophilic state in the human population and directly contributed to enhanced inflammation. Indeed, in some inflammatory diseases, at least a subset of patients can be identified as hypercoagulable. Therefore, anticoagulants such as warfarin or apixaban may have a therapeutic role in some inflammatory diseases.

TAM receptor tyrosine kinases as emerging targets of innate immune checkpoint blockade for cancer therapy

Cancer immunotherapy utilizing T-cell checkpoint inhibitors has shown tremendous clinical success. Yet, this mode of treatment is effective in only a subset of patients. Unresponsive patients tend to have non-T-cell-inflamed tumors that lack markers associated with the activation of adaptive anti-tumor immune responses. Notably, elimination of cancer cells by T cells is critically dependent on the optimal activity of innate immune cells. Therefore, identifying new targets that regulate innate immune cell function and promote the engagement of adaptive tumoricidal responses is likely to lead to the development of improved therapies against cancer. Here, we review the TAM receptor tyrosine kinases-TYRO3, AXL, and MERTK-as an emerging class of innate immune checkpoints that participate in key steps of anti-tumoral immunity. Namely, TAM-mediated efferocytosis, negative regulation of dendritic cell activity, and dysregulated production of chemokines collectively favor the escape of malignant cells. Hence, disabling TAM signaling may promote engagement of adaptive immunity and complement T-cell checkpoint blockade.

The Role of TAM Family Receptors in Immune Cell Function: Implications for Cancer Therapy

The TAM receptor protein tyrosine kinases-Tyro3, Axl, and Mer-are essential regulators of immune homeostasis. Guided by their cognate ligands Growth arrest-specific gene 6 (Gas6) and Protein S (Pros1), these receptors ensure the resolution of inflammation by dampening the activation of innate cells as well as by restoring tissue function through promotion of tissue repair and clearance of apoptotic cells. Their central role as negative immune regulators is highlighted by the fact that deregulation of TAM signaling has been linked to the pathogenesis of autoimmune, inflammatory, and infectious diseases. Importantly, TAM receptors have also been associated with cancer development and progression. In a cancer setting, TAM receptors have a dual regulatory role, controlling the initiation and progression of tumor development and, at the same time, the associated anti-tumor responses of diverse immune cells. Thus, modulation of TAM receptors has emerged as a potential novel strategy for cancer treatment. In this review, we discuss our current understanding of how TAM receptors control immunity, with a particular focus on the regulation of anti-tumor responses and its implications for cancer immunotherapy.

TAM receptor signaling in immune homeostasis

The TAM receptor tyrosine kinases (RTKs)-TYRO3, AXL, and MERTK-together with their cognate agonists GAS6 and PROS1 play an essential role in the resolution of inflammation. Deficiencies in TAM signaling have been associated with chronic inflammatory and autoimmune diseases. Three processes regulated by TAM signaling may contribute, either independently or collectively, to immune homeostasis: the negative regulation of the innate immune response, the phagocytosis of apoptotic cells, and the restoration of vascular integrity. Recent studies have also revealed the function of TAMs in infectious diseases and cancer. Here, we review the important milestones in the discovery of these RTKs and their ligands and the studies that underscore the functional importance of this signaling pathway in physiological immune settings and disease.

Tyro3, Axl, and Mertk receptor signaling in inflammatory bowel disease and colitis-associated cancer

Three receptor tyrosine kinases, Tyro3, Axl, and Mertk (TAM) and their ligands Gas6 and Protein S, have emerged as potent negative regulators of innate immune responses. A number of studies using genetic ablation of TAM loci in mice have elucidated the mechanism of TAM engagement and function during the immune response and removal of apoptotic cells. Following phagocytosis of apoptotic cells or the induction of T-cell dependent adaptive immune responses, ligand-induced TAM signaling dampens proinflammatory cytokine production and thus prevents exaggerated or prolonged inflammation. It is believed that the TAM pathway may play an important role in the pathogenesis of inflammatory bowel disease. Suppression of inflammation and removal of apoptotic cells followed by tissue repair are essential processes for disease remission and the successful management of inflammatory bowel disease. In light of the key role of TAMs in controlling inflammatory responses, here, we review the recent advances on TAM research vis-à-vis the resolution of intestinal inflammation. Targeted activation of TAM receptor tyrosine kinases may represent a potent therapeutic opportunity in inflammatory bowel disease.

TAM receptors, Gas6, and protein S: roles in inflammation and hemostasis

TAM receptors (Tyro3, Axl, and Mer) belong to a family of receptor tyrosine kinases that have important effects on hemostasis and inflammation. Also, they affect cell proliferation, survival, adhesion, and migration. TAM receptors can be activated by the vitamin K–dependent proteins Gas6 and protein S. Protein S is more commonly known as an important cofactor for protein C as well as a direct inhibitor of multiple coagulation factors. To our knowledge, the functions of Gas6 are limited to TAM receptor activation. When activated, the TAM receptors have effects on primary hemostasis and coagulation and display an anti-inflammatory or a proinflammatory effect, depending on cell type. To comprehend the effects that the TAM receptors and their ligands have on hemostasis and inflammation, we compare studies that report the different phenotypes displayed by mice with deficiencies in the genes of this receptor family and its ligands (protein S+/−, Gas6−/−, TAM−/−, and variations of these). In this manner, we aim to display which features are attributable to the different ligands. Because of the effects TAM receptors have on hemostasis, inflammation, and cancer growth, their modulation could make interesting therapeutic targets in thromboembolic disease, atherosclerosis, sepsis, autoimmune disease, and cancer.

Biology of the TAM receptors

The TAM receptors--Tyro3, Axl, and Mer--comprise a unique family of receptor tyrosine kinases, in that as a group they play no essential role in embryonic development. Instead, they function as homeostatic regulators in adult tissues and organ systems that are subject to continuous challenge and renewal throughout life. Their regulatory roles are prominent in the mature immune, reproductive, hematopoietic, vascular, and nervous systems. The TAMs and their ligands--Gas6 and Protein S--are essential for the efficient phagocytosis of apoptotic cells and membranes in these tissues; and in the immune system, they act as pleiotropic inhibitors of the innate inflammatory response to pathogens. Deficiencies in TAM signaling are thought to contribute to chronic inflammatory and autoimmune disease in humans, and aberrantly elevated TAM signaling is strongly associated with cancer progression, metastasis, and resistance to targeted therapies.

T cell-derived protein S engages TAM receptor signaling in dendritic cells to control the magnitude of the immune response

Dendritic cell (DC) activation is essential for the induction of immune defense against pathogens, yet needs to be tightly controlled to avoid chronic inflammation and exaggerated immune responses. Here, we identify a mechanism of immune homeostasis by which adaptive immunity, once triggered, tempers DC activation and prevents overreactive immune responses. T cells, once activated, produced Protein S (Pros1) that signaled through TAM receptor tyrosine kinases in DCs to limit the magnitude of DC activation. Genetic ablation of Pros1 in mouse T cells led to increased expression of costimulatory molecules and cytokines in DCs and enhanced immune responses to T cell-dependent antigens, as well as increased colitis. Additionally, PROS1 was expressed in activated human T cells, and its ability to regulate DC activation was conserved. Our results identify a heretofore unrecognized, homeostatic negative feedback mechanism at the interface of adaptive and innate immunity that maintains the physiological magnitude of the immune response.

Genetic dissection of TAM receptor-ligand interaction in retinal pigment epithelial cell phagocytosis

Although TAM receptor tyrosine kinases play key roles in immune regulation, cancer metastasis, and viral infection, the relative importance of the two TAM ligands-Gas6 and Protein S-has yet to be resolved in any setting in vivo. We have now performed a genetic dissection of ligand function in the retina, where the TAM receptor Mer is required for the circadian phagocytosis of photoreceptor outer segments by retinal pigment epithelial cells. This process is severely attenuated in Mer mutant mice, which leads to photoreceptor death. We find that retinal deletion of either Gas6 or Protein S alone yields retinae with a normal number of photoreceptors. However, concerted deletion of both ligands fully reproduces the photoreceptor death seen in Mer mutants. These results demonstrate that Protein S and Gas6 function as independent, bona fide Mer ligands, and are, to a first approximation, interchangeable with respect to Mer-driven phagocytosis in the retina.

Upregulation of anticoagulant proteins, protein S and tissue factor pathway inhibitor, in the mouse myocardium with cardio-specific TNF-α overexpression

Heart failure (HF) has been recognized as a hypercoagulable state. However, the natural anticoagulation systems in the failing heart have not been studied. Recent experimental and clinical data have indicated that not only the thrombomodulin (TM)/protein C (PC) pathway but also the protein S (PS)/tissue factor pathway inhibitor (TFPI) system function as potent natural anticoagulants. To investigate the balance between procoagulant and anticoagulant activities in the failing heart, we measured the cardiac expression of tissue factor (TF), type 1 plasminogen activator inhibitor (PAI-1), TM, PC, PS, and TFPI by RT-PCR and/or Western blot analysis in male transgenic (TG) mice with heart-specific overexpression of TNF-α. Both procoagulant (TF and PAI-1) and anticoagulant (PS and TFPI) factors were upregulated in the myocardium of 24-wk-old TG (end-stage HF) but not in that of 4-wk-old TG (early decompensated HF) compared with the wild-type mice. Both factors were also upregulated in the infarcted myocardium at 3 days after coronary ligation in the wild-type mice. The expression of TM was downregulated in the TG heart, and PC was not detected in the hearts. The transcript levels of PS orphan receptors, Mer and Tyro3, but not Axl, were significantly upregulated in the TG heart. Double immunohistochemical staining revealed that myocardial infiltrating CD3-positive T cells may produce PS in the TG myocardium. In conclusion, the PS/TFPI was upregulated in the myocardium of a different etiological model of HF, thus suggesting a role for the PS/TFPI system in the protection of the failing heart under both inflammatory and hypercoagulable states.

Macrophage-tumor crosstalk: role of TAMR tyrosine kinase receptors and of their ligands

Ample clinical and preclinical evidence indicates that macrophages interact with tumor cells as well as with virtually all populations of host cells present in the tumor microenvironment. This crosstalk can strongly promote malignancy, but also has in principle the potential to inhibit tumor growth. Thus, it is of the utmost importance to improve our understanding of the mechanisms driving the pro- and antimalignant behavior of tumor-associated macrophages (TAMs) in order to develop better anticancer therapies. In this review, we discuss the biological consequences of reciprocal interactions between TAMs, cancer cells, endothelial cells, fibroblasts and other leukocyte subfractions within tumors. It was recently elucidated that tumors specifically educate macrophages to secrete growth arrest-specific gene 6 (Gas6), the common ligand of the Tyro3, Axl, Mer receptor (TAMR) family. In turn, Gas6 fosters tumor growth by promoting cancer cell proliferation. Therefore, the Gas6-TAMR axis might represent a novel target for disrupting tumor-macrophage crosstalk. We summarize here what is known about TAMR and their ligands in (human) cancer biology. In order to shed more light on the role of macrophages in human cancer, we additionally provide an overview of what is currently known about the prognostic impact of TAMs in human cancer.

Single nucleotide polymorphisms in inflammation-related genes are associated with venous thromboembolism

BACKGROUND

Various genetic risk factors are known to increase the risk of venous thromboembolism (VTE). Increasing evidence suggests a "cross-talk" between the coagulation and inflammatory cascade. Therefore, polymorphisms in genes involved in inflammation may influence susceptibility towards VTE. The aim of the study was to investigate the role of single nucleotide polymorphisms (SNPs) in inflammation genes for susceptibility towards VTE.

METHODS

The study group consisted of 108 (47 men and 61 women) Dutch patients with documented VTE and 325 healthy controls from the same geographical area (117 men and 208 women). Odds ratios (OR) and 95% confidence intervals (95% CI) for VTE separately and if indicated by gender were calculated to assess whether genotype and allele frequency were associated with thrombosis.

RESULTS

Heterozygosity for SNP -899C/T of the interleukin 1-alpha gene (IL1A -899C/T) was under-represented in VTE patients compared to the control group (OR=0.51, 95% CI 0.32-0.82). The IL6 -174 CC genotype was more frequent in male patients with VTE compared to male controls (OR=4.06, 95% CI 1.43-11.5). Female patients carried significantly more IL13 (intron3) TT genotype (OR=5.60, 95% CI 1.94-18.5) compared to female controls. The allelic frequency of IL4 -589 T allele was significantly increased in female patients (OR=1.72, 95% CI 1.05-2.81) in contrast to men where no differences were observed.

CONCLUSION

Four SNPs in inflammatory-related genes of IL1A, IL4, IL6, and IL13 may be associated with VTE. These results need to be confirmed in independent groups with larger number of patients.

Active immune response protects Stat6VT transgenic mice from developing a lymphoproliferative disorder

Stat6 is a transcription factor that regulates important cellular processes such as proliferation, differentiation, and survival through mediating IL-4 and IL-13 signaling. Importantly, increasing evidence indicates of a role for Stat6 in lymphoproliferative disorders. Mice expressing a constitutively active form of Stat6 (Stat6VT) primarily in T lymphocytes were generated, and it has been recently described that a small percentage (approximately 5%) of these mice develop a spontaneous lymphoproliferative disorder (LPD) resulting in dramatic splenomegaly and altered splenic cell populations. Here, we report that Stat6VT mice housed in a non-pathogen-free environment have an increased incidence (37%) of the LPD. Additionally, examination of the expression of Stat6-regulated genes known to have roles in tumorigenesis demonstrated that there appears to be no one genetic alteration common to lymphocytes from Stat6VT/LPD mice. Interestingly, however, uniform exposure to antigen via immunization resulted in complete abrogation of the LPD in Stat6VT mice.

Influence of smoking during pregnancy on haemostasis in healthy full term neonates

BACKGROUND

Clinical and experimental researches have linked smoking to disturbances of coagulation and fibrinolysis. Several potential mechanisms are incriminated involving inflammation, fibrinogen synthesis and clotting factors. Based on the fact that the majority of tobacco components cross the placental barrier, the objective of our current study is to investigate the influence of smoking during pregnancy on neonatal haemostasis.

STUDY DESIGN

The study was based on a comparative evaluation of coagulation and fibronolysis between healthy full term infants of women who smoked during pregnancy and a control group. Subjects consisted of 39 newborns of smoking and 43 newborns of nonsmoking mothers. Blood samples were obtained shortly after birth and before the administration of vitamin K. Investigation included: PT, INR, aPTT, fibrinogen, coagulation factors II, V, VII, VIII, IX, X, XI, XII, vWillebrand (vWF), protein C and S, APCr, anti-thrombin (AT), t-PA and PAI-1. The independent t- test was used to compare the differences between the values of coagulation and fibrinolytic parameters at the p<0.05 level.

RESULTS

We discovered a statistically significant decrease in factor II and protein S levels and an elevation in t-PA and factor VIII concentrations in newborns of smoking mothers, without clinical manifestations of altered haemostasis. There were no significant differentiations in other coagulation or fibrinolytic parameters.

CONCLUSION

The alteration in factor II, protein S, t-PA and factor VIII in neonates exposed in utero to tobacco smoke is not accompanied by loss in the balance between coagulation and fibrinolytic pathways.

TAM receptors are pleiotropic inhibitors of the innate immune response

The activation of Toll-like receptors (TLRs) in dendritic cells (DCs) triggers a rapid inflammatory response to pathogens. However, this response must be tightly regulated because unrestrained TLR signaling generates a chronic inflammatory milieu that often leads to autoimmunity. We have found that the TAM receptor tyrosine kinases-Tyro3, Axl, and Mer-broadly inhibit both TLR and TLR-induced cytokine-receptor cascades. Remarkably, TAM inhibition of inflammation is transduced through an essential stimulator of inflammation-the type I interferon receptor (IFNAR)-and its associated transcription factor STAT1. TLR induction of IFNAR-STAT1 signaling upregulates the TAM system, which in turn usurps the IFNAR-STAT1 cassette to induce the cytokine and TLR suppressors SOCS1 and SOCS3. These results illuminate a self-regulating cycle of inflammation, in which the obligatory, cytokine-dependent activation of TAM signaling hijacks a proinflammatory pathway to provide an intrinsic feedback inhibitor of both TLR- and cytokine-driven immune responses.

Gas6 and protein S. Vitamin K-dependent ligands for the Axl receptor tyrosine kinase subfamily

Gas6 and protein S are two homologous secreted proteins that depend on vitamin K for their execution of a range of biological functions. A discrete subset of these functions is mediated through their binding to and activation of the receptor tyrosine kinases Axl, Sky and Mer. Furthermore, a hallmark of the Gas6-Axl system is the unique ability of Gas6 and protein S to tether their non receptor-binding regions to the negatively charged membranes of apoptotic cells. Numerous studies have shown the Gas6-Axl system to regulate cell survival, proliferation, migration, adhesion and phagocytosis. Consequently, altered activity/expression of its components has been detected in a variety of pathologies such as cancer and vascular, autoimmune and kidney disorders. Moreover, Axl overactivation can equally occur without ligand binding, which has implications for tumorigenesis. Further knowledge of this exquisite ligand-receptor system and the circumstances of its activation should provide the basis for development of novel therapies for the above diseases.

Thrombophilia and Recurrent Pregnancy Loss

Many unanswered questions regarding thrombophilia and recurrent pregnancy loss exist. For example, does a true association exist? Are thrombotic mechanisms relevant? Is a second messenger necessary to cause the manifestation of thrombosis? At present it seems that thrombophilia are associated with and may even cause some cases of pregnancy loss. The role of treatment remains to be determined. Although the aim of physicians working in this field is entirely laudable, to allow childless couples to have children, it is necessary to have good evidence of effect before treatment is given to all patients. A serious ethical dilemma remains, however, namely should treatment that may be effective be denied to patients who have prior pregnancy losses? Denial of treatment is extremely distressing for the patient and the physician. The author's own practice is to offer treatment after a full explanation, particularly because treatment is generally prescribed in the antiphospholipid syndrome and justified in hereditary thrombophilias according to the report of Carp and colleagues, showing a 25% improvement in live birth rates in treated patients. When treatment fails, however, the embryo should be karyotyped to exclude chromosomal aberrations.

Intact type 1 immunity and immune-associated coagulative responses in mice lacking IFN gamma-inducible fibrinogen-like protein 2

Fibrinogen-like protein 2 (Fgl2, fibroleukin) is a leukocyte product that exhibits significant homology to secreted proteins of diverse function, including growth factors, lectins, and components of extracellular matrix. Prior studies found that Fgl2 is IFN gamma-inducible, possesses direct coagulant activity, and inhibits T cell proliferation and dendritic cell maturation in vitro. Here, we demonstrate that Fgl2 expression is up-regulated during type 1 immunity in vivo and establish that such up-regulation is IFN gamma-, signal transducer and activation of transcription protein 1-, and IFN response factor 1-dependent. To investigate functional roles for Fgl2 during type 1 immunity, we generated Fgl2-deficient mice. Those animals are born at predicted Mendelian frequencies, appear overtly healthy, and contain normal numbers and frequencies of lymphoid cells. Although Fgl2 is IFN gamma-inducible and putatively regulates T cell activation/proliferation, we demonstrate that Fgl2-deficient and control mice exhibit similar degrees of T cell expansion, immunopathology, and/or pathogen burdens during protozoan (Toxoplasma gondii), bacterial (Yersinia enterocolitica, Listeria monocytogenes, and Mycobacterium tuberculosis), and viral (murine gamma-herpesvirus-68 and Sendai) infections. Fgl2-deficient mice also reject allografts with similar kinetics as control mice. Moreover, despite prior reports that Fgl2 functions as a procoagulant enzyme, we demonstrate that Fgl2-deficient and control mice produce similar levels of fibrin, a product of the coagulation cascade, during T. gondii infection and allograft rejection. Together, our findings suggest that Fgl2, although highly conserved and IFN gamma-inducible, is not a critical mediator of either type 1 immunity or immune-associated coagulant activity.

Identification of novel IL-4/Stat6-regulated genes in T lymphocytes

IL-4, primarily produced by T cells, mast cells, and basophiles, is a cytokine which has pleiotropic effects on the immune system. IL-4 induces T cells to differentiate to Th2 cells and activated B lymphocytes to proliferate and to synthesize IgE and IgG1. IL-4 is particularly important for the development and perpetuation of asthma and allergy. Stat6 is the protein activated by signal transduction through the IL-4R, and studies with knockout mice demonstrate that Stat6 is critical for a number of IL-4-mediated functions including Th2 development and production of IgE. In the present study, novel IL-4- and Stat6-regulated genes were discovered by using Stat6(-/-) mice and Affymetrix oligonucleotide arrays. Genes regulated by IL-4 were identified by comparing the gene expression profile of the wild-type T cells induced to polarize to the Th2 direction (CD3/CD28 activation + IL-4) to gene expression profile of the cells induced to proliferate (CD3/CD28 activation alone). Stat6-regulated genes were identified by comparing the cells isolated from the wild-type and Stat6(-/-) mice; in this experiment the cells were induced to differentiate to the Th2 direction (CD3/CD28 activation + IL-4). Our study demonstrates that a number a novel genes are regulated by IL-4 through Stat6-dependent and -independent pathways. Moreover, elucidation of kinetics of gene expression at early stages of cell differentiation reveals several genes regulated rapidly during the process, suggesting their importance for the differentiation process.

Targeting of the chemokine receptor CCR1 suppresses development of acute and chronic cardiac allograft rejection

Although mononuclear cell infiltration is a hallmark of cellular rejection of a vascularized allograft, efforts to inhibit rejection by blocking leukocyte-endothelial cell adhesion have proved largely unsuccessful, perhaps in part because of persistent generation of chemokines within rejecting grafts. We now provide, to our knowledge, the first evidence that in vivo blockade of specific chemokine receptors is of therapeutic significance in organ transplantation. Inbred mice with a targeted deletion of the chemokine receptor CCR1 showed significant prolongation of allograft survival in 4 models. First, cardiac allografts across a class II mismatch were rejected by CCR1(+/+) recipients but were accepted permanently by CCR1(-/-) recipients. Second, CCR1(-/-) mice rejected completely class I- and class II-mismatched BALB/c cardiac allografts more slowly than control mice. Third, levels of cyclosporin A that had marginal effects in CCR1(+/+) mice resulted in permanent allograft acceptance in CCR1(-/-) recipients. These latter allografts showed no sign of chronic rejection 50-200 days after transplantation, and transfer of CD4(+) splenic T cells from these mice to naive allograft recipients significantly prolonged allograft survival, whereas cells from CCR1(+/+) mice conferred no such benefit. Finally, both CCR1(+/+) and CCR1(-/-) allograft recipients, when treated with a mAb to CD4, showed permanent engraftment, but these allografts showed florid chronic rejection in the former strain and were normal in CCR1(-/-) mice. We conclude that therapies to block CCR1/ligand interactions may prove useful in preventing acute and chronic rejection clinically.

Application of differential cDNA screening techniques to the identification of unique gene expression in tumours and lymphocytes

Development, differentiation and cell death in all organisms are mediated by tightly regulated programs of differential gene expression. Furthermore, changes in gene expression profiles are responsible for tumour formation and tumour progression, as well as for many other human diseases. Thus, the definition of distinct patterns of gene expression is not only essential for understanding complex biological processes but also leads to the identification of novel targets for therapy of various diseases.

Cross-linking of protein S bound to lymphocytes promotes aggregation and inhibits proliferation

Recently, we reported that expression of the anticoagulant protein S is IL-4-inducible in primary T cells, and that protein S inhibits lymphoid cell procoagulant activity. Here, using a flow cytometric assay, we demonstrate that protein S binds to the surface of B and T lymphocytes. In addition, we show that cross-linking of protein S bound to lymphocytes induces aggregation and inhibits growth in cultures of primary B and T lymphocytes. Thus, our studies suggest that protein S is an IL-4-inducible T cell product that can affect B and T cell growth and aggregation via a lymphocyte protein S receptor. Interestingly, protein S joins thrombin and factor Xa as coagulation factors that modulate lymphocyte activation, suggesting that the clotting pathway may regulate wound-related inflammatory responses.