Novel biological functions of interleukin-4: formation of tube-like structures by vascular endothelial cells in vitro and angiogenesis in vivo

Homocysteine potentiates amyloid β -induced death receptor 4- and 5-mediated cerebral endothelial cell apoptosis, blood brain barrier dysfunction and angiogenic impairment

Cerebrovascular dysfunction has been implicated as a major contributor to Alzheimer's Disease (AD) pathology, with cerebral endothelial cell (cEC) stress promoting ischemia, cerebral-blood flow impairments and blood-brain barrier (BBB) permeability. Recent evidence suggests that cardiovascular (CV)/cerebrovascular risk factors, including hyperhomocysteinemia (Hhcy), exacerbate AD pathology and risk. Yet, the underlying molecular mechanisms for this interaction remain unclear. Our lab has demonstrated that amyloid beta 40 (Aβ40) species, and particularly Aβ40-E22Q (AβQ22; vasculotropic Dutch mutant), promote death receptor 4 and 5 (DR4/DR5)-mediated apoptosis in human cECs, barrier permeability, and angiogenic impairment. Previous studies show that Hhcy also induces EC dysfunction, but it remains unknown whether Aβ and homocysteine function through common molecular mechanisms. We tested the hypotheses that Hhcy exacerbates Aβ-induced cEC DR4/5-mediated apoptosis, barrier dysfunction, and angiogenesis defects. This study was the first to demonstrate that Hhcy specifically potentiates AβQ22-mediated activation of the DR4/5-mediated extrinsic apoptotic pathway in cECs, including DR4/5 expression, caspase 8/9/3 activation, cytochrome-c release and DNA fragmentation. Additionally, we revealed that Hhcy intensifies the deregulation of the same cEC junction proteins mediated by Aβ, precipitating BBB permeability. Furthermore, Hhcy and AβQ22, impairing VEGF-A/VEGFR2 signaling and VEGFR2 endosomal trafficking, additively decrease cEC angiogenic capabilities. Overall, these results show that the presence of the CV risk factor Hhcy exacerbates Aβ-induced cEC apoptosis, barrier dysfunction, and angiogenic impairment. This study reveals specific mechanisms through which amyloidosis and Hhcy jointly operate to produce brain EC dysfunction and death, highlighting new potential molecular targets against vascular pathology in comorbid AD/CAA and Hhcy conditions.

Human Keratinocytes and Fibroblasts Co-Cultured on Silk Fibroin Scaffolds Exosomally Overrelease Angiogenic and Growth Factors

Objectives: The optimal healing of skin wounds, deep burns, and chronic ulcers is an important clinical problem. Attempts to solve it have been driving the search for skin equivalents based on synthetic or natural polymers. Methods: Consistent with this endeavor, we used regenerated silk fibroin (SF) from Bombyx mori to produce a novel compound scaffold by welding a 3D carded/hydroentangled SF-microfiber-based nonwoven layer (C/H-3D-SFnw; to support dermis engineering) to an electrospun 2D SF nanofiber layer (ESFN; a basal lamina surrogate). Next, we assessed-via scanning electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, differential scanning calorimetry, mono- and co-cultures of HaCaT keratinocytes and adult human dermal fibroblasts (HDFs), dsDNA assays, exosome isolation, double-antibody arrays, and angiogenesis assays-whether the C/H-3D-SFnws/ESFNs would allow the reconstitution of a functional human skin analog in vitro. Results: Physical analyses proved that the C/H-3D-SFnws/ESFNs met the requirements for human soft-tissue-like implants. dsDNA assays revealed that co-cultures of HaCaTs (on the 2D ESFN surface) and HDFs (inside the 3D C/H-3D-SFnws) grew more intensely than did the respective monocultures. Double-antibody arrays showed that the CD9⁺/CD81⁺ exosomes isolated from the 14-day pooled growth media of HDF and/or HaCaT mono- or co-cultures conveyed 35 distinct angiogenic/growth factors (AGFs). However, versus monocultures' exosomes, HaCaT/HDF co-cultures' exosomes (i) transported larger amounts of 15 AGFs, i.e., PIGF, ANGPT-1, bFGF, Tie-2, Angiogenin, VEGF-A, VEGF-D, TIMP-1/-2, GRO-α/-β/-γ, IL-1β, IL-6, IL-8, MMP-9, and MCP-1, and (ii) significantly more strongly stimulated human dermal microvascular endothelial cells to migrate and assemble tubes/nodes in vitro. Conclusions: Our results showed that both cell-cell and cell-SF interactions boosted the exosomal release of AGFs from HaCaTs/HDFs co-cultured on C/H-3D-SFnws/ESFNs. Hence, such exosomes are an asset for prospective clinical applications as they advance cell growth and neoangiogenesis and consequently graft take and skin healing. Moreover, this new integument analog could be instrumental in preclinical and translational studies on human skin pathophysiology and regeneration.

IL-4-loaded alginate/chitosan multilayer films for promoting angiogenesis through both direct and indirect means

Vascularization remains a major challenge in tissue engineering. In tissue repair with the involvement of biomaterials, both the material properties and material-induced immune response can affect angiogenesis. However, there is a scarcity of research on biomaterials that modulate angiogenesis simultaneously from both perspectives. Meanwhile, the effects and mechanisms of biomaterial-induced macrophages on angiogenesis remain controversial. In this study, a cytokine-controlled release system from our previous work was employed, and the effects thereof on angiogenesis through both direct and indirect means were investigated. Alginate/chitosan multilayer films were fabricated on interleukin (IL)-4-loaded titania nanotubes to achieve a sustained release of IL-4. The released IL-4 and the multilayers synergistically promoted angiogenic behaviors of endothelial cells (ECs), while up-regulating the expression of early vascular markers. Furthermore, polarized macrophages (both M1 and M2) notably elevated the expression of late vascular markers in ECs via the high expression of pro-maturation factor angiogenin-1. After subcutaneous implantation, the IL-4-loaded implants induced increased neovascularization in a short period, with the surrounding tissue returning to normal at the later stage. Therefore, the proposed IL-4-loaded implants exhibited superior pro-angiogenic capability in vitro and in vivo through both direct stimulation of ECs and the indirect induction of a suitable immune microenvironment.

Adult Human Vascular Smooth Muscle Cells on 3D Silk Fibroin Nonwovens Release Exosomes Enriched in Angiogenic and Growth-Promoting Factors

Background. Our earlier works showed the quick vascularization of mouse skin grafted Bombyx mori 3D silk fibroin nonwoven scaffolds (3D-SFnws) and the release of exosomes enriched in angiogenic/growth factors (AGFs) from in vitro 3D-SFnws-stuck human dermal fibroblasts (HDFs). Here, we explored whether coronary artery adult human smooth muscle cells (AHSMCs) also release AGFs-enriched exosomes when cultured on 3D-SFnws in vitro. Methods. Media with exosome-depleted FBS served for AHSMCs and human endothelial cells (HECs) cultures on 3D-SFnws or polystyrene. Biochemical methods and double-antibody arrays assessed cell growth, metabolism, and intracellular TGF-β and NF-κB signalling pathways activation. AGFs conveyed by CD9⁺/CD81⁺ exosomes released from AHSMCs were double-antibody array analysed and their angiogenic power evaluated on HECs in vitro. Results. AHSMCs grew and consumed D-glucose more intensely and showed a stronger phosphorylation/activation of TAK-1, SMAD-1/-2/-4/-5, ATF-2, c-JUN, ATM, CREB, and an IκBα phosphorylation/inactivation on SFnws vs. polystyrene, consistent overall with a proliferative/secretory phenotype. SFnws-stuck AHSMCs also released exosomes richer in IL-1α/-2/-4/-6/-8; bFGF; GM-CSF; and GRO-α/-β/-γ, which strongly stimulated HECs’ growth, migration, and tubes/nodes assembly in vitro. Conclusions. Altogether, the intensified AGFs exosomal release from 3D-SFnws-attached AHSMCs and HDFs could advance grafts’ colonization, vascularization, and take in vivo—noteworthy assets for prospective clinical applications.

Challenging the Paradigm: Anti-Inflammatory Interleukins and Angiogenesis

Angiogenesis is a vital biological process, and neovascularization is essential for the development, wound repair, and perfusion of ischemic tissue. Neovascularization and inflammation are independent biological processes that are linked in response to injury and ischemia. While clear that pro-inflammatory factors drive angiogenesis, the role of anti-inflammatory interleukins in angiogenesis remains less defined. An interleukin with anti-inflammatory yet pro-angiogenic effects would hold great promise as a therapeutic modality to treat many disease states where inflammation needs to be limited, but revascularization and reperfusion still need to be supported. As immune modulators, interleukins can polarize macrophages to a pro-angiogenic and reparative phenotype, which indirectly influences angiogenesis. Interleukins could also potentially directly induce angiogenesis by binding and activating its receptor on endothelial cells. Although a great deal of attention is given to the negative effects of pro-inflammatory interleukins, less is described concerning the potential protective effects of anti-inflammatory interleukins on various disease processes. To focus this review, we will consider IL-4, IL-10, IL-13, IL-19, and IL-33 to be anti-inflammatory interleukins, all of which have recognized immunomodulatory effects. This review will summarize current research concerning anti-inflammatory interleukins as potential drivers of direct and indirect angiogenesis, emphasizing their role in future therapeutics.

Recruitment of M1 Macrophages May Not Be Critical for Protection against Colitis-Associated Tumorigenesis

A close connection between inflammation and the risk of developing colon cancer has been suggested in the last few years. It has been estimated that patients diagnosed with some types of inflammatory bowel disease, such as ulcerative colitis or Crohn's disease, have up to a 30% increased risk of developing colon cancer. However, there is also evidence showing that the activation of anti-inflammatory pathways, such as the IL-4 receptor-mediated pathway, may favor the development of colon tumors. Using an experimental model of colitis-associated colon cancer (CAC), we found that the decrease in tumor development in global IL4Rα knockout mice (IL4RαKO) was apparently associated with an inflammatory response mediated by the infiltration of M1 macrophages (F480+TLR2+STAT1+) and iNOS expression in colon tissue. However, when we developed mice with a specific deletion of IL4Rα in macrophages (LysMcreIL4Rα-/lox mice) and subjected them to CAC, it was found that despite presenting a large infiltration of M1 macrophages into the colon, these mice were as susceptible to colon-tumorigenesis as WT mice. These data suggest that in the tumor microenvironment the absence of IL4Rα expression on macrophages, as well as the recruitment of M1 macrophages, may not be directly associated with resistance to developing colon tumors. Therefore, it is possible that IL4Rα expression in other cell types, such as colonic epithelial cells, could have an important role in promoting the development of colitis-associated colon tumorigenesis.

CD4 T-cells regulate angiogenesis and myogenesis

Ischemic diseases, such as peripheral artery disease, affect millions of people worldwide. While CD4+ T-cells regulate angiogenesis and myogenesis, it is not understood how the phenotype of these adaptive immune cells regulate these regenerative processes. The secreted factors from different types of CD4+ T-cells (Th1, Th2, Th17, and Treg) were utilized in a series of in vitro assays and delivered from an injectable alginate biomaterial into a murine model of ischemia to study their effects on vascular and skeletal muscle regeneration. Conditioned medium from Th2 and Th17  T-cells enhanced angiogenesis in vitro and in vivo, in part by directly stimulating endothelial sprouting. Th1 conditioned medium induced vascular regression in vitro and provided no benefit to angiogenesis in vivo. Th1, Th2, and Th17 conditioned medium, to varying extents, enhanced muscle precursor cell proliferation and inhibited their differentiation in vitro, and prolonged early stages of muscle regeneration in vivo. Treg conditioned medium had a moderate or no effect on these processes in vitro and no discernible effect in vivo. These findings suggest that Th2 and Th17 T-cells may enhance angiogenesis and myogenesis in ischemic injuries, which may be useful in the design of immunomodulatory biomaterials to treat these diseases.

Effect of Cytokines on the Formation Tube-Like Structures by Endothelial Cells in the Presence of Trophoblast Cells

Despite ample data on cytokine secretion in the uteroplacental interface, the influence of microenvironment cells, in particular, trophoblast cells on angiogenesis and the role of cytokines in this process remain poorly studied. We studied the influence of cytokines on the formation of tube-like structures by endothelial cells in the presence of trophoblast cells and showed that trophoblast cells suppressed the angiogenic potential of endothelial cells. Antiangiogenic cytokines IFN-γ, IL-10, TNF-α, and TGFβ via modulation of trophoblast cells stimulated the formation of tube-like structures by endothelial cells. In the co-culture of endothelial and trophoblast cells, the effects of cytokines changed and they gained additional regulatory functions.

Neuronal Interleukin-4 as a Modulator of Microglial Pathways and Ischemic Brain Damage

After ischemic stroke, various damage-associated molecules are released from the ischemic core and diffuse to the ischemic penumbra, activating microglia and promoting proinflammatory responses that may cause damage to the local tissue. Here we demonstrate using in vivo and in vitro models that, during sublethal ischemia, local neurons rapidly produce interleukin-4 (IL-4), a cytokine with potent anti-inflammatory properties. One such anti-inflammatory property includes its ability to polarize macrophages away from a proinflammatory M1 phenotype to a "healing" M2 phenotype. Using an IL-4 reporter mouse, we demonstrated that IL-4 expression was induced preferentially in neurons in the ischemic penumbra but not in the ischemic core or in brain regions that were spared from ischemia. When added to cultured microglia, IL-4 was able to induce expression of genes typifying the M2 phenotype and peroxisome proliferator activated receptor γ (PPARγ) activation. IL-4 also enhanced expression of the IL-4 receptor on microglia, facilitating a "feedforward" increase in (1) their expression of trophic factors and (2) PPARγ-dependent phagocytosis of apoptotic neurons. Parenteral administration of IL-4 resulted in augmented brain expression of M2- and PPARγ-related genes. Furthermore, IL-4 and PPARγ agonist administration improved functional recovery in a clinically relevant mouse stroke model, even if administered 24 h after the onset of ischemia. We propose that IL-4 is secreted by ischemic neurons as an endogenous defense mechanism, playing a vital role in the regulation of brain cleanup and repair after stroke. Modulation of IL-4 and its associated pathways could represent a potential target for ischemic stroke treatment.

SIGNIFICANCE STATEMENT

Depending on the activation signal, microglia/macrophages (MΦ) can behave as "healing" (M2) or "harmful" (M1). In response to ischemia, damaged/necrotic brain cells discharge factors that polarize MΦ to a M1-like phenotype. This polarization emerges early after stroke and persists for days to weeks, driving secondary brain injury via proinflammatory mediators and oxidative damage. Our study demonstrates that, to offset this M1-like polarization process, sublethally ischemic neurons may instead secrete a potent M2 polarizing cytokine, interleukin-4 (IL-4). In the presence of IL-4 (including when IL-4 is administered exogenously), MΦ become more effective in the cleanup of ischemic debris and produce trophic factors that may promote brain repair. We propose that IL-4 could represent a potential target for ischemic stroke treatment/recovery.

Intracellular signaling pathways involved in the release of IL-4 and VEGF from human keratinocytes by activation of kinin B1 receptor: functional relevance to angiogenesis

The injured skin produces a number of mediators that directly or indirectly modulate cell chemotaxis, migration, proliferation, and angiogenesis. Components of the kinin pathway including the kinin B1 receptor (B1R) have been found to occur in the human skin, but information about its role on keratinocyte biology is still scarce. Our aim was to determine whether stimulation of B1R causes the secretion of IL-4 and/or VEGF from human keratinocytes and to evaluate the role of the B1R agonist Lys-des[Arg(9)]bradykinin and IL-4 on various stages of angiogenesis, such as cell migration, proliferation, and release of metalloproteases. By using ELISA and Western blotting, we showed that HaCaT keratinocytes stimulated with the B1R agonist release IL-4 and VEGF. Stimulation of B1R also caused transient c-JunN-terminal kinase phosphorylation and JunB nuclear translocation, transcription factor that regulates IL-4 expression. The 3D-angiogenesis assay, performed on spheroids of EA.hy923 endothelial cells embedded in a collagen matrix, showed that their cumulative sprout area increased significantly following stimulation with either IL-4 or B1R agonist. Furthermore, these ligands produced significant endothelial cell migration and release of metalloproteases 2 and 9, but did not increase endothelial cell proliferation as measured by 5-bromo-2'-deoxyuridine incorporation. Our results provide experimental evidence that establishes IL-4 and B1R agonist as important angiogenic factors of relevance for skin repair.

Association study between clinicopathological variables and periodontal breakdown in gingival pyogenic granuloma

OBJECTIVE

The aim was to investigate a possible association between the immunoexpression of interleukin (IL)-4 and clinicopathological parameters with the periodontal breakdown observed in gingival pyogenic granuloma (PG).

MATERIALS AND METHODS

Paraffin-embedded samples of gingival PG (n = 46) were prepared for histological and immunohistochemical assessment. Demographic and clinical parameters were assessed by criteria based on age stratum, gender, smoking habit, evolution course, location, lesion size, macroscopic appearance, predisposing factors, recurrence, and periodontal breakdown. Histological assessment included the appearance of epithelial lining, microvessel density, inflammatory infiltrate density, interstitial fibrosis, and histological arrangement. A staining intensity distribution (SID) score was used to assess IL-4 immunoreactivity. The association between candidate predictor variables and periodontal breakdown was analyzed individually and adjusted for confounding using a bivariate binary logistic regression model.

RESULTS

Mean IL-4 SID values were significantly increased for long-standing and large lesions, presence of periodontal breakdown, high microvessel density, and moderate-to-severe inflammatory infiltrate density. While bivariate and univariate analyses revealed a positive association of the evolution course ≥12 months, lesion size >1 cm, high microvessel density, moderate-to-severe inflammatory infiltrate density, and IL-4 SID score ≥8.04 with periodontal breakdown, after bivariate logistic regression analysis, only the evolution course ≥12 months, moderate-to-severe inflammatory infiltrate density, and IL-4 SID score ≥8.04 remained as robust predictors of periodontal damage. Confounding and interaction effects between candidate predictor variables were also noted.

CONCLUSION

These findings suggest that while evolution course, inflammatory infiltrate density, and the overexpression of IL-4 may act as predictors of periodontal breakdown in gingival PG, there are mutual confounding and synergistic biological interactive effects with respect to the lesion size and microvessel density in the susceptible host that may be also associated with the bone resorption and tissue destruction.

CLINICAL RELEVANCE

Although the first-line therapy of gingival PG continues to be the surgical excision, this approach poses unwanted complications such as severe mucogingival defects and recurrence. Hence, early diagnosis and detection of these three significant predictor variables as well as timely surgical excision might help prevent the periodontal tissue destruction observed in some of these lesions.

Polymorphisms of interleukin-4, -10 and 12B genes and diabetic retinopathy

In diabetic retinopathy (DR) and other angiogenesis-associated diseases, increased levels of cytokines, inflammatory cells, and angiogenic factors are present. We investigated the hypothesis that rs2243250 polymorphism of the interleukin 4 (IL-4) gene or rs1800896 polymorphism of the interleukin 10 (IL-10) gene, and rs3212227 polymorphism of the 3’ untranslated region (3’ UTR) of the interleukin-12 p40 gene (IL12B) may be associated with the development of proliferative diabetic retinopathy (PDR) in Caucasians with type 2 diabetes (DM2). This cross sectional case — control study included 189 patients with PDR and 187 patients with type 2 diabetes without PDR. Polymorphisms rs1800896 of the IL-10 gene, rs2243250 of the IL-4 gene, and rs3212227 of IL12B gene were analyzed by ARMS -PCR and RFLP -PCR methods. Multivariate analysis demonstrated the GG genotype of the rs1800896 polymorphism of the IL-10 gene to be associated with increased risk for PDR (OR=1.99; 95% CI=1.11–3.57; P=0.02), whereas the TT genotype of the rs2243250 polymorphism of the IL-4 gene and the AA genotype of the rs3212227 polymorphism of the IL-12 gene were not independent risk factors for PDR. Our findings suggest that the genetic variations at the IL-10 promoter gene might be a genetic risk factor for PDR in Caucasians with type 2 diabetes.

Alternative activation of tumor-associated macrophages by IL-4: priming for protumoral functions

Although macrophages were originally recognized as major immune effector cells, it is now appreciated that they also play many important roles in the maintenance of tissue homeostasis, and are involved in a variety of pathological conditions including cancer. Several studies have demonstrated the contributions of tumor-associated macrophages (TAMs) to tumor initiation, progression, and metastasis. However, the detailed mechanisms underlying how TAMs differ molecularly from their normal counterparts and how the conversion to TAMs occurs have only just begun to be understood. TAMs have been proposed to exhibit phenotypes of 'alternatively activated' macrophages, though there has been limited evidence directly linking the phenotypes of TAMs to the alternative activation of macrophages. This review will focus on IL-4, the prototypic cytokine that induces the alternative activation of macrophages, and review current knowledge regarding the contributions of IL-4 to the phenotypes of TAMs and its effects on tumorigenesis.

Hypoxia-induced mitogenic factor (HIMF/FIZZ1/RELMalpha) increases lung inflammation and activates pulmonary microvascular endothelial cells via an IL-4-dependent mechanism

Hypoxia-induced mitogenic factor (HIMF), also known as found in inflammatory zone 1 and resistin-like molecule α, belongs to a novel class of cysteine-rich secreted proteins. It exhibits mitogenic and chemotactic properties during pulmonary hypertension-associated vascular remodeling, as well as fibrogenic properties during pulmonary fibrosis. HIMF expression in the lung was reported to be regulated by Th2 cytokines (IL-4 and IL-13) via the transcription factor STAT6 pathway in a bleomycin-induced pulmonary fibrosis model. However, in this study, we found that in the hypoxia-induced pulmonary hypertension model, lung HIMF expression is increased in IL-4 and STAT6 knockout (KO) mice to the same degree as in wild-type (WT) mice, suggesting that induction of HIMF expression does not require Th2 regulation in this model. We also found that HIMF-induced proliferative activity, hypertrophy, collagen, and extracellular matrix deposition in the pulmonary arteries are significantly less in IL-4 KO mice than in WT mice. In addition, HIMF-induced production of angiogenic factors/chemokines, such as vascular endothelial growth factor, MCP-1, and stromal-derived factor-1, in the lung resident cells, as well as macrophage infiltration, were significantly suppressed in the lungs of IL-4 KO mice. We also show that IL-4 was significantly increased in the lungs of HIMF-treated WT mice. Our in vitro studies using pulmonary microvascular endothelial cells revealed that HIMF stimulated cell proliferation, vascular endothelial growth factor expression, and MCP-1 production in a manner that is dependent on the IL-4/IL-4Rα system. These findings suggest that IL-4 signaling may play a significant role in HIMF-induced lung inflammation and vascular remodeling.

IL-4 is proangiogenic in the lung under hypoxic conditions

IL-4-mediated proangiogenic and proinflammatory vascular responses have been implicated in the pathogenesis of chronic lung diseases such as asthma. Although it is well known that hypoxia induces pulmonary angiogenesis and vascular alterations, the underlying mechanism of IL-4 on the pulmonary vasculature under hypoxic conditions remains unknown. In this context, we designed the present study to determine the functional importance of IL-4 for pulmonary angiogenesis under hypoxic conditions using IL-4 knockout (KO) animals. Our results show that hypoxia significantly increased IL-4R alpha expression in wild-type (WT) control lungs. Even though hypoxia significantly up-regulated vascular endothelial growth factor (VEGF) receptor expression in the lungs of both genotypes, hypoxia-induced VEGF, VCAM-1, HIF-1alpha, and ERK phosphorylation were significantly diminished in IL-4 KO lungs as compared with WT control lungs. In addition, hypoxia-induced pulmonary angiogenesis and proliferating activities in the airway and pulmonary artery were significantly suppressed in IL-4 KO lungs as compared with WT control lungs. We also isolated primary lung fibroblasts from these genotypes and stimulated these cells with hypoxia. Hypoxia-induced VEGF production was significantly suppressed in lung fibroblasts from IL-4 KO mice. These in vitro results are in accordance with the in vivo data. Furthermore, we observed a significant increase of hypoxia-induced pulmonary angiogenesis in STAT6 KO mice similar to that in WT controls. In conclusion, IL-4 has proangiogenic properties in the lung under hypoxic conditions via the VEGF pathway, and this is independent of the STAT6 pathway.

Pathologic correlates of primary central nervous system lymphoma defined in an orthotopic xenograft model

PURPOSE

The prospect for advances in the treatment of patients with primary central nervous system lymphoma (PCNSL) is likely dependent on the systematic evaluation of its pathobiology. Animal models of PCNSL are needed to facilitate the analysis of its molecular pathogenesis and for the efficient evaluation of novel therapeutics.

EXPERIMENTAL DESIGN

We characterized the molecular pathology of CNS lymphoma tumors generated by the intracerebral implantation of Raji B lymphoma cells in athymic mice. Lymphoma cells were modified for bioluminescence imaging to facilitate monitoring of tumor growth and response to therapy. In parallel, we identified molecular features of lymphoma xenograft histopathology that are evident in human PCNSL specimens.

RESULTS

Intracerebral Raji tumors were determined to faithfully reflect the molecular pathogenesis of PCNSL, including the predominant immunophenotypic state of differentiation of lymphoma cells and their reactive microenvironment. We show the expression of interleukin-4 by Raji and other B lymphoma cell lines in vitro and by Raji tumors in vivo and provide evidence for a role of this cytokine in the M2 polarization of lymphoma macrophages both in the murine model and in diagnostic specimens of human PCNSL.

CONCLUSION

Intracerebral implantation of Raji cells results in a reproducible and invasive xenograft model, which recapitulates the histopathology and molecular features of PCNSL, and is suitable for preclinical testing of novel agents. We also show for the first time the feasibility and accuracy of tumor bioluminescence in the monitoring of a highly infiltrative brain tumor.

IL-13 attenuates vascular tube formation via JAK2-STAT6 pathway

BACKGROUND

Interleukin (IL)-13, which is a cytokine produced by type 2 helper T cells, has pathophysiological roles in allergic inflammation and fibrosis formation. IL-13 shares many functional properties with IL-4, which is known to inhibit angiogenesis.

METHODS AND RESULTS

The effects of IL-13 on angiogenesis were examined using human coronary artery endothelial cells (HCAECs), in addition to investigating the mechanism(s) of this action. Using an in vitro assay of angiogenesis it was demonstrated that IL-13, as well as IL-4, significantly inhibited capillary-like tube formation. Migration of HCAECs, considered to be a process of new capillary tube formation, was also significantly inhibited by IL-13. IL-13 activated signal transduction and transcription 6 (STAT6) as a result of the activation of Janus kinase 2 (JAK2). The inhibitory effect of IL-13 on angiogenesis was abolished by depletion of JAK2 and STAT6 by RNA interference.

CONCLUSION

IL-13 has anti-angiogenic activity as a result of activation of JAK2 and subsequent activation of STAT6.

Targeted cancer gene therapy using a hypoxia inducible factor dependent oncolytic adenovirus armed with interleukin-4

There is a need for novel therapies targeting hypoxic cells in tumors. These cells are associated with tumor resistance to therapy and express hypoxia inducible factor-1 (HIF-1), a transcription factor that mediates metabolic adaptation to hypoxia and activates tumor angiogenesis. We previously developed an oncolytic adenovirus (HYPR-Ad) for the specific killing of hypoxic/HIF-active tumor cells, which we now armed with an interleukin-4 gene (HYPR-Ad-IL4). We designed HYPR-Ad-IL4 by cloning the Ad E1A viral replication and IL-4 genes under the regulation of a bidirectional hypoxia/HIF-responsive promoter. The IL-4 cytokine was chosen for its ability to induce a strong host antitumor immune response and its potential antiangiogenic activity. HYPR-Ad-IL4 induced hypoxia-dependent IL-4 expression, viral replication, and conditional cytolysis of hypoxic, but not normoxic cells. The treatment of established human tumor xenografts with HYPR-Ad-IL4 resulted in rapid and maintained tumor regression with the same potency as that of wild-type dl309-Ad. HYPR-Ad-IL4-treated tumors displayed extensive necrosis, fibrosis, and widespread viral replication. Additionally, these tumors contained a distinctive leukocyte infiltrate and prominent hypoxia. The use of an oncolytic Ad that locally delivers IL-4 to tumors is novel, and we expect that HYPR-Ad-IL4 will have broad therapeutic use for all solid tumors that have hypoxia or active HIF, regardless of tissue origin or genetic alterations.

Effect of interleukin-4 on vascular endothelial growth factor production in rheumatoid synovial fibroblasts

Interleukin (IL)-4 has been demonstrated to have anti-inflammatory and anti-tumour activity. Because aberrant angiogenesis is a significant pathogenic component of tumour growth and chronic inflammation, we investigated the effect of IL-4 on the production of vascular endothelial growth factor (VEGF) by synovial fibroblasts derived from patients with rheumatoid arthritis (RA). Fibroblast-like synoviocytes (FLS) were prepared from synovial tissues of RA and incubated with different concentrations of IL-4 in the presence or absence of transforming growth factor (TGF)-beta. VEGF level was measured by enzyme-linked immunosorbent assay and semiquantitative reverse transcription--polymerase chain reaction. Treatment of FLS with IL-4 alone caused a dose-dependent increase in VEGF levels. In contrast, IL-4 exhibited the inhibitory effect on VEGF production when FLS were stimulated with TGF-beta. Combined treatment of IL-4 and IL-10 inhibited TGF-beta-induced VEGF production in an additive fashion. TGF-beta increased the induction of cyclooxygenase-2 mRNA, which was inhibited significantly by the treatment of IL-4. NS-398, a COX-2 inhibitor, inhibited TGF-beta-induced VEGF production in a dose-dependent manner. Furthermore, exogenous addition of prostaglandin E2 (PGE2) restored IL-4 inhibition on TGF-beta induced VEGF production. Collectively, our results suggest that IL-4 have an anti-angiogenic effect, especially in the inflammatory milieu of RA by inhibiting the VEGF production in synovial fibroblasts.

Inhibition of angiogenesis by interleukin-4 gene therapy in rat adjuvant-induced arthritis

OBJECTIVE

Interleukin-4 (IL-4) can modulate neovascularization. In this study, we used a gene therapy approach to investigate the role of IL-4 in angiogenesis in rat adjuvant-induced arthritis (AIA), a model for rheumatoid arthritis.

METHODS

Rats received an adenovirus producing IL-4 (AxCAIL-4), a control virus without insert, or control vehicle (phosphate buffered saline) intraarticularly before arthritis onset. At peak onset of arthritis, rats were killed. Vascularization was determined in the synovial tissue, and correlations with inflammation were assessed. Ankle homogenates were used in angiogenesis assays in vitro and in vivo, and protein levels of cytokines and growth factors were assessed by enzyme-linked immunosorbent assay. Synovial tissue expression of alphav integrins was determined by immunohistochemistry.

RESULTS

IL-4 induced a reduction in synovial tissue vessel density, which was paralleled by a decrease in inflammation. AxCAIL-4 joint homogenates significantly (P < 0.05) inhibited both endothelial cell (EC) migration and tube formation in vitro. Similarly, AxCAIL-4 inhibited capillary sprouting in the rat aortic ring assay, and vessel growth in the in vivo Matrigel plug assay. The angiostatic effect occurred despite high levels of vascular endothelial growth factor (VEGF), and was associated with down-regulation of the proangiogenic cytokines IL-18, CXCL16, and CXCL5 and up-regulation of the angiogenesis inhibitor endostatin. Of interest, AxCAIL-4 also resulted in decreased EC expression of the alphav and beta3 integrin chains.

CONCLUSION

In rat AIA, IL-4 reduces synovial tissue vascularization via angiostatic effects, mediates inhibition of angiogenesis via an association with altered pro- and antiangiogenic cytokines, and may inhibit VEGF-mediated angiogenesis and exert its angiostatic role in part via alphavbeta3 integrin. This knowledge of the specific angiostatic effects of IL-4 may help optimize target-oriented treatment of inflammatory arthritis.

Gene expression and angiotropism in primary CNS lymphoma

Primary CNS lymphoma is an aggressive form of non-Hodgkin lymphoma whose growth is restricted to the central nervous system. We used cDNA microarray analysis to compare the gene expression signature of primary CNS lymphomas with nodal large B-cell lymphomas. Here, we show that while individual cases of primary CNS lymphomas may be classified as germinal center B-cell, activated B-cell, or type 3 large B-cell lymphoma, brain lymphomas are distinguished from nodal large B-cell lymphomas by high expression of regulators of the unfolded protein response (UPR) signaling pathway, by the oncogenes c-Myc and Pim-1, and by distinct regulators of apoptosis. We demonstrate that interleukin-4 (IL-4) is expressed by tumor vasculature as well as by tumor cells in CNS lymphomas. We also identify high expression in CNS lymphomas of several IL-4-induced genes, including X-box binding protein 1 (XBP-1), a regulator of the UPR. In addition, we demonstrate expression of the activated form of STAT6, a mediator of IL-4 signaling, by tumor cells and tumor endothelia in CNS lymphomas. High expression of activated STAT6 in tumors was associated with short survival in an independent set of patients with primary CNS lymphoma who were treated with high-dose intravenous methotrexate therapy.

Cyclic strain-mediated regulation of vascular endothelial cell migration and tube formation

Hemodynamic forces exerted by blood flow (cyclic strain, shear stress) affect the initiation and progression of angiogenesis; however, the precise signaling mechanism(s) involved are unknown. In this study, we examine the role of cyclic strain in regulating bovine aortic endothelial cell (BAEC) migration and tube formation, indices of angiogenesis. Considering their well-documented mechanosensitivity, functional inter-dependence, and involvement in angiogenesis, we hypothesized roles for matrix metalloproteinases (MMP-2/9), RGD-dependent integrins, and urokinase plasminogen activator (uPA) in this process. BAECs were exposed to equibiaxial cyclic strain (5% strain, 1Hz for 24h) before their migration and tube formation was assessed by transwell migration and collagen gel tube formation assays, respectively. In response to strain, both migration and tube formation were increased by 1.83+/-0.1- and 1.84+/-0.1-fold, respectively. Pertussis toxin, a Gi-protein inhibitor, decreased strain-induced migration by 45.7+/-32% and tube formation by 69.8+/-13%, whilst protein tyrosine kinase (PTK) inhibition with genistein had no effect. siRNA-directed attenuation of endothelial MMP-9 (but not MMP-2) expression/activity decreased strain-induced migration and tube formation by 98.6+/-41% and 40.7+/-31%, respectively. Finally, integrin blockade with cRGD peptide and siRNA-directed attenuation of uPA expression reduced strain-induced tube formation by 85.7+/-15% and 84.7+/-31%, respectively, whilst having no effect on migration.

CONCLUSIONS

Cyclic strain promotes BAEC migration and tube formation in a Gi-protein-dependent PTK-independent manner. Moreover, we demonstrate for the first time a putative role for MMP-9 in both strain-induced events, whilst RGD-dependent integrins and uPA appear only to be involved in strain-induced tube formation.

T Cell Immunity Induced by Live, Necrotic, and Apoptotic Tumor Cells

The rules that govern the engagement of antitumor immunity are not yet fully understood. Ags expressed by tumor cells are prone to induce T cell tolerance unless the innate immune system is activated. It is unclear to what extent tumors engage this second signal link by the innate immune system. Apoptotic and necrotic (tumor) cells are readily recognized and phagocytosed by the cells of the innate immune system. It is unknown how this affects the tumor's immunogenicity. Using a murine melanoma (B16m) and lymphoma (L5178Y-R) model, we studied the clonal sizes and cytokine signatures of the T cells induced by these tumors in syngeneic mice when injected as live, apoptotic, and necrotic cells. Both live tumors induced a type 2 CD4 cell response characterized by the prevalent production of IL-2, IL-4, and IL-5 over IFN-gamma. Live, apoptotic, and necrotic cells induced CD4 (but no CD8) T cells of comparable frequencies and cytokine profiles. Therefore, live tumors engaged the second signal link, and apoptotic or necrotic tumor cell death did not change the magnitude or quality of the antitumor response. A subclone of L5178Y-R, L5178Y-S cells, were found to induce a high-frequency type 1 response by CD4 and CD8 cells that conveyed immune protection. The data suggest that the immunogenicity of tumors, and their characteristics to induce type 1 or type 2, CD4 or CD8 cell immunity is not primarily governed by signals associated with apoptotic or necrotic cell death, but is an intrinsic feature of the tumor itself.

Intratumor CpG-oligodeoxynucleotide injection induces protective antitumor T cell immunity

Tumor cells are typically poorly immunogenic. The same mechanisms that evolved to avoid the induction of immune responses against self tissues, and, hence, autoimmune disease, also have to be overcome for immune therapy of cancer. Toll-like receptor-activating microbial products such as CpG motif containing DNA are among the primary stimuli that the immune system uses to distinguish between infectious nonself (that is to be attacked) and noninfectious self (that must not be attacked). We tested in a murine RMA lymphoma/C57BL/6 model whether providing the infectious nonself context in a tumor-by injecting CpG-oligodeoxynucleotides directly into the tumor-would elicit a protective antitumor response. Complete remission of established solid tumors was achieved in immune competent mice, but not in T cell/B cell-deficient RAG-1 knockout mice. Intratumor injection of CpG-oligodeoxynucleotides was shown to induce a tumor-specific CD4(+) and CD8(+) T cell response of the type 1 effector class, and T cells adoptively transferred the protection to RAG-1 knockout mice. The data show that intratumor injection of CpG-oligodeoxynucleotides is a promising strategy for rendering tumors immunogenic.

Synergistic effect of TNF-alpha in soluble VCAM-1-induced angiogenesis through alpha 4 integrins

In our present study we focused on soluble VCAM-1 (sVCAM-1)/alpha(4) integrin-induced angiogenesis and found that this type of angiogenesis was mediated through p38 mitogen-activated protein kinase and focal adhesion kinase (FAK). HUVEC expressed both alpha(4) and beta(1) integrins, and it was reported that expression of alpha(4) integrin and its counterreceptor, sVCAM-1/VCAM-1, was enhanced in response to an inflammatory cytokine, TNF-alpha. In endothelial cells phosphorylation of p38 and FAK, but not that of extracellular signal-regulated kinase 1/2 was induced by sVCAM-1. Migration of endothelial cells was stimulated in response to sVCAM-1 at similar levels as those induced by vascular endothelial growth factor, and sVCAM-1-induced migration was almost completely blocked by neutralizing Ab against alpha(4) integrin, by either an inhibitor of p38 (SB203580), or by adenovirus containing FAK-related nonkinase. sVCAM-1 also induced the formation of blood vessels in Matrigel plug assay in vivo, and this neovascularization was blocked by SB203580 or neutralizing Ab against alpha(4) integrin. Moreover, we also confirmed that both TNF-alpha and sVCAM-1 could synergistically induce angiogenesis in the corneas of mice when each factor at used dose could not induce. This angiogenesis by TNF-alpha and sVCAM-1 was almost completely blocked by coadministration of SB203580 and also by neutralizing Ab against alpha(4) integrin. These results suggest that sVCAM-1/alpha(4) integrin induces angiogenesis through p38 and FAK signaling pathways.

IL-4 expression delays eosinophil-independent vasculopathy and fibrosis during allograft rejection in the mouse

Transplant vasculopathy in the mouse is thought to be dependent on IL-4 and mediated by IL-5 and eosinophils, whereas in the rat and human systems, IL-4 is associated with the absence of transplant vasculopathy and down-regulation of a Th1-type response. In this study we tested the possibility that the apparent difference in the role of IL-4 in transplant vasculopathy is related to protocol differences rather than to the species being studied. Using a protocol that closely resembles that used in rat and human studies, we developed a model of transplant vasculopathy in the mouse that is associated with Th1-type cytokines and independent of IL-5 and eosinophil infiltration. In this model IL-4 promotes a significant delay in vasculopathy in the graft (P = 0.04) and a decrease in the incidence of allograft rejection (P = 0.02). The data suggest that the role of IL-4 in transplant vasculopathy can be controlled by the protocol used to treat the transplant recipient.

Dexamethasone inhibits the anti-tumor effect of interleukin 4 on rat experimental gliomas

Retroviral-mediated gene transfer of the IL-4 gene into experimental gliomas can cause tumor rejection, supporting the clinical use of this form of gene therapy for glioblastomas (GBM). In a clinical setting, the administration of dexamethasone (dex) is a standard procedure for GBM patients. This led us to examine the effects of dex on IL-4 gene therapy. We injected intracranially Fischer 344 rats with phosphate-buffered saline, 9L gliosarcoma cells mixed with E86.L4SN(200) cells (retroviral producer cells, RPC, transducing IL-4 cDNA) and 9L cells mixed with PA317.STK.SBA cells (control RPC expressing the HSV-tk gene). The rats from each group were treated with 0, 50, 100 or 250 microg dex/kg/day released by osmotic pumps implanted subcutaneously. While 80-100% of rats receiving 9L cells mixed with IL-4 RPC and not treated by dex survived for at least 2 months following tumor injection, only 50% and 17% of rats receiving 50 or 100 microg/kg/day of dex, respectively, reached this time point. These results indicate that dex significantly diminished the anti-tumor effect of IL-4. Thus, in a clinical setting, IL-4 gene transfer should be performed when low levels of dex are administered or in the absence of dex.

Autoreactive T cells promote post-traumatic healing in the central nervous system

In general, autoimmune responses are considered harmful to the host. In the best-defined model of autoimmune disease, murine experimental allergic encephalomyelitis (EAE), for example, brain-protein-specific autoimmune responses of both major classes, type-1 and type-2, have been implicated in causing brain pathology. We induced type-1 and type-2 autoimmunity to myelin oligodendrocyte protein (MOG) in C57.BL/6 mice. Instead of using pertussis toxin (PTX) to open the blood-brain barrier (BBB), which is the classic procedure, we set an aseptic cerebral injury (ACI) to see what the consequences of pre-primed, autoreactive type-1 and type-2 memory T cells gaining access to the brain in the course of sterile tissue injury would be. Neither of these autoimmune response types induced pathology; on the contrary, both accelerated re-vascularization and post-traumatic healing. The data suggest that induction of either type-1 or type-2 autoimmune responses is not inherently noxious to the host, but can have beneficial effects on tissue repair. Autoimmune pathology may develop only if molecules of microbial origin such as pertussis toxin additionally induce the "infectious nonself/danger" reaction in the antigen-presenting cells (APC) of the target organ itself.

Angiogenesis: is it the key to controlling the healing process?

Much research has been undertaken on the complex processes involved in angiogenesis. This may lead to the development of new treatments that help to improve patients' quality of life

Dendritic cells derived from peripheral monocytes express endothelial markers and in the presence of angiogenic growth factors differentiate into endothelial-like cells

CD14-positive monocytes obtained from human peripheral blood were cultured with GM-CSF and IL-4. During the early culture phase immature dendritic cells (DCs) developed which not only expressed CD1a, HLA-DR and CD86, but also expressed the endothelial cell markers von Willebrand factor (vWF), VE-cadherin and VEGF receptors Flt-1 and Flt-4. Further maturation of DCs was achieved by prolonged cultivation with TNFalpha. These cells showed typical DC morphology and like professional antigen-presenting cells (APCs) expressed CD83 and high levels of HLA-DR and CD86. However, if immature DCs were grown with VEGF, bFGF and IGF-1 on fibronectin/vitronectin-coated culture dishes, a marked change in morphology into caudated or oval cells occurred. In the presence of these angiogenic growth factors the cultured cells developed into endothelial-like cells (ELCs), characterized by increased expression of vWF, KDR and Flt-4 and a disappearance of CD1a and CD83. Addition of IL-4 and Oncostatin M also increased VE-cadherin expression, and the loosely adherent cells formed clusters, cobblestones and network-like structures. vWF- expressing ELCs mainly originated from CD1a-positive cells, and VEGF was responsible for the decrease in the expression of the DC markers CD1a and CD83. In mixed leukocyte cultures, mature DCs were more potent APCs than ELCs. Moreover, Ac-LDL uptake, and the formation of tubular structures on a plasma matrix was restricted to ELCs. These results suggest that in the presence of specific cytokines immature DCs have the potential to differentiate along different lineages, i.e. into a cell type resembling ELCs.

The activity of soluble VCAM-1 in angiogenesis stimulated by IL-4 and IL-13

IL-13 is a multifunctional lymphokine sharing a number of biological properties with IL-4. We previously observed that IL-4 shows angiogenic activities in vitro as well as in vivo. In this study we examined the effect of IL-13 on angiogenesis in vitro and in vivo and also the underlying mechanisms. Human IL-13 significantly stimulated the formation of tube-like structures in collagen gels by human microvascular endothelial cells and bovine aortic endothelial cells by about 3-fold over the controls in the absence of the cytokines. Administration of murine IL-13 led to neovascularization when implanted in the rat cornea. Coadministration of neutralizing mAb to the IL-4R inhibited both tubular morphogenesis in vitro and activation of STAT6 induced by IL-4 or IL-13. Both IL-4 and IL-13 markedly increased mRNA levels of VCAM-1 in vascular endothelial cells, and the production of the soluble form of VCAM-1 was also stimulated in response to IL-4 or IL-13. Administration of anti-VCAM-1 Ab in vitro blocked tubular morphogenesis induced by IL-4 and IL-13. Angiogenesis induced in vivo in rat cornea by IL-4 and IL-13 was also inhibited by Ab against the rat alpha4 integrin subunit. These findings suggest that angiogenesis dependent on IL-4 and IL-13 is mainly mediated through a soluble VCAM-1/alpha4 integrin pathway.

Interleukin 6 promotes vasculogenesis of murine brain microvessel endothelial cells

Interleukin 6 (IL-6) is a cytokine that acts on a wide range of tissues influencing cell growth and differentiation. Here we show that IL-6 plays a role in the early vascular development (vasculogenesis) in the central nervous system (CNS). We report that IL-6 induces the proliferation of brain microvascular endothelial cells in vitro. Furthermore, IL-6 significantly accelerates the formation of tube-like structures by these cells in Matrigel basement matrix. Moreover, IL-6 mRNA is expressed in vivo in two physiological conditions in which vascularization in the CNS is important: (1) during normal brain development, (2) during the healing process of a traumatic brain injury. Expression of IL-6 mRNA coincides with the expression of vascular endothelial growth factor (VEGF) mRNA in the developing brain with decreasing expression following birth. However, IL-6 mRNA can be detected in the healing adult murine brain tissue by in situ hybridization coinciding with the period of intense tissue reorganization. The transient upregulation of IL-6 mRNA during normal brain development and at brain injury site and the effect of IL-6 on in vitro vasculogenesis suggest that IL-6 may play a role in normal physiology of vascularization in the CNS.

The relationship between angiogenesis and the immune response in carcinogenesis and the progression of malignant disease

Recent studies have demonstrated that angiogenesis and suppressed cell-mediated immunity (CMI) play a central role in the pathogenesis of malignant disease facilitating tumour growth, invasion and metastasis. In the majority of tumours, the malignant process is preceded by a pathological condition or exposure to an irritant which itself is associated with the induction of angiogenesis and/or suppressed CMI. These include: cigarette smoking, chronic bronchitis and lung cancer; chronic oesophagitis and oesophageal cancer; chronic viral infections such as human papilloma virus and ano-genital cancers, chronic hepatitis B and C and hepatocellular carcinoma, and Epstein-Barr virus (EBV) and lymphomas; chronic inflammatory conditions such as Crohn's disease and ulcerative colitis and colorectal cancer; asbestos exposure and mesothelioma and excessive sunlight exposure/sunburn and malignant melanoma. Chronic exposure to growth factors (insulin-like growth factor-I in acromegaly), mutations in tumour suppressor genes (TP53 in Li Fraumeni syndrome) and long-term exposure to immunosuppressive agents (cyclosporin A) may also give rise to similar environments and are associated with the development of a range of solid tumours. The increased blood supply would facilitate the development and proliferation of an abnormal clone or clones of cells arising as the result of: (a) an inherited genetic abnormality; and/or (b) acquired somatic mutations, the latter due to local production and/or enhanced delivery of carcinogens and mutagenic growth factors. With progressive detrimental mutations and growth-induced tumour hypoxia, the transformed cell, to a lesser or greater extent, may amplify the angiogenic process and CMI suppression, thereby facilitating further tumour growth and metastasis. There is accumulating evidence that long-term treatment with cyclo-oxygenase inhibitors (aspirin and indomethacin), cytokines such as interferon-alpha, anti-oestrogens (tamoxifen and raloxifene) and captopril significantly reduces the incidence of solid tumours such as breast and colorectal cancer. These agents are anti-angiogenic and, in the case of aspirin, indomethacin and interferon-alpha have proven immunomodulatory effects. Collectively these observations indicate that angiogenesis and suppressed CMI play a central role in the development and progression of malignant disease.

Interleukin-18 acts as an angiogenesis and tumor suppressor

Interleukin-18 (IL-18), also called interferon-gamma (IFN-gamma)-inducing factor, has recently been characterized as a potent IFN-gamma-inducing cytokine. We now report that IL-18 is a novel antiangiogenic and antitumor cytokine. In vitro, IL-18 specifically inhibits fibroblast growth factor-2-stimulated proliferation of capillary endothelial cells. In vivo, IL-18 is sufficiently potent to suppress the fibroblast growth factor-induced corneal neovascularization by systemic administration in mice. This cytokine also inhibits embryonic angiogenesis in the chick chorioallantoic membrane assay. Systemic and intralesional administrations of IL-18 produce a significant suppression of the growth of murine T241 fibrosarcoma in syngeneic C57Bl6/J and immunodeficient SCID mice. The antitumor effect appears to be potent because an average of >75% inhibition of primary tumor growth was observed at a dose of 50 microg/kg/day. In cell culture, murine T241 fibrosarcoma cells are insensitive to recombinant IL-18 at concentrations that significantly inhibit endothelial cell proliferation. Immunohistochemical studies of tumor tissues reveal hypovascularization of the IL-18-treated tumors. These results suggest that IL-18 may participate in the regulation of a switch of tumor angiogenesis.-Cao, R., Farnebo, J., Kurimoto, M., Cao, Y. Interleukin-18 acts as an angiogenesis and tumor suppressor.