Transforming growth factor beta: the good, the bad, and the ugly

Local and systemic cytokine expression during experimental chronic Trypanosoma cruzi infection in a Cebus monkey model

Cebus apella is an acceptable model for chronic chagasic cardiomyopathy (CCC), since it is possible to experimentally induce cardiac lesions after 1 year of Trypanosoma cruzi infection. The T. cruzi Y strain, shown previously to produce CCC in C. apella monkeys, was used to experimentally infect 10 monkeys. Parasitological, serological and clinical parameters were monitored during a 19-month follow-up, and systemic cytokine responses were assessed sequentially in five monkeys selected according to the differential parasitemia pattern exhibited. Ten additional monkeys, infected with the same strain for 5, 10 and 12 years, were analysed cross-sectionally. Three monkeys/time point and one uninfected control animal were sacrificed for gross pathology, histology, presence of parasites, and local cytokine gene expression. Elevated expression of interleukin (IL)-4 was observed throughout the study in monkeys that had persistent, high parasitemias, whereas a high level of interferon (IFN)-gamma was seen in monkeys that controlled parasitemias soon after infection. Chronically infected monkeys expressed a nonpolarized, Th0-type response. Cardiac tissue collected from a monkey that succumbed to acute infection had elevated levels of proinflammatory cytokine [IL-1beta, IL-6, tumour necrosis factor-alpha] and interstitial cell adhesion molecule (ICAM)-1, platelet-derived growth factor (PDGF)-alpha, transforming growth factor (TGF)-beta and IL-10 transcripts. Cytokine production in cardiac tissue of chronically infected monkeys was also characterized by elevated expression of ICAM-1, PDGF-alpha and TGF-beta, which correlated with the detection of T. cruzi DNA by polymerase chain reaction.

Activation of rat alveolar macrophage-derived latent transforming growth factor beta-1 by plasmin requires interaction with thrombospondin-1 and its cell surface receptor, CD36

Transforming growth factor-beta-1 (TGF-beta1) is secreted by cells in a latent form (L-TGF-beta1) noncovalently bound to a latency-associated peptide. Activated alveolar macrophages obtained from rat lungs after bleomycin-induced pulmonary injury released increased amounts of active TGF-beta1 as well as plasmin, a protease, and thrombospondin-1 (TSP-1), a trimeric glycoprotein. Previously we had demonstrated that plasmin was critical to the activation of L-TGF- beta1. In the present study we demonstrated that TSP-1 is also important for the activation of L-TGF- beta1 because the activation can be inhibited by anti-TSP-1 monoclonal antibody. Proteins obtained from alveolar macrophage cell lysates immunoprecipitated with antibodies specific for TSP-1 were identified on immunoblots as LAP and TGF-beta1, indicating that TSP-1/L-TGF-beta1 complexes are present on alveolar macrophages. However, in the presence of plasmin both latency-associated peptide and TGF-beta1 were decreased in the same cell lysates, indicating that L-TGF-beta1 associated with TSP-1 is released by plasmin. Using immunofluorescence and antibodies to TGF-beta1 and CD36, a receptor for TSP-1, there was colocalization of TGF-beta1 with CD36. Because TSP-1 but not TGF-beta1 is a natural ligand for CD36, these findings suggest that the L-TGF-beta1 in a complex with TSP-1 localizes to the macrophage cell surface when TSP-1 interacts with its receptor, CD36. Furthermore, the association of TSP-1/L-TGF-beta1 complex with CD36 is necessary to the activation of L-TGF-beta1 because antibodies to CD36 prevent the colocalization of TGF-beta1 with CD36 as observed by immunofluorescence and inhibit activation of the L-TGF-beta1 by explanted alveolar macrophages. These findings suggest that activation of L-TGF-beta1 by plasmin occurs at the cell surface of activated alveolar macrophages and requires a TSP-1/CD36 interaction.

Bone and bone healing

Bone is composed of cells and organic matrix (30%), and minerals (70%). A vascular network consisting of nutrient, metaphyseal, and periosteal vessels richly supplies adult bone. Fracture healing consists of three interrelated phases: inflammatory, repair, and remodeling, and culminates in the ability of bone to return to original tissue structure. Many growth factors and regulatory proteins have been implicated in bone repair. Of these, transforming growth factor-B appears to be the major regulator of bone metabolism. This regulates differentiation and proliferation of mesenchymal cells into chondroblasts, osteoblasts, and osteoclasts.

Photopheresis: clinical applications and mechanism of action

Photopheresis is a leukapheresis-based therapy that utilizes 8-methoxypsoralen and ultraviolet A irradiation. Photopheresis is currently available at approximately 150 medical centers worldwide. Recent evidence suggests that this therapy used as a single agent may significantly prolong life, as well as induce a 50%-75% response rate among individuals with advanced cutaneous T cell lymphoma (CTCL). Furthermore, a 20%-25% complete response rate with photopheresis alone, or in combination with other biologic response modifiers, has been obtained at our institution among patients with Sezary syndrome. These complete responses have been characterized by the complete disappearance of morphologically atypical cells from the skin and blood. The use of sensitive molecular techniques has also confirmed the sustained disappearance of the malignant T cell clone from the blood of patients with complete responses. In addition to the treatment of CTCL, numerous reports indicate that photopheresis is a potent agent in the therapy of acute allograft rejection among cardiac, lung, and renal transplant recipients. Chronic graft versus host disease also appears to be quite responsive to photopheresis therapy. Likewise, there may also be a potential role for photopheresis in the therapy of certain autoimmune diseases that are poorly responsive to conventional therapy. The immunologic basis for the responses of patients with these conditions is likely due to the induction of anticlonotypic immunity directed against pathogenic clones of T lymphocytes. Treatment-induced apoptotic death of pathogenic T cells and activation of antigen presenting cells are postulated to have important effects in this therapeutic process.

Partial IgA-Deficiency with Increased Th2-Type Cytokines in TGF-β1 Knockout Mice

Though it has been shown that TGF-β1 directs B cells to switch to IgA in vitro, no studies have assessed TGF-β1 effects on mucosal vs systemic immunity in vivo. When the B cell functions of TGF-β1 gene-disrupted (TGF-β1−/−) mice were analyzed, significantly decreased IgA levels and increased IgG and IgM levels in serum and external secretions were observed. Further, analysis of Ab forming cells (AFC) isolated from both mucosal and systemic lymphoid tissue showed elevated IgM, IgG, and IgE, with decreased IgA AFC. A lack of IgA-committed B cells was seen in TGF-β1−/− mice, especially in the gastrointestinal (GI) tract. Splenic T cells triggered via the TCR expressed elevated Th2-type cytokines and, consistent with this observation, a 31-fold increase in serum IgE was seen in TGF-β1−/− mice. Thus, uncontrolled B cell responses, which include elevated IgE levels, a lack of antiinflammatory IgA, and an excess of complement-binding IgG and IgM Abs, will promote inflammation at mucosal surfaces in TGF-β1−/− mice and likely contribute to pulmonary and GI tract lesions, ultimately leading to the early death of these mice.

Myofibroblast proliferation, fibrosis, and defective pancreatic repair induced by cyclosporin in rats

BACKGROUND

Full recovery is always achieved after caerulein induced pancreatitis. Cyclosporin stimulates transforming growth factor beta (TGF-beta) and may interfere with pancreatic regeneration.

AIM

To investigate the effects of cyclosporin after caerulein induced pancreatitis or after caerulein injury.

METHODS

Protocol A: rats received cyclosporin daily (20 mg/kg) and caerulein pancreatitis was induced on days 2 and 8. Protocol B: six courses of caerulein pancreatitis were induced at weekly intervals. Cyclosporin was administered on induction and the day before. Rats recovered for two weeks before being killed. Control groups received saline, cyclosporin, or caerulein alone.

RESULTS

Protocol A: plasma TGF-beta1 and tissue collagenase rose after pancreatitis but decreased towards baseline values on day 15, matching a low collagen content. Morphology disclosed minimal inflammatory infiltration and some interstitial cells immunoreactive for smooth muscle alpha-actin (SMA). TGF-beta1 increased, and remained high in cyclosporin treated groups (cyclosporin alone and cyclosporin plus caerulein). Rats treated with cyclosporin and caerulein showed severe pancreatic weight reduction, abundant inflammatory infiltrates, increased SMA immunoreactive interstitial cells, high collagen content, and delayed collagenase response. No SMA immunoreactive cells were detected in normal rats. Cyclosporin alone also increased SMA immunoreactive cells, despite the absence of inflammatory infiltration and fairly conserved pancreatic structure. Protocol B: the combined pulse treatment induced appreciable collagen deposition and resulted in a smaller pancreas than controls. Morphological examination showed atrophy, fibrosis, fibroblast proliferation, and mononuclear infiltrates.

CONCLUSION

Cyclosporin greatly distorts pancreatic repair, transforming caerulein induced pancreatitis into a fibrotic chronic-like disease. The mechanism involves TGF-beta, myofibroblasts, and defective collagenase activation.

TGF-beta is elevated in the CSF of patients with severe traumatic brain injuries and parallels blood-brain barrier function

Traumatic brain injury (TBI) induces local and systemic immunologic changes, release of cytokines, and cell activation. Perpetuation of these cascades may contribute to secondary damage to the brain. Therefore, the ability of the antiinflammatory mediator transforming growth factor-beta (TGF-beta) to downregulate intrathecal immunoactivation may be of fundamental value for diminishing the incidence and extent of secondary insults. In this study, the release of TGF-beta into cerebrospinal fluid (CSF) and serum of 22 patients with severe TBI was analyzed with respect to the function of the blood-brain barrier (BBB) for 21 days. Levels of TGF-beta in CSF increased to their maximum on the first day (median, 1.26 ng/mL), thereafter decreasing gradually over time. Median TGF-beta values in serum always remained within the reference interval (6.5 to 71.5 ng/mL). Daily assessment of the CSF-serum albumin quotient (QA) and of the CSF-serum TGF-beta quotient (QTGF-beta) showed a strong correlation between maximal QTGF-beta and QA, indicating a passage of this cytokine from the periphery to the intrathecal compartment across the BBB. However, calculation of the TGF-beta index (QTGF-beta/Q(A)) suggested a cerebral production of TGF-beta in 9 of 22 patients. Levels of TGF-beta could not be correlated with extent of initial injury by computed tomography (CT), CD4/CD8 ratios, acute lung injury, or clinical outcome as rated by the Glasgow Outcome Scale (GOS). Although increased levels of TGF-beta in CSF seem to parallel BBB function, a partial intrathecal production is suggested, possibly modulated by elevation of interleukin-6 (IL-6). Thus, TGF-beta may function as a factor in the complex cytokine network following TBI, acting as an antiinflammatory and neuroprotective mediator.

Osteomimetic properties of prostate cancer cells: a hypothesis supporting the predilection of prostate cancer metastasis and growth in the bone environment

BACKGROUND

Unlike most other malignancies, prostate cancer metastasizes preferentially to the skeleton and elicits osteoblastic reactions.

METHODS

We present a hypothesis, based upon results obtained from our laboratory and others, on the nature of progression of prostate cancer cells and their predilection to growth and metastasis in the bone microenvironment. We propose the hypothesis that osseous metastatic prostate cancer cells must be osteomimetic in order to metastasize, grow, and survive in the skeleton. The reciprocal interaction between prostate cancer and bone stromal growth factors, including basic fibroblast growth factor (bFGF), hepatocyte growth factor/scatter factor (HGF/SF), and especially the insulin growth factor (IGF) axis initiates bone tropism, and is enhanced by prostate secreted endothelin-1 (ET-1) and urokinase-type plasminogen activator (uPA). Growth factors and peptides that have differentiating activity, such as transforming growth factor beta (TGF-beta), parathyroid hormone-related protein (PTH-rp), and the bone morphogenetic proteins (BMPs), can shift local homeostasis to produce the characteristic blastic phenotype, via interaction with prostate-secreted human kalikrein 2 (hK2), and prostate-specific antigen (PSA). This proposal asserts that altering the expression of certain critical transcription factors, such as Cbfa and MSX in prostate cancer cells, which presumably are under the inductive influences of prostate or bone stromal cells, can confer profiles of gene expression, such as osteopontin (OPN), osteocalcin (OC), and bone sialoprotein (BSP), that mimic that of osteoblasts.

RESULTS AND CONCLUSIONS

Elucidation of common proteins, presumably driven by the same promoters, expressed by both prostate cancer and bone stromal cells, could result in the development of novel preventive and therapeutic strategies for the treatment of prostate cancer skeletal metastasis. Agents developed using these strategies could have the potential advantage of interfering with growth and enhancing apoptosis in both prostate cancer and bone stromal compartments. The selective application of gene therapy strategy, driven by tissue-specific and tumor-restricted promoters for the safe delivery and expression of therapeutic genes in experimental models of prostate cancer metastasis, is discussed.

Nasal administration of transforming growth factor-beta1 induces dendritic cells and inhibits protracted-relapsing experimental allergic encephalomyelitis

Cytokines have a crucial role in initiation and perturbation of EAE that represents an animal model of multiple sclerosis (MS). Administration of transforming growth factor-beta1 (TGF-beta1) to EAE mice improves clinical EAE and prevents relapses by unknown mechanisms. Administering low doses of TGF-beta1 nasally, we confirmed that TGF-beta1 inhibited development and relapse of protracted-relapsing EAE (PR-EAE) in DA rats. Infiltration of CD4+ T-cells and macrophages within the central nervous system was clearly reduced, while proliferation and IFN-gamma secretion of mononuclear cells (MNC) was augmented in TGF-beta1-treated EAE rats compared to PBS-treated control EAE rats. TGF-beta1 administered nasally also increased nitric oxide production and CD4+ T cell apoptosis. TGF-beta1 treated rats showed augmented proliferation of dendritic cells (DC) compared to MNC. These data imply that low doses of TGF-beta1 given by the nasal route prevent PR-EAE and upregulate DC functions that may be involved for disease prevention.

Induction of nitric oxide production in infiltrating leukocytes following in vivo irradiation of tumor-bearing mice

Nitric oxide (NO) has been implicated both in regression and progression of tumors due to its production by both tumor cells and infiltrating leukocytes. Ionizing radiation causes the regression of tumors, and can augment the production of NO by macrophages in vitro. We examined the cellular and systemic production of NO in mice in which radiation-resistant RIF-1 fibrosarcoma cells were implanted subcutaneously and were then either irradiated or sham-treated at the tumor site. Ten days following implantation of the tumors, CD45- tumor cells and CD45+ leukocytes were derived from resected tumors immediately after irradiation with 60 Gy, a dose previously reported to reduce tumor growth. Leukocytes from tumors of irradiated hosts produced spontaneously up to four-fold more NO than did either leukocytes from unirradiated mice or CD45- tumor cells from either unirradiated or irradiated mice. Between days 10-14 following tumor implantation, serum NO2-/NO3- increased in both irradiated and unirradiated mice to an equal extent, culminating in levels higher than those of non-tumor-bearing mice. Though NO production is elevated in macrophages treated with 1-10 Gy of radiation in vitro, higher doses may be required by tumor-infiltrating macrophages in vivo and thus may indicate that tumor-infiltrating macrophages are deactivated.

Transforming growth factor beta1 (TGFbeta1) mRNA level correlates with magnetic resonance imaging disease activity in multiple sclerosis patients

Eight relapsing-remitting multiple sclerosis (MS) patients were tested for the level of transforming growth factor beta1 (TGFbeta1) mRNA in peripheral blood mononuclear cells every 15 days for 6 months. Disease activity was evaluated every 4 weeks by magnetic resonance imaging (MRI) and neurological examination. An inverse correlation was found between the level of TGFbeta1 mRNA and MRI disease activity. The level of TGFbeta1 mRNA predicted the presence of disease activity in the scans performed 2-4 weeks later with high sensitivity (88%) and specificity (87.5%) suggesting that TGFbeta1 mRNA quantification could be an indicator of disease activity in MS.

Immunocytochemical localization of latent transforming growth factor-beta1 activation by stimulated macrophages

Transforming growth factor-beta1 (TGF-beta) is secreted in a latent form consisting of mature TGF-beta noncovalently associated with its amino-terminal propeptide, which is called latency associated peptide (LAP). Biological activity depends upon the release of TGF-beta from the latent complex following extracellular activation, which appears to be the key regulatory mechanism controlling TGF-beta action. We have identified two events associated with latent TGF-beta (LTGF-beta) activation in vivo: increased immunoreactivity of certain antibodies that specifically detect TGF-beta concomitant with decreased immunoreactivity of antibodies to LAP. Macrophages stimulated in vitro with interferon-gamma and lipopolysaccharide reportedly activate LTGF-beta via cell membrane-bound protease activity. We show through dual immunostaining of paraformaldehyde-fixed macrophages that such physiological TGF-beta activation is accompanied by a loss of LAP immunoreactivity with concomitant revelation of TGF-beta epitopes. The induction of TGF-beta immunoreactivity colocalized with immunoreactive betaglycan/RIII in activated macrophages, suggesting that LTGF-beta activation occurs on the cell surface. Confocal microscopy of metabolically active macrophages incubated with antibodies to TGF-beta and betaglycan/RIII prior to fixation supported the localization of activation to the cell surface. The ability to specifically detect and localize LTGF-beta activation provides an important tool for studies of its regulation.

Inhibition of transforming growth factor beta production by nitric oxide-treated chondrocytes: implications for matrix synthesis

OBJECTIVE

Nitric oxide (NO) is generated copiously by articular chondrocytes activated by interleukin-1beta (IL-1beta). If NO production is blocked, much of the IL-1beta inhibition of proteoglycan synthesis is prevented. We tested the hypothesis that this inhibitory effect of NO on proteoglycan synthesis is secondary to changes in chondrocyte transforming growth factor beta (TGFbeta).

METHODS

Monolayer, primary cultures of lapine articular chondrocytes and cartilage slices were studied. NO production was determined as nitrite accumulation in the medium. TGFbeta bioactivity in chondrocyte- and cartilage-conditioned medium (CM) was measured with the mink lung epithelial cell bioassay. Proteoglycan synthesis was measured as the incorporation of 35S-sodium sulfate into macromolecules separated from unincorporated label by gel filtration on PD-10 columns.

RESULTS

IL-1beta increased active TGFbeta in chondrocyte CM by 12 hours; by 24 hours, significant increases in both active and latent TGFbeta were detectable. NG-monomethyl-L-arginine (L-NMA) potentiated the increase in total TGFbeta without affecting the early TGFbeta activation. IL-1beta stimulated a NO-independent, transient increase in TGFbeta3 at 24 hours; however, TGFbeta1 was not changed. When NO synthesis was inhibited with L-NMA, IL-1beta increased CM concentrations of TGFbeta1 from 24-72 hours of culture. L-arginine (10 mM) reversed the inhibitory effect of L-NMA on NO production and blocked the increases in TGFbeta1. Anti-TGFbeta1 antibody prevented the restoration of proteoglycan synthesis by chondrocytes exposed to IL-1beta + L-NMA, confirming that NO inhibition of TGFbeta1 in IL-1beta-treated chondrocytes effected, in part, the decreased proteoglycan synthesis. Furthermore, the increase in TGFbeta and proteoglycan synthesis seen with L-NMA was reversed by the NO donor S-nitroso-N-acetylpenicillamide. Similar results were seen with cartilage slices in organ culture. The autocrine increase in CM TGFbeta1 levels following prior exposure to TGFbeta1 was also blocked by NO.

CONCLUSION

NO can modulate proteoglycan synthesis indirectly by decreasing the production of TGFbeta1 by chondrocytes exposed to IL-1beta. It prevents autocrine-stimulated increases in TGFbeta1, thus potentially diminishing the anabolic effects of this cytokine in chondrocytes.

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

Transforming growth factor-beta isoforms regulate the surface expression of membrane cofactor protein (CD46) and CD59 on human keratinocytes [corrected]

We studied the regulation of the expression of complement regulatory proteins, membrane cofactor protein (MCP), decay accelerating factor (DAF) and CD59, on human keratinocytes by supernatant of activated mononuclear cells and by some individual cytokines present therein. Cultured keratinocytes expressed MCP, DAF and CD59. Supernatant of activated mononuclear cells and recombinant forms of transforming growth factor (TGF)-beta variants (beta1, beta2 and beta3) up-regulated MCP and CD59 but not DAF. Recombinant IL-1alpha, IL-2, IL-6, TNF-alpha and IFN-gamma had no influence. TGF-beta present in the supernatant was likely responsible for up-regulation of MCP and CD59. A monoclonal anti-TGF-beta antibody, which neutralized TGF-beta1, -beta2 and -beta3, did not inhibit the up-regulation of MCP and CD59 by the supernatant. These results indicated that TGF-beta and an additional factor(s) present in the supernatant may be responsible for up-regulating the expression of MCP and CD59 on keratinocytes; both may be acting non-synergistically.

Astrocyte-Derived Monocyte-Chemoattractant Protein-1 Directs the Transmigration of Leukocytes Across a Model of the Human Blood-Brain Barrier

The migration of leukocytes across the blood-brain barrier (BBB) into the central nervous system is critical in the pathogenesis of central nervous system inflammatory diseases. The production of chemokines, such as monocyte-chemoattractant protein-1 (MCP-1), by endothelial cells (EC) and astrocytes may initiate and amplify this process. Using a coculture of human EC and astrocytes to model the BBB, we demonstrated that exogenous MCP-1 induces the transmigration of monocytes in a dose-dependent manner. TNF-α, IFN-γ, or IL-1β treatment of cocultures also induced significant migration of monocytes that correlates with the induction of MCP-1 protein. TGF-β, previously shown to induce MCP-1 expression in astrocytes, but not in EC, caused migration of monocytes across cocultures, but not across EC grown alone. Monocytes and lymphocytes transmigrated across cytokine-treated cocultures in greater numbers than across EC alone. Astrocytes were the main source of cytokine-induced MCP-1, supporting a role for astrocytes in facilitating leukocyte transmigration. A blocking Ab to MCP-1 inhibited MCP-1- and cytokine-induced transmigration of monocytes by 85–90%. Cytokine treatment of cocultures also resulted in the transmigration of activated, CD69-positive lymphocytes. The MCP-1-mediated transmigration of monocytes across cocultures was blocked using an Ab to ICAM-1 and inhibited by 55% using an Ab to E-selectin. These data suggest a central role for astrocyte-derived MCP-1 in directing the migration of monocytes and lymphocytes across the BBB.

A critical role for transforming growth factor-beta in donor transfusion-induced allograft tolerance

Donor-specific (DST) or nonspecific blood transfusions administered before transplantation can enhance survival of vascularized allografts both in humans and animals but the immunological mechanisms of this effect remain unclear. We have analyzed the expression and the role of endogenous TGF-beta1 in a model of heart allograft tolerance, induced by pregraft DST in adult rats. We reported previously that this tolerance occurs despite a strong infiltration of leukocytes into the graft that are unable to produce both Th1- and Th2-related cytokines in vivo. Allografts from DST-treated rats express high levels of TGF-beta1 mRNA and active protein. This phenomenon is correlated with the rapid infiltration of leukocytes producing high amounts of TGF-beta1. TGF-beta1-producing cells are virtually absent among early infiltrating cells in rejected grafts but are found at a later time point. The induction of allograft tolerance in vivo is abrogated by administration of neutralizing anti-TGF-beta mAb. Moreover, overexpression of active TGF- beta1 in heart allografts using a recombinant adenovirus leads to prolonged graft survival in unmodified recipients. Taken together, our results identify TGF-beta as a critical cytokine involved in the suppression of allograft rejection induced by DST and suggest that TGF-beta-producing regulatory cells are also involved in allograft tolerance.

Leptin expression in porcine adipose tissue is not increased by endotoxin but is reduced by growth hormone

The physiologic response to infection includes reductions in tissue concentrations of anabolic growth factors as a means of reducing growth and conserving nutrients for immunologic processes. This repartitioning of nutrients is accompanied by anorexia, which has been linked to increased leptin expression. Furthermore, leptin and growth hormone (GH) concentrations are inversely related, with leptin being required for normal GH release. The objective of this study was to determine if pretreatment with GH would influence endotoxin-induced changes in leptin expression or attenuate endotoxin-induced reductions in serum insulin-like growth factor-1 (IGF-1) and IGF-1 expression in liver and longissimus muscle. In experiment 1, 40 pigs were assigned to four treatments (n = 10 per treatment) arranged as a 2x2 factorial with GH (s.c. injection, 2 mg 1 h before challenge and 2 mg 2 h after challenge) and endotoxin (single i.m. injection, 25 microg/kg body weight) as main effect variables. Pretreatment with GH resulted in a marked increase (p<0.001) in serum GH within 1 h that was sustained throughout the study. Endotoxin challenge reduced (p<0.003) serum IGF-1 independent of GH (GH x endotoxin, p>0.682), and reduced (p<0.05) IGF-1 expression in longissimus muscle but not liver. Leptin mRNA abundance was reduced 56% (p<0.005) by GH but was not affected by endotoxin (p>0.81). In experiment 2, 36 pigs (n = 12 per treatment) were either allowed ad libitum feed consumption with no injection or deprived of feed and injected twice with either saline or endotoxin 24 h apart. Feed deprivation reduced leptin expression (p<0.05). However, endotoxin did not change leptin expression but markedly increased (p<0.05) serum haptoglobin. These data indicate that changes in IGF-1 status in endotoxin-challenged pigs are independent of serum GH and that leptin expression is not increased by endotoxin challenge in the pig. These data also indicate a regulatory linkage between GH and leptin in vivo.

Oral Delivery of Group A Streptococcal Cell Walls Augments Circulating TGF-β and Suppresses Streptococcal Cell Wall Arthritis

Oral administration of autoantigens can influence the outcome of experimental autoimmune diseases, yet little is known about nonself Ag-induced tolerance. In this study, we administered group A streptococcal cell wall (SCW) peptidoglycan-polysaccharide complexes orally and monitored the impact on SCW-induced erosive polyarthritis. Oral administration of low dose SCW (3 μg/day), initiated 7 days before an arthritogenic dose of systemic SCW, virtually eliminated the joint swelling and destruction typically observed during both the acute and chronic phases of the arthritis. High (300 μg), but not intermediate (30 μg), dose regimens also profoundly inhibited the disease. Most previous studies have demonstrated that prior feeding is required for efficacy, yet oral feeding of low dose SCW suppressed the evolution of arthritis even when administration was begun 10–15 days after induction of the arthritis. While the synovial inflammatory cell infiltration and expression of proinflammatory cytokines were markedly suppressed, no local enhancement of the regulatory cytokines IL-4, IL-10, and TGF-β was detected. Oral administration of low dose SCW, however, up-regulated circulating levels of TGF-β, concomitant with decreased circulating TNF-α and suppression of chronic arthritis. Moreover, IL-10 was increased in tolerized spleen lymphocytes, and unexpectedly, this SCW-specific IL-10 production was TGF-β dependent. These data support a pivotal role for TGF-β, although not necessarily in the joint, in the regulation of specific immune tolerance responsible for suppressed synovial inflammation and matrix destruction. The distant induction and up-regulation of regulatory cytokines and/or cells may contribute to the inhibition of the immune response through blunted infiltration of inflammatory cells to the joint.

The function of TGF-beta-mediated innocent bystander suppression associated with physiological self-tolerance in vivo

Innocent bystander suppression has been demonstrated in experimental models of transplantation tolerance and oral tolerance. This phenomenon is associated with expression of cytokines such as TGF-beta or/and type II cytokines (e.g., IL-4, IL-10). However, the mechanism responsible for bystander suppression is poorly understood, as is its role in antigen-specific self-tolerance. Here, we describe a series of investigations using an antigen coimmunization strategy to examine the outcome of bystander suppression in vivo in a well-characterized physiological model, using beef insulin transgenic (BI-Tg) mice, for self-tolerance. Our results demonstrate that: (1) T-cell-mediated peripheral hyporesponsiveness, or CD4(+) regulatory type II Th cell-mediated adoptive transfer of peripheral hyporesponsiveness (defined by an ELISA antibody assay), is antigen-specific at induction but effector-nonspecific (bystander suppression) when the self-antigen (BI) and a control antigen (chicken ovalbumin) are coadministered in BI-Tg mice; (2) bystander suppression is manifest as a local and transient, rather than a systemic and long-term, phenomenon; (3) bystander suppression is both time and antigen dose dependent; and (4) anti-TGF-beta Mab abolishes the effect of bystander suppression in vivo. We suggest that TGF-beta-mediated innocent bystander suppression associated with physiological self-tolerance thus produces no major biological consequence for general immune responsiveness. It may prevent the activation of auto(or cross)-reactive lymphocytes.

Periapical inflammatory responses and their modulation

Periapical inflammatory responses occur as a consequence of bacterial infection of the dental pulp, as a result of caries, trauma, or iatrogenic insult. Periapical inflammation stimulates the formation of granulomas and cysts, with the destruction of bone. These inflammatory responses are complex and consist of diverse elements. Immediate-type responses--including vasodilatation, increased vascular permeability, and leukocyte extravasation--are mediated by endogenous mediators, including prostanoids, kinins, and neuropeptides. Non-specific immune responses--including polymorphonuclear leukocyte and monocyte migration and activation, and cytokine production--are elicited in response to bacteria and their products. Interleukin-1 and prostaglandins in particular have been implicated as central mediators of periapical bone resorption. Chronic periapical inflammation further involves specific T- and B-cell-mediated anti-bacterial responses, and activates a network of regulatory cytokines which are produced by Th1- and Th2-type T-lymphocytes. Various naturally occurring and genetically engineered models of immunodeficiency are beginning to help elucidate those components of the immune system which protect the pulpal/periapical complex. Both specific and non-specific responses interface with and are regulated by the neural system. The modulation of these responses by immune response modifies, cytokine antagonists, and other novel therapeutic agents is discussed. As an experimental model, periapical inflammation has many advantages which permit it to be used in studies of microbial ecology and pathogenesis, host response, neuroimmunology, and bone resorption and regeneration.

Engagement of cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) induces transforming growth factor beta (TGF-beta) production by murine CD4(+) T cells

Evidence indicates that cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) may negatively regulate T cell activation, but the basis for the inhibitory effect remains unknown. We report here that cross-linking of CTLA-4 induces transforming growth factor beta (TGF-beta) production by murine CD4(+) T cells. CD4(+) T helper type 1 (Th1), Th2, and Th0 clones all secrete TGF-beta after antibody cross-linking of CTLA-4, indicating that induction of TGF-beta by CTLA-4 signaling represents a ubiquitous feature of murine CD4(+) T cells. Stimulation of the CD3-T cell antigen receptor complex does not independently induce TGF-beta, but is required for optimal CTLA-4-mediated TGF-beta production. The consequences of cross-linking of CTLA-4, together with CD3 and CD28, include inhibition of T cell proliferation and interleukin (IL)-2 secretion, as well as suppression of both interferon gamma (Th1) and IL-4 (Th2). Moreover, addition of anti-TGF-beta partially reverses this T cell suppression. When CTLA-4 was cross-linked in T cell populations from TGF-beta1 gene-deleted (TGF-beta1(-/-)) mice, the T cell responses were only suppressed 38% compared with 95% in wild-type mice. Our data demonstrate that engagement of CTLA-4 leads to CD4(+) T cell production of TGF-beta, which, in part, contributes to the downregulation of T cell activation. CTLA-4, through TGF-beta, may serve as a counterbalance for CD28 costimulation of IL-2 and CD4(+) T cell activation.

Astrocyte expression of monocyte chemoattractant protein-1 is differentially regulated by transforming growth factor beta

The pathophysiology of central nervous system (CNS) inflammatory disease is dependent, in part, on leukocyte recruitment across the blood-brain barrier. The expression of cytokines and chemokines by astrocytes may contribute to this process. Astrocytes express monocyte chemoattractant protein-1 (MCP-1), an activator of monocytes and a chemoattractant for monocytes and activated T cells. We examined the regulation of MCP-1 expression in human fetal astrocytes following cytokine treatment in the presence and absence of transforming growth factor beta (TGF-beta). TGF-beta, TNFalpha and IL-1beta, but not IFNgamma, induced MCP-1 mRNA and protein. TGF-beta, in cotreatment with TNFalpha caused an additive increase in MCP-1 mRNA, but not protein. In combination with IFNgamma, TGF-beta significantly increased MCP-1 mRNA and protein, as compared to either untreated, TGF-beta- or IFNgamma-treated astrocytes. However, TGF-gamma in cotreatment with IL-1beta decreased MCP-1 mRNA and protein, as compared to IL-1beta alone. Treatment of astrocytes with TGF-beta prior to TNFalpha, IFNgamma or IL-1beta treatment significantly increased MCP-1 expression. The kinetics of cytokine expression in the CNS may differentially regulate astrocyte-derived MCP-1 expression and subsequent recruitment and activation of leukocytes.

Genetic vaccination-induced immune responses to the human immunodeficiency virus protein Rev: emergence of the interleukin 2-producing helper T lymphocyte

Rev M10 is a trans-dominant negative inhibitor of HIV replication. Hence, stable transduction of CD4+ T cells with Rev M10 represents a novel gene therapy aimed at inhibiting HIV replication within these cells, thereby slowing the progression of AIDS. However, the immune system may recognize Rev M10 as foreign and target transduced cells for elimination. In the current study, mice were genetically immunized with a plasmid encoding Rev M10, to (1) identify immune parameters that may be induced by Rev M10 gene transfer, (2) determine the impact of repeated introduction of the Rev M10-encoding plasmid on the immune response to the transgene product, and (3) determine if cotransfection with a plasmid encoding TGFbeta1 would suppress the response. Kinetic studies revealed that Rev-specific IL-2-producing helper T lymphocytes (HTLs) appeared following the second genetic immunization, peaked after the third, and persisted at peak levels for at least 6 weeks. Rev-specific HTLs were CD4+, and the development of these cells was ablated by cotransfection with TGFbeta1. Other cytokines were not readily detectable when immune splenocytes were restimulated with Rev in vitro, and Rev-specific IgG antibodies were not present in the sera of these mice. To our knowledge, this represents the first report that genetic immunization with Rev M10 induces an immune response that is dominated by IL-2-producing HTLs. Further, this study demonstrates the potential utility of introducing immunosuppressive genes as a means to control the immune response to foreign transgene products.

Activated thyroglobulin possesses a transforming growth factor-beta activity

Thyroglobulin (Tg), the thyroid hormone precursor, is a major protein component in the thyroid gland and may have other important functions. Here, we show that bovine Tg inhibited 125I-labeled transforming growth factor-beta1 (125I-TGF-beta1) binding to cell-surface TGF-beta receptors in mink lung epithelial cells with an IC50 of approximately 300 nM. After disuccinimidyl suberate (DSS) modification, reduction/alkylation, treatment with 8 M urea, 0. 1% SDS, or acidic pH (pH 4-5), Tg exhibited a approximately 5-10-fold increase of 125I-TGF-beta1 binding inhibitory activity with IC50 of approximately 30-60 nM. This inhibitory activity was an intrinsic property of the Tg and could not be segregated from Tg protein by 5% SDS-polyacrylamide gel electrophoresis or by immunoprecipitation using antiserum to Tg. Untreated Tg did not affect DNA synthesis but blocked the TGF-beta-induced inhibition of DNA synthesis in mink lung epithelial cells. After DSS activation, Tg possessed TGF-beta agonist activity and inhibited DNA synthesis of mink lung epithelial cells and rat thyroid cells. The activated Tg also exerted a small but significant TGF-beta agonist activity in transcriptional activation of plasminogen activator inhibitor-1. These results suggest that Tg possesses an authentic TGF-beta activity which can be induced by chemical modifications and treatments with denaturing agents and acidic pH.

Integrin-mediated interactions influence the tissue specificity of CD8+ cytolytic T lymphocytes

We previously reported that CD8+ cytotoxic T lymphocytes (CTL) elicited in response to allogeneic renal epithelial cells (anti-REC CTL) preferentially lyse REC targets as compared to conventional lymphoid cell (LC) targets. It is often tacitly assumed that such cell type specificity results from CTL recognition of tissue-restricted MHC/peptide complexes. However, we herein report that anti-REC CTL uniquely express CD103, an integrin with known specificity for the epithelial cell-restricted ligand E-cadherin, and are deficient in expression of CD11a (LFA-1), an integrin known to play a critical accessory role in promoting lysis of LC targets. We demonstrate that CD8+ CTL clones with disparate CD103/CD11a phenotypes but identical specificities for allo-MHC/peptide can exhibit marked differences in cell type specificity. Antibody blocking studies provided direct evidence that CD103 serves as an accessory molecule that promotes lysis of REC targets. Taken together, these data indicate that integrin-mediated accessory interactions can influence the capacity of CD8+ CTL to discriminate between different cell types.

Transforming growth factor beta in fracture repair

Transforming growth factor betas are a group of polypeptide growth factors that have a wide range of activities in the musculoskeletal and immunological systems. They are thought to play an important role in the development, induction, and repair of bone. This family of closely related genes includes the five known transforming growth factor betas and also the bone morphogenetic proteins. With the development of new techniques to analyze gene expression, the broad range of cellular activities regulated by transforming growth factor beta is beginning to be understood. The critical role that transforming growth factor beta plays in the regulation and stimulation of mesenchymal precursor cells for chondrocytes, osteoblasts, and osteoclasts is now emerging based on a series of in vitro studies. Although transforming growth factor betas appear to stimulate proliferation of precursor cells, it appears that transforming growth factor betas have an inhibitory effect on mature cell lines. In vivo studies indicate the presence of transforming growth factor beta protein and transforming growth factor beta gene expression in normal fracture healing, whereas exogenous transforming growth factor beta administration stimulates the recruitment and proliferation of osteoblasts in fracture healing. Although the cascade of events that leads to bone formation and repair is not completely understood, transforming growth factor beta's central role in the regulation of fracture healing is not disputed.

CREB binding protein is a required coactivator for Smad-dependent, transforming growth factor beta transcriptional responses in endothelial cells

The transforming growth factor-beta (TGF-beta) superfamily of growth factors and cytokines has been implicated in a variety of physiological and developmental processes within the cardiovascular system. Smad proteins are a recently described family of intracellular signaling proteins that transduce signals in response to TGF-beta superfamily ligands. We demonstrate by both a mammalian two-hybrid and a biochemical approach that human Smad2 and Smad4, two essential Smad proteins involved in mediating TGF-beta transcriptional responses in endothelial and other cell types, can functionally interact with the transcriptional coactivator CREB binding protein (CBP). This interaction is specific in that it requires ligand (TGF-beta) activation and is mediated by the transcriptional activation domains of the Smad proteins. A closely related, but distinct endothelial-expressed Smad protein, Smad7, which does not activate transcription in endothelial cells, does not interact with CBP. Furthermore, Smad2,4-CBP interactions involve the COOH terminus of CBP, a region that interacts with other regulated transcription factors such as certain signal transduction and transcription proteins and nuclear receptors. Smad-CBP interactions are required for Smad-dependent TGF-beta-induced transcriptional responses in endothelial cells, as evidenced by inhibition with overexpressed 12S E1A protein and reversal of this inhibition with exogenous CBP. This report demonstrates a functional interaction between Smad proteins and an essential component of the mammalian transcriptional apparatus (CBP) and extends our insight into how Smad proteins may regulate transcriptional responses in many cell types. Thus, functional Smad-coactivator interactions may be an important locus of signal integration in endothelial cells.

CCAAT/enhancer binding proteins beta and delta regulate alpha1-acid glycoprotein gene expression in rat intestinal epithelial cells

Isoforms of CCAAT/enhancer binding protein (C/EBP) are expressed in rodent intestine as well as in the rat intestinal epithelial cell line IEC-6. However, no specific roles have been attributed to these isoforms in intestinal epithelial cells. To determine whether C/EBP family members could be implicated in the regulation of acute-phase response gene expression in intestinal epithelial cells, we have studied the effect of glucocorticoids on expression of the alpha1-acid glycoprotein gene and C/EBP isoforms in IEC-6 cells. Glucocorticoids induced alpha1-acid glycoprotein gene expression in these cells. This induction coincided with an increase of DNA-binding capacity of both C/EBPbeta and C/EBPdelta to the B1 and B2 C/EBP-interacting sites localized in the rat AGP promoter. Transforming growth factor beta, (TGFbeta), a cytokine involved in the transcriptional regulation of several acute-phase plasma proteins, antagonized the glucocorticoid-dependent induction of alpha1-acid glycoprotein gene expression. In parallel, TGFbeta downregulated the DNA-binding capacities of both the C/EBPbeta and C/EBPdelta isoforms. Mutations of the B1 or the B2 C/EBP-interacting site strongly reduced the responsiveness of the alpha1-acid glycoprotein promoter to glucocorticoids and TGFbeta. These results demonstrate a functional role for C/EBPbeta and C/EBPdelta in rat intestinal epithelial cells and suggest that these isoforms represent important modulators of the acute-phase response and of glucocorticoid, as well as TGFbeta, responsiveness.

Post-transcriptional inhibition of CD40 gene expression in microglia by transforming growth factor-beta

Microglia are one of the major glial cell types within the central nervous system, and can function as immune effector cells upon activation. CD40 is a cell surface receptor belonging to the TNF receptor family that plays a critical role in the regulation of immune responses. In this study, we investigated the expression of CD40 on microglia, and the role of transforming growth factor-beta (TGF-beta), an immunosuppressive cytokine, in regulating CD40 expression. Microglia constitutively express very low levels of CD40, and IFN-gamma enhances CD40 mRNA and protein expression in these cells. IFN-gamma-induced CD40 mRNA expression is partially sensitive to the protein synthesis inhibitor puromycin, suggesting that ongoing protein synthesis is necessary for optimal induction of CD40 mRNA by IFN-gamma. TGF-beta inhibits IFN-gamma-induced CD40 protein and mRNA expression. Inhibition of IFN-gamma-induced CD40 mRNA levels by TGF-beta in microglia is not due to inhibition of CD40 transcription; rather, inhibition is due to enhanced degradation of CD40 mRNA. These results indicate that TGF-beta can inhibit expression of an immunologically important receptor, CD40, in microglia, and does so at the post-transcriptional level by destabilizing CD40 mRNA. TGF-beta inhibition of CD40 expression may be one of the mechanisms by which TGF-beta exerts its suppressive effects on immune responses.

TGF-beta: a balancing act

Regulation of developmental processes as well as host defense and repair mechanisms requires the maintenance of a delicate balance of positive and negative regulatory signals. TGF-beta, a molecule known for its many diverse activities, can promote or inhibit cell growth and function. Disruption of the balance between these opposing activities can contribute to aberrant development, malignancy, or pathogenic immune and inflammatory responses. TGF-beta transgenic mouse studies highlight the essential function(s) of TGF-beta and its receptors and provide insight to potential therapeutic approaches to manipulate TGF-beta expression.

Thrombospondin-1 is a major activator of TGF-beta1 in vivo

The activity of TGF-beta1 is regulated primarily extracellularly where the secreted latent form must be modified to expose the active molecule. Here we show that thrombospondin-1 is responsible for a significant proportion of the activation of TGF-beta1 in vivo. Histological abnormalities in young TGF-beta1 null and thrombospondin-1 null mice were strikingly similar in nine organ systems. Lung and pancreas pathologies similar to those observed in TGF-beta1 null animals could be induced in wild-type pups by systemic treatment with a peptide that blocked the activation of TGF-beta1 by thrombospondin-1. Although these organs produced little active TGF-beta1 in thrombospondin null mice, when pups were treated with a peptide derived from thrombospondin-1 that could activate TGF-beta1, active cytokine was detected in situ, and the lung and pancreatic abnormalities reverted toward wild type.

Plasmid DNA encoding transforming growth factor-beta1 suppresses chronic disease in a streptococcal cell wall-induced arthritis model

Transforming growth factor beta is a potent immunomodulator with both pro- and antiinflammatory activities. Based on its immunosuppressive actions, exogenous TGF-beta has been shown to inhibit autoimmune and chronic inflammatory diseases. To further explore the potential therapeutic role of TGF-beta, we administered a plasmid DNA encoding human TGF-beta1 intramuscularly to rats with streptococcal cell wall-induced arthritis. A single dose of 300 microg plasmid DNA encoding TGF-beta1, but not vector DNA, administered at the peak of the acute phase profoundly suppressed the subsequent evolution of chronic erosive disease typified by disabling joint swelling and deformity (articular index = 8.17+/-0. 17 vs. 1.25+/-0.76, n = 6, day 26, P < 0.01). Moreover, delivery of the TGF-beta1 DNA even as the chronic phase commenced virtually eliminated subsequent inflammation and arthritis. Both radiologic and histopathologic as well as molecular evidence supported the marked inhibitory effect of TGF-beta1 DNA on synovial pathology, with decreases in the inflammatory cell infiltration, pannus formation, cartilage and bone destruction, and the expression of proinflammatory cytokines that characterize this model. Increases in TGF-beta1 protein were detected in the circulation of TGF-beta1 DNA-treated animals, consistent with the observed therapeutic effects being TGF-beta1 dependent. These observations provide the first evidence that gene transfer of plasmid DNA encoding TGF-beta1 provides a mechanism to deliver this potent cytokine that effectively suppresses ongoing inflammatory pathology in arthritis.

Regulation of immune responses by TGF-beta

The transforming growth factor beta (TGF-beta) family of proteins are a set of pleiotropic secreted signaling molecules with unique and potent immunoregulatory properties. TGF-beta 1 is produced by every leukocyte lineage, including lymphocytes, macrophages, and dendritic cells, and its expression serves in both autocrine and paracrine modes to control the differentiation, proliferation, and state of activation of these immune cells. TGF-beta can modulate expression of adhesion molecules, provide a chemotactic gradient for leukocytes and other cells participating in an inflammatory response, and inhibit them once they have become activated. Increased production and activation of latent TGF-beta have been linked to immune defects associated with malignancy and autoimmune disorders, to susceptibility to opportunistic infection, and to the fibrotic complications associated with chronic inflammatory conditions. In addition to these roles in disease pathogenesis, TGF-beta is now established as a principal mediator of oral tolerance and can be recognized as the sine qua non of a unique subset of effector cells that are induced in this process. The accumulated knowledge gained through extensive in vitro functional analyses and from in vivo animal models, including newly established TGF-beta gene knockout and transgenic mice, supports the concept that clinical therapies based on modulation of this cytokine represent an important new approach to the treatment of disorders of immune function.

Homeostasis and self-tolerance in the immune system: turning lymphocytes off

The immune system responds in a regulated fashion to microbes and eliminates them, but it does not respond to self-antigens. Several regulatory mechanisms function to terminate responses to foreign antigens, returning the immune system to a basal state after the antigen has been cleared, and to maintain unresponsiveness, or tolerance, to self-antigens. Here, recent advances in understanding of the molecular bases and physiologic roles of the mechanisms of immune homeostasis are examined.

Cloning and sequencing of equine transforming growth factor-beta 1 (TGF beta-1) cDNA

Transforming growth factor beta (TGF-beta) belongs to a family of peptide growth factors which control critical stages of cell proliferation and differentiation. We report the cloning and sequencing of the cDNA for TGF-beta type 1 isoform of the horse. The predicted mature equine TGF beta-1 peptide is 112 amino acids in length and exhibits 99% identity to mature human TGF beta-1.

A novel member of the transforming growth factor-beta (TGF-beta) superfamily from the filarial nematodes Brugia malayi and B. pahangi

Transforming growth factor-beta (TGF-beta) superfamily genes encode products controlling pattern formation, cell differentiation, and immune-mediated inflammation. Members of this superfamily are known in multicellular organisms from mammals to the model nematode Caenorhabditis elegans. Using PCR with oligonucleotides complementary to highly conserved motifs in the TGF-beta superfamily, we first isolated a genomic clone from the filarial nematode Brugia malayi. This gene, termed Bm-tgh-1 (TGF-beta homolog-1), spans 2.5 kb of genomic DNA and contains seven exons. Transcripts of this gene are poorly represented in cDNA libraries, but a full-length cDNA was isolated by RACE from B. pahangi (Bp-tgh-1). The tgh-1 genes from the two species are >98% identical at the nucleotide and amino acid levels, differing at 18/1576 base pairs and 5/428 amino acids; all nonsynonymous substitutions are in the long N-terminal propeptide. They show a high level of similarity throughout all seven exons to a C. elegans gene on cosmid T25F10. Homology to other members of the TGF-beta superfamily is restricted to the C-terminal domain which contains the mature active protein. Key features shared with other members of the superfamily include the tetrabasic proteolytic cleavage site to release an active C-terminal peptide, seven cysteines arrayed in identical fashion, and conserved sequence motifs. tgh-1 is most similar to the BMP-1 subfamily involved in developmental signaling in nematodes, insects, and vertebrates. RT-PCR on first-strand cDNA from both Brugia species, with primers specific to the 3' end, showed that tgh-1 is not expressed in the microfilarial stage, but is detectable in the mosquito-derived infective larvae and is maximal in maturing parasites around the time of molting in the mammalian host. Adult parasites show a relatively low level of expression. The identification of tgh-1, and its preferential expression in developing parasites, suggests that it may be involved in key developmental events in the complex filarial life cycle.

Cytokine-induced inflammation in the central nervous system revisited

Cytokines play an essential role as mediators of the immune response. They usually function as part of a network of interactive signals that either activate, enhance, or inhibit the ensuing reaction. An important contribution of this cytokine cascade is the induction of an inflammatory response that recruits and activates subsets of leukocytes that function as effector cells in the response to the sensitizing antigen. Proinflammatory cytokines activate endothelial cells (EC) to express adhesion molecules and induce the release of members of the chemokine family, thus focusing and directing the inflammatory response to sites of antigen recognition. However, the vasculature of the central nervous system (CNS) is highly specialized and restricts the access of components of the immune system to the CNS compartment. In this review, we address the question as to whether endothelial cells in the CNS respond differently to specific cytokines known to induce either a proinflammatory effect or a regulatory effect in systemic vascular beds.

Transforming growth factor-beta 1 regulates chemokine and complement production by human proximal tubular epithelial cells

Previously it has been demonstrated that human proximal tubular epithelial cells (PTEC) are able to produce chemokines (such as IL-8 and MCP-1) and complement components (such as C2, C3, C4 and factor H), and that production of these proteins is regulated by pro-inflammatory cytokines such as interleukin-1 alpha (IL-1alpha), tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). Since TGF-beta is also expressed in the renal interstitium during inflammation, we investigated the effect of TGF-beta on the production of chemokines and complement components by PTEC in culture. Transforming growth factor-beta 1 up-regulated IL-8 production by an average of 4.17 +/- 1.0 fold. macrophage chemoattractant phagocyte (MCP-1) production, on the other hand, was down-regulated by TGF-beta 1 by an average of 2.2 +/- 0.7 fold. The production of C3 and C4 was also down-regulated after incubation with TGF-beta 1 (1.9 +/- 0.3- and 3.0 +/- 1.2-fold, respectively). All effects were dose- and time-dependent and were found to be specific for TGF-beta 1, as assessed by inhibition of the effect with a neutralizing antibody against TGF-beta 1. These data, together with the knowledge that TGF-beta, chemokines and complement components play a role in several types of renal disease, suggest that TGF-beta is involved in the regulation of local expression of chemokines and complement components by tubular cells.

Generation of an Inhibitory Circuit Involving CD8+ T Cells, IL-2, and NK Cell-Derived TGF-β: Contrasting Effects of Anti-CD2 and Anti-CD3

Although the phenomenon of immunosuppression is well established, the mechanisms involved in the generation of lymphocytes with down-regulatory activity are poorly understood. Unlike anti-CD3 antibodies, mitogenic combinations of anti-CD2 antibodies do not stimulate human PBL to produce IgM or IgG. In determining the reason for this difference, we have found that anti-CD2 triggers an inhibitory circuit facilitated by TGF-β provided by NK cells. Stimulation of PBL with anti-CD2, but not anti-CD3, generated substantial amounts of active TGF-β. NK cells were found to be a significant source of TGF-β and were the only lymphocyte population that constitutively produced this cytokine. Anti-CD2 enhanced the production of active TGF-β by purified NK cells. TGF-β. After the removal of NK cells or the addition of anti-TGF-β, anti-CD2 could stimulate Ig production. Anti-TGF-β had to be added within the first 24 h for a maximal effect. Moreover, a short, overnight exposure of CD8+ T cells to TGF-β could prime them for suppressor activity provided that IL-2 was also present. Thus, the presence of active TGF-β coincident with CD8+ T cell activation can condition these cells to mediate down-regulatory activity, and NK cells can serve as the source of this cytokine.

Inhibition of nuclear factor kappa B attenuates proinflammatory cytokine and inducible nitric-oxide synthase expression in postischemic myocardium

We have previously reported that induction of nuclear factor-kappa B (NF-kappa B) occurs in a biphasic manner in postischemic myocardium. Because interleukin-1 (IL-1), IL-6, tumor necrosis factor-alpha (TNF-alpha), and inducible nitric-oxide synthase (iNOS) contain kappa B-response elements, and since transforming growth factor-beta 1 (TGF-beta 1) down-modulates both cytokine and iNOS expression, we studied their temporal expression during myocardial ischemia/reperfusion (I/R). Northern and Western analyses showed low levels of IL-6 and no signal for IL-1 beta, TNF-alpha and iNOS under basal conditions. Their expression rose significantly over sham-operated controls by 1 h reperfusion, and persisted high for various periods. Under basal conditions, low levels of TGF-beta 1 were detected, which rose significantly at 3 h reperfusion, and remained high until 24 h reperfusion. Administration of diethyldithiocarbamate (DDC) inhibited induction of NF-kappa B and concomitantly the expression of IL-1 beta, IL-6, TNF-alpha as well as iNOS. However, expression of TGF-beta was not altered. Our results indicate that ischemia/reperfusion induces NF-kappa B, and upregulates kappa B-response genes. Administration of DDC inhibits NF-kappa B levels, and attenuates expression of inflammatory cytokines and iNOS.

The anagen hair cycle induces systemic immunosuppression of contact hypersensitivity in mice

Contact hypersensitivity (CHS) to picryl chloride (PCl) is depressed in C57BL/6 mice when CHS is induced via early anagen skin. We have now further dissected this phenomenon in vivo. The elicitation phase for CHS was suppressed when anagen was induced 4 days after PCl sensitization of telogen animals. Sensitization of mice via abdominal skin with all hair follicles in telogen, and back skin follicles in anagen, significantly reduced the magnitude of the ear swelling response. Consecutive applications of two sensitizing doses of hapten, first on induced anagen back skin and then on telogen abdominal skin 7 days later, failed to induce tolerance. Furthermore, spleen cell transfer of sensitized anagen mice into telogen mice did not inhibit CHS response in the recipients. The current study suggests that a temporary state of systemic hyporesponsiveness, mediated, e.g., by hair cycle-dependent production of immunosuppressive cytokines rather than hapten-specific T suppressor cell activities, plays a critical role.

Macrophages that have ingested apoptotic cells in vitro inhibit proinflammatory cytokine production through autocrine/paracrine mechanisms involving TGF-beta, PGE2, and PAF

Apoptosis in vivo is followed almost inevitably by rapid uptake into adjacent phagocytic cells, a critical process in tissue remodeling, regulation of the immune response, or resolution of inflammation. Phagocytosis of apoptotic cells by macrophages has been suggested to be a quiet process that does not lead to production of inflammatory mediators. Here we show that phagocytosis of apoptotic neutrophils (in contrast to immunoglobulin G-opsonized apoptotic cells) actively inhibited the production of interleukin (IL)-1beta, IL-8, IL-10, granulocyte macrophage colony-stimulating factor, and tumor necrosis factor-alpha, as well as leukotriene C4 and thromboxane B2, by human monocyte-derived macrophages. In contrast, production of transforming growth factor (TGF)-beta1, prostaglandin E2, and platelet-activating factor (PAF) was increased. The latter appeared to be involved in the inhibition of proinflammatory cytokine production because addition of exogenous TGF-beta1, prostaglandin E2, or PAF resulted in inhibition of lipopolysaccharide-stimulated cytokine production. Furthermore, anti-TGF-beta antibody, indomethacin, or PAF receptor antagonists restored cytokine production in lipopolysaccharide-stimulated macrophages that had phagocytosed apoptotic cells. These results suggest that binding and/or phagocytosis of apoptotic cells induces active antiinflammatory or suppressive properties in human macrophages. Therefore, it is likely that resolution of inflammation depends not only on the removal of apoptotic cells but on active suppression of inflammatory mediator production. Disorders in either could result in chronic inflammatory diseases.

Interleukin 10 is a growth factor for a population of regulatory T cells

Induction and maintenance of peripheral tolerance are important mechanisms to maintain the balance of the immune system. In addition to the deletion of T cells and their failure to respond in certain circumstances, active suppression mediated by T cells or T-cell factors has been proposed as a mechanism for maintaining peripheral tolerance. However, the inability to isolate and clone regulatory T cells involved in antigen-specific inhibition of immune responses has made it difficult to understand the mechanisms underlying such suppression. Here, we show that chronic activation of both human and murine CD4+ T cells in the presence of interleukin (IL)-10 gives rise to CD4+ T-cell clones with low proliferative capacity, producing high levels of IL-10, low levels of IL-2 and no IL-4. These antigen-specific T-cell clones suppress the proliferation of CD4+ T cells in response to antigen, and prevent colitis induced in SCID mice by pathogenic CD4+CD45RBhigh splenic T cells. Thus IL-10 drives the generation of a CD4+ T-cell subset, designated T regulatory cells 1 (Tr1), which suppresses antigen-specific immune responses and actively downregulates a pathological immune response in vivo.

Transforming growth factor-beta inhibition of cytokine-induced vascular cell adhesion molecule-1 expression in human astrocytes

Leukocyte transmigration across the blood-brain barrier (BBB) is a cardinal feature of central nervous system (CNS) inflammation. Astrocytes form an integral part, both structurally and functionally, of the BBB. Vascular cell adhesion molecule-1 (VCAM-1), a member of the immunoglobulin gene superfamily, is involved in extravasation into inflamed tissues and activation of T-lymphocytes. In this study, we investigated the role of TGF-beta, an immunosuppressive cytokine, in regulating cytokine-induced VCAM-1 expression in astrocytes. Human astroglioma cell lines and primary human fetal astrocytes were examined for VCAM-1 gene expression after treatment with proinflammatory cytokines (TNF-alpha, IL-1beta, IFN-gamma) in the absence or presence of TGF-beta. Astroglioma cell lines as well as primary human fetal astrocytes expressed low levels of VCAM-1 constitutively, and the proinflammatory cytokines induced marked increases in VCAM-1 expression, particularly TNF-alpha and IL-1beta. The inclusion of TGF-beta1 or TGF-beta2 with the proinflammatory cytokines inhibited VCAM-1 gene expression to varying degrees (33-93%) in all the astroglioma cell lines and primary fetal cells. These results indicate that TGF-beta is an important regulator of cytokine induced VCAM-1 expression on astrocytes and may prove useful clinically in controlling CNS inflammation.

Substance P diminishes lipopolysaccharide and interferon-gamma-induced TGF-beta 1 production by cultured murine macrophages

Recent evidence has demonstrated the importance of substance P and its receptor in macrophage-mediated inflammatory responses. While previous studies have shown that substance P can augment proinflammatory monokine production, little is known about the effects of this neuropeptide on the production of monokines that might limit inflammation. In the present study we have investigated the effect of substance P treatment on the production of transforming growth factor-beta 1 (TGF-beta 1) in cultured murine macrophages. We report that, while substance P agonist alone elicited increases in TGF-beta 1 mRNA expression and modest increases in TGF-beta 1 secretion, substance P dramatically diminished LPS- or IFN-gamma-induced TGF-beta 1 production. These results suggest a previously unrecognized mechanism where substance P may act as a proinflammatory mediator by limiting the production of excessive levels of TGF-beta 1 by LPS- or IFN-gamma-activated macrophages.