Production of transforming growth factor beta by human T lymphocytes and its potential role in the regulation of T cell growth

Interferon-gamma reverses the stimulation of collagen but not fibronectin gene expression by transforming growth factor-beta in normal human fibroblasts

It has recently become apparent that several cytokines and growth factors are capable of modulating fibroblast proliferation and biosynthetic activity. To understand the role of these factors in connective tissue regulation, we examined the effects of the simultaneous addition of interferon-gamma (IFN-gamma) and transforming growth factor-beta (TGF-beta) on normal human dermal fibroblast collagen and fibronectin production. In addition, in vitro transcription rates and steady-state mRNA levels for these molecules were determined by nuclear run-off assays and Northern and dot-blot hybridization using specific human cDNA probes. Treatment of cultures with TGF-beta caused stimulation of collagen and fibronectin production. Addition of IFN-gamma to the TGF-beta-treated cultures abrogated the stimulatory effects of TGF-beta on collagen production in a dose-dependent manner and resulted in a net inhibition of collagen production. In contrast, the increase in fibronectin synthesis induced by TGF-beta was augmented further by IFN-gamma. These changes in collagen and fibronectin production were accompanied by parallel changes in the steady-state mRNA levels for these proteins. The effects of TGF-beta plus IFN-gamma on fibronectin gene expression appeared to be mediated entirely by transcriptional mechanisms, whereas the effects on collagen gene expression resulted from a combination of transcriptional and post-transcriptional events.

Transforming growth factor-beta in human aqueous humor

The transforming growth factor-beta s are peptide growth factors known to play a central role in wound healing. Using a specific, in vitro assay of cell growth inhibition, we have detected transforming growth factor-beta (TGF-beta) in 24/24 aqueous humor specimens from eyes undergoing cataract extraction with intraocular lens implantation. The amount of TGF-beta ranged from 2.3 to 8.1 ng/ml (mean +/- SD = 4.5 +/- 1.7 ng/ml), with 61% present in the active form. Subtyping of TGF-beta was performed by addition of antibodies specific for the beta 1 and beta 2 isoforms to the growth inhibition assay, and confirmed with a sandwich enzyme-linked immunosorbent assay. None of the TGF-beta detected was of the beta 1 isoform; in contrast, the beta 2 isoform was present in every sample, implying that it might have originated from ocular tissues. The presence of this potent modulator of tissue repair in aqueous humor suggests a role in the healing processes following intraocular surgery, including glaucoma filtration surgery.

A new surface antigen on intraepithelial lymphocytes in the intestine

A new surface molecule has been discovered on mouse intestinal intraepithelial lymphocytes (IEL) using a rat anti-mouse IEL monoclonal antibody, M290. It was expressed at high levels on nearly all IEL and on a majority of T cells in the gut lamina propria. M290 stained, with lower intensity, a small minority of T cells in other lymphoid tissues. Expression was biased towards the CD8+ subset. Stimulation of peripheral T cells with mitogens did not induce expression of the new antigen but addition of transforming growth factor beta to stimulated T cells had a marked inductive effect. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of IEL surface components precipitated with M290 showed principal bands at 135, 120, 28 and 24 kDa (reduced) and 135, 100, 24 and 21 kDa (nonreduced). Precipitation with antibodies to integrin subunits showed that the new molecular complex was not a member of the beta 1, beta 2, or beta 3 integrin families although all of these were represented on IEL. A 13-amino acid N-terminal sequence obtained from the 120-kDa beta subunit of the antigen prepared from an M290+ T hybridoma (MTC-1) did not show homology with integrins. Pulse-chase studies using MTC-1 cells showed that the 135-kDa alpha subunit was derived from a 147-kDa precursor. The function of this new molecular complex is not yet known.

Functional dichotomy between Langerhans cells that present antigen to naive and to memory/effector T lymphocytes

The general thrust of this volume is to review the roles of accessory cells in regulating T and B lymphocytes. To that end, we have summarized the evidence that indicates the crucial role that Langerhans cells play in the induction and expression of immunity to antigens that gain access to, or arise within, skin. Langerhans cells accomplish this important goal by their abilities to (a) activate naive T cells to antigens not previously encountered by the host, and (b) activate memory/effector T cells specific for previously encountered antigens. Arguments have been advanced to support the view that the functional properties of Langerhans cells used to present antigens to naive T cells differ substantially from the properties that equip Langerhans cells to activate effector T cells. The arguments are based in part on the fact that Langerhans cells carry out these functions in two very different environments: in the epidermis, and in the draining lymph node. The arguments are also based on results of in vitro experiments that reveal distinct differences in antigen processing and presenting properties of Langerhans cells freshly obtained from mouse and human skin as compared to Langerhans cells that have been cultured in vitro for 2-3 days. We propose that freshly explanted Langerhans cells faithfully reflect the functional program of intraepidermal Langerhans cells, and are able to present antigen to memory/effector T cells that enter the epidermal compartment. To accomplish this task, epidermal LC pick up environmental antigens, process them with great efficiency, and then present them in situ, without further upregulation of "accessory" signals (cell-adhesion molecules, secretion of additional cytokines). They can carry out this function, even in the presence of TGFB--a a cytokine which is constitutively made by keratinocytes, and which we have found to profoundly inhibit antigen presentation by most other types of "professional" antigen-presenting cells. Intraepidermal Langerhans cells are also capable of carrying cutaneous antigens through the dermal epidermal junction and migrating to the draining lymph node. We further propose that cultured Langerhans cells are fated to present antigens to unprimed/naive T cells, and thereby to initiate immune responses to new cutaneous antigens. Cultured LC process antigens less efficiently than fresh cells, but their unique capacity to present antigen effectively to unprimed T cells rests chiefly on the fact that they have significantly upregulated cell surface adhesion molecules, expression of MHC molecules, and secretion of activating cytokines--the "accessory" signals that are required for arousing naive T cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Transforming growth factor-beta bound to soluble derivatives of the beta amyloid precursor protein of Alzheimer's disease

Transforming growth factors beta (TGF beta) are multifunctional polypeptides that participate in regulation of growth, differentiation and function of many cell types. The mature TGF beta molecule is a 25 kDa protein composed of two 12.5 kDa monomers linked by disulfide bonds. Human glioblastoma cells secrete biologically active TGF beta 2. Here we report that in addition to the free form of TGF beta 2, a stable complex between a approximately 110 kDa binding protein and TGF beta 2 was isolated from glioblastoma cell supernatant. This binding protein was purified and was found to show sequence identity to part of the beta amyloid precursor protein (beta APP), to be specifically labeled by several different antisera to beta APP, and to be affinity labeled with TGF beta by crosslinking. The complex formation between TGF beta and beta APP may have important implications in regulation of biological activity of the two proteins and in delivery or clearance of TGF beta and beta APP in the brain and other compartments.

Multiple suppressive effects of transforming growth factor beta 1 on the immune response in chickens

The immunosuppressive effect of human recombinant TGF-beta 1 on chicken immune responses in vitro was evaluated. TGF-beta 1 at 1-10 ng/ml reduced T cell proliferation in response to concanavalin A by 50-80% and B cell proliferation in response to LPS by greater than 90%. In contrast, when added to immune spleen cells, it reduced the secondary PFC response to sheep erythrocytes by less than 50%, particularly when added at the same time as antigen on Day 2 of incubation. When TGF-beta 1 was added during a 2-day incubation to nylon wool-nonadherent immune or normal spleen cells, it caused the maintenance and/or appearance of suppressor cells. These suppressor cells, in coculture with immune spleen cells, inhibited the secondary PFC response in vitro without any further exposure to TGF-beta 1. The phenotype of the cells giving rise to suppressor cells under the influence of TGF-beta 1 was CT8+, TCR2+(alpha,beta), CT4-, TCR1-(gamma,delta) cells. The results suggest that, in addition to direct suppressive effects on the proliferation of B cells and of some T cells, TGF-beta 1 may suppress immune responses by maintaining or by promoting the development of suppressor T cells.

Functional and phenotypic characteristics of recombinant interleukin-2 or T-cell growth factor-activated splenic lymphoid cells from patients with gastric or hepatocellular carcinoma

Fourteen days' culture of human spleen cells with recombinant interleukin-2 (rIL-2) or T-cell growth factor (TCGF) results in the generation of lymphokine-activated killer (LAK) effector cells that have the unique property of lysing natural killer (NK)-resistant human tumor cells, Daudi, and NK-sensitive K562 cells. LAK cells were generated from patients with advanced cancer or liver cirrhosis. The splenic LAK-effector cell types were analyzed by two-color flow cytometry. The rIL-2-induced LAK cells showed an increased proportion of CD8+CD11- and CD57+CD16- and a decreased proportion of CD4+Leu-8- cells. In contrast, TCGF-induced LAK cells revealed a significantly increased proportion of CD8+CD11- and CD4+Leu-8- cells and a decreased proportion of CD57+CD16- cells. Thus, splenic LAK cells with different surface phenotypes were induced by the cultivation with rIL-2 or TCGF. Furthermore, TCGF-induced LAK cell activities in patients with cancer were found to be lower than the rIL-2-induced LAK cell activities. It was noted that the TCGF-activated splenic lymphoid cells did not inhibit the effector process of tumor cell lysis by LAK cells that had been activated by rIL-2. Other mechanisms of lower LAK cell activities of TCGF-activated splenic lymphoid cells from patients with cancer were discussed. The findings suggest that spleens of examined patients with gastric or hepatocellular carcinoma do not seem to be responsible for suppression of cell-mediated antitumor immunity.

Transforming growth factor type beta 1 modulates the effects of basic fibroblast growth factor on growth and phenotypic expression of rat astroblasts in vitro

In a search of the growth factors possibly involved in brain ontogenesis we have examined the effects of transforming growth factor beta 1 (TGF-beta 1) on the growth and phenotypic expression of rat astroblasts in primary culture. Along TGF-beta 1 elicited only a slight negative effect on the growth of these cells. However, this factor was found to modulate the mitogenic effects of other growth factors. On quiescent cells it potentiates the mitogenic effect of basic fibroblast growth factor (bFGF) but not that of other growth factors, namely, epidermal growth factor (EGF), platelet-derived growth factor (PDGF), and thrombin. TGF-beta 1 did not modulate significantly the stimulatory effect of these growth factors on the activity of the enzyme glutamine synthetase (GS); but kinetic studies showed that TGF-beta 1 delays the stimulation of GS activity. DNA synthesis monitored by the incorporation of [125I]iododeoxyuridine (125I-dUrd) was maximum after 24-30 h of treatment with bFGF. With bFGF plus TGF-beta 1 the maximum was shifted to 30-36 h. This shift is compatible with the idea that TGF-beta 1 induces responsiveness in some cells which are otherwise unresponsive to the mitogenic action of bFGF, and that this induction requires some time. This hypothesis is sustained by the observation that in cells treated for only 12 h with bFGF, the treatment with TGF-beta 1 for the same 12 h or for longer time did not stimulate significantly the cell growth. Stimulation occurred only when the bFGF treatment was continued after 12 h. Potentiation of the mitogenic effect of bFGF and shift of the maximum 125I-dUrd incorporation towards 24 h was seen with cells pretreated with TGF-beta 1. This potentiation effect decreased with increasing time between the two treatments. The potentiation effect of TGF-beta 1 is not mediated by an induction of new bFGF membrane receptors as seen by binding studies.

Growth regulatory activities of endothelial extracellular matrix: mediation by transforming growth factor-beta

The potential of transforming growth factor-beta (TGF-beta) to modulate the growth of endothelial cells via alterations in the cell's extracellular matrix (ECM) was examined. Rat brain endothelial cells were cultured in the presence or absence of TGF-beta, and subsequently ECM was prepared from the cell cultures by hypotonic lysis of the cells. Untreated endothelial cells were then cultured on the various matrices. Cells grown on TGF-beta-treated ECM showed a significant decrease in cell number (41 +/- 6% mean growth inhibition at 6 days, P less than 0.005 by paired T-test) compared with cells grown on untreated ECM. The growth inhibitory activity of the ECM was depleted by 9 days of culture, and resumption of exponential cell growth was observed. A similar phenomenon was observed if anti-TGF-beta neutralizing antibodies were incubated with the ECM. When the TGF-beta-treated matrix was exposed to a brief dithiothreitol treatment in order to inactivate residual TGF-beta, an approximately equal degree of growth inhibition was observed initially, but the reversal of inhibition occurred at an earlier time point than that with unreduced TGF-beta-treated matrix. Analyses of the composition of matrices synthesized in the presence or absence of TGF-beta revealed about a twofold increase in the accumulation of various radioactive metabolic precursors in the TGF-beta-treated matrices. However, no qualitative alterations in the matrix or cellular-associated proteins or glycoproteins were observed, as analyzed by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. An increase in cell-associated heparan sulfate, however, was observed in TGF-beta-treated cells. The results suggest that certain growth regulatory effects of TGF-beta may be mediated, at least in part, by alterations in the ECM.

Co-localization of transforming growth factor beta 2 with alpha 1(I) procollagen mRNA in tissue sections of patients with systemic sclerosis

The role of transforming growth factor beta 2 (TGF-beta 2) in the pathogenesis of systemic sclerosis (SSc) was investigated by in situ hybridization of skin biopsies from six patients with SSc. Two patients with acute systemic lupus erythematosis (SLE), one with acute dermatomyositis (DM), and three healthy individuals were used as controls. TGF-beta 2 mRNA was found to be co-localized with pro alpha 1(I) collagen expression around dermal blood vessels in all patients with the inflammatory stage of SSc, whereas there was no expression of either gene in the dermis of patients in the fibrotic stage, the SLE patients or the normal controls. These findings provide evidence that TGF-beta 2 released by inflammatory cells around blood vessels may play a role in mediating the collagen gene disregulation in fibrosis.

Detection of transforming growth factor-beta in rheumatoid arthritis synovial tissue: lack of effect on spontaneous cytokine production in joint cell cultures

The presence of transforming growth factor-beta (TGF-beta) in inflammatory joint disease was investigated. Synovial fluid from patients with rheumatoid arthritis (RA) and patients with other non-autoimmune inflammatory joint diseases contained high levels of both active and latent TGF-beta. Levels of active TGF-beta did not correlate with drug regimen in either patient group or with the recovery period in the individuals with non-RA joint disease. Freshly isolated synovial cells from individuals with RA were shown by Northern blotting to express the mRNA for TGF-beta 1 and to secrete latent TGF-beta protein which could be neutralized by antibodies to TGF-beta 1 and TGF-beta 2. Lipopolysaccharide-stimulated peripheral blood mononuclear cells from normal donors produced interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-alpha) which was inhibited by pretreatment of these cells with recombinant TGF-beta. Cytokine production was not inhibited if the addition of TGF-beta was used after the inducing stimulus, suggesting that in activated cells cytokine production cannot be inhibited. This was confirmed by the observation that neither TGF-beta 1 or TGF-beta 2 inhibited spontaneous IL-1 or TNF-alpha production by rheumatoid synovial mononuclear cells in culture. These findings show that despite the presence of active TGF-beta in RA synovial joints and the spontaneous production of latent (potentially active) TGF-beta by RA cells in culture, additional TGF-beta did not inhibit ongoing cytokine synthesis in vitro. This suggests that TGF-beta may not inhibit cytokine production in the rheumatoid joint although it cannot be ruled out that in vivo TGF-beta already has an immunosuppressive effect which cannot be further increased in vitro by exogenous protein.

Regulation of the testis

The testicular cells are regulated by factors produced locally in the testis. These factors include peptide growth factors, pro-opiomelanocortin derivatives, neuropeptides and steroids. Several agents able to affect steroido- and spermatogenesis can also affect leukocytes and many of the testis-regulating factors are produced by immune cells, suggesting that testicular cells and leukocytes may interact. In the present article, the effects of various testicular cell and leukocyte produced factors on steroido- and spermatogenesis are reviewed. The possibility that leukocytes may produce substances able to affect the testicular functions suggests that inhibition of immune system activation in the testis may be important also for reasons other than protection of autoantigenic germ cells from an autoimmune attack.

Effect of transforming growth factor beta on the EL4 thymoma variant EL4/6.1: dissociation of inhibition of proliferation from expression of IL-1 and IL-2 receptors

In order to further characterize the action of transforming growth factor beta (TGF-beta) on lymphoid cells, we investigated the effects of porcine TGF-beta 1 and -2 on the IL-1 sensitive EL4/6.1 thymoma cell line. The proliferation of EL4/6.1 thymoma cells was inhibited by TGF-beta 1 and TGF-beta 2 (1 ng/ml) to a similar degree, the population doubling time was increased by 50-60%, total inhibition was not achieved. This decrease of proliferation was associated with an increase of the number of cells in the G0/G1 compartment of the cell cycle. TGF-beta-mediated inhibition could not be overcome by adding exogenous rIL-1 nor was the binding capacity for IL-1 reduced. In addition, TGF-beta did not interfere with the induction of IL-2 receptors by a combination of Ionomycin+PMA+IL-1. The data suggest that TGF-beta mediated inhibition of thymocyte/lymphocyte proliferation is not associated with an inhibition of the expression or the induction of expression of IL-2 or IL-1 receptors.

Transforming growth factor beta 1-induced changes in cell migration, proliferation, and angiogenesis in the chicken chorioallantoic membrane

Application of TGF beta 1 (10-100 ng) to the chicken chorioallantoic membrane (CAM) for 72 h resulted in a dose-dependent, gross angiogenic response. The vascular effects induced by TGF beta 1 were qualitatively different than those induced by maximal doses of basic FGF (bFGF) (500 ng). While TGF beta 1 induced the formation of large blood vessels by 72 h, bFGF induced primarily small blood vessels. Histologic analysis revealed that TGF beta 1 stimulated pleiotropic cellular responses in the CAM. Increases in fibroblast and epithelial cell density in the area of TGF beta 1 delivery were observed as early as 4 h after TGF beta 1 treatment. By 8 h, these cell types also demonstrated altered morphology and marked inhibition of proliferation as evidenced by 3H-thymidine labeling. Thus, the TGF beta 1-stimulated accumulation of these cell types was the result of cellular chemotaxis from peripheral areas into the area of TGF beta 1 delivery. Microscopic angiogenesis in the form of capillary sprouts and increased endothelial cell density first became evident at 16 h. By 24 h, capillary cords appeared within the mesenchyme of the CAM, extending towards the point of TGF beta 1 delivery. 3H-thymidine labeling revealed that the growth of these capillary cords was due to endothelial cell proliferation. Finally, perivascular mononuclear inflammation did not become evident until 48 h of treatment, and its presence correlated spatially and temporally with the gross and histological remodelling of newly formed capillary cords into larger blood vessels. In summary, these data suggest that, in the chicken CAM, TGF beta 1 initiates a sequence of cellular responses that results in growth inhibition, cellular accumulation through migration, and microvascular angiogenesis.

Activation of the immune system in the testis

The present concept for the mechanism of prolonged transplant survival in the testis suggests that lymphocyte activation is inhibited locally in this site by testicular products. As the testis produces several immunoregulatory factors, the behaviour of lymphocytes in the testis may depend on the net effect of all these factors on intralymphocytic events. In the present article, the extra- and intracellular events associated with lymphocyte activation are reviewed and the steps of lymphocyte activation which might be subject to interference by testicular factors are identified.

Testicular immunoregulatory factors

The present data indicate that immune cells are regulated locally in the testis by Leydig cells, Sertoli cells and resident testicular macrophages. The effects of these cells are mediated by several peptide factors, including protectin, a group of high molecular weight testicular immunosuppressive factors, and testicular interleukin-1 alpha-like factor. The testicular interleukin-1 alpha-like factor is produced by Sertoli cells and is under hypophyseal control. Its synthesis starts at puberty concomitantly with the onset of spermatogenesis and it may act as a spermatogonial growth factor. Protectin, which is under hypophyseal control, may be involved in the mechanism of prolonged transplant survival in the testicular interstitial tissue. Its levels increase at puberty. Both the testicular interleukin-1 alpha-like activity and protectin may be important in testicular pathophysiology.

Structure and expression of germline epsilon transcripts in human B cells induced by interleukin 4 to switch to IgE production

Interleukin 4 (IL-4)-induced IgE production coincides with the appearance of the 2.2-kb productive epsilon-mRNA, but is preceded by synthesis of a 1.7-kb epsilon-RNA. Analysis of cDNA copies of the 5' end of this RNA indicated that the 1.7-kb epsilon-RNA is a germline epsilon immunoglobulin heavy chain transcript with an exon mapping 5' to the switch region. Transcription through switch regions has been implicated in the control of class switching. However, IL-4 or cloned CD4+ T cells were able to induce germline epsilon transcripts without inducing IgE synthesis, for which both signals were required. These results indicate that induction of human germline epsilon-RNA does not necessarily result in IgE synthesis, and that additional regulatory mechanisms are involved in class switching.

Low levels of interleukin-4 and high levels of transforming growth factor beta in rheumatoid synovitis

Since interleukin-4 (IL-4) displays agonistic effects on both T and B cells, we studied whether this lymphokine is involved in rheumatoid synovitis, a disease characterized by intense T cell infiltration and B cell stimulation. Rheumatoid arthritis synovial fluids (RA SF) contained no (less than 15 pg/ml) or very low amounts (less than 25 pg/ml) of IL-4, as measured by a sensitive and specific enzyme-linked immunosorbent assay. No IL-4 was produced by unstimulated rheumatoid synovial membrane. RA SF were found to inhibit phorbol myristate acetate (PMA)-dependent proliferation of normal peripheral blood lymphocytes (PBL). An inhibitory fraction with an apparent molecular weight of 150 kd was isolated by gel filtration. The inhibitory fraction strongly blocked the proliferation of PBL induced by PMA, PMA + IL-2, or PMA + IL-4. However, this fraction was less effective in blocking the proliferation of PBL induced by PMA + IL-2 + IL-4. High levels of transforming growth factor beta (TGF beta) were found in these RA SF, and an anti-TGF beta antibody was able to partially reduce the inhibitory activity. RA SF were found to inhibit phytohemagglutinin-induced IL-4 production by PBL. These data indicate that IL-4, similar to other T cell lymphokines, cannot be detected in RA SF and that RA SF contains an inhibitory activity, related in part to TGF beta, which blocks mitogen-induced proliferation of PBL, at least in part through an inhibition of T cell-derived lymphokine release.

Susceptibility and resistance of human autoimmune T cell activation to the immunoregulatory effects of transforming growth factor (TGF) beta 1, beta 2, and beta 1.2

The transforming growth factors type beta (TGF-beta) regulate immune responses by suppressing a variety of leukocyte functions. Using a panel of human autoimmune T cell lines specific for the acetylcholine receptor (AchR) we investigated the immunoregulatory effects of TGF-beta 1, TGF-beta 2, and TGF-beta 1.2. The cytokines have identical effects inhibiting activation of most T line cells and the activation-dependent changes in interleukin-2 (IL-2) receptor and T cell receptor expression. IL-2-dependent growth was not modulated by TGF-beta. However, autoimmune T cell lines specific for AchR differ in their susceptibility to TGF-beta and some are completely refractory. Resistance of autoimmune T cell activation to immunosuppressive cytokines might be an element in the development of chronic autoimmune disease.

Transforming growth factor-beta 1 (TGF-beta 1) is a bifunctional immune regulator for mucosal IgA responses

Porcine transforming growth factor-beta 1 (TGF-beta 1) exerts a unique bifunctional immunoregulatory effect on IgA responses in murine mesenteric and Peyer's patches lymphocyte cultures. TGF-beta 1 is a potent costimulator of LPS-induced IgA responses. The enhancement was observed at TGF-beta 1 at 0.1 to 10 ng/ml in both early and late phases of IgA responses from Day 5 to Day 14 in cultures. On the contrary, TGF-beta 1 exerts a profound immunosuppressive effect on IL-5-induced IgA synthesis. TGF-beta 1 is a natural cytokine produced by intestinal epithelial cells and may account for the polyclonal production and secretion of IgA at the mucosal surface and ensure the integrity of the primary host defense by mucosa-associated lymphoid tissues (MALT).

Transactivation of the transforming growth factor beta 1 (TGF-beta 1) gene by human T lymphotropic virus type 1 tax: a potential mechanism for the increased production of TGF-beta 1 in adult T cell leukemia

We examined the effect of the human T lymphotropic virus type 1 (HTLV-I) Tax gene product on the human transforming growth factor beta 1 (TGF-beta 1) promoter. Transfection of deleted constructs of the TGF-beta 1 promoter revealed regions homologous with AP-1 binding sites that were required for Tax-induced transactivation of the TGF-beta 1 promoter. In addition, we examined the expression and secretion of TGF-beta in fresh leukemic cells isolated from patients with adult T cell leukemia (ATL) and in HTLV-1-infected T cell lines. We report that fresh leukemic cells from ATL patients constitutively produce high levels of TGF-beta 1 mRNA and secrete TGF-beta 1 but not TGF-beta 2 into the culture medium. In addition, long-term ATL cell lines expressed significant amounts of TGF-beta 1 mRNA as well as detectable levels of TGF-beta 1 protein. These results suggest a role for Tax in the upregulation of TGF-beta 1 in HTLV-I-infected cells.

Transforming growth factor-beta 1 modulates the effect of 1 alpha, 25-dihydroxyvitamin D3 on leukemic cells

The human leukemic cells HL-60, U937, KG-1 and THP-1 incubated with transforming growth factor-beta 1 (TGF-beta 1) were studied by examining cell surface antigens and macrophage-specific activities. The addition of 0.5 ng/ml (20 pM) of TGF-beta 1 with 1 alpha, 25-dihydroxyvitamin D3 [1 alpha, 25(OH)2D3] induced more Leu-M3 (CD14)-positive cells (approximately 80%) than 5 X 10(-8) M 1 alpha, 25(OH)2D3 alone did (30 to 50%), although original HL-60 cells did not express any Leu-M3 antigen at all. Tumor necrosis factor-alpha (TNF-alpha) with TGF-beta 1 and 1 alpha, 25(OH)2D3 was found to potentiate the expression of these surface antigens. Furthermore, the phagocytic activity was also induced strongly. The expression of CR3 (CD11b) antigen was also increased, and all Leu-M3-positive cells were found CR3-positive when HL-60, U937, and THP-1 cells were treated with these stimulants. In contrast, CR3 but not Leu-M3 was induced in KG-1 cells after the same treatment. This may indicate that the responsiveness of leukemic cells to TGF-beta 1 and 1 alpha, 25(OH)2D3 might vary depending on a differentiation stage of the target cells. Furthermore, K562 cells originated from a more undifferentiated precursor, were not able to respond to these two inducers. These results suggested that some of TGF-beta superfamily proteins might represent potent modulators in hematopoiesis, especially in the development of monocytes-macrophages or their precursors.

The transforming growth factor-betas. A new family of immunoregulatory molecules

Within the past three years there has been a rapid expansion in our knowledge of the role TGF-beta mediates in regulating immune responses in vitro. Whether the TGF-beta will be clinically useful to suppress immune responses to transplanted organs or autoimmune responses is unknown. However, now that highly purified quantities of TGF-beta are available through recombinant DNA technologies, questions concerning the in vivo immunosuppressive activities of TGF-beta can be answered.

Differential effects of transforming growth factor-beta and epidermal growth factor on the cell cycle of cultured rabbit articular chondrocytes

We examined the effect of transforming growth factor (TGF-beta) on the proliferative rate and cell cycle of cultured rabbit articular chondrocytes using cell counting, cytofluorometry, and [3H]-thymidine incorporation. In the presence of 2% or 10% FCS (fetal calf serum), TGF-beta at 0.01, 0.1, 1, and 10 ng/ml had an inhibitory effect on cell proliferation after 24 h exposure with a dose dependence only for 2% FCS. Flow cytometric analysis of cell DNA content at that time showed that a high proportion of cells were arrested in late S-phase (SQ or G2Q) in either 2% or 10% FCS-containing medium. In both cases, a disappearance of the cell blockage occurred between 24 and 48 h after TGF-beta addition. However, whereas a stimulation of cell proliferation rate was observed at that time in cultures containing 10% FCS, a dose-dependence inhibition of cell growth was detected, in contrast, for 2% FCS-treated cells. Presence of TGF-beta during the last 24 h was not necessary to release the arrested cells. Furthermore, platelet-poor plasma at 10% produced the same effects as FCS, suggesting that platelet-derived factors, such as platelet-derived growth factor (PDGF), could not be responsible for the release of blocked cells in this case. We compared the effect of TGF-beta to that of epidermal growth factor (EGF), used at an optimal concentration (10 ng/ml). In both slowly growing (2% FCS) and proliferating chondrocytes (10% FCS), EGF caused a significant increase of cell proliferation as early as 24 h. No arrest in late S-phase but an augmentation of the percentage of cells in S- and G2M-phases were observed. When combined, TGF-beta and EGF did not induce synergistic effect on the chondrocyte proliferation, as estimated by cell counting. [3H]-thymidine labeling showed that the factors induced identical maxima of incorporation but the peak occurred earlier for TGF-beta than for EGF (approximately 6 h versus 12 h, respectively). Although both factors induce similar cell-number increases at 48 h in 10% FCS-containing medium, these proliferative effects were due to different actions on the cell cycle. The present study indicates that TGF-beta induces first a recruitment of chondrocytes in noncycling SQ- or G2Q-blocked cells. The, the release of these cells may produce either apparent stimulation of cell proliferation if sufficient levels of an unknown serum factor are present (10% FCS) or an inhibition of growth rate when only reduced amounts of this factor are available (2% FCS).(ABSTRACT TRUNCATED AT 400 WORDS)

Cellular mechanisms of TGF-beta action

Transforming growth factor beta (TGF-beta), initially identified in platelet extracts by virtue of its ability to confer anchorage-independent growth and a neoplastic phenotype on mesenchymal cells, has subsequently been identified as a potent inhibitor of proliferation in most cells of epithelial origin. Our laboratory has investigated the role of specific second messengers in mediating the transcriptional responses of fibroblasts following addition of TGF-beta 1. Our studies indicate that TGF-beta 1, alone and in conjunction with epidermal growth factor (EGF), is capable of stimulating increases in both phosphoinositide metabolism and calcium influx, leading to significant increases in intracellular levels of Ca++ and inositol trisphosphate (IP3). Our data indicated that Ca++ influx and inositol phosphate release are coupled in Rat-1 cells, and suggested that influx of Ca++ from the extracellular medium is required for the change in IP3 accumulation observed in response to both EGF and TGF-beta 1. Using nuclear run-on analysis of the transcription of rat transin, a secreted metalloproteinase homologous to human stromelysin, we have also demonstrated a significant inhibition of transin transcription within 10 min of TGF-beta 1 treatment. The ability of TGF-beta 1 to inhibit transin gene transcription was not related to the TGF-beta 1-induced influx of Ca++ or to an increase in intracellular inositol phosphates, since inhibiting production of these second messengers failed to inhibit repression of the transin gene.

Immunohistochemical evidence of a role for transforming growth factor beta in the pathogenesis of nodular sclerosing Hodgkin's disease

Transforming growth factor beta (TFG-beta) is a multifunctional growth factor that promotes the growth of fibroblasts, collagen synthesis and angiogenesis, and stimulates monocyte migration and activation, but suppresses the growth and differentiation of immune lymphocytes and killer cells. Previously we demonstrated biologic activity for TGF-beta in supernatants of fresh Hodgkin's disease (HD) cell cultures and the cell line L428 derived from nodular sclerosing HD. This study was undertaken to find evidence of TGF-beta activity directly in tissues affected by HD. Formalin-fixed tissue from 14 patients with HD, including 8 nodular sclerosis, 4 mixed cellularity, 1 lymphocyte predominance, and 1 lymphocyte depletion type were studied by immunoperoxidase technique with antibody CC (1-30) raised against a synthetic polypeptide with the same N-terminal amino acid sequence as TGF-beta 1. Transforming growth factor beta activity was demonstrated in six cases of nodular sclerosis but not in other histologic types of HD. Staining for TGF-beta was found in the cytoplasm of Reed-Sternberg (RS) cells in one case and on the surface of RS cells and their lacunar variants in five cases. Transforming growth factor beta activity associated with the extracellular matrix was localized mainly around blood vessels, zones of necrosis, at the margins of bands of collagen sclerosis, and in areas containing syncytia of RS cells. In two cases TGF-beta was associated with collections of epithelioid histiocytes or granulomas. Small lymphocytes, granulocytes, and germinal center cells were unreactive. These results suggest that TGF-beta is a growth factor of biologic importance in HD and may be responsible for many of the histologic features, such as nodular sclerosis and granulomas, that may have prognostic significance.

Transforming growth factor-beta and the initiation of chondrogenesis and osteogenesis in the rat femur

We have investigated the ability of exogenous transforming growth factor-beta (TGF-beta) to induce osteogenesis and chondrogenesis, critical events in both bone formation and fracture healing. Daily injections of TGF-beta 1 or 2 into the subperiosteal region of newborn rat femurs resulted in localized intramembranous bone formation and chondrogenesis. After cessation of the injections, endochondral ossification occurred, resulting in replacement of cartilage with bone. Gene expression of type II collagen and immunolocalization of types I and II collagen were detected within the TGF-beta-induced cartilage and bone. Moreover, injection of TGF-beta 2 stimulated synthesis of TGF-beta 1 in chondrocytes and osteoblasts within the newly induced bone and cartilage, suggesting positive autoregulation of TGF-beta. TGF-beta 2 was more active in vivo than TGF-beta 1, stimulating formation of a mass that was on the average 375% larger at a comparable dose (p less than 0.001). With either TGF-beta isoform, the dose of the growth factor determined which type of tissue formed, so that the ratio of cartilage formation to intramembranous bone formation decreased as the dose was lowered. For TGF-beta 1, reducing the daily dose from 200 to 20 ng decreased the cartilage/intramembranous bone formation ratio from 3.57 to zero (p less than 0.001). With TGF-beta 2, the same dose change decreased the ratio from 3.71 to 0.28 (p less than 0.001). These data demonstrate that mesenchymal precursor cells in the periosteum are stimulated by TGF-beta to proliferate and differentiate, as occurs in embryologic bone formation and early fracture healing.

Transforming growth factor beta induces the production of interleukin 6 by human peripheral blood mononuclear cells

Previous studies have indicated that the cytokine transforming growth factor beta 1 (TGF beta 1) has immunosuppressive properties and can inhibit the production of tumor necrosis factor (TNF) and Interleukin 1 (IL 1) by human peripheral blood mononuclear cells. In this study, we have examined the effects of TGF beta 1 on the production of Interleukin 6 (IL 6) by human peripheral blood mononuclear cells. Treatment with only TGF beta 1 leads to the induction of IL 6, and this was both dose- and time-dependent. The effect of TGF beta 1 was evident at the level of IL 6 mRNA, suggesting TGF beta 1-induced de novo synthesis of IL 6. Induction of IL 6 by TGF beta 1 was specific, as other cytokines made by mononuclear cells (TNF and IL 1) were not induced by TGF beta 1. Furthermore, when a panel of stimuli were compared for their ability to induce IL 1, TNF and IL 6 in the presence or absence of TGF beta 1, IL 6 levels were augmented in the presence of TGF beta 1, while the induction of IL 1 and TNF was inhibited significantly. These results indicate that TGF beta 1 has complex effects on the production of cytokines by peripheral blood mononuclear cells and that TGF beta 1 is not inhibitory for all cytokine production. The ability of TGF beta 1 to induce IL 6 suggests that IL 6 may mediate some of the effects of TGF beta 1.

Secretion and binding of transforming growth factor beta by scleroderma and normal dermal fibroblasts

The production and binding of transforming growth factor beta (TGF beta) were compared in dermal fibroblast lines derived from scleroderma patients and normal control donors. The mean +/- SEM 24-hour level of secretion of TGF beta by fibroblast lines derived from the involved skin of scleroderma patients was 30.8 +/- 5.5 pmoles/10(6) cells, and it was 29.7 +/- 5.8 pmoles/10(6) cells for fibroblast lines derived from the normal skin of the healthy donors. Thus, we found that the fibroblasts themselves produced TGF beta. TGF beta production was equivalent in fibroblast lines derived from clinically involved and uninvolved skin of scleroderma patients. The mean +/- SEM number of TGF beta receptors per cell on scleroderma fibroblasts was 9,736 +/- 1,375, with a mean +/- SEM Kd of 25.2 +/- 3.9 pM. This value was similar in control fibroblasts, at 12,431 +/- 2,425 TGF beta receptors per cell, with a mean +/- SEM Kd of 27.1 +/- 5.2 pM.

Molecular characterization of germ-line immunoglobulin A transcripts produced during transforming growth factor type beta-induced isotype switching

The addition of transforming growth factor type beta to lipopolysaccharide-stimulated murine B-cell cultures enhances isotype switching to IgA and induces the appearance of two sizes of alpha mRNA transcripts. One of these is the same size as mRNA for secreted IgA but the other, which is 300-400 base pairs (bp) shorter, does not correlate in size with any form of productive alpha mRNA. Both sizes of transcript were shown to contain germ-line sequences 5' to the alpha switch region, suggesting that the longer transcripts included both germ-line and productive forms of alpha mRNA, whereas the shorter transcripts were only germ-line alpha mRNA. We isolated cDNA clones corresponding to the shorter, 1.3-kilobase (kb), transcript by using an anchored polymerase chain reaction and a specific primer for the constant region. Analyses of these cDNA clones show that the short transcript consists of a 126-bp exon located approximately 1.5 kb 5' to the alpha switch region spliced to the first exon of the alpha constant region locus. Furthermore, a minor fraction of the longer, approximately 1.7 kb, transcripts also contains this exon. These results demonstrate that transforming growth factor type beta-mediated isotype switching to IgA is preceded by transcriptional activation of the heavy-chain locus.

Transforming growth factors type beta 1 and beta 2 suppress rat astrocyte autoantigen presentation and antagonize hyperinduction of class II major histocompatibility complex antigen expression by interferon-gamma and tumor necrosis factor-alpha

The transforming growth factors (TGF) type beta 1 and beta 2 are regulatory cytokines strongly affecting rat astrocyte immune functions. Both cytokines suppressed presentation of autoantigen by astrocytes: highly encephalitogenic T cells cocultured with TGF-beta-treated astrocytes in the presence of myelin basic protein did not become activated to transfer experimental allergic encephalomyelitis, a central nervous system (CNS) autoimmune disease. Furthermore, TGF-beta 1 and -beta 2 antagonized hyperinduction of astrocyte major histocompatibility complex (MHC) class II antigen expression by interferon-gamma and tumor necrosis factor-alpha. Thus, TGF-beta might be a potential regulator of CNS inflammation.

Regulation of interleukin-2 and interleukin-6 production from T-cells: involvement of interleukin-1 beta and transforming growth factor-beta

The effect of recombinant (r) interleukin-1 beta (rIL-1 beta) and transforming growth factor-beta (TGF-beta) on the production of interleukin-2 (IL-2) and interleukin-6 (IL-6) from an antigen-specific (LBRM-33-1A5) and an antigen-nonspecific (EL-4-NOB-1) T-cell line was investigated. rIL-1 beta induced the production of IL-2 and IL-6 from EL-4-NOB-1 cells in a dose-related manner. The LBRM-33-1A5 cells required phytohemagglutinin (PHA) in addition to rIL-1 beta in order to produce IL-2 and IL-6. IL-2 production was found to precede IL-6 production in both cell lines. No IL-2 or IL-6 production was observed by adding r murine tumor necrosis factor-alpha or r murine interferon gamma to the cells. The presence of 1 ng/ml TGF-beta reduced IL-2 and IL-6 production from both T-cell lines by more than 80%. The inhibition of IL-2 and IL-6 production was still evident by a concentration as low as 10 pg/ml of TGF-beta. rIL-1 beta and PHA also stimulated murine thymocytes to produce IL-6 which was inhibited up to 85% in the presence of 1 ng/ml TGF-beta. Taken together these results suggest that TGF-beta may suppress immune responses by inhibiting the endogenous production of IL-2 and IL-6.

Exogenous transforming growth factor-beta 2 enhances connective tissue formation and wound strength in guinea pig dermal wounds healing by secondary intent

The presence of transforming growth factor-beta (TGF-beta) at the site of acute injury, its ability to attract inflammatory and connective tissue cells, and its stimulatory effect on the deposition of connective tissue matrix combine to suggest that it may play a key role in the response to injury. The effect of exogenous TGF-beta form 2 on dermal wounds healing by secondary intent was investigated using a sponge composed of collagen and heparin as a delivery vehicle. Longitudinal lenticular-shaped wounds on the dorsum of adult guinea pigs were treated at the time of wounding with delivery vehicle containing 0.5, 1, or 5 micrograms of purified, bovine bone-derived TGF-beta 2, and were compared with wounds that received vehicle only or were untreated. At days 8 and 14 the amount of connective tissue in the wounds and the extent of epithelialization were determined by histomorphometric methods, and wound breaking strength was determined. At day 8, but not at day 14, wounds treated with 1 or 5 micrograms of TGF-beta 2 contained a significantly higher proportion of connective tissue than did wounds treated with vehicle only, and they also exhibited higher wound strength. No effect on wound size or re-epithelialization was detected. The observations provide evidence that a single treatment with exogenous TGF-beta 2 delivered in collagen/heparin sponge vehicle can accelerate repair in guinea pig dermal wounds allowed to heal by secondary intent.

Progressive interstitial collagen deposition in Coxsackievirus B3-induced murine myocarditis

Myocardial fibrosis can be produced in certain inbred strains of mice after coxsackievirus B subtype 3 (CVB3) infection. The mechanism responsible for this interstitial matrix alteration is unknown. The presumption is that fibrosis occurs in areas of myocyte damage and inflammation associated with viral infection, analogous to scar formation after cell injury in other organ systems. To test this hypothesis, we examined the hearts of A/J strain mice infected with three CVB3 variants (Crowell [CVB3-CR], Woodruff [CVB3-WD], and Lerner [CVB3-LR]), each known to cause different degrees of acute myocardial injury. With these three variants, virus was present in the heart until day 28 after inoculation but was absent thereafter. Fourteen days after inoculation, inflammation with myocyte necrosis was seen in discrete foci throughout the myocardium with all three variants. Collapse and disorganization of the usually delicate connective tissue matrix identifiable by silver impregnation was seen in these areas of myocyte injury. Persistent, diffuse lymphocytic infiltration of the myocardium was seen 55 days after inoculation with CVB3-WD and CVB3-LR, but hearts initially infected with CVB3-CR showed only rare interstitial lymphocytes comparable to uninfected control hearts. The focal scars produced by myocyte necrosis 14 days after inoculation were accentuated and heavily collagenized 55 days after inoculation with CVB3-WD and CVB3-LR; however, these foci were indistinct 55 days after inoculation with CVB3-CR. Furthermore, the usually delicate network of interstitial collagen fibers surrounding individual myocytes became thickened throughout the heart 55 days after inoculation with CVB3-WD and CVB3-LR, away from visibly scarred areas produced early after infection with these variants. This diffuse reticulin thickening was not seen after infection with the Crowell variant. Only the virus variants associated with persistent interstitial inflammation at day 55 developed major collagen matrix alterations and interstitial fibrosis. We conclude that this persistent interstitial lymphocytic infiltration reflects altered immune function related to specific virus variants in this animal strain. We postulate that these lymphocytes are part of a delayed immunopathogenic response uncoupled from the original viral injury and inflammatory damage. Potential mechanisms by which this interstitial lymphocytic infiltration results in fibrosis are discussed.

Evaluation of transforming growth factor beta and type I procollagen gene expression in fibrotic skin diseases by in situ hybridization

Full thickness biopsies of affected skin and fascia from one patient with diffuse fasciitis and eosinophilia (DF), two patients with generalized morphea (GM), and five patients with progressive systemic sclerosis (PSS) of recent onset were examined for the expression of transforming growth factor beta 1 (TGF beta 1) and type I procollagen genes by in situ hybridization with human sequence-specific cDNA. An increased number of fibroblasts showing clearly detectable expression of pro alpha 1(I)collagen gene was found in all fibrotic lesions when compared with unaffected skin from the patient with DF and skin from two normal individuals examined in parallel. Expression of the TGF beta 1 gene was noted in a fibroblast subpopulation of the affected tissues from the patients with DF and GM. In contrast, the TGF beta 1 gene was not expressed at a detectable level in affected skin from the five patients with PSS. The results suggest that TGF beta 1 may play a role in the development of skin fibrosis in cases of DF and GM. However, from these studies, we cannot implicate TGF beta 1 in the pathogenesis of skin fibrosis in PSS.

Interleukin 2 (IL 2) inhibitor in rheumatoid synovial fluid: correlation with prognosis and soluble IL 2 receptor levels

A soluble activity inhibiting over 50% of the CTLL-2 cell line response to recombinant human interleukin 2 (IL 2) was found in 17 of 29 (59%) rheumatoid synovial fluids. To study the prognosis value of this activity, 16 rheumatoid synovial fluids were collected before a radiation synovectomy of the knee with 7 mCi of 90Yt. Patients with a good clinical result after the synovectomy had a lower IL 2 inhibitory activity than those with a bad or incomplete result (P less than 0.01). Levels of inhibitory activity and of soluble IL 2 receptors were correlated with each other and with the response of the synovitis to the radiation synovectomy. These results extend the clinical usefulness of soluble IL 2 receptor measurements and indicate a correlation between the immune activation of the rheumatoid synovitis and its clinical activity.

Transforming growth factors and the regulation of cell proliferation

The number of different growth regulatory molecules which have been isolated and characterized is continuing to increase. As more information is obtained, it has become apparent that the cooperative actions of many factors with distinct activities is necessary for appropriate proliferative responses. An interplay of both growth stimulatory and growth inhibitory factors is essential for normal growth. Of crucial importance, therefore, is the appropriate regulation of growth factors. Unregulated expression, synthesis, posttranslational processing or activation of either positive or negative growth signals may contribute to neoplastic transformation (Fig. 3). Altered responses to normally positive or negative signals by transformed cells have been demonstrated by several investigators [64, 79, 84]. While altered growth factor responses in transformed cells are well documented, the mechanisms responsible for the loss of growth control are poorly understood and are likely to be both complex and numerous. Continued efforts to dissect and comprehend fully growth factor action on normal cells will be necessary before an understanding of neoplastic transformation can be achieved.

Parathyroid hormone-related protein is a possible autocrine growth inhibitor for lymphocytes

Adult T-cell leukemia (ATL)-related cells have the ability to produce a newly-isolated calcium-regulating protein, parathyroid hormone-related protein (PTHrP). The present study revealed that lectin-stimulated normal lymphocytes produce immunoreactive (IR)-PTHrP. When the T-cell-enriched fraction was purified from normal lymphocytes and then treated with lectin, a similar amount of IR-PTHrP was detected, suggesting that IR-PTHrP is an actual product of T-lymphocytes. A biologically active fragment of PTHrP, PTHrP(1-34), suppressed DNA synthesis in lectin-stimulated lymphocytes at concentrations greater than 50 pg/mL; the same concentration range of IR-PTHrP detected in the cultured media of lectin-stimulated lymphocytes. Therefore, it is reasonable to postulate that PTHrP is a cytokine inhibiting the cellular growth of normal lymphocytes.

Response of bone marrow stromal cells to adipogenic antagonists

Adipocytes constitute a major part of the bone marrow stroma in vivo and may play an active role in lymphohematopoiesis. Earlier studies had shown that the bone marrow stromal cell clone BMS2 was capable of adipocyte differentiation in vitro, in addition to its well-defined ability to support B lymphopoiesis. We now demonstrate that the process of adipogenesis in this functional bone marrow stromal cell clone can be inhibited by the cytokines interleukin-1 alpha, tumor necrosis factor, and transforming growth factor beta. Exposure of preadipocyte BMS2 cells to these agents blocked the induction of adipocyte differentiation as assessed by morphologic criteria and analysis of the neutral lipid content. Both interleukin-1 alpha and tumor necrosis factor elicited a rapid transient elevation in the steady-state mRNA levels of c-fos, c-jun, and JE. When added to differentiated adipocytes, the three cytokines continued to act as adipogenic antagonists. This was indicated by concentration- and time-dependent decreases in the activity of an adipocyte-specific enzyme, lipoprotein lipase. These changes in enzyme activity correlated directly with a decrease in steady-state levels of lipoprotein lipase mRNA. Another RNA marker of adipocyte differentiation (adipsin) was less influenced by the adipogenic antagonists. This may reflect the longer half-life of this mRNA transcript compared with those of lipoprotein lipase. Our results dramatically demonstrate that the differentiation state of bone marrow stromal cells can be modulated by exogenous factors in vitro. It is also the first report that transformation growth factor beta regulates the activity of lipoprotein lipase. These data suggest potential physiologic actions for these cytokines in vivo within the overall context of lymphohematopoiesis.

A highly immunogenic tumor transfected with a murine transforming growth factor type beta 1 cDNA escapes immune surveillance

A highly immunogenic C3H-derived UV-induced tumor was cotransfected with a murine transforming growth factor type beta 1 (TGF-beta 1) cDNA and a neomycin-resistance gene. Stable clones were isolated and used in vitro and in vivo to determine the effects of endogenously produced TGF-beta on cytolytic T-lymphocyte (CTL) responses. Tumor cells producing TGF-beta, though retaining expression for class I major histocompatibility complex molecules and the tumor-specific antigen, did not stimulate primary CTL responses in vitro and were not effective in vivo for directly stimulating primary CTL or in priming for CTL responses. Furthermore, TGF-beta-producing tumors grew progressively in transiently immunosuppressed mice without losing the tumor antigen; thus, TGF-beta produced by tumors may promote escape from immune surveillance.

The down-regulation of the mitogenic fibrinogen receptor (MFR) in serum-containing medium does not occur in defined medium

Normal human hemopoietic cells such as early bone marrow progenitors, or lymphoma-derived cell lines such as Raji or JM cells, possess a low-affinity receptor specific for fibrinogen. This receptor triggers a mitogenic effect. It differs from the glycoprotein IIb-IIIa which is involved in fibrinogen-induced platelet aggregation. We demonstrate here that this mitogenic fibrinogen receptor (MFR) can be internalized or reexpressed, depending on culture conditions. Internalization was temperature-dependent. At 37 degrees C in the presence of cycloheximide or actinomycin D, the half-life of cell surface MFRs was 2 h, independent of receptor occupancy. Binding of fibrinogen to the MFR resulted in a down-regulation which was fibrinogen dose-dependent. This occurred in serum-supplemented medium but not in defined medium supplemented with fatty acids. Reexpression of MFRs could be induced in 28 to 42 h by serum removal. The down-regulation of mitogenic receptors in plasma or serum could explain why normal cells do not proliferate in the peripheral blood.