Expression of matrix metalloproteinases and tissue inhibitors of metalloproteinases in the mouse uterus during the peri-implantation period

In this study the SEB-activated LAK cytotoxicity was identified and characterized in human peripheral blood lymphocytes (PBMC). After 3 days of SEB stimulation, the PBMC acquired a cytotoxicity against traditional LAK targets, K-562 and Daudi, beside that human glomerular endothelial cells (HGEC) were effectively lysed. The magnetic separation of SEB-stimulated CD5+ T cells revealed that the dominant LAK cytotoxicity remained in the CD5- lymphocyte fraction. The major part of the SEB-generated cytotoxicity of CD5- cells could be blocked with specific antibodies to IL-2 and IFN-gamma. The IFN-gamma pretreatment of HGEC reduced the target sensitivity, but because of the upregulation of MHC class II on HGEC surface, these cells were able to present SEB to CD5+ cells. These results suggested that in bacterial superantigen-mediated infection, the non-T (NK cells-derived) LAK cells might have a primary pathogenic role, and the adverse effect of IFN-gamma, that was massively secreted from superantigen-stimulated cells, requires greater consideration.     

Staphylococcal enterotoxin B-activated T cells can be redirected to inhibit multicycle virus replication

Cell-mediated immunity is a crucial part of recovery from virus infections. Adoptive transfer of T cells into infected animals is restricted by the need for Ag-specific and MHC-restricted T cells. One way to overcome these limitations is to use bifunctional Abs to redirect the T cells against virus-infected cells. We have demonstrated that bifunctional Abs can inhibit virus replication in the presence of activated T cells. To generate a large number of activated T cells in a short time, we tested the ability of the superantigen, staphylococcal enterotoxin B (SEB), to activate T cells. We demonstrate that SEB-activated T cells are effective killers when bridged to Fc receptor-bearing target cells using anti-CD3 Abs. SEB T cells can lyse virus-infected target cells in the presence of HHA6, a bifunctional Ab specific for the V beta 8 TCR product and the H1 hemagglutinin of influenza A/PR/8/34 virus. In addition, bifunctional Ab and SEB T cells can inhibit multicycle virus replication in vitro. In a conventional 4-h chromium release assay, SEB-activated CD8 T cells are efficient killers, whereas CD4 T cells are not. Yet both subpopulations have the ability to inhibit multicycle replication in vitro. Superantigens may represent a potent method for generation of effector cells for use in redirected immunotherapy protocols.     

In vitro prevention and reversal of lipopolysaccharide desensitization by IFN-gamma, IL-12, and granulocyte-macrophage colony-stimulating factor

LPS tolerance is characterized by a diminished monocytic synthesis of TNF-alpha and, interestingly, IL-10 after LPS restimulation. We wondered whether granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-12, and IFN-gamma can prevent or reverse this down-regulation of TNF-alpha and IL-10 production. The LPS-induced TNF-alpha amounts in desensitized PBMC treated with GM-CSF, IFN-gamma, or IL-12 and in naive, non-cytokine-primed cultures were similar, while much more TNF-alpha was induced in cytokine-primed naive cells. The effect of IL-12 was dependent on the presence of nonmonocytic cells and could be completely blocked with an IFN-gamma antiserum. Treatment of LPS-desensitized pure monocytes with IFN-gamma or GM-CSF resulted in a very high TNF-alpha expression and no difference to cytokine-primed naive monocytes was evident any longer. While IFN-gamma and IL-12 decreased IL-10 expression in naive PBMC, it was increased by both and by GM-CSF in LPS-tolerant cultures. Again, only IL-12 was dependent on the presence of nonmonocytic cells. For prevention of LPS tolerance, similar results were obtained. Recently, we have shown that IL-10 and TGF-beta mediate LPS desensitization in vitro and can be used to establish LPS hyporesponsiveness in the absence of LPS. IFN-gamma and GM-CSF prevented and reversed down-regulation of TNF-alpha and IL-10 synthesis also in the model of IL-10/TGF-beta1-induced LPS hyporesponsiveness, while IL-12 was ineffective because of its obvious inability to induce IFN-gamma. In summary, after LPS desensitization/hyporesponsiveness, IFN-gamma and GM-CSF tended to normalize pro- and anti-inflammatory monocytic behavior. Our results suggest that during LPS desensitization/hyporesponsiveness, monocytes acquire a hitherto unknown functional state with an altered reaction to biologic response modifiers.     

Role of transforming growth factor-beta in the preferential induction of T helper cells of type 1 by staphylococcal enterotoxin B

Stimulation of murine CD4+ T cells with staphylococcal enterotoxin B (SEB) results in the preferential development of T helper (Th) 1 cells [i.e. high interferon (IFN)-gamma and low interleukin (IL)-4, IL-5 and IL-10]; whereas in response to plate-bound anti-CD3 or anti-T cell receptor-alpha beta, Th1 as well as Th2 cells develop. In the present study, we examined the mechanism which is responsible for the selective Th1 development in the SEB system. The addition of IL-4 resulted in a strong development of Th2 cells showing that SEB stimulation can result in Th2 differentiation. Co-stimulation with anti-CD28 was insufficient in this regard. Lack of Th2 development in the SEB system was in part due to the inhibitory effect of endogenously produced transforming growth factor-beta (TGF-beta), because anti-TGF-beta allowed the development of Th2 cells. Similarly, TGF-beta inhibited Th2 development and stimulated Th1 development in the anti-CD3 system. This shift was only partially prevented by also including IL-4 in the cultures. The effects of TGF-beta could only partially be explained by stimulation of IFN-gamma or inhibition of IL-4 as intermediatory cytokines: (1) TGF-beta stimulated Th1 development even in the presence of anti-IL-4 and anti-IFN-gamma, and (2) a strong inhibitory effect of anti-TGF-beta on Th1 development was still observed when anti-IL-4 and IFN-gamma were simultaneously added to the cultures. It is concluded that SEB favors Th1 development by stimulation of TGF-beta production. Inhibition of Th2 development by TGF-beta is due, in part, to inhibition of IL-4 and stimulation of IFN-gamma, and, in part, to a direct effect of TGF-beta on the responding T cells.     

The bacterial superantigen Staphylococcal enterotoxin B stimulates lymphocyte locomotor capacity during culture in vitro

The bacterial superantigen Staphylococcal enterotoxin B (SEB) was investigated for its effects on lymphocyte locomotion in vitro. Culture of peripheral blood mononuclear cells (PBMC) for 24-72 hr in SEB (1-100 micrograms/ml) increased the proportion of lymphocytes in locomotor (polarized) morphology and capable of invading collagen gels, to the same extent as the established locomotor activator, anti-CD3 (alpha-CD3), though the conventional antigen, tetanus toxoid was ineffective. The cells responding to SEB were predominantly T cells. SEB had no effect on lymphocyte locomotion in short-term (45 min) assays, thus its effect is to stimulate growth-related locomotor capacity and it does not act as a chemoattractant. During culture of PBMC in SEB, the chemokines interleukin-8 (IL-8) and macrophage chemotactic protein-1 (MCP-1) were released into the culture medium. The presence of anti-IL-8, but not of anti-MCP-1, either during culture or added to SEB culture supernatants and tested in short-term assays, inhibited the development of polarization suggesting that IL-8, which is a lymphocyte chemoattractant, also plays a key role in SEB-induced locomotor activation. Among SEB-activated lymphocytes, CD45RO+CD45RA- lymphocytes showed enhanced locomotor responses, but a relation was not found between locomotor activity and the presence of cell surface CD69.     

Perspective evaluation of the post-graduate courses of the Nursing Department at UFRN (1980-1992)

Superantigens have been used to study peripheral tolerance in CD4+ T cells. The superantigen SEB induces T cell anergy by promoting the differentiation of SEB-activated virgin T cells into anergic memory T cells. Memory T cells from SEB or antigen-primed mice do not proliferate when they are cultured with SEB. The present studies were performed to determine whether memory T cells fail to interact with SEB antigen-presenting cells or whether SEB promotes incomplete or negative signals in memory T cells. When murine virgin and memory T cells were separated on the basis of CD45RB expression and cultured with SEB-pulsed B cells, SEB induced the expression of CD25, which then mediated proliferation when IL-2 was added to the cultures. In addition, SEB promoted the expression of the CD40L, which is required for T helper cell function. Finally, PMA induced a costimulatory signal leading to the proliferation of these cells. Surprisingly, the agents, i.e., IL-2 and PMA, which induced TM cell proliferation in conjunction with SEB failed to induce lymphokine secretion. However, in the presence of IL-4 plus IL-5, the T memory cells induced the SEB-pulsed B cells to secrete IgM and IgG. These results suggest that memory T cells are not simply unresponsive to SEB but are actively anergized.     

Tumor necrosis factor alpha enhances secretion of transforming growth factor beta2 in MCF-7 breast cancer cells

We studied the effect of tumor necrosis factor alpha (TNF-alpha) on transforming growth factor beta (TGF-beta) secretion by human breast cell lines to further characterize the antitumor effects of TNF-alpha. We found that TNF-alpha increased the secretion of TGF-beta in two established breast cancer cell lines (MCF-7 and ZR-75-1) but not in two immortalized human mammary epithelial cell lines (184B5 and MCF-10A). In MCF-7 cells, TNF-alpha increased the secretion of total TGF-beta 6.1-fold within 72 h in a dose-dependent manner. The secretion of both latent and active forms of TGF-beta was increased, and their ratio altered from 25:1 to 12:1 in the medium. TNF-alpha converted the secretory pattern of TGF-beta by MCF-7 cells from the heterodimeric form TGF-beta1.2 to the homodimeric form TGF-beta2. Immunoblot analysis under nonreducing conditions identified four molecular mass species of TGF-beta secreted in the culture media of untreated MCF-7 cells (238, 210, 40-55, and 25 kDa). Under reducing conditions, three molecular mass species of TGF-beta were identified: 88, 44, and 12 kDa. Gel filtration analysis demonstrated that the secreted TGF-beta within the range of 12-88 kDa was biologically active. TNF-alpha treatment did not alter the size of molecular mass species secreted by MCF-7 cells and did not change steady-state levels of mRNA for TGF-beta1 or TGF-beta2. These findings indicate that TNF-alpha may regulate quantitatively and qualitatively TGF-beta secretion by human breast cancer cells in vitro. The diverse biological activities of TGF-beta may also allow TNF-alpha to regulate the growth and metabolism of human mammary epithelial cells and/or stromal cells in a paracrine manner.     

Changes in murine jejunal morphology evoked by the bacterial superantigen Staphylococcus aureus enterotoxin B are mediated by CD4+ T cells

Bacterial superantigens (SAgs) are potent T-cell stimuli that have been implicated in the pathophysiology of autoimmune and inflammatory disease. We used Staphylococcus aureus enterotoxin B (SEB) as a model SAg to assess the effects of SAg exposure on gut form and cellularity. BALB/c, SCID (lacking T cells) and T-cell-reconstituted SCID mice were treated with SEB (5 or 100 microg intraperitoneally), and segments of the mid-jejunum were removed 4, 12, or 48 h later and processed for histochemical or immunocytochemical analysis of gut morphology and major histocompatibility complex class II (MHC II) expression and the enumeration of CD3+ T cells and goblet cells. Control mice received saline only. SEB treatment of BALB/c mice caused a time- and dose-dependent enteropathy that was characterized by reduced villus height, increased crypt depth, and a significant increase in MHC II expression. An increase in the number of CD3+ T cells was observed 48 h after exposure to 100 microg of SEB. Enteric structural alterations were not apparent in SEB-treated SCID mice compared to saline-treated SCID mice. In contrast, SEB challenge of SCID mice reconstituted with a mixed lymphocyte population or purified murine CD4+ T cells resulted in enteric histopathological changes reminiscent of those observed in SEB-treated BALB/c mice. These findings implicate CD4+ T cells in this SEB-induced enteropathy. Our results show that SAg immune activation causes significant changes in jejunal villus-crypt architecture and cellularity that are likely to impact on normal physiological processes. We speculate that the elevated MHC II expression and increased number of T cells could allow for enhanced immune responsiveness to other SAgs or environmental antigens.     

IL-9 production of naive CD4+ T cells depends on IL-2, is synergistically enhanced by a combination of TGF-beta and IL-4, and is inhibited by IFN-gamma

Dense CD4+ T cells isolated from naive mice produce only trace amounts of IL-9 when stimulated by immobilized anti-CD3 in combination with anti-CD28 Abs. In this situation, IL-9 production is significantly stimulated by TGF-beta and further enhanced by the addition of IL-4, which, by itself, has only a minimal influence. IFN-gamma was found to inhibit the enhancing effect of IL-4. However, increasing amounts of IL-4 in the presence of a constant concentration of IFN-gamma could overcome the inhibitory activity of IFN-gamma. The application of CD4+ T cells isolated from IL-2 knockout mice unequivocally revealed that IL-2 is essential for the production of IL-9 by T cells. In addition, the use of T cells from IL-4 knockout mice elucidated that the basic (IL-2 + TGF-beta) mediated IL-9 production is independent of IL-4. Therefore, our results demonstrate that optimal IL-9 production of naive dense CD4+ T cells is positively regulated at different levels: 1) by IL-2, which is essential for IL-9 secretion; 2) followed by TGF-beta, which promotes a considerable increase in IL-9 production above the level induced by IL-2; and 3) finally, by IL-4, which requires the presence of IL-2 and TGF-beta to strongly enhance the production of IL-9. IFN-gamma inhibits the production of IL-9 mainly at the level of IL-4 by neutralizing the effect of this cytokine.     

IFN-gamma production of adult rat astrocytes triggered by TNF-alpha

IFN-gamma plays an important role in modulating inflammatory responses within the CNS. The cell type responsible for IFN-gamma production within the CNS is less well defined. We examined the production and regulation of IFN-gamma by adult rat astrocytes. IFN-gamma was hardly detectable in cultured astrocytes, while addition of TNF-alpha dose-dependently induced IFN-gamma production by astrocytes. No IFN-gamma production by astrocytes could be induced by LPS, IL-10 or TGF-beta 1. TNF-alpha-induced IFN-gamma production by astrocytes was inhibited by treatment of astrocytes with TGF-beta 1, but not IL-10. TNF-alpha induced IFN-gamma production by astrocytes was confirmed by using immunocytochemical staining. The data suggest that astrocyte-derived IFN-gamma induced by TNF-alpha may participate in local immune reactions of the brain in an autocrine and paracrine fashion.     

Neutralizing antibodies to IFN-gamma-inducing factor prevent experimental autoimmune encephalomyelitis

Specific oligonucleotide primers were used to identify and isolate IFN-gamma-inducing factor (IGIF) from the brain of rats with developing experimental autoimmune encephalomyelitis (EAE), a T cell-mediated autoimmune disease of the central nervous system that serves as a model for multiple sclerosis. IGIF was highly transcribed in the brain at the onset and during the course of active EAE. PCR products encoding rat IGIF were used to generate the recombinant protein that was used to induce anti-IGIF neutralizing Abs. These Abs significantly reduced the production of IFN-gamma by primed T cells proliferating in response to their target myelin basic protein epitope and by Con A-activated T cells from naive donors. When administered to rats during the development of either active or transferred EAE, these Abs significantly blocked the development of disease. Splenic T cells from protected rats were cultured with the encephalitogenic myelin basic protein epitope and evaluated for production of IL-4 and IFN-gamma. These cells, which proliferated, exhibited a profound increase in IL-4 production that was accompanied by a significant decrease in IFN-gamma and TNF-alpha production. Thus, we suggest that perturbation of the Th1/Th2 balance toward Th2 cells is the mechanism underlying EAE blockade by anti-IGIF immunotherapy.     

Carbachol stimulates transactivation of epidermal growth factor receptor and mitogen-activated protein kinase in T84 cells. Implications for carbachol-stimulated chloride secretion

We have examined the role of tyrosine phosphorylation in regulation of calcium-dependent chloride secretion across T84 colonic epithelial cells. The calcium-mediated agonist carbachol (CCh, 100 microM) stimulated a time-dependent increase in tyrosine phosphorylation of a range of proteins (with molecular masses ranging up to 180 kDa) in T84 cells. The tyrosine kinase inhibitor, genistein (5 microM), significantly potentiated chloride secretory responses to CCh, indicating a role for CCh-stimulated tyrosine phosphorylation in negative regulation of CCh-stimulated secretory responses. Further studies revealed that CCh stimulated an increase in both phosphorylation and activity of the extracellular signal-regulated kinase (ERK) isoforms of mitogen-activated protein kinase. Chloride secretory responses to CCh were also potentiated by the mitogen-activated protein kinase inhibitor, PD98059 (20 microM). Phosphorylation of ERK in response to CCh was mimicked by the protein kinase C (PKC) activator, phorbol myristate acetate (100 nM), but was not altered by the PKC inhibitor GF 109203X (1 microM). ERK phosphorylation was also induced by epidermal growth factor (EGF) (100 ng/ml). Immunoprecipitation/Western blot studies revealed that CCh stimulated tyrosine phosphorylation of the EGF receptor (EGFr) and increased co-immunoprecipitation of the adapter proteins, Shc and Grb2, with the EGFr. An inhibitor of EGFr phosphorylation, tyrphostin AG1478 (1 microM), reversed CCh-stimulated phosphorylation of both EGFr and ERK. Tyrphostin AG1478 also potentiated chloride secretory responses to CCh. We conclude that CCh activates ERK in T84 cells via a mechanism involving transactivation of the EGFr, and that this pathway constitutes an inhibitory signaling pathway by which chloride secretory responses to CCh may be negatively regulated.     

Increased in vitro induced CD4+ and CD8+ T cell IFN-gamma and CD4+ T cell IL-10 production in stable relapsing multiple sclerosis

Multiple sclerosis (MS) is presumed to be a T-cell mediated chronic inflammatory disease of the central nervous system. Investigators previously demonstrated increased IFN-gamma (pro-inflammatory) and IL-10 (counterregulatory anti-inflammatory) in MS. The balance of pro-inflammatory and counterregulatory anti-inflammatory cytokines may be important in the stabilization of disease activity. Purified CD4+ and CD8+ T cells from patients with clinically definite, stable relapsing MS (RRMS) were stimulated by anti-CD3 mAb or Con A for 48 hours and cytokine supernatants analysed for production of IL-2, IL-6, IFN-gamma, TNF-alpha (potential pro-inflammatory) and IL-4, IL-10, and TGF-beta (potential counterregulatory anti-inflammatory). Con A activated CD4+ and CD8+ T cell proinflammatory cytokine IL-2 secretion, CD4+ T cell IL-6 secretion, CD4+ and CD8+ T cell TNF-alpha secretion and CD8+ T cell IFN-gamma secretion was decreased significantly in RRMS subjects compared to controls. CD3 activated CD4+ and CD8+ T cell IL-6 secretion and CD4+ T cell TNF-alpha secretion was significantly decreased in MS subjects compared to controls. In contrast, there was increased CD3-induced IFN-gamma in both CD4+ and CD8+ T cells and counterregulatory anti-inflammatory CD3-induced IL-10 secretion in CD4+ T cells in RRMS compared to controls. These data suggest that an equilibrium of a pro-inflammatory (IFN-gamma) and a counterregulatory anti-inflammatory (IL-10) cytokine may define stable clinically definite early RRMS.     

Functional mapping of CD11b/CD18 epitopes important in neutrophil-epithelial interactions: a central role of the I domain

In the intestine, lung, and urinary tract, neutrophil (polymorphonuclear leukocyte, PMN) transepithelial migration is dependent on the leukocyte beta2 integrin CD11b/CD18. While the regions of CD11b involved in recognition of several soluble ligands are known, those that mediate PMN-epithelial interactions have not been investigated. In this study, mAbs reactive with four extracellular regions on CD11b, the NH2-terminal region, I (inserted) domain, cation-binding region, and region proximal to the transmembrane domain (C domain), were analyzed for the ability to block CD11b/CD18-mediated interactions with T84 intestinal epithelial cells. In such a manner, epitope mapping was applied to the complex interactions between CD11b/CD18 and a cell-based ligand system. I domain Abs strongly inhibited both adhesion of PMN to epithelial cells and PMN migration across T84 epithelial monolayers. However, the profile of inhibition was distinct from that of other known ligands of CD11b/CD18. CBRM1/32, an Ab to a discontinuous epitope residing within the NH2- and cation-binding domains, strongly inhibited both adhesion and transmigration responses. C domain Abs had minimal effects on adhesion and transmigration. These findings appear applicable to other epithelia, since similar results were obtained in transmigration experiments with CF15 human airway epithelial cells. Finally, Ab inhibition profiles were confirmed with adhesion assays of isolated epithelial cells to purified CD11b/CD18. These findings demonstrate the central role of the I domain and the participation of a discontinuous region shared by the NH2- and cation-binding domains in mediating PMN-adhesive interactions with epithelial cells.     

Mechanisms associated with defective TH1 cytokine production in HIV infection

Qualitative and quantitative changes in immune functions of different T-cell subsets associated with infection by human immunodeficiency virus type 1 (HIV-1) were analyzed by flow cytometric assessment of intracytoplasmic cytokines. The T(H)1 cytokines, interleukin-2 (IL-2) and interferon-gamma (IFN-gamma), were produced by both CD4 and CD8 T-cell subsets. When normal peripheral blood mononuclear cells (PBMC) were activated in culture, both cytokines were produced predominantly by CD4 (CD4) cell and only a minor fraction of normal CD8 cells produced these cytokines. In the cultures of PBMC from HIV-1-infected individuals (HIV+PBMC), more HIV+CD8 cells produced IL-2 and IFN-gamma. Production of IFN-gamma by HIV+CD4 cells was markedly reduced, while IL-2nd tumor necrosis factor-alpha (TNF-alpha) production by HIV+CD4 remained relatively intact until the disease progressed further. Normal CD4 cells which were isolated by using a cell sorter, FACSCalibur was still able to produce IL-2 and TNF-alpha. But for full production of IFN-gamma, normal CD4 required some accessory cells, the identity of which could not yet be established.     

Perforin-deficient CD8+ T cells provide immunity to Listeria monocytogenes by a mechanism that is independent of CD95 and IFN-gamma but requires TNF-alpha

CD8+ T cells are effective mediators of immunity against Listeria monocytogenes, but the mechanisms by which they provide antilisterial immunity are poorly understood. CD8+ T cells efficiently lyse target cells in vitro by at least two independent pathways. To test the hypothesis that CD8+ T cell-mediated immunity to L. monocytogenes is dependent on perforin or CD95 (Fas, Apo-1), we used C57BI/6 (B6) and perforin-deficient (PO) mice to generate CD8+ T cell lines specific for the L. mono cytogenes-encoded Ag listeriolysin O (LLO). Both lines specifically produce IFN-gamma and TNF-alpha, and mediate target cell lysis in vitro. Cytolysis mediated by the PO-derived CD8+ T cell line is delayed relative to the B6-derived line and is completely inhibited by anti-CD95 Abs. In vivo, PO-derived CD8+ T cells provide specific antilisterial immunity in B6 hosts, CD95-deficient hosts, and IFN-gamma-depleted hosts. However, PO-derived CD8+ T cells fail to provide antilisterial immunity in hosts depleted of TNF-alpha. These results indicate that single Ag-specific CD8+ T cells derived from PO mice can mediate antilisterial immunity by a mechanism that is independent of CD95 or IFN-gamma, but requires TNF-alpha.     

Ambiguous role of interleukin-12 in Yersinia enterocolitica infection in susceptible and resistant mouse strains

Endogenous interleukin-12 (IL-12) mediates protection against Yersinia enterocolitica in C57BL/6 mice by triggering gamma interferon (IFN-gamma) production in NK and CD4+ T cells. Administration of exogenous IL-12 confers protection against yersiniae in Yersinia-susceptible BALB/c mice but exacerbates yersiniosis in resistant C57BL/6 mice. Therefore, we wanted to dissect the different mechanisms exerted by IL-12 during Yersinia infections by using different models of Yersinia-resistant and -susceptible mice, including resistant C57BL/6 mice, susceptible BALB/c mice, intermediate-susceptible wild-type 129/Sv mice, 129/Sv IFN-gamma-receptor-deficient (IFN-gamma R-/-) mice and C57BL/6 tumor necrosis factor (TNF) receptor p55 chain-deficient (TNFR p55-/-) mice. IFN-gamma R-/- mice turned out to be highly susceptible to infection by Y. enterocolitica compared with IFN-gamma R+/+ mice. Administration of IL-12 was protective in IFN-gamma R+/+ mice but not in IFN-gamma R-/- mice, suggesting that IFN-gamma R-induced mechanisms are essential for IL-12-induced resistance against yersiniae. BALB/c mice could be rendered Yersinia resistant by administration of anti-CD4 antibodies or by administration of IL-12. In contrast, C57BL/6 mice could be rendered more resistant by administration of transforming growth factor beta (TGF-beta). Furthermore, IL-12-triggered toxic effects in C57BL/6 mice were abrogated by coadministration of TGF-beta. While administration of IL-12 alone increased TNF-alpha levels, administration of TGF-beta or TGF-beta plus IL-12 decreased both TNF-alpha and IFN-gamma levels in Yersinia-infected C57BL/6 mice. Moreover, IL-12 did not induce toxicity in Yersinia-infected TNFR p55-/- mice, suggesting that TNF-alpha accounts for IL-12-induced toxicity. Taken together, IL-12 may induce different effector mechanisms in BALB/c and C57BL/6 mice resulting either in protection or exacerbation. These results are important for understanding the critical balance of proinflammatory and regulatory cytokines in bacterial infections which is decisive for beneficial effects of cytokine therapy.