Regulatory effects of IL-13 on synovial fluid macrophages and blood monocytes from patients with inflammatory arthritis.

Activated macrophages are central to the destructive processes of chronic inflammatory arthritis. In this study, it was hypothesized that IL-13, a product predominantly of 'Th2-type' lymphocytes, may be used therapeutically to down-regulate monocyte/macrophage activities at sites of chronic inflammation. Synovial fluid mononuclear cells were isolated from 12 patients with chronic inflammatory arthritis. Peripheral blood mononuclear cells (PBMC) were isolated at the same time as synovial fluid cells from all 12 patients. IL-13 significantly inhibited lipopolysaccharide (LPS)-induced tumour necrosis factor-alpha (TNF-alpha) production by mononuclear cells from peripheral blood, but not synovial fluid. In contrast, IL-13 inhibited LPS-induced IL-1 beta production by all cells, and as a positive response to IL-13, CD23 expression was increased on both cell populations. Blood monocytes cultured for 7 days with granulocyte-macrophage colony-stimulating factor (GM-CSF) or M-CSF responded to IL-13 in a manner similar to that detected for synovial fluid-derived cells, with suppression of LPS-induced IL-1 beta, but not TNF-alpha, production. In all experiments, the responses to IL-13 were very similar to those detected to IL-4, but differed from those measured with IL-10. Thus, the responses to IL-13 by synovial fluid cells and cultured monocytes are not equal to those of blood monocytes. The similar responses to IL-4 and IL-13 support claims of a common element for signalling from the IL-4 and IL-13 receptors. Furthermore, the activity of a common receptor chain may be altered by monocyte activation and differentiation.     

Effects of in vitro hyperthermia on proliferative responses and lymphocyte activity

Fever is induced by both exogenous products like endotoxin, and endogenous cytokines, most notably IL-1 and IL-6, and tumour necrosis factor (TNF). These mediators are believed to interact with the hypothalamus, to induce enhanced body temperature. However, little is known about the biological effects of fever on the function of the immune system. We here report that a 90-min pulse of mild hyperthermia (40°C) induces enhanced proliferation of peripheral blood mononuclear cells (PBMC). This proliferative response was completely inhibited by antibodies to MHC class II, which had no effect on mitogen-induced proliferation of PBMC. The enzyme-linked immunospot (ELISPOT) assay is a sensitive method for detection of single cells secreting antibodies or cytokines. A 90-min pulse of mild hyperthermia (40°C) induced a significantly enhanced immunoglobulin production in PBMC, as determined by ELISPOT, indicating B cell activation. The T cell cytokine pattern both with and without stimulation with hyperthermia differed between individuals. Enhanced interferon-gamma (IFN-γ) secretion was noted at 39–41°C. This IFN-γ response was inhibited by antibodies to MHC class II and thus was MHC class II-restricted and dependent on antigen-presenting cells. None of the individuals tested showed IL-4 response after stimulation with hyperthermia. These findings favour the notion that fever may play an important role in immune responses, and it is possible that fever may act as a physiological adjuvant, with effects on the immune system both in infection and inflammation of other origins.     

Serine leucocyte proteinase inhibitor-treated monocyte inhibits human CD4(+) lymphocyte proliferation

Serine leucocyte proteinase inhibitor (SLPI) is the main serine proteinase inhibitor produced by epithelial cells and has been shown to be a pleiotropic molecule with anti-inflammatory and microbicidal activities. However, the role of SLPI on the adaptive immune response is not well established. Therefore, we evaluated the effect of SLPI on lymphocyte proliferation and cytokine production. Human peripheral blood mononuclear cells (PBMC) were treated with mitogens plus SLPI and proliferation was assessed by [(3) H]thymidine uptake. The SLPI decreased the lymphocyte proliferation induced by interleukin-2 (IL-2) or OKT3 monoclonal antibodies in a dose-dependent manner. Inhibition was not observed when depleting monocytes from the PBMC and it was restored by adding monocytes and SLPI. SLPI-treated monocyte slightly decreased MHC II and increased CD18 expression, and secreted greater amounts of IL-4, IL-6 and IL-10 in the cell culture supernatants. SLPI-treated monocyte culture supernatant inhibited the CD4(+) lymphocyte proliferation but did not affect the proliferation of CD8(+) cells. Moreover, IL-2 increased T-bet expression and the presence of SLPI significantly decreased it. Finally, SLPI-treated monocyte culture supernatant dramatically decreased interferon-γ but increased IL-4, IL-6 and IL-10 in the presence of IL-2-treated T cells. Our results demonstrate that SLPI target monocytes, which in turn inhibit CD4 lymphocyte proliferation and T helper type 1 cytokine secretion. Overall, these results suggest that SLPI is an alarm protein that modulates not only the innate immune response but also the adaptive immune response.     

Immune regulation by platelet-activating factor: II. Mediation of suppression by cytokine-stimulated endothelial cells in vitro

Human umbilical vein endothelial cells (EC) can respond to endotoxin or to the inflammatory cytokines tumor necrosis factor (TNF) and interleukin 1 (IL-1) by producing platelet-activating factor (PAF). When EC were preexposed to TNF-alpha (25 U/ml) for 1 h, and then washed, their subsequent coculture with peripheral blood mononuclear cells (PBMC) resulted in suppressed proliferative response of the latter to the mitogen Con A (P less than 0.05). This effect was completely reversed by the concomitant use of the PAF receptor antagonist BN 52021 (0.1 mM). Preexposure of EC to IL-1 beta (0.5 U/ml) induced similar effects, but IL-1 and TNF were not additive. Removal of monocytes from the PBMC population abolished the effects. On the other hand, coculture of monocytes with cytokine-preexposed EC resulted in significant induction of suppressor activity on lymphocyte proliferation. Our data indicate that EC, preexposed to inflammatory cytokines, can modulate lymphocyte functions via the production of PAF and its action on monocytes.     

Immunogenic Versus Tolerogenic Dendritic Cells: A Matter of Maturation

Allergic diseases result from the interaction with IgE bound to cell surface receptors. Therefore, rational therapeutic approaches to allergic diseases would be aimed at decreasing IgE and/or at blocking the binding of IgE to effector cells such as mast cells and monocytes. Our investigation of the mechanism of IgE synthesis in man shows that IgE synthesis by peripheral blood mononuclear cells (PBMC) absolutely requires the presence of IL-4 and requires endogenous IL-6, because antibody to IL-6 inhibits IgE production completely. IgE synthesis requires T/B cell contact and involves interactions between B cell surface MHC Class II molecules and T cell surface receptors, as antibodies to both of these cell surface molecules inhibit IgE synthesis. Furthermore, alloreactive T cell clones which are unable to engage the B cell MHC Class II molecules fail to induce IgE synthesis in spite of their ability to secrete IL-4.

Studies on the immunoglobulin sites that are involved in IgE binding to high affinity receptors on mast cells and basophils have used recombinant fragments of IgE to block mast cell binding. These studies suggest that a stretch of 76 amino acids which straddles the C?2 and C?3 domains is essential for this binding. Parallel studies on IgE binding to low affinity receptors on monocyles and B cells suggest that sequences within C?3 are involved in this binding. Peptides or analogues that inhibit IgE binding to its cellular receptors may be useful in the treatment of allergic diseases.     

The effects of monocytes on the transendothelial migration of T lymphocytes.

In vivo cell-mediated immune reactions are characterized by mixtures of monocytes and T cells. The purpose of this study was to investigate the role of monocytes on T-cell migration and induction of endothelial adhesion molecules. The in vitro model consisted of adding peripheral blood mononuclear cells (PBMC), T cells or mixtures of monocytes and T cells, to endothelial cells on a porous membrane and using flow cytometry to distinguish between the monocyte and lymphocyte components. PBMC and PBMC supernatants were highly potent at upregulating intercellular adhesion molecule-1 (ICAM-1) and inducing expression of vascular cell adhesion molecule-1 (VCAM-1) and E-selectin. Induction by supernatants was inhibited by antibodies to tumour necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL)-1 beta. Using monocyte-enriched populations, as few as one monocyte to 100 endothelial cells was sufficient to upregulate adhesion molecules. Fixed monocytes also induced adhesion molecules and expressed surface-bound cytokines. In contrast, highly purified unstimulated T cells were not found to induce adhesion molecules at 4, 6, 24 or 48 hr of coculture. Purified T cells showed low-level migration through resting (VCAM-1 negative) endothelium, which was approximately doubled by addition of small numbers of monocytes or TNF-alpha. In conclusion, monocytes, via cell surface or released cytokines play an essential role in allowing large-scale recruitment of T cells to inflammatory sites in vivo.     

Enhanced ELISPOT detection of antigen-specific T cell responses from cryopreserved specimens with addition of both IL-7 and IL-15--the Amplispot assay

The importance of the enzyme-linked immunosorbent spot (ELISPOT) assay as a tool for studying immune responses in vitro is becoming increasingly apparent. However, there remains a need for enhanced sensitivity for the detection of low frequency antigen-specific T cell responses. We reasoned that the addition of a combination of the cytokines interleukin (IL)-7 and IL-15 would selectively increase interferon-gamma (IFN-gamma) production from antigen-stimulated CD4+ and CD8+ effector memory T cells. Freshly isolated or cryopreserved peripheral blood mononuclear cells (PBMC) from four healthy donors were analysed by ELISPOT for the frequency of purified protein derivative (PPD)-specific CD4+ T cells or cytomegalovirus (CMV) peptide-specific CD8+ T cells. Addition of IL-7 and IL-15 increased the number of PPD-specific CD4+ T cells up to 2.4-fold in fresh PBMC and up to 18-fold in cryopreserved PBMC. The cytokines also increased the number of CMV peptide-specific CD8+ T cells in fresh PBMC up to 7.5-fold. No additional increases were seen when antibodies to co-stimulatory molecules CD28 and CD49d were applied together with the cytokine combination. These data demonstrate that the sensitivity of the ELISPOT assay may be significantly augmented by addition of the cytokines IL-7 and IL-15 to antigen-stimulated cells. This method will be particularly useful for the assessment of antigen-stimulated cytokine production by T cells in cryopreserved biological specimens.     

Retinoic Acid Enhances the Production of IL-10 While Reducing the Synthesis of IL-12 and TNF-α from LPS-Stimulated Monocytes/Macrophages

Vitamin A and its metabolites, e.g., all trans-retinoic acid (atRA) and 9-cis-retinoic acid have attracted considerable attention as compounds that have a broad range of immune modulating effects on both humoral and cellular immune responses. The cellular and molecular mechanisms that underlie the effects of retinoids on the immune system remain to be more clearly defined. These immune modulating effects of atRA may be mediated by cytokines elaborated by monocytes and other cell types. To further understand the mechanism(s) by which retinoids affect the immune response, we examined the effects of atRA on several proinflammatory and immune modulating cytokines produced by monocytes. The effects of atRA on LPS-induced mRNA expression of IL-10, IL-12p40, TNF-α, IL-18, and TGF-β in the THP-1 monocyte/macrophage cell line and in cord blood mononuclear cells were measured by competitive RT-PCR. The ELISPOT was employed to evaluate IL-10 and TNF-α protein production enumerating the number of IL-10 and TNF-α producing cells. The addition of atRA to cell cultures potentiated the LPS-induced IL-10 mRNA expression and the number of IL-10 secreting cells from THP-1 cells and cord blood mononuclear cells. In contrast, the addition of atRA inhibited the LPS-induced TNF-α and IL-12p40 mRNA expression, and the number of ELISPOT positive cells for TNF-α. atRA did not change the LPS-induced mRNA expression of IL-18 and TGF-β. These results suggest that atRA may have multiple effects on LPS-induced monocyte/macrophage derived cytokines. While atRA downregulated the proinflammatory cytokines, e.g., IL-12 and TNF-α, the production of an immune modulating cytokine, IL-10 was enhanced by atRA. The effects of atRA on these cytokines may play an important role in the modulation of the immune and inflammatory responses.     

Regulation of human CD4(+) alphabeta T-cell-receptor-positive (TCR(+)) and gammadelta TCR(+) T-cell responses to Mycobacterium tuberculosis by interleukin-10 and transforming growth factor beta

Mycobacterium tuberculosis is the etiologic agent of human tuberculosis and is estimated to infect one-third of the world's population. Control of M. tuberculosis requires T cells and macrophages. T-cell function is modulated by the cytokine environment, which in mycobacterial infection is a balance of proinflammatory (interleukin-1 [IL-1], IL-6, IL-8, IL-12, and tumor necrosis factor alpha) and inhibitory (IL-10 and transforming growth factor beta [TGF-beta]) cytokines. IL-10 and TGF-beta are produced by M. tuberculosis-infected macrophages. The effect of IL-10 and TGF-beta on M. tuberculosis-reactive human CD4(+) and gammadelta T cells, the two major human T-cell subsets activated by M. tuberculosis, was investigated. Both IL-10 and TGF-beta inhibited proliferation and gamma interferon production by CD4(+) and gammadelta T cells. IL-10 was a more potent inhibitor than TGF-beta for both T-cell subsets. Combinations of IL-10 and TGF-beta did not result in additive or synergistic inhibition. IL-10 inhibited gammadelta and CD4(+) T cells directly and inhibited monocyte antigen-presenting cell (APC) function for CD4(+) T cells and, to a lesser extent, for gammadelta T cells. TGF-beta inhibited both CD4(+) and gammadelta T cells directly and had little effect on APC function for gammadelta and CD4(+) T cells. IL-10 down-regulated major histocompatibility complex (MHC) class I, MHC class II, CD40, B7-1, and B7-2 expression on M. tuberculosis-infected monocytes to a greater extent than TGF-beta. Neither cytokine affected the uptake of M. tuberculosis by monocytes. Thus, IL-10 and TGF-beta both inhibited CD4(+) and gammadelta T cells but differed in the mechanism used to inhibit T-cell responses to M. tuberculosis.     

Dual roles for class II major histocompatibility complex molecules in staphylococcal enterotoxin-induced cytokine production and in vivo toxicity.

The staphylococcal enterotoxins (SE) specifically bind to class II major histocompatibility complex (MHC) proteins, resulting in activation of monocytes and T cells. The SE cause weight loss in mice, which is dependent on T-cell stimulation and tumor necrosis factor alpha (TNF-alpha) production. Here we use a mutant of staphylococcal enterotoxin A that binds class II MHC molecules and activates monocytes but not T cells to evaluate the relative contributions of monocyte- and T-cell-stimulatory activities to in vivo toxicity. The mutant toxin did not cause weight loss in B10. BR mice but did stimulate monocyte TNF-alpha production in vitro, as did the wild-type toxin. Addition of a supernatant from toxin-activated T cells enhanced monocyte-stimulatory activity of both mutant and wild-type toxins fivefold. The effect of the supernatant could be mimicked by recombinant gamma interferon (IFN-gamma) and was inhibited by antibody to IFN-gamma. These results suggest that toxin-induced monocyte TNF-alpha production is upregulated by IFN-gamma, which likely represents the T-cell requirement in SE-mediated weight loss. Our studies thus implicate two distinct class II MHC-dependent signaling pathways for SE, the first involving direct signal transduction through class II MHC molecules mediated by either mutant or wild-type toxin and the second requiring T-cell stimulation by toxin-class II MHC complexes with consequent production of IFN-gamma. We suggest that both pathways are required for optimal monocyte TNF-alpha production in vitro and SE-induced toxicity in vivo.     

Cultured human monocytes secrete fibronectin in response to activation by proinflammatory cytokines

We studied the effects of the cytokines IL-1alpha, IL-6, tumour necrosis factor-alpha (TNF-alpha), IL-4, IL-10, IL-13 and transforming growth factor-beta (TGF-beta) on fibronectin (FN) production by cultured-human monocytes. IL-1alpha, IL-6 and TNF-alpha all increased FN production, an indicator of monocyte activation. These cytokines increased FN production in a dose-dependent fashion, with a 4-h treatment being sufficient to measure FN production by radioimmunoassay. Conversely, IL-4, IL-10 and IL-13 strongly inhibited cytokine-induced FN production, while TGF-beta only partially inhibited FN production. The combination of suboptimal doses of cytokines (IL-1alpha + IL-6, IL-1alpha + TNF-alpha, IL-6 + TNF-alpha), which could not singly induce substantial amounts of FN, were able to induce FN production by cultured monocytes. Northern blot analysis with a cDNA specific for FN confirmed the expression of FN mRNA in cultured monocytes stimulated with a single cytokine or a combination of cytokines. Our data demonstrate that monocytes may not always require high concentrations of cytokines for activation in vitro, and that the synergistic or additive action of low levels of cytokines on monocyte activation may be sufficient to promote immune or inflammatory reactions. Our data also suggest that certain T cell cytokines may regulate monocyte activation.     

Selective enhancement of endothelial cell VCAM-1 expression by interleukin-10 in the presence of activated leucocytes.

Although initially described as an immunomodulatory cytokine, interleukin-10 (IL-10) has also been proposed to exert proinflammatory effects both in vivo and in vitro. In particular, studies in IL-10 transgenic mice have suggested that IL-10 may activate vascular endothelium to promote leucocyte adhesion and extravasation. In the present study we investigated whether IL-10 activates endothelial cells either directly or indirectly, via signals produced by leucocytes in the endothelial cell environment, using a co-culture of human umbilical vein endothelial cells and peripheral blood mononuclear cells (PBMC). No direct effects of IL-10 on endothelial cell responses were observed. However, in the presence of phytohaemagglutinin-activated PBMC, IL-10 increased the expression on endothelial cells of vascular cell adhesion molecule-1 (VCAM-1) but not of intercellular adhesion molecule-1, E-selectin or major histocompatibility complex (MHC) antigens, an effect mediated by PBMC-derived soluble factors. We also observed that interferon-gamma (IFN-gamma) antagonized VCAM-1 expression on endothelial cells mediated by IL-4 and IL-13. Since IL-10 has previously been documented to down-regulate release of IFN-gamma by PBMC, we propose that the IL-10-mediated reduction of IFN-gamma production by PBMC results in enhanced responsiveness of endothelial cells to PBMC-derived IL-4 and IL-13, and thus increased expression of VCAM-1. Our results suggest that the relative balance of cytokines produced by infiltrating cells in developing inflammatory lesions may differentially modulate endothelial responsiveness in vivo, and that IL-10 might indirectly stabilize VCAM-1 expression on endothelial cells by affecting the balance of leucocyte-derived cytokines in the endothelial environment.     

Monocyte - Mediated Regulation of Antigen - Driven IFNgamma Production by T Cells. The Role of Endogenously Produced TNF

The question was asked whether tumour necrosis factor alpha (TNF) is involved in regulation of interferon gamma (IFNgamma) production by T cells. Monocytes were exposed to exogenous TNF or to TNF synthesis inhibitors (pentoxifylline, PTX and adriamycin, ADR) and then used as antigen (PPD) presenting cells for autologous T cells. The ability of T lymphocytes to release IFNgamma was assessed after 3 days of culture. Preincubation of monocytes with rTNF enhanced their ability to induce IFNgamma production while TNF synthesis inhibitors decreased it. Anti-TNF and anti-TNF-R2 monoclonal antibodies (mAbs) inhibited monocyte ability to present PPD for IFNgamma production which suggested that endogenously produced TNF by monocytes had to be released and acted on TNF-R2 on the monocyte surface. The enhancing effect of exogenous TNF was also abrogated by anti-TNF-R2 mAb. Pretreatment of monocytes with rTNF enhanced, while pretreatment with PTX decreased, PPD-induced IL-6 production. An increased production of IL-4 was found in cultures of PTX - treated, PPD-pulsed monocytes with T cells. This may indicate that in the relative absence of monocyte costimulatory signal(s), probably IL-6, Th₂ cells are stimulated. These results indicate that TNF is involved in control of monocyte-mediated regulation of cytokine production by T cells.     

Effects of activin A on IgE synthesis and cytokine production by human peripheral mononuclear cells.

Activin A not only stimulates the synthesis and release of pituitary follicle-stimulating hormone, but exerts various effects on haematopoietic cells, embryos, and fibroblasts. In the present study we have examined effects of activin A on IgE synthesis and cytokine production by peripheral blood mononuclear cells (PBMC) in normal humans. When PBMC were cultured in the presence of IL-4, activin A significantly augmented IgE production induced by IL-4. Activin A did not affect, however, IgE production from highly purified B cells when they were stimulated with anti-CD40 MoAb and IL-4. The fact that in the latter condition IgE synthesis was T cell- and monocyte-independent indicated that activin A does not directly influence B cells for IgE synthesis. Rather, production as well as gene expression of IL-6, which is known to enhance IgE synthesis by purified monocytes, was induced by activin A alone. In addition, activin A induced other monokines such as IL-1 and tumour necrosis factor (TNF)-alpha from monocytes. In contrast, activin A neither induced nor augmented the production of TNF-beta or interferon-gamma (IFN-gamma), both of which are known to be exclusively generated by T cells. These data indicate that activin A plays a certain role in physiological functions for monocytes in normal humans.     

Monocyte - Mediated Regulation of Antigen - Driven IFNgamma Production by T Cells. The Role of Endogenously Produced TNF

The question was asked whether tumour necrosis factor alpha (TNF) is involved in regulation of interferon gamma (IFNgamma) production by T cells. Monocytes were exposed to exogenous TNF or to TNF synthesis inhibitors (pentoxifylline, PTX and adriamycin, ADR) and then used as antigen (PPD) presenting cells for autologous T cells. The ability of T lymphocytes to release IFNgamma was assessed after 3 days of culture. Preincubation of monocytes with rTNF enhanced their ability to induce IFNgamma production while TNF synthesis inhibitors decreased it. Anti-TNF and anti-TNF-R2 monoclonal antibodies (mAbs) inhibited monocyte ability to present PPD for IFNgamma production which suggested that endogenously produced TNF by monocytes had to be released and acted on TNF-R2 on the monocyte surface. The enhancing effect of exogenous TNF was also abrogated by anti-TNF-R2 mAb. Pretreatment of monocytes with rTNF enhanced, while pretreatment with PTX decreased, PPD-induced IL-6 production. An increased production of IL-4 was found in cultures of PTX - treated, PPD-pulsed monocytes with T cells. This may indicate that in the relative absence of monocyte costimulatory signal(s), probably IL-6, Th₂ cells are stimulated. These results indicate that TNF is involved in control of monocyte-mediated regulation of cytokine production by T cells.     

瑞香素对人PBMC的细胞因子和TLRs mRNA表达的影响

目的观察瑞香素对人外周血单个核细胞的细胞因子和Toll样受体表达的影响,研究瑞香素增强淋巴细胞功能的作用机制。方法分离人外周血T、B细胞和单核细胞,分别加入瑞香素,37℃,5%CO2培养48 h后,采用实时荧光定量PCR检测瑞香素对T细胞IL-2、IFN-γ,B细胞IL-12,单核细胞IL-1 mRNA及T、B细胞TLR1～10的mRNA表达的影响;同时检测先用抗TLR4单抗封闭,再用瑞香素处理细胞后上述细胞因子和TLRs的mRNA表达变化。结果瑞香素能明显上调T细胞IL-2及IFN-γ、B细胞IL-12、单核细胞IL-1 mRNA和T细胞TLR1、TLR4,B细胞TLR4、TLR9 mRNA的表达(P﹤0.05),其中T细胞IL-2、B细胞IL-12、单核细胞IL-1 mRNA的表达和T细胞TLR4,B细胞TLR4、TLR9 mRNA表达可被抗TLR4单抗部分阻断。结论瑞香素增强淋巴细胞的免疫功能的可能机制是通过上调T细胞TLR1、TLR4,B细胞TLR4、TLR9的表达,分别参与其细胞内信号转导,从基因转录水平促进T、B细胞分泌细胞因子。     

Testosterone inhibits immunoglobulin production by human peripheral blood mononuclear cells

We studied the in vitro effect of testosterone on spontaneous immunoglobulin production by human peripheral blood mononuclear cells (PBMC). Testosterone inhibited IgG and IgM production by PBMC both from males and females. The inhibitory effect of testosterone was revealed at doses more than 1 nm, increased dose-dependently, and reached a plateau at 100 nm. At doses <1000 nm, testosterone did not reduce cell viability. Testosterone treatment reduced IgG production by 59.0% and that of IgM by 61.3% compared with control. Immunoglobulin production by B cells was also suppressed by testosterone, though the magnitude of the suppressive effect on B cells was lower than that on whole PBMC; testosterone-induced decrease of IgG production compared with control was 26.9% and that of IgM was 24.9%. Exogenous IL-6 partially restored the impaired immunoglobulin production of testosterone-treated PBMC; IgG production in testosterone culture was increased by IL-6 from 35.6% to 66.5% of control and that of IgM was also increased from 38.9% to 71.2%, respectively. Testosterone treatment reduced IL-6 production of monocytes by 78.4% compared with control, but neither affected that of T cells or B cells. These results suggest that testosterone may suppress immunoglobulin production of human PBMC directly by inhibiting B cell activity and indirectly by reducing IL-6 production of monocytes. It is thus indicated that this hormone may have protective and therapeutic effects on human autoimmune diseases.     

Interaction of platelet-activating factor with interferon-gamma in the stimulation of interleukin-1 production by human monocytes

Platelet-activating factor (PAF) produces both early and late inflammatory responses in vivo. The late and persistent responses to PAF may result from the production of cytokines, such as interleukin-1 (IL-1). The effects of PAF on IL-1 release by human monocytes were studied with PAF alone and in combination with interferon-gamma. These studies involved the use of D10.G4.1 cells in a proliferation assay to determine the actual concentration of active IL-1 in monocyte supernatant and pellet fractions. These studies confirmed that PAF stimulates IL-1 release at two different ranges of PAF concentrations, 100 fM to 1 pM and 100 pM to 1 nM. PAF inhibited IL-1 release at 1 or 10 pM. PAF effects on IL-1 release were specific to the form of PAF that is biologically active in most system; (S)-PAF and lyso-PAF had no effect. When monocytes were incubated with both PAF and interferon-gamma, IL-1 release was greatly stimulated at the same two ranges of PAF concentrations, 100 fM to 1 pM and 100 pM to 1 nM of PAF. PAF and interferon-gamma interacted synergistically to enhance significantly the release of IL-1.     

A central role for monocytes in Toll-like receptor-mediated activation of the vasculature

There is increasing evidence that activation of inflammatory responses in a variety of tissues is mediated co-operatively by the actions of more than one cell type. In particular, the monocyte has been implicated as a potentially important cell in the initiation of inflammatory responses to Toll-like receptor (TLR)-activating signals. To determine the potential for monocyte-regulated activation of tissue cells to underpin inflammatory responses in the vasculature, we established cocultures of primary human endothelial cells and monocytes and dissected the inflammatory responses of these systems following activation with TLR agonists. We observed that effective activation of inflammatory responses required bidirectional signalling between the monocyte and the tissue cell. Activation of cocultures was dependent on interleukin-1 (IL-1). Although monocyte-mediated IL-1β production was crucial to the activation of cocultures, TLR specificity to these responses was also provided by the endothelial cells, which served to regulate the signalling of the monocytes. TLR4-induced IL-1β production by monocytes was increased by TLR4-dependent endothelial activation in coculture, and was associated with increased monocyte CD14 expression. Activation of this inflammatory network also supported the potential for downstream monocyte-dependent T helper type 17 activation. These data define co-operative networks regulating inflammatory responses to TLR agonists, identify points amenable to targeting for the amelioration of vascular inflammation, and offer the potential to modify atherosclerotic plaque instability after a severe infection.