In vitro production of interleukin-4 and interferon-gamma by lymph node cells from BALB/c mice infested with nymphal Ixodes ricinus ticks.

In this study we compared the ability of lymphocytes taken from axillary and brachial lymph nodes of BALB/c mice that had been infested once three times with 15 nymphal Ixodes ricinus ticks, to produce interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) after in vitro stimulation with concanavalin A (Con A). They released high levels of IL-4 and low levels of IFN-gamma. An increase of IFN-gamma between the first and the third tick infestation was observed. Salivary gland extracts from female I. ricinus ticks induced specific in vitro proliferation of lymphocytes from infested mice. IL-4 production was correlated with the salivary gland extracts' ability to stimulate tick-specific lymphocyte proliferation. Its levels remained high from the first to the third infestation. IFN-gamma production was not necessarily associated with tick salivary gland antigen stimulation. In BALB/c mice, anti-tick immune response induction is regional and the contribution of other similar secondary lymphoid organs is negligible. Only cells from the lymph nodes which drained the tick-fixation site proliferated in vitro in the presence of tick antigens, and when stimulated with Con A produced IL-4 and IFN-gamma.     

Immunosuppression and cytokine production in mice infested with Ixodes ricinus ticks: a possible role of laminin and interleukin-10 on the in vitro responsiveness of lymphocytes to mitogens.

T cells from BALB/c mice infested 9 days before with Ixodes ricinus nymphs had a suppressed response to in vitro concanavalin A (Con A) stimulation compared to cells from uninfested mice. When laminin (the main component of the extracellular matrix) was used as a coating agent, the Con A response of naive mice was characterized by a decrease in cell proliferation, whereas there was no significant effect on the mitogen response of cells from infested mice. In contrast, an increased response to lipopolysaccharide (LPS) was observed when assaying lymph node cells of infested mice, probably reflecting an increase in B-lymphocyte number or activity. LPS cell stimulation was not modified by laminin. Supernatants of lymph node cells, taken 9 days after the first infestation of mice, stimulated with Con A in vitro, contained interleukin-10 (IL-10) but no significant levels of IL-5 as tested by enzyme-linked immunosorbent assay. At this stage of the infestation all T cells reactive with tick antigens generated in lymph nodes that drain the tick fixation site, were CD4+ cells, as determined by CD4+ depletion. With cells taken 9 days after the third infestation an increase of IL-5 and IL-10 was observed. The IL-10 levels were higher than the IL-5. According to these observations, we conclude that the reduction of T-cell proliferation in response to Con A observed in lymph node cells from infested mice, may be due to the combined effect of laminin interaction with T lymphocytes during migration and IL-10 production by these lymphocytes.     

Synthesis of Cytokines During Tumour Development in Mice Immunized with the Mycobacterial Antigen Complex A60

The authors have previously reported on the ability of A60, an immunodominant antigenic complex of Mycobacterium bovis BCG, to prevent cancer development in mice challenged with EMT 6 tumour cells. Such effect proved to rely on neoplastic cell lysis by cytolytic T lymphocytes and activated macrophages. The involvement of cytokines in triggering the immune response leading to tumour rejection is analysed in the present work. The synthesis of IL-2, IFN-α and TNF-α was strongly increased in A60-primed mice. Cancer development depressed the blood levels of these three cytokines. In vitro cultures of lymphocytes from lymph nodes and blood of A60-primed mice produced higher levels of these cytokines in the presence of A60, as  compared to cultures lacking A60. Such effect was inhibited by co-incubation of lymphocytes with EMT  6  tumour cells. In vitro cultures of macrophages yielded higher levels of TNF-α in the presence of A60 and co-incubation of these cells with EMT 6 tumour cells also inhibited TNF-α production. The enhanced synthesis of IL-2 and IFN-α, which promote activation of cytolytic T lymphocytes and macrophages, accounts for the increased tumour cell lysis induced in vivo by A60. The A60-promoted synthesis of TNF-α is partly responsible for the latter effect. The inhibitory action of EMT-6 tumour cells on cytokine synthesis is a powerful mechanism of tumour escape from the immune system's control.     

Immunological Determinants in a Mouse Model of Chemical-Induced Asthma After Multiple Exposures

In a mouse model of chemical-induced asthma, we investigated the effects of multiple challenges, using toluene diisocyanate (TDI), a known cause of occupational asthma. On days 1 and 7, BALB/ c mice received TDI or vehicle (acetone/olive oil). On days 10, 13 and 16 the mice received an intranasal instillation of TDI. Ventilatory function (Penh) was monitored by whole body plethysmography for 40 min after each challenge. Reactivity to methacholine was measured 22 h later. Pulmonary inflammation, TNF-α and MIP-2 levels were assessed 24 h after the last challenge by broncho-alveolar lavage (BAL). Other immunological parameters included total IgE, lymphocyte sub-populations in auricular and cervical lymph nodes, and IL-4, IFN-γ and IL-13 levels in supernatants of lymph node cells, cultured with or without concanavalin A. Early ventilatory function and airway reactivity increased in all groups that received a dermal application and one or multiple intranasal challenges of TDI. After multiple challenges, lung inflammation was characterized by neutrophils (∼15%), and eosinophils (∼4%), along with an increase in BAL MIP-2 and TNF-α levels. The auricular and cervical lymph node cells of all sensitized mice showed an increase in B cells, Th cells and an increased concentration of in vitro release of IL-4, IFN-γ and IL-13 after stimulation with concanavalin A. Total serum IgE was elevated in dermally TDI-sensitized mice. This protocol including multiple challenges results in a model that resembles human asthma, indicating that responses found in the model using a single challenge could be a good first indication for the development of asthma.     

Probiotic Bacteria Induce Regulatory Cytokine Production via Dendritic Cells

Probiotic bacteria, e.g. Lactobacillus spp., may improve diseases such as chronic inflammatory bowel disease. We examined cytokine production and phenotypic change after in vitro stimulation of T cells from healthy volunteers using different probiotic strains.
Methods:  T cells were cultured from colonic biopsies from eight healthy volunteers (Agnholt and Kaltoft, Exp Clin Immunogenet 2001;18:213–25), and dendritic cells were matured from their peripheral blood mononuclear cells. T-cell cultures were stimulated with autologous bacterial sonicate or strains of Lactobacillus spp., with and without the addition of dendritic cells. Cytokine levels (TNF-α, IFN-γ, IL-10 and GM-CSF) and phenotype (CD3, CD4, CD25 and CD69) were measured on day 4.
Results:  Lactobacillus spp. induced higher productions of TNF-α and IL-10 than did autologous bacteria. In presence of dendritic cells, the production of all cytokines increased. However, the increases of IFN-γ and TNF-α were more pronounced in wells with autologous bacteria than in wells with Lactobacillus spp. The addition of dendritic cells upregulated CD25 expression without simultaneous upregulation of CD69. The upregulation was pronounced after stimulation with Lactobacillus rhamnosus GG compared with autologous bacteria and other lactobacilli.
Discussion:  In presence of dendritic cells, autologous bacteria induced inflammatory cytokines, while probiotics mainly induced regulatory cytokines. Lactobacillus rhamnosus GG induced a regulatory phenotype (cd25⁺), in part mediated by dendritic cells. Future studies will address whether this shift to a CD25⁺ phenotype represents a differentiation into competent regulatory T cells. In a clinical context, such cells might be used for treatment of inflammatory diseases.     

Mechanisms of eosinophilia in mice infested with larval Haemaphysalis longicornis ticks.

Infestation of larval Haemaphysalis longicornis ticks induced a threefold increase of eosinophils in the peripheral blood of normal WBB6F1- +/+ mice 2 days after tick infestation. In genetically mast cell-deficient WBB6F1- W/Wv mice, a threefold increase of blood eosinophils was observed 6 days after the tick infestation. However, marked infiltration of eosinophils was detected in the tick infestation sites of the WBB6F1- +/+ mice but not the WBB6F1- W/Wv mice. When the mast cell deficiency of WBB6F1- W/Wv mice had been rescued locally by intradermal injections of WBB6F1- +/+ mouse-derived cultured mast cells, a rapid increase of blood eosinophils and tissue infiltration of eosinophils were revealed following tick infestation. The intravenous (i.v.) injection of immune spleen or lymph node cells obtained from WBB6F1- +/+ mice 10 days after tick infestation led to significant eosinophilia in naive recipient mice. Treatment with anti-Thy-1.2 or anti-CD4 monoclonal antibody (mAb) and complement (C) completely abolished the eosinophilia; the early response (2 days after tick challenge) is dependent on mast cells at the feeding site, and the late response (6 days after tick challenge) is dependent on T lymphocytes. Since amplified interleukin-5 (IL-5) cDNA was detectable in the spleen cells 4 days after tick infestation, the late response might be mediated by IL-5. The infiltration of eosinophils at the feeding site of skin appeared to be dependent on mast cells.     

Dendritic cells from Peyer's patches and mesenteric lymph nodes differ from spleen dendritic cells in their response to commensal gut bacteria

Commensal gut bacteria have potent effects on the immune system, which are partially mediated by intestinal dendritic cells (DC). Distinct commensals confer different properties to in vitro -generated DC. The aim of the present study was to reveal strain-dependent maturation patterns in primary DC. To this end, we compared the response of mouse Peyer's patch (PP) DC, mesenteric lymph node (MLN) DC and spleen DC to the commensal bacteria, Bifidobacterium longum Q46, Lactobacillus acidophilus X37 and Escherichia coli Nissle 1917. Bacterial maturation of DC occurred independently of tissue origin. Expression of CCR7 and CD103 on the surface of MLN DC, necessary for the induction of gut-homing regulatory T cells, increased with stimulation by Gram-positive commensals. Bacteria-dependent cytokine production (IL-6, IL-10 and TNF-α) was similar in spleen and MLN DC, and contaminant cells in these DC preparations produced IFN-γ in response to L. acidophilus . In contrast, PP DC produced IL-6 only in response to E. coli , little IL-10 and no TNF-α, and this low cytokine production was not due to inhibition by IL-10 or TGF-β. Bifidobacteria downregulate IL-6, TNF-α and IL-12 production induced in in vitro -generated DC by L. acidophilus . Similar inhibition was observed in splenic DC, but not in MLN DC. MLN cells responded to bacterial stimulation with higher IFN-γ production than spleen cells, possibly due to the presence of more responsive natural killer cells. Commensal bacteria therefore play specific roles in the gut immune system distinguishable from the effect they would have if recognized by the systemic immune system.     

Contribution of Intestinal Epithelial Cells to Innate Immunity of the Human Gut – Studies on Polarized Monolayers of Colon Carcinoma Cells

The aim was to establish an in vitro model for studies of innate defence mechanisms of human intestinal epithelium. Ultrastructural characterization and determination of mRNA expression levels for apical glycocalyx and mucous components showed that polarized, tight monolayers of the colon carcinoma cell lines T84 and Caco2 acquire the features of mature- and immature columnar epithelial cells, respectively. Polarized monolayers were challenged with non-pathogenic Gram+ and Gram− bacteria from the apical side and the proinflammatory cytokines interferon-γ (IFN-γ), tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) from the basolateral side. Immune responses were estimated as changes in mRNA expression levels for the mucous component mucin-2 (MUC2), the glycocalyx components carcinoembryonic antigen (CEA), CEA-related cell adhesion molecule-1 (CEACAM1), CEACAM6, CEACAM7 and MUC3, the antimicrobial factors human β-defensin-1 (hBD1), hBD2, hBD3 and lysozyme, the chemokine IL-8 and the cytokines IL-6 and TNF-α. Tight monolayer cells were generally unresponsive to bacterial challenge, but increased their hBD2 levels when challenged with Bacillus megaterium. T84 cells also increased their TNF-α levels upon bacterial challenge. Tight monolayer cells responded to cytokine challenge suggesting awareness of basolateral attack. TNF-α induced significantly increased levels of IL-8 and TNF-α itself in both cell lines suggesting recruitment and activation of immune cells in the underlying mucosa in vivo . Cytokine challenge also increased levels of CEACAM1, which includes two functionally different forms, CEACAM1-L and CEACAM1-S. In T84 cells, IFN-γ was selective for CEACAM1-L while TNF-α upregulated both forms. Increased CEACAM1 expression may influence epithelial function and communication between epithelial cells and intraepithelial lymphocytes.     

T-cell lymphokine response to orally administered proteins during priming and unresponsiveness.

Feeding antigens induces an immunological unresponsiveness termed oral tolerance but under some conditions, for example following the administration of cyclophosphamide (CY), immunity can be induced. These observations have usually been made by studying antibody production and delayed hypersensitivity with little attention given to other measurements of cellular activation. We have therefore examined the lymphokines produced by T cells obtained after the induction of oral tolerance or intragastric priming. Cells isolated from the spleen and Peyer's patches (PP) of tolerized mice could secrete high levels of interferon-gamma (IFN-gamma) and moderate levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) in response to antigen while interleukin-2 (IL-2), IL-3 and IL-4 could not be detected. Mesenteric lymph node (MLN) cells of tolerized mice did not respond to antigen unless spleen adherent cells were added to the cultures where IFN-gamma and GM-CSF were produced. Intragastric priming was achieved by feeding antigen to CY-treated mice. T cells from the spleen, MLN and PP of these mice could produce GM-CSF, IFN-gamma, some IL-3 but little or no IL-2 and IL-4. The ability of MLN cells to proliferate with antigen in vitro was low and corresponded to low IL-2 production. Thus T cells from fed mice secrete a defined pattern of lymphokines which differs in tolerizing and priming regimes.     

Patterns of cytokine production and proliferation by T lymphocytes differ in mice vaccinated or infected with Schistosoma mansoni.

C57BL/6 mice vaccinated with irradiated cercariae of Schistosoma mansoni are highly resistant to challenge infection. To examine the role of T-helper (Th) activity in these vaccinated (V20) mice, cells from skin- and lung-draining lymph nodes (LN) and the spleen were cultured in vitro with soluble schistosomular antigen. Peak proliferation and release of T-cell growth factor (TCGF) by axillary LN cells on Day 5, and by mediastinal LN cells on Day 18, reflected the kinetics of parasite migration. High levels of interferon-gamma (IFN-gamma) were detected and production was prolonged, particularly in the mediastinal LN. The majority of the above activity was ablated with anti-CD4 antibody. IFN-gamma production by spleen cells increased, whilst proliferation and TCGF release remained low. Although levels of proliferation were similar, more IFN-gamma was released by LN cells from V20 mice than by those from mice infected with normal parasites (NI). This difference in IFN-gamma production was magnified by the greater number of cells in LN of V20 than NI mice. On Day 22 post-exposure, 24-fold more IFN-gamma was produced per pair of axillary LN in the former group. LN cells from V20 mice produced interleukin (IL)-2 and IL-4, whereas those from NI mice released IL-2 but negligible IL-4. Greater quantities of IL-3 were secreted by cells from V20 than from NI mice. These results support the conclusion that IFN-gamma-producing memory Th cells, generated in the LN of V20 mice, play an important role in protective immunity against S. mansoni.     

Influence of repeated infestations with pathogen-free Ixodes scapularis (Acari: Ixodidae) on in vitro lymphocyte proliferation responses of C3H/HeN mice

In the United States, Ixodes scapularis Say has been implicated as the vector of at least three human pathogens. Tick induced modulation of host immunity is increasingly recognized as an important factor in successful transmission or establishment of tick-borne pathogens. This study was conducted to determine the effects of repeated infestations with pathogen-free I. scapularis nymphs on in vitro proliferative responses of splenic lymphocytes from C3H/HeN mice. Lymphocytes from repeatedly infested and uninfested mice were exposed to concanavalin A (Con A), Escherichia coli Castellini & Chalmers lipopolysaccharide (LPS), or I. scapularis salivary gland soluble proteins (SGSP), to determine if lymphocyte responses differed between tick-exposed and nonexposed mice. Female C3H/HeN mice were infested one to four times with pathogen-free I. scapularis nymphs, with a 14-d tick-free period between each exposure. After each infestation, tick biology parameters were measured and lymphocyte proliferative responses assessed. Acquired resistance to I. scapularis was not evident in mice subjected to tick feeding. Significant differences in the responses of lymphocytes exposed to I. scapularis SGSP were observed between infested and noninfested mice. In contrast, few differences between infested and noninfested mice were evident for lymphocytes exposed to Con A or LPS. Our results suggest that repeated exposure to I. scapularis nymphs does not affect Con A or LPS-induced proliferation of splenic lymphocytes, but significantly effects lymphocyte responses to tick salivary gland antigens.     

Susceptibility of BALB/c mice to nymphs and larvae of Ixodes ricinus after modulation of IgE production with anti-interleukin-4 or anti-interferon-γ monoclonal antibodies

BALB/c mice infested three times with nymphs or larvae of Ixdoes ricinus ticks do not acquire resistance as assessed by evaluation of both tick attachment and the weight of engorged nymphs or larvae. Tick challenge causes a gradual increase in total IgE antibody production from the first to the third infestation. Anti-tick IgG antibodies are never detected. When the mice are treated with anti-interleukin-4 (anti-IL-4) or anti-interferon-gamma (anti-IFN-γ) monoclonal antibodies (mAbs) 1 day before each infestation, they produce fewer or more IgE antibodies, respectively. No effect is observed on IgG antibodies. In IL-4-deficient mice, no IgE or IgG antibody is produced. However, these treatments and the use of IL-4-deficient mice have no negative effect on either tick attachment or the weight of engorged nymphs or larvae. Treatment with anti-IL-4 mAb and the use of IL-4-deficient mice inhibits and abolishes the switching of IgE, respectively, but these are apparently not sufficient to shift the response toward Th1 cells. Received: 18 July 1997 / Accepted: 12 November 1997     

The effect of vitamin A depletion on antigen-stimulated trapping of peripheral lymphocytes in local lymph nodes of rats

The effect of vitamin A depletion on antigen-stimulated trapping of peripheral lymphocytes in lymphatic organs was studied in rats. Distribution of [3H]-uridine-labelled syngenic peripheral lymphocytes was quantified by assaying radioactive content of brachial and axillary lymph nodes, spleen and liver of normal and vitamin A-depleted F344/Ducrj rats immunized with sheep red blood cells. Localization of labelled cells in the ipsilateral brachial lymph nodes of the normal rats was stimulated by three times upon immunization with sheep erythrocytes as compared with the contralateral nodes. Recruitment of cells in axillary lymph nodes, spleen and liver was not significantly different from non-immunized values. The vitamin A-depleted rats exhibited marked deterioration in antigen-stimulated trapping of labelled cells in the draining brachial lymph nodes. These results suggest that this effect of vitamin A depletion is due to derangement of integrity of lymphocyte-trapping mechanism in the draining lymph nodes and not to any change in nature of lymphocytes per se.     

Production of tumor necrosis factor-α and interleukin-6 in whole blood stimulated by live Gram-negative and Gram-positive bacteria

Objective: To investigate the production of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) induced by live Gram-negative and Gram-positive bacteria in whole blood in vitro.
Methods: In all, 49 different isolates were studied. Each of the 49 different isolates was incubated for 4 h with whole blood at a ratio of one monocyte per 1–5 bacteria. Plasma was then separated and frozen, and the concentrations of TNF-α and IL-6 were measured by enzyme immunoassays.
Results: There was a positive correlation between TNF-α and IL-6 values, r =0.9. Gram-negative bacteria induced higher levels of both TNF-α and IL-6 than Gram-positive bacteria. Group G streptococci (GGS) induced higher levels of TNF-α than Streptococcus pneumoniae, Staphylococcus aureus, Staphylococcus epidermidis and group A streptococci (GAS). Klebsiella pneumoniae induced higher levels of TNF-α than Haemophilus influenzae, Escherichia coli and Neisseria meningitidis. GGS induced higher levels of IL-6 than Staphylococcus epidermidis, Staphylococcus aureus and GAS. When the relative amounts of cytokine induced by the strains were compared to serum concentrations measured on admission in patients with bacteremia caused by the same bacterial isolates there was no significant correlation.
Conclusion: Species- and strain-related differences in cytokine-inducing properties were found which may have significance in clinical infections.     

Successive tick infestations selectively promote a T-helper 2 cytokine profile in mice

Several studies have revealed that T lymphocytes and cytokines play a crucial role in determining the outcome of parasitic infections in terms of protective immunity. In this study we found that Rhipicephalus sanguineus tick saliva stimulates transforming growth factor-beta (TGF-beta), and reduces interleukin-12 (IL-12) secretion by cells from normal C3H/HeJ mice. Moreover, murine lymph node cells harvested 6 days after the fourth infestation with ticks presented an 82.4% decrease in their proliferative response to concanavalin A (Con A) compared with the response of control cells. In addition, lymph node cells cultured in the presence of Con A showed a T-helper 2-type (Th2-type) cytokine profile, represented by augmented IL-4 and IL-10 and TGF-beta. On the other hand, the IL-2, interferon-gamma (IFN-gamma) and IL-12 synthesis was significantly inhibited. These results indicate that ticks may modulate the host's immune response through saliva injection. Considering that C3H/HeJ mice develop no protective immunity to R. sanguineus infestation, our results suggest that tick-induced Th2-type cytokines and a decreased proliferative response probably lead the host to a susceptible state to both tick and tick-transmitted pathogens.     

Cytokine Production in Hearts of Trypanosoma cruzi-Infected CBA Mice: Do Cytokine Patterns in Chronic Stage Reflect the Establishment of Myocardial Pathology?

The authors analysed cytokine production in hearts of Trypanosoma cruzi -infected CBA-J mice by in situ immunocytochemical staining. Cellular infiltrates were recorded in hearts from both acute and chronic stages, but were not apparent in control hearts. In the acute heart, CD8 cells predominated, with associated production of IL-4, IL-6 and TNF-α. Cytokine production was characterized by IL-4, IL-5, IL-6 and TNF-α in the chronic heart, and numbers of CD4 and CD8 cells were more equal. At this stage, calcified infarctions and associated fibrosis were apparent, mimicking chronic human Chagas' heart pathology. The authors consider the CBA mouse an appropriate model of chronic T. cruzi infection, and suggest that local cytokine production reflects establishment of heart pathology.     

Regulation of IFN-γ production in granulocyte-macrophage colony-stimulating factor-deficient mice

Granulocyte-macrophage colony-stimulating factor-deficient (GM-CSF−/−) mice produce far lower serum levels of IFN-γ in response to LPS than GM-CSF+/+ mice. CD4⁺ and CD8⁺ T cells from LPS-injected GM-CSF−/− mice showed a deficiency in IFN-γ production and proliferative activity in response to IL-2 and IL-12, whereas IFN-γ production by NK cells was not compromised. These defects of T cells were reversed by administration of GM-CSF in vivo, but not by supplementation with GM-CSF in vitro. GM-CSF−/− mice do not have an intrinsic defect in IFN-γ production, because IL-12 injection induces the same high levels of IFN-γ in GM-CSF−/− and GM-CSF+/+ mice. To investigate the inhibitory effect of LPS on GM-CSF−/− T cells and the indirect restorative activity of GM-CSF, we tested the action of supernatants from cultured dendritic cells (DC). A factor or factors in the DC supernatant normalized serum IFN-γ levels and T cell responses in LPS-injected GM-CSF−/− mice. IL-18 reproduced some but not all of these in vivo and in vitro effects of DC supernatants. Our results indicate that GM-CSF is important in protecting T cells from inhibitory signals generated during immunization or exposure to LPS, and that this effect of GM-CSF is indirect and mediated by factors produced by DC.     

Immunosuppressive effects of<Emphasis Type="Italic"> Ixodes ricinus</Emphasis> tick saliva or salivary gland extracts on innate and acquired immune response of BALB/c mice

Saliva and salivary gland extract (SGE) of Ixodes ricinus ticks have suppressive effects on the innate immune response of BALB/c mice. Tick saliva prevents hemolysis of sheep red blood cells (SRBC) by the human alternative pathway of complement. The adaptive immune response is also modulated by tick antigens (saliva or SGE). When stimulated in vitro with increasing doses of tick antigens, the proliferation and IL-4 production of draining lymph node T cells of mice infested with nymphal ticks increase, peak and then decrease. These results indicate that immunostimulative and immunosuppressive molecules have competing effects in tick saliva or in SGE. I. ricinus saliva inhibits, in a dose-dependent manner, splenic T cell proliferation in response to concanavalin A (ConA). Tick SGE or saliva injected intraperitoneally to BALB/c mice simultaneously with SRBC systemically immunosuppress the anti-SRBC response as shown in vitro by the reduced responsiveness of sensitized splenic T cells to restimulation with SRBC. In brief some components of SGE or tick saliva reduce the responsiveness of draining lymph node T cells and of sensitized splenic T cells in vitro. The responsiveness of naive splenic T cells to ConA stimulation in vitro is also decreased by tick saliva. Modulation of host responses by tick antigens may facilitate tick feeding, transmission and the propagation of pathogens.     

TNF Inhibitors are Produced Spontaneously by Rheumatoid and Osteoarthritic Synovial Joint Cell Cultures: Evidence of Feedback Control of TNF Action

We have proposed the hypothesis that tumour necrosis factor α (TNF-α) has a pivotal role in the pathogenesis of rheumatoid arthritis, based on in vitro observations that in RA synovial joint cell cultures removal of TNF-α, inhibited other potentially pathogenic cytokines such as the equally pro-inflammatory cytokine interleukin 1 (IL-I) and the macrophage activating factor, GM-CSF. Here we describe that in both rheumatoid (RA) and osteoarthritic (OA) synovial cultures there is a homeostatic mechanism to regulate the activities of TNF-α. This concept is based on several observations. First in these synovial joint cell cultures the substantial discrepancy between the levels of bioactive and immunoreactive TNF-α indicates the presence of an inhibitor. Second, TNF binding proteins are produced spontaneously, which are the soluble variants of surface p75 and p55 TNF receptor. The amount of soluble TNF receptors (sTNF-R) produced varied between cultures; p75 sTNF-R was more abundant than p55 sTNF-R (as detected by ELISA), and both were produced at higher levels by RA synovial joint cells in culture, compared to OA cultures. These TNF binding proteins act as endogenous inhibitors of TNF-a, since blocking their activity in synovial joint cell culture supernatants with MoAb to p55 and p75 sTNF-R enhanced their cytotoxic activity in the TNF bioassay. The regulation of production of these sTNF-R in synovial joint cell cultures is important as the balance between TNF-a and sTNF-R production may determine the outcome of the inflammatory process.