Nuclear appearance of a factor that binds the CD28 response element within the interleukin-2 enhancer correlates with interleukin-2 production

Activation of T lymphocytes requires the combined signaling of the T cell receptor and costimulatory molecules such as CD28. The ability of T cells to produce interleukin-2 (IL-2) is a critical control point in T lymphocyte activation. The IL-2 enhancer contains a functional motif named CD28 response element (CD28RE) that serves a role as a target for mitogenic T cell activation signals. The CD28RE sequence reveals similarity to the consensus kappaB binding motif. Here we demonstrate that CD28RE binds an inducible protein with a molecular mass of approximately 35 kDa called nuclear factor of mitogenic-activated T cells (NF-MATp35) that is clearly different from the known NF- kappaB/Rel family members. Induction of NF-MATp35 was shown to depend on de novo protein synthesis and was restricted to T cells that received a mitogenic combination of T cell stimuli, not necessarily including CD28 signaling. Nonmitogenic T cell stimulation did not result in appearance of NF-MATp35. These results indicate that mitogenic combinations of T cell activation signals are integrated at the level of NF-MATp35 induction. Similar to its effect on IL-2 production, cyclosporin A inhibited the induction of NF-MATp35. Taken together, these data demonstrate that the nuclear appearance of NF-MATp35 shows excellent correlation with IL-2 production, which is a unique characteristic among nuclear factors implicated in the control of IL-2 gene expression.

Human IL-13 production is negatively influenced by CD3 engagement. Enhancement of IL-13 production by cyclosporin A

IL-13, a T cell-derived cytokine, shares many of its biologic activities with the Th2 cytokine IL-4, including induction of a class switch to IgE and anti-inflammatory properties. Its potential impact on development of Th2 responses makes it interesting to determine how the production of IL-13 is regulated and which cell types produce IL-13. In this work, we show that IL-13 is produced optimally by T cells when stimulated with a combination of anti-CD28 and PMA. Unexpectedly, additional ligation of the TCR complex with Abs to CD3 caused an approximately fivefold inhibition of IL-13 production. Moreover, this inhibition could be reversed by cyclosporin A (CsA). The effect of CsA did not depend on the presence of PMA; upon CD3 and CD28 stimulation, CsA equally enhanced IL-13 production. Both naive and memory CD4+ T cells and CD8+ T cells produced IL-13, and production in all cell types could be enhanced by CsA. In contrast to IL-13, IL-4 production was observed mainly in CD4+ memory cells, required costimulation through CD3, and was inhibited by CsA. The unusual regulation and relative abundance of IL-13 make it an important candidate to be controlled tightly by dose and type of TCR ligands. CsA is used widely to inhibit T cell function. The finding that IL-13 production is enhanced instead of diminished in the presence of CsA may explain the Th2-inducing effects of CsA in vivo.

Human IL-13 production is negatively influenced by CD3 engagement. Enhancement of IL-13 production by cyclosporin A

IL-13, a T cell-derived cytokine, shares many of its biologic activities with the Th2 cytokine IL-4, including induction of a class switch to IgE and anti-inflammatory properties. Its potential impact on development of Th2 responses makes it interesting to determine how the production of IL-13 is regulated and which cell types produce IL-13. In this work, we show that IL-13 is produced optimally by T cells when stimulated with a combination of anti-CD28 and PMA. Unexpectedly, additional ligation of the TCR complex with Abs to CD3 caused an approximately fivefold inhibition of IL-13 production. Moreover, this inhibition could be reversed by cyclosporin A (CsA). The effect of CsA did not depend on the presence of PMA; upon CD3 and CD28 stimulation, CsA equally enhanced IL-13 production. Both naive and memory CD4+ T cells and CD8+ T cells produced IL-13, and production in all cell types could be enhanced by CsA. In contrast to IL-13, IL-4 production was observed mainly in CD4+ memory cells, required costimulation through CD3, and was inhibited by CsA. The unusual regulation and relative abundance of IL-13 make it an important candidate to be controlled tightly by dose and type of TCR ligands. CsA is used widely to inhibit T cell function. The finding that IL-13 production is enhanced instead of diminished in the presence of CsA may explain the Th2-inducing effects of CsA in vivo.

Regulation of bioactive IL-12 production in lipopolysaccharide-stimulated human monocytes is determined by the expression of the p35 subunit

IL-12 enhances IFN-gamma production by NK cells and T lymphocytes and plays a pivotal role in the development of Th1 cells. Bioactive IL-12 (p70) is composed of two subunits, p35, which is only secreted as part of the p70 dimer, and p40, which can also be secreted by itself. The IL-12 subunits are encoded by two separate genes. Therefore, we studied to what extent the expression of each of the subunits contributes to the regulation of IL-12 production. We found that in LPS-stimulated whole blood and purified monocytes, p70 and p40 production are enhanced by IFN-gamma and inhibited by IL-10 and IL-4. However, IFN-gamma and IL-10 had stronger effects on p70 production than on p40 production, and IL-4 affected p40 production more strongly. Concomitantly, in all experimental conditions tested, p40 production greatly exceeded p70 production, suggesting that p35 expression was limiting. Analysis of p35 and p40 mRNA expression by PCR confirmed this notion. Resting purified monocytes expressed neither p40 nor p35 mRNA. The effects of IFN-gamma, IL-10, and IL-4 on the p35 mRNA expression in LPS-stimulated purified monocytes were similar to the effects of these cytokines on p70 protein production, and the p40 mRNA expression corresponded to p40 protein production. Our results imply that production of the two IL-12 subunits is differently regulated for each subunit, mainly at the level of mRNA expression, and that the level of bioactive IL-12 production in monocytes in response to LPS and cytokines is determined by the level of p35 expression.

Regulation of bioactive IL-12 production in lipopolysaccharide-stimulated human monocytes is determined by the expression of the p35 subunit

IL-12 enhances IFN-gamma production by NK cells and T lymphocytes and plays a pivotal role in the development of Th1 cells. Bioactive IL-12 (p70) is composed of two subunits, p35, which is only secreted as part of the p70 dimer, and p40, which can also be secreted by itself. The IL-12 subunits are encoded by two separate genes. Therefore, we studied to what extent the expression of each of the subunits contributes to the regulation of IL-12 production. We found that in LPS-stimulated whole blood and purified monocytes, p70 and p40 production are enhanced by IFN-gamma and inhibited by IL-10 and IL-4. However, IFN-gamma and IL-10 had stronger effects on p70 production than on p40 production, and IL-4 affected p40 production more strongly. Concomitantly, in all experimental conditions tested, p40 production greatly exceeded p70 production, suggesting that p35 expression was limiting. Analysis of p35 and p40 mRNA expression by PCR confirmed this notion. Resting purified monocytes expressed neither p40 nor p35 mRNA. The effects of IFN-gamma, IL-10, and IL-4 on the p35 mRNA expression in LPS-stimulated purified monocytes were similar to the effects of these cytokines on p70 protein production, and the p40 mRNA expression corresponded to p40 protein production. Our results imply that production of the two IL-12 subunits is differently regulated for each subunit, mainly at the level of mRNA expression, and that the level of bioactive IL-12 production in monocytes in response to LPS and cytokines is determined by the level of p35 expression.

Interleukin 10 release during endotoxaemia in chimpanzees: role of platelet-activating factor and interleukin 6

Interleukin (IL-)10 has been demonstrated to inhibit endotoxin-induced production of a number of pro-inflammatory cytokines. The present study sought to compare the appearances in the circulation of IL-10, IL-6 and IL-8, and to assess the roles of endogenously produced platelet-activating factor (PAF) and IL-6 in IL-10 release during endotoxaemia in chimpanzees. Intravenous injection of endotoxin (lot EC-5, 4 ng/kg, n = 8) induced a transient rise in serum IL-10 concentrations, peaking after 2 h (213 +/- 70 pg/ml; P < 0.05). No correlations existed between peak IL-10 levels, and peak IL-6 and IL-8 levels. Neither infusion of the specific PAF antagonist TCV-309 (n = 4), nor infusion of a neutralizing anti-IL-6 monoclonal antibody (n = 4) influenced endotoxin-induced IL-10 release. IL-10 release elicited by injection of endotoxin is not mediated by PAF or IL6.

Cytokine production (IL-6 and TNF alpha) in whole blood cell cultures of patients with systemic lupus erythematosus

Whole blood cell culture has great advantage over isolated peripheral blood mononuclear cell culture, because it needs only small amounts of blood and is fast to perform. The current report focuses on the measurement of IL-6 and TNF alpha produced by peripheral blood monocytes of patients with systemic lupus erythematosus (SLE) in the whole blood cell culture system. After an initial triggering with lipopolysaccharide (LPS), a specific stimulus for monocytes, a decreased production of IL-6 relative to the controls was observed. Dividing our SLE patients according to treatment with corticosteroids, overall the IL-6 production was decreased in the patients treated with corticosteroids. TNF alpha production was comparable with normals, with the exception of an increased spontaneous production and using LPS stimulus of 4 pg/ml. In the patients treated with corticosteroids a decreased TNF production was observed, in contrast to the non-treated patients in which an increased TNF production was found compared with the controls using LPS doses higher than 62 pg/ml. The impaired acute phase reaction (APR) that has been described in the literature, might be explained by our observation of a decreased production of mainly IL-6. However, also this study showed that treatment has a strong impact on ex vivo IL-6 and TNF production.

Leucine-58 in the putative 5th helical region of human interleukin (IL)-6 is important for activation of the IL-6 signal transducer, gp130

A model of the tertiary structure of human IL-6, derived from the crystal-structure of granulocyte-colony stimulating factor, reveals a 5th helical region in the loop between the first and second alpha-helix. To investigate the importance of this region for biological activity of IL-6, residues Glu-52, Ser-53, Ser-54, Lys-55, Glu-56, Leu-58, and Glu-60 were individually replaced by alanine. IL-6.Leu-58Ala displayed a 5-fold reduced biological activity on the IL-6 responsive human cell lines XG-1 and A375. This reduction in bioactivity was shown to be due to a decreased capacity of the mutant protein to trigger IL-6 receptor-alpha-chain-dependent binding to the IL-6 signal transducer, gp130.

Development of human IL-6 receptor antagonists

We have shown that through mutagenesis of IL-6 it is possible to separate receptor binding from signal transduction of the cytokine. Mutations in residues important for signal transduction via gp130 result in IL-6 variants that can competitively inhibit wtIL-6 activity in vitro. The differential effects of these signaling deficient mutants on various cell lines of human origin suggest that receptor composition and/or signal transduction pathways may vary between cells of different origin. The observations that three sites have been identified which are important for gp130 interaction raises the question what the role of each region is in the stepwise formation of the active IL-6 receptor complex. The overall tertiary conformation of the beta-site mutants is intact, as judged from their binding characteristics to conformation specific mAbs and IL-6R alpha. As can be deduced from Figure 1, beta-site mutations may therefore affect a direct interaction with gp130, dimerization of IL-6, or maybe a conformational change in IL-6R alpha, important for gp130 interaction. A future challenge will therefore be to determine the function of each of the beta-sites in IL-6 receptor interaction.

Co-stimulation of T cells via CD28 inhibits human IgE production; reversal by pertussis toxin

In lymphocyte cultures, IgE production was achieved by stimulating T cells with anti-CD2 and IL-2. Here we show that anti-CD28, in the presence or absence of IL-2, reduces this IgE production approximately 10-fold. This inhibition of IgE production was almost completely reversed by Pertussis toxin (PT). PT had no effect on IgE production when the cells were stimulated in the absence of anti-CD28. No major effects of PT were found on IgM production. PT had no effect on purified B cells, stimulated with IL-4 and anti-CD40. In the presence of saturating amounts of rIL-4 similar results were obtained, albeit the absolute amounts of IgE produced were higher in all situations. Furthermore, PT-induced IgE production was still dependent on IL-4, as was evident from experiments in which anti-IL-4 was added to the culture. The IgE enhancing effect was dependent on the adenosine diphosphate (ADP)-ribosyltransferase activity of PT, because a mutant molecule lacking this activity was not able to restore anti-CD28-induced inhibition of IgE synthesis. Thus, we show that co-stimulation with anti-CD28 causes an inhibition of T cell-dependent IgE production by B cells, which inhibition can be specifically overcome by PT. An analysis of the molecular pathways underlying this phenomenon may contribute to our understanding of the regulation of IgE synthesis in (patho)physiological conditions.

Prostaglandin-E2 is a potent inhibitor of human interleukin 12 production

During human immunodeficiency virus infection and allergic diseases, characterized by a dominant T helper (Th) 2 response, overproduction of prostaglandin E2 (PGE2) is observed. In this paper we studied the effect of PGE2 on interleukin (IL)-12 synthesis, because this cytokine has been described to be essential in induction of Th1 responses. IL-12 synthesis was induced in monocytes that were stimulated with Neisseria meningitidis-derived lipopolysaccharide in whole blood cultures. PGE2 almost completely inhibited lipopolysaccharide induced IL-12 production, whereas IL-6 production was only partially inhibited by PGE2. In contrast, the production of IL-10 was approximately twofold enhanced at these conditions. The effects of PGE2 were due to its cAMP-inducing capacity, since they could be mimicked by other cAMP inducers. Recombinant human IL-10 also inhibited IL-12 and IL-6 production. However, the inhibitory effect of PGE2 on IL-12 production was independent of IL-10 since neutralizing anti-IL-10 antibodies were unable to reverse this inhibition. These results suggest that the capacity of an antigen to induce PGE2 synthesis may play a crucial role in the development of either a Th1 or Th2 response.

Development of an interleukin (IL) 6 receptor antagonist that inhibits IL-6-dependent growth of human myeloma cells

The pleiotropic cytokine interleukin 6 (IL-6) plays a role in the pathogenesis of various diseases, such as multiple myeloma, autoimmune and inflammatory diseases and osteoporosis. Therefore, specific inhibitors of IL-6 may have clinical applications. We previously succeeded in developing receptor antagonists of IL-6 that antagonized wild-type IL-6 activity on the human Epstein-Barr virus (EBV)-transformed B cell line CESS and the human hepatoma cell line HepG2. However, these proteins still had agonistic activity on the human myeloma cell line XG-1. We here report the construction of a novel mutant protein of IL-6 in which two different mutations are combined that individually disrupt the association of the IL-6/IL-6 receptor (R) alpha complex with the signaltransducing "beta" chain, gp130, but leave the binding of IL-6 to IL-6R alpha intact. The resulting mutant protein (with substitutions of residues Gln160 to Glu, Thr163 to Pro, and replacement of human residues Lys42-Ala57 with the corresponding residues of mouse IL-6) was inactive on XG-1 cells and weakly antagonized wild-type IL-6 activity on these cells. By introducing two additional substitutions (Phe171Leu, Ser177Arg), the affinity of the mutant protein for IL-6R alpha was increased fivefold, rendering it capable of completely inhibiting wild-type IL-6 activity on XG-1 cells. Moreover, this mutant also antagonized the activity of IL-6, but not that of leukemia inhibitory factor, oncostatin M, or GM-CSF on the human erythroleukemia cell line TF-1, demonstrating its specificity for IL-6. These data demonstrate the feasibility of developing specific IL-6R antagonists. The availability of such antagonists may offer an approach to specifically inhibit IL-6 activity in vivo.

IgE production in atopic patients is not related to IL-4 production

To analyse whether there is a general defect in T or B cell function in atopic individuals we have measured cytokine and IgE production by peripheral blood lymphocytes, isolated from 19 atopic donors (17 asthma/rhinitis and two dermatitis patients) in comparison with 19 non-atopic controls. After stimulation of lymphocytes with anti-CD2 and anti-CD28, we found no significant difference in IL-2, IL-4 and interferon-gamma (IFN-gamma) production. To examine the correlation between the production of IgE and IL-4, we stimulated lymphocytes with anti-CD2 and rIL-2. Under this condition both T cell IL-4 and B cell IgE production can be measured. No significant difference was found for the amount of IgE and IL-4 produced between the two groups (P > 0.05). The non-atopic donors showed a good correlation between IL-4 and IgE production (r = 0.70). Surprisingly, within the atopic group there was no correlation between IgE and IL-4 production at all (r = -0.04). The ratio of IgE to IL-4 was higher (although not significantly) in the atopic group. Our data suggest that in atopic donors IgE production is less dependent on IL-4, and that other cytokines are involved.

Development of a human interleukin-6 receptor antagonist

Neutralizing monoclonal antibodies specific for human interleukin-6 (IL-6) bind two distinct sites on the IL-6 protein (sites I and II). Their interference with IL-6 receptor binding suggested that site I is a receptor-binding site of IL-6, whereas site II is important for signal transduction. Mutagenesis of site II could therefore result in the isolation of IL-6 receptor antagonists. To test this hypothesis, a panel of IL-6 mutant proteins was constructed that did not bind to a site II-specific monoclonal antibody. One such site II mutant protein (with double substitution of Gln-160 with Glu and Thr-163 with Pro) was found to be an antagonist of human IL-6. It was inactive on human CESS cells, weakly active on human HepG2 cells, but active on mouse B9 cells. It could specifically antagonize the activity of wild-type IL-6 on CESS and HepG2 cells. The binding affinity of this variant for the 80-kDa IL-6 receptor was similar to that of wild-type IL-6. High affinity binding to CESS cells, however, was abolished, suggesting that the mutant protein is inactive because the complex of the 80-kDa IL-6 receptor and the mutant protein cannot associate with the signal transducer gp130. The human IL-6 antagonist protein may be potentially useful as a therapeutic agent.

Measurement of interleukin-6 production by monocytes for in vitro safety testing of hemoglobin solutions

Induction of interleukin-6 (IL-6) production by isolated human mononuclear blood cells was taken as in vitro model for the induction of inflammatory reactions. The model was very sensitive to bacterial endotoxin (detection limit < 10pg/ml). Hemoglobin (Hb) solutions, prepared under non-sterile conditions also induced IL-6 production, which correlated with a positive reaction in the Limulus assay. Purification of the Hb solutions with a detergent prevented IL-6 production, showing that pure Hb itself does not activate the monocytes. We conclude that this assay is a useful and sensitive test of contamination with components that can induce inflammatory reactions, especially microbial products.

Interleukin-8 (IL-8) in synovial fluid of rheumatoid and nonrheumatoid joint effusions

IL-8 was measured in knee joint synovial fluid of 60 patients with rheumatoid arthritis, 8 with gout, 6 with osteoarthritis and 4 with meniscus lesions. IL-8 could be demonstrated in most SF samples. The highest levels were observed in rheumatoid joint effusions, yet mean levels were not significantly different between the different subgroups (mean +/- SE; RA 1537 +/- 3049 pg/ml, gout 570 +/- 952 pg/ml, OA/ML 178 +/- 188 pg/ml). In RA patients, IL-8 levels could not be related to various serological, clinical or radiological parameters. However, a correlation was observed between SF levels of IL-8 with those of lactate, LDH, beta 2-microglobulin and glucose. These observations suggest that next to the laboratory parameters IL-8 will be a parameter of the activity of the local inflammatory process. The results also demonstrate that IL-8 is not a disease-specific marker of joint inflammation.

Interleukin-6 mediates host defense responses induced by abdominal surgery

BACKGROUND

Cytokines have been implicated as pivotal mediators of the host defense reaction. In patients undergoing surgery we investigated the relationship between such mediators and postoperative host defense responses.

METHODS

Tumor necrosis factor (TNF) was determined with an immunoradiometric assay, interleukin (IL)-6 by a B9-cell bioassay, and endotoxin by a chromogenic limulus lysate assay. C-reactive protein, alpha 1-antitrypsin, and alpha 2-macroglobulin were quantified by nephelometric assay.

RESULTS

In 19 consecutive patients undergoing pancreaticoduodenectomy, a large increase in portal, and a significantly lower increase in peripheral, IL-6 levels was observed. No significant increase in TNF levels was noted. Fever developed in 16 patients within 24 hours (84%). The highest peripheral IL-6 levels correlated logarithmically (R = 0.59; p = 0.0039) with the peak body temperatures. C-reactive protein levels correlated with IL-6 levels (R = 0.49; p = 0.020). Increased IL-6 levels were observed in all nine patients undergoing either hemihepatectomy, breast reduction, or extensive breast reconstruction; however, only patients undergoing hemihepatectomy had endotoxemia.

CONCLUSIONS

We conclude that abdominal surgery causes acute release of IL-6, but not TNF, in the portal circulation. IL-6 seems to be a major endogenous mediator of fever and the acute-phase response. The presence of endotoxin might be synergistic but is not obligatory for the host defense response after surgical trauma.

Pentoxifylline attenuates neutrophil activation in experimental endotoxemia in chimpanzees

Costimulation of neutrophils and cytokines may play an important role in organ injury in sepsis. Pentoxifylline inhibits various neutrophil functions in vitro, and attenuates endotoxin-induced production of TNF in both in vitro and in vivo models. To assess the effect of pentoxifylline on neutrophil activation in endotoxemia, nine adult chimpanzees (Pan troglodytes) were i.v. injected with saline (n = 2), Escherichia coli endotoxin (4 ng/kg; n = 4), or E. coli endotoxin (4 ng/kg) in combination with pentoxifylline (500 mg/3 h, starting 30 min before the endotoxin injection; n = 3). Serial blood samples were obtained for measurements of leukocyte counts and the granulocytic proteinases elastase complexed with alpha 1-antitrypsin and lactoferrin, and cytokines during the next 5 h. No changes were observed in the saline-treated chimpanzees. Endotoxin induced a marked leukocytosis and neutrophilia, which were slightly reduced by pentoxifylline. In contrast, pentoxifylline almost completely prevented endotoxin-induced neutrophil degranulation: peak elastase-alpha 1-antitrypsin was 164 +/- 21 ng/ml (mean +/- SE) after endotoxin alone, vs 71 +/- 7 ng/ml after endotoxin with pentoxifylline (t = 3 h; p &lt; 0.05); peak lactoferrin was 329 +/- 15 and 182 +/- 5 ng/ml, respectively (t = 5 h; p &lt; 0.05). Pentoxifylline also inhibited the endotoxin-induced release of TNF (271 +/- 26 vs 55 +/- 23 pg/ml at t = 1.5 h; p &lt; 0.05) and IL-6 (225 +/- 42 vs 73 +/- 25 pg/ml at t = 2 h; p &lt; 0.05). IL-8 release was not significantly inhibited by pentoxifylline. In none of the animals activation of the C system could be detected. We conclude that pentoxifylline attenuates neutrophil activation in endotoxemia in chimpanzees, probably in part by inhibiting the release of TNF.

Pentoxifylline attenuates neutrophil activation in experimental endotoxemia in chimpanzees

Costimulation of neutrophils and cytokines may play an important role in organ injury in sepsis. Pentoxifylline inhibits various neutrophil functions in vitro, and attenuates endotoxin-induced production of TNF in both in vitro and in vivo models. To assess the effect of pentoxifylline on neutrophil activation in endotoxemia, nine adult chimpanzees (Pan troglodytes) were i.v. injected with saline (n = 2), Escherichia coli endotoxin (4 ng/kg; n = 4), or E. coli endotoxin (4 ng/kg) in combination with pentoxifylline (500 mg/3 h, starting 30 min before the endotoxin injection; n = 3). Serial blood samples were obtained for measurements of leukocyte counts and the granulocytic proteinases elastase complexed with alpha 1-antitrypsin and lactoferrin, and cytokines during the next 5 h. No changes were observed in the saline-treated chimpanzees. Endotoxin induced a marked leukocytosis and neutrophilia, which were slightly reduced by pentoxifylline. In contrast, pentoxifylline almost completely prevented endotoxin-induced neutrophil degranulation: peak elastase-alpha 1-antitrypsin was 164 +/- 21 ng/ml (mean +/- SE) after endotoxin alone, vs 71 +/- 7 ng/ml after endotoxin with pentoxifylline (t = 3 h; p < 0.05); peak lactoferrin was 329 +/- 15 and 182 +/- 5 ng/ml, respectively (t = 5 h; p < 0.05). Pentoxifylline also inhibited the endotoxin-induced release of TNF (271 +/- 26 vs 55 +/- 23 pg/ml at t = 1.5 h; p < 0.05) and IL-6 (225 +/- 42 vs 73 +/- 25 pg/ml at t = 2 h; p < 0.05). IL-8 release was not significantly inhibited by pentoxifylline. In none of the animals activation of the C system could be detected. We conclude that pentoxifylline attenuates neutrophil activation in endotoxemia in chimpanzees, probably in part by inhibiting the release of TNF.

Isotype-specific cross-linking of select human Fc gamma R isoforms triggers release of IL-6

Anti-CD3 MoAbs are widely used in T cell activation studies, and are effective in immunosuppressive therapy. We used a panel of mouse (m) anti-CD3 switch variant MoAbs of five different isotypes to study IL-6 release from accessory cells. Incubation of human (h) mononuclear cells with anti-CD3 MoAbs resulted in increased IL-6 levels with MoAbs of mIgG1 and mIgG2a isotypes, with no effect of mIgG2b or mIgA. This suggested involvement of IgG Fc receptors (Fc gamma R) in triggering IL-6 production. To evaluate the role of different Fc gamma R molecules individually we used a panel of hFc gamma R-transfected mouse fibroblasts, and Jurkat T cells as a model. IL-6 secretion by CD32 transfectants expressing the hFc gamma RIIa high-responder (HR) allelic form was triggered by mIgG1 anti-CD3 MoAb, with no effect of four other isotypes. None of the anti-CD3 MoAbs induced IL-6 secretion by CD32 transfectants expressing either a variant of this receptor, containing only a single intracellular amino acid (CT-), the hFc gamma RIIa low-responder (LR) allelic form, or hFc gamma RIIb1. hFc gamma RI (CD64) transfectants exhibited IL-6 production after incubation with mIgG2a anti-CD3 MoAb, and to a lesser extent with mIgG2b, and mIgG1 MoAb. Indirect involvement of T cells in triggering IL-6 secretion could be excluded by experiments in which transfectants were cultured with immobilized anti-CD3 MoAb. These data indicate that cross-linking of either hFc gamma RI, or hFc gamma RIIaHR by appropriate anti-CD3 MoAbs triggers IL-6 production of accessory cells, and not T cells. This may also take place in vivo during immunosuppressive therapy with anti-CD3 MoAbs, and related antibody-mediated immune responses.

Endotoxin and tumor necrosis factor-alpha-induced interleukin-8 release in humans

Neutrophil recruitment and activation are thought to play an important role in tissue damage observed in septicemia. Interleukin-8 (IL-8) is a small cytokine with important neutrophil-activating and chemoattractant properties. IL-8 release was studied after injection of human volunteers with low doses of either endotoxin (2 ng/kg of body weight) or tumor necrosis factor-alpha (TNF alpha) (50 micrograms/m2). After TNF-alpha injection, IL-8 appeared at 30 min, whereas increased levels were first observed after 90 min in endotoxin-challenged volunteers. Peak levels were measured at 120 min after both endotoxin (192 +/- 193 ng/L) and TNF alpha (500 +/- 236 ng/L) injection. These data indicate that IL-8 is released in humans after injection of endotoxin and TNF alpha and suggest that endotoxin-induced IL-8 release is mediated by TNF alpha.

Evidence for a role of CD28RE as a response element for distinct mitogenic T cell activation signals

T lymphocytes can be induced to produce interleukin (IL)-2 and proliferate upon T cell receptor (TcR) occupancy together with a CD28-induced co-stimulatory signal. The T cell surface molecule CD28 is believed to function as a regulator in T cell activation at both the level of lymphokine mRNA stabilization and gene transcription. Activation of IL-2 gene transcription via CD28 has been shown to be mediated through a kappa B-like sequence, called CD28RE. DNA binding analysis revealed that the CD28-induced signal is involved in the induction of CD28RE binding activity. Here, we demonstrate that the induction of CD28RE binding activity is not specific for the CD28-induced signal. Our data indicate that distinct mitogenic T cell activation signals converge on the induction of CD28RE binding activity, and suggest a crucial role for this activity in the IL-2 enhancer responsiveness to different modes of T cell activation.

On the interaction of IgG subclasses with the low affinity Fc gamma RIIa (CD32) on human monocytes, neutrophils, and platelets. Analysis of a functional polymorphism to human IgG2

An allotypic form of the low affinity IgG Fc receptor Fc gamma RIIa (CD32), termed low responder (LR) because of its weak reactivity with mouse (m) IgG1, interacts efficiently with human (h) IgG2. Fc gamma RIIaLR is the first known human FcR that binds this IgG subclass. In this study, we analyzed the role of Fc gamma RIIa in binding of stable hIgG-subclass dimers, and in induction of T cell mitogenesis using chimeric anti-CD3 mAb. We demonstrate that the functional polymorphism to hIgG2 is expressed on the majority of Fc gamma R-bearing peripheral blood cells: monocytes, neutrophils, and platelets. We were able to assess Fc gamma RII-mediated IgG-binding without interference of other Fc gamma R-classes, by blockade of Fc gamma RI on monocytes, and by using neutrophils of an individual deficient for the Fc gamma RIIIB gene. This study indicates as subclass specificity: hIgG3 >hIgG1,hIgG2 >> hIgG4 for Fc gamma RIIaLR and hIgG3,hIgG1 >> hIgG2 > hIgG4 for Fc gamma RIIaHR. Comparing the serum hIgG levels of individuals homozygous for the two fc gamma RIIa allotypic forms, we observed significantly lower hIgG2 serum levels in individuals expressing the hIgG2-binding LR allotypic form. This observation may implicate that Fc gamma RIIa regulates hIgG subclass production or turnover in man.