Identification of C3 beta chain as the human serum eosinophil cytotoxicity inhibitor.

An eosinophil cytotoxicity inhibitor (ECI) was purified from serum of a human subject with severe allergic dermatitis. Molecular weight of the isolated polypeptide (75,000) and its NH2-terminal amino acid sequence identified it as the beta chain of the C3 complement component (apparently free, but perhaps attached to very small fragments of the alpha chain). Free beta chain, prepared from normal plasma by reduction of C3, inhibited both eosinophil cytotoxicity and neutrophil adherence functions, with half-maximal activity at approximately 250 ng/ml. Apparently free C3 beta chain was detected in certain human biological fluids associated with inflammation; the presence of C3 beta chain correlated with ECI activity. This evidence demonstrates a potential role for free C3 beta chain as a suppressor of eosinophil and neutrophil functions in inflammation.

A serum factor that suppresses the cytotoxic function of cytokine-stimulated human eosinophils.

A human subject (NR) was identified whose eosinophils and neutrophils failed to respond to TNF in vitro in 29 of 33 experiments, using several biological assays. There was a response rate to TNF of 100% among 37 control subjects whose leukocytes were tested in parallel. NR serum contained an activity that inhibited the cytotoxic function of TNF- and GM-CSF-stimulated normal human eosinophils. A similar activity was detected in 4 of 122 control sera and in sera of two subjects with hypereosinophilia. This activity (ECI) had an apparent molecular weight of 80,000-100,000 and was sensitive to heating at 80 degrees C or to trypsin treatment. HPLC sizing chromatography increased the titer of ECI by a factor of 50 to 2,000 in experiments using NR serum or other sera with detectable inhibitory activity. In seven experiments using sera with no inhibitory activity, HPLC generated ECI of the same apparent molecular weight. The effect of HPLC on ECI activity required the separation of serum components and did not result from exposure to HPLC system components or other sample processing methods. This suggests that ECI in serum can be stabilized in an inactive or partially active form and that HPLC removes the stabilizing component. ECI suppressed TNF-stimulated eosinophil cytotoxic function when added to cultures up to 4 h after exposure of eosinophils to cytokine. However, ECI did not protect L929 cells from the toxic effects of TNF. Thus, ECI did not act by preventing the initial interaction of TNF with eosinophils or by interfering with the binding of TNF to its receptor on L929 cells. The results suggest that ECI is a component of a feedback mechanism that suppresses functions of cytokine-activated eosinophils in inflammation.

Regulation of human eosinophil viability, density, and function by granulocyte/macrophage colony-stimulating factor in the presence of 3T3 fibroblasts.

Normodense human peripheral blood eosinophils were isolated under sterile conditions from the 22/23 and 23/24% interfaces and the cell pellet of metrizamide gradients. After culture for 7 d in RPMI media in the presence of 50 pM biosynthetic (recombinant) human granulocyte/macrophage colony-stimulating factor (rH GM-CSF), 43 +/- 7% (mean +/- SEM, n = 8) of the cells were viable; in the absence of rH GM-CSF, no eosinophils survived. The rH GM-CSF-mediated viability was concentration dependent; increased survival began at a concentration of 1 pM, a 50% maximal response was attained at approximately 3 pM, and a maximal effect was reached at concentrations of greater than or equal to 10 pM rH GM-CSF. In the presence of rH GM-CSF and mouse 3T3 fibroblasts, 67 +/- 6% (mean +/- SEM, n = 8) of the eosinophils survived for 7 d. In a comparative analysis, there was no difference in eosinophil viability after 7 and 14 d (n = 3) in the presence of 50 pM GM-CSF and fibroblasts. Culture with fibroblasts alone did not support eosinophil survival. The addition of fibroblast-conditioned media to rH GM-CSF did not further improve eosinophil viability, indicating a primary role for GM-CSF in supporting these eosinophil cell suspensions ex vivo and a supplementary role for 3T3 fibroblasts. Eosinophils cultured for 7 d localized on density gradient sedimentation at the medium/18, 18/20, and 20/21 interfaces of metrizamide gradients, indicating a change to the hypodense phenotype from their original normodense condition. In addition, the cultured eosinophils generated approximately 2.5-fold more LTC4 than freshly isolated cells when stimulated with the calcium ionophore A23187 and manifested sevenfold greater antibody-dependent killing of S. mansoni larvae than the freshly isolated, normodense cells from the same donor. Thus we demonstrate the rH GM-CSF dependent conversion in vitro of normodense human eosinophils to hypodense cells possessing the augmented biochemical and biological properties characteristic of the hypodense eosinophils associated with a variety of hypereosinophilic syndromes. In addition, these studies provide a culture model of at least 14 d suitable for the further characterization of hypodense eosinophils.

Opposing regulatory effects of thioredoxin and eosinophil cytotoxicity-enhancing factor on the development of human immunodeficiency virus 1.

Exogenous recombinant human thioredoxin (rTRX, > or = 500 nM), a dithiol reductase enzyme, inhibited the expression of human immunodeficiency virus (HIV) 1BaL in human macrophages (M phi) by 71% (range, 26-100%), as evaluated by p24 antigen production and the integration of provirus at 14 d after infection. The stoichiometric reducing agent N-acetylcysteine (NAC) also inhibited HIV production, but to a lesser degree, and only at 30,000-fold higher concentrations. Exogenous rTRX is cleaved by M phi to generate the inflammatory cytokine, eosinophil cytotoxicity-enhancing factor (ECEF). In contrast to rTRX, rECEF (concentrations from 50 pM to 2 microM) enhanced the production of HIV by 67% (range, 33-92%). Thus, whereas TRX is a potent inhibitor of the expression of HIV in human M phi, cleavage of TRX to ECEF creates a mediator with the opposite effect. TRX also inhibited the expression of integrated provirus in the chronically infected OM 10.1 cell line, showing that it can act at a step subsequent to viral infection and integration.

Ges, A human GTPase of the Rad/Gem/Kir family, promotes endothelial cell sprouting and cytoskeleton reorganization.

Rad, Gem/Kir, and mRem (RGK) represent a unique GTPase family with largely unknown functions (Reynet, C., and C.R. Kahn. 1993. Science. 262:1441-1444; Cohen, L., R. Mohr, Y. Chen, M. Huang, R. Kato, D. Dorin, F. Tamanoi, A. Goga, D. Afar, N. Rosenberg, and O. Witte. Proc. Natl. Acad. Sci. USA. 1994. 91:12448-12452; Maguire, J., T. Santoro, P. Jensen, U. Siebenlist, J. Yewdell, and K. Kelly. 1994. Science. 265:241-244; Finlin, B.S., and D.A. Andres. 1997. J. Biol. Chem. 272:21982-21988). We report that Ges (GTPase regulating endothelial cell sprouting), a human RGK protein expressed in the endothelium, functions as a potent morphogenic switch in endothelial cells (ECs). Ges function is sufficient to substitute for angiogenic growth factor/extracellular matrix (ECM) signals in promoting EC sprouting, since overexpression of Ges in ECs cultured on glass leads to the development of long cytoplasmic extensions and reorganization of the actin cytoskeleton. Ges function is also necessary for Matrigel-induced EC sprouting, since this event is blocked by its dominant negative mutant, Ges(T94N), predicted to prevent the activation of endogenous Ges through sequestration of its guanine nucleotide exchange factor. Thus, Ges appears to be a key transducer linking extracellular signals to cytoskeleton/morphology changes in ECs.

Effects on Trichinella spiralis of host responses to purified antigens.

Purification of two antigens (48-kilodalton polypeptide and a group with major subunits of 50 and 55 kilodaltons) from the infective larvae of the parasitic nematode Trichinella spiralis was recently reported. Immunization of mice with either of these antigens induces strong resistance to a subsequent challenge infection. In the study reported here the mechanism of this resistance was investigated by monitoring the parasite's life cycle in mice immunized with the antigens. Immunized mice were able to expel intestinal adult worms and to inhibit the fecundity of adult female worms at an accelerated rate compared to control mice. Accelerated expulsion and inhibition of fecundity may account entirely for the level of resistance induced by immunization. Although the effects of the immune response apparently are exerted on adult worms, the target antigens are expressed only by developing larvae. This suggests that immune effector mechanisms act on intestinal larvae in such a way that they develop into defective adults.

Eosinophils cocultured with endothelial cells have increased survival and functional properties.

Human peripheral blood eosinophils, cells often associated with allergic and parasitic diseases, were maintained in vitro for at least 14 days when they were cocultured with bovine endothelial cells and for at least 7 days when cultured with either bovine or human endothelial cell-derived conditioned medium. The cocultured eosinophils became hypodense and generated about three times as much leukotriene C4 upon activation with calcium ionophore and killed about three times as many antibody-coated larvae of Schistosoma mansoni as freshly isolated normodense eosinophils. That these cells can be maintained in vitro by coculture with endothelial cells, and the surprising finding that the cocultured eosinophils have biochemical, cytotoxic, and density properties similar to those of eosinophils in patients with allergic and other disorders, will facilitate investigation of the regulation and role of these cells in health and disease.

Human eosinophils express functional interleukin 2 receptors.

Because T cell-derived cytokines may affect the functioning of eosinophils, we have investigated the capacity of human eosinophils to respond to IL-2. IL-2 was a potent chemoattractant with ED50 of 10(-12) M with eosinophils from all normal and eosinophilic donors tested. The monoclonal antibodies anti-Tac and TU27 against p55 (Tac/CD25) and p75 receptor subunits, respectively, each inhibited IL-2-dependent eosinophil migration. The molar potency of IL-2 and the inhibitory activity of each of the above antibodies suggest that high affinity heterodimeric IL-2 receptor complexes mediated the migration responses of eosinophils to IL-2. Binding of monoclonal antibody against p75 was not detectable by flow cytometry, and high affinity binding sites for 125I-IL-2 were below the limits of quantitation on eosinophils from individuals with eosinophilia. Expression of p55 (Tac/CD25) by eosinophils, without requirement for in vitro activation, was demonstrable by flow cytometry, radioimmunoprecipitation, and Northern blotting for mRNA. Surface expression of p55 on eosinophils from normal or eosinophilic individuals increased during culture for 24-48 h with a biologic activity purified from stimulated U937 cells and to a lesser extent with granulocyte-macrophage CSF or lymphocyte chemoattractant factor but not with nine other cytokines. These studies indicate that blood eosinophils respond to IL-2 and identify one mechanism whereby activation of T lymphocytes may influence the function of eosinophils.

Human eosinophils have prolonged survival, enhanced functional properties, and become hypodense when exposed to human interleukin 3.

Human eosinophils were cultured in the presence of recombinant human IL-3 for up to 14 d and their biochemical, functional, and density properties were assessed. After 3 d of culture in 10 pM IL-3, eosinophils had a viability of 70% compared with only 10% in enriched medium alone. Neither IL-1 alpha, IL-2, IL-4, tumor necrosis factor, basic fibroblast growth factor, nor platelet-derived growth factor maintained eosinophil viability. The 7- and 14-d survival of the cultured eosinophils was 55 and 53%, respectively. No other cell type, including neutrophils, was present after culture. After 7 d of culture, the normodense eosinophils were converted to hypodense cells as assessed by density centrifugation. Eosinophils exposed to 1,000 pM IL-3 for 30 min or cultured in 10 pM IL-3 for 7 d generated approximately threefold more leukotriene C4 (LTC4) in response to calcium ionophore than freshly isolated cells. Furthermore, whereas freshly isolated eosinophils killed only 14% of the antibody-coated Schistosoma mansoni larvae, these eosinophils killed 54% of the larvae when exposed to 100 pM IL-3. The enhanced helminth cytotoxicity was maintained for 7 d when eosinophils were cultured in the presence of both 10 pM IL-3 and 3T3 fibroblasts, but not when eosinophils were cultured in the presence of IL-3 alone. IL-3 thus maintains the viability of eosinophils in vitro, augments the calcium ionophore-induced generation of LTC4, enhances cytotoxicity against antibody-sensitized helminths, and induces the eosinophils to become hypodense cells. These phenotypic changes in the eosinophil may be advantageous to host defense against helminthic infections but may be disadvantageous in conditions such as allergic disease.

Orally active trifluoromethyl ketone inhibitors of human leukocyte elastase.

This paper describes the development a series of peptidyl trifluoromethyl ketone inhibitors of human leukocyte elastase which are found to have excellent pharmacological profiles. Methods have been developed that allow for the synthesis of these inhibitors in stereochemically pure form. Two of these compounds, 1k and 1l, have high levels of oral bioavailability in several species. Compound 1l has entered development as ZD8321 and is presently undergoing clinical evaluation. These compounds demonstrate that peptidyl trifluoromethyl ketone inhibitors can achieve high levels of oral activity and bioavailability, and therefore they may prove useful as therapeutic agents in the treatment of diseases in which elastase is implicated.

Hemopoietins for eosinophils. Glycoprotein hormones that regulate the development of inflammation in eosinophilia-associated disease.

Granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and interleukin-5 (IL-5) are T lymphocyte-derived glycoproteins that stimulate the development of eosinophils from bone marrow precursors. These eosinophil hemopoietins also regulate functions of mature eosinophils, enhancing their ability to infiltrate tissues and to secrete biologically active substances at the tissue site. In these ways, the eosinophil hemopoietins have a major impact on the development of eosinophilia-associated disease.

The regulation of human eosinophil function by cytokines.

The factors responsible for eosinophil regulation fall broadly into three categories - endogenous chemotactic molecules, factors derived from invading organisms and the cytokines. As David Silberstein and John David reveal, cytokines appear to prime eosinophils for a cytotoxic response to invading organisms. While it seems unlikely that there is a common mechanism for this enhancement of cytotoxicity (and the concomitant inflammation at the site of challenge), much effort is being expanded in order to determine the relationships between the less well characterized eosinophil-stimulating activities and their modes of action.

Antigens from trichinella spiralis that induce a protective response in the mouse.

A series of monoclonal antibodies was generated for the purpose of studying antigens of the infective L1 larva of Trichinella spiralis. Primary immunization of donor BALB/c mice was by oral infection with L1 larvae. Secondary immunization and screening procedures for hybridoma clones employed a pool of affinity-purified antigens recognized by pooled serum from infected rabbits. Three monoclonal antibodies, chosen for their high reactivity in screening assays and their unique specificities, were raised in quantity, purified, and attached to Sepharose 4B for affinity chromatography. The antigens selected by each affinity column were of different m.w. (37K, 48K, and 50/55K) and possessed different abilities to induce protection. The 48K antigen induced a high level of protection at biologically relevant doses (1.0 and 0.1 micrograms protein/mouse). The 50/55K antigen induced a lower level of protection than the 48K antigen, but was still effective at similar doses. The 37K antigen elicited protection only at a dose of 50 micrograms protein/mouse, and was not as effective as the unpurified antigen at any dose. Earlier studies indicated that many antigens involved in the immune response are secreted. Therefore, worm secretions and two subcellular fractions of homogenized worms (S2 = cytosol, S3 = soluble portion of the large particle fraction) were analyzed for content of the three purified antigens by a double antibody sandwich enzyme-linked assay. The 48K and 50/55K antigens represent significant components of the secretions (12% and 5%, respectively) but relatively minor components of the S2 and S3 fractions. The 37K antigen represents a major component of the S2 fraction, but is essentially absent from S3 and secretions. Immunocytolocalization studies employing immunoperoxidase methods on infected muscle tissue show that the 48K antigen is located in the beta-stichocytes, the lining of the gut, and the surface of the cuticle. The 50/55K antigen was detected in the alpha-stichocytes and was occasionally observed in the gut or on the cuticle. The 37K antigen was detected only in the pseudocoelom. The results from the quantitative ELISA and immunocytolocalization show that the two antigens that induce a protective response are secreted proteins. These data constitute the first account of antigens purified from a nematode that induce a strong protective response. One of these (48K) confers a level of protection comparable to that elicited by exposure of an entire infection.

Tumor necrosis factor enhances eosinophil toxicity to Schistosoma mansoni larvae.

Tumor necrosis factor (TNF) is a monocyte product that kills or inhibits the growth of certain tumor cells. Its cell source and physical characteristics suggest that it is similar to a monokine, eosinophil-cytotoxicity-enhancing factor (M-ECEF), that activates human eosinophil toxicity to Schistosoma mansoni larvae. The availability of recombinant human TNF allowed us to test this possibility. The data show that TNF has no direct effect on the parasites but enhances eosinophil toxicity to the parasites in a dose-dependent fashion. This effect is specific for eosinophils and not neutrophils. TNF and the eosinophil-specific activity of TNF are coeluted with M-ECEF in reversed-phase HPLC. Further, M-ECEF activity in HPLC fractions is reduced by treatment with rabbit anti-TNF antibody and protein A-Sepharose. This demonstrates physical similarity and at least partial immunological identity of TNF and a fraction of M-ECEF. Thus, TNF can enhance eosinophil function and may constitute an important immunological regulatory mechanism. This effect should be considered when TNF is applied clinically.

Inhibition of IgG-triggered human eosinophil function by IL-4.

Triggering of eosinophil secretory and cytotoxic functions by stimulation of the IgG and IgE FcR is thought to have major importance in the pathophysiology of tissue eosinophilia. We studied the ability of human rIL-4 to regulate this triggering event in human eosinophils. At doses ranging from 0.1 to 10 pg/ml, IL-4 suppressed eosinophil secretion of beta-glucuronidase and arylsulfatase by up to 65% after stimulation with IgG-coated Sepharose beads. This effect required prolonged preincubation (16 h) of eosinophils with IL-4; no effect was detected after 1 h preincubation. Enzyme secretion stimulated by IgE-coated beads was not affected. Further, IL-4 (after 16 h preincubation), suppressed eosinophil antibody-dependent killing of schistosomula (Schistosoma mansoni) targets by 24 to 39% in four experiments (p less than 0.05). Flow microfluorimetry analysis showed that IL-4 reduced the expression of IgG FcR, but not IgE FcR, suggesting that this mechanism underlies the suppression of IgG-mediated secretion. Taken collectively, these results demonstrate a mechanism for T lymphocyte suppression of IgG-stimulated eosinophil functions via IL-4.

Characterization of a factor from the U937 cell line that enhances the toxicity of human eosinophils to Schistosoma mansoni larvae.

A factor produced by lipopolysaccharide-stimulated human monocytes, monocyte-derived eosinophil cytotoxicity-enhancing factor (M-ECEF), increases the ability of human eosinophils to kill larvae of Schistosoma mansoni. In order to purify this monokine, a continuous cell line was sought as a generator of source material. It was found that high titers of an ECEF-like activity could be obtained from the U937 cell line cultured in serum-free medium. Production of this activity was optimal when cells were cultured with PMA for 2 days and were further treated with LPS for 2 days. PMA and LPS alone did not enhance eosinophil cytotoxicity and could be separated completely from U937-ECEF activity by reversed-phase HPLC. Thus, the activity was not due to carry-over of these two stimuli. U937-ECEF was compared with M-ECEF by a number of analytical methods. ECEF from both sources was resistant to several denaturing treatments but was sensitive to proteases or to reduction and alkylation. U937-ECEF exhibited activity profiles similar, if not identical, to those of M-ECEF when subjected to molecular sizing HPLC in the presence of 8 M urea, isoelectric focusing, and reversed-phase HPLC. The activity has apparent m.w. of 17,000 and 32,000, isoelectric points ranging from 3.8 to 5.1, and one or more reversed-phase HPLC retention times, depending on the method of sample preparation. These results demonstrate certain physical characteristics of M-ECEF, show that the U937 cell line is an appropriate source for the purification of M-ECEF, and provide information that will allow the design of a purification strategy. Although it appears that tumor necrosis factor (TNF) or a TNF-like molecule is a component of M-ECEF, a major component of M-ECEF is different from TNF as judged by the 1) physical characteristics of M-ECEF, 2) low direct toxicity of M-ECEF to L929 cells, 3) comparative stability of M-ECEF to heat treatment, and 4) inability of an anti-TNF monoclonal antibody to remove M-ECEF activity.