Lysosomal and cytosolic sialidases in rabbit alveolar macrophages: demonstration of increased lysosomal activity after in vivo activation with bacillus Calmette-Guerin

TGF-beta: a possible autocrine immune regulator

TGF-beta is a potent regulator of immune functions both in vitro and in vivo. The majority of studies have examined changes in immune functions after the addition of TGF-beta that had been previously activated by acid treatment. Peripheral blood mononuclear cells (PBMC) and tumour cells can each produce latent TGF-beta. The role of endogenously produced latent TGF-beta as an autocrine or paracrine regulator of immune functions has not been extensively studied. Monoclonal antibody (mAb) 4A11 was used to detect and neutralize the activity of endogenous TGF-beta 1 produced during lymphocyte activation. We demonstrate that PBMC, after stimulation with interleukin 2 or phytohaemagglutinin-P/12-O-tetradecanoylphorbol 13-acetate, secrete significant quantities of latent TGF-beta 1. Addition of neutralizing mAbs specific for TGF-beta 1 enhances the proliferative response of the PBMC. CHO cell lines engineered to produce latent TGF-beta 1 were poor stimulators of cytotoxic T lymphocyte generation in vitro and significantly suppress natural killer cell activity in nu/nu mice. We conclude that mechanisms exist in vitro and in vivo to convert latent TGF-beta into an active form which can then regulate immune functions in an autocrine/paracrine manner. The possible role of latent TGF-beta produced by tumour cells in immune surveillance is discussed.

Effects of secretory leucocyte protease inhibitor on the production of the anti-inflammatory cytokines, IL-10 and transforming growth factor-beta (TGF-beta), by lipopolysaccharide-stimulated macrophages

We studied the effects of secretory leucocyte protease inhibitor (SLPI) on the production of the anti-inflammatory cytokines, IL-10 and TGF-beta, by lipopolysaccharide (LPS)-stimulated macrophages, using half-sized SLPI (1/2 SLPI) containing the C-terminal domain (Arg58-Ala107). ELISA testing of macrophage culture fluids showed a temporary production of IL-10 by the macrophages in the early phase (24 h) after LPS stimulation at low (1 ng/ml) or high (10 microg/ml) concentrations. On the other hand, TGF-beta production was initiated after day 3 and progressively increased. 1/2 SLPI significantly increased IL-10 and TGF-beta production by macrophages in response to a low dose as well as a high dose of LPS. Reverse transcription-polymerase chain reaction analysis showed that 1/2 SLPI caused a significant increase in the expression of both IL-10 and TGF-beta mRNAs by LPS-stimulated macrophages. Thus, although the profile of macrophage TGF-beta production by LPS-stimulated macrophages is markedly different from that of their IL-10 production, SLPI causes an up-regulation of the production of these anti-inflammatory cytokines by LPS-stimulated macrophages.

Proliferation of type II pneumocytes and alteration in their apical surface membrane antigenicity in pulmonary sarcoidosis

STUDY OBJECTIVE

To evaluate both the proliferation of type II pneumocytes in the alveolitis associated with pulmonary sarcoidosis and any alteration in their surface membrane antigenicity.

MATERIALS AND METHODS

We investigated 20 transbronchial lung biopsy (TBLB) specimens from 20 patients with pulmonary sarcoidosis, 7 TBLB specimens from 7 sarcoidosis patients without pulmonary involvement, and 19 normal lung specimens, using colloidal iron stain and immunostaining with anti-Thomsen-Friedenreich (TF) antigen and anti-surfactant protein-A monoclonal antibodies.

RESULTS

The density of type II pneumocytes was significantly higher in the pulmonary sarcoidosis specimens ([mean +/- SD] 11.1+/-3.7 per 1 mm alveolar septal length) than in the nonpulmonary sarcoidosis (7.8+/-1.3) or normal lung specimens (7.2+/-0.8). TF antigen was directly expressed on the apical surface of some type II pneumocytes in the pulmonary sarcoidosis specimens, but it was completely masked by sialic acids in the nonpulmonary sarcoidosis specimens and in the normal lung tissues.

CONCLUSIONS

In pulmonary sarcoidosis, type II pneumocytes proliferated and the antigenicity of the surface membrane was altered. It is suggested that these type II pneumocytes may be vulnerable to injury by natural anti-TF antibodies that are cytotoxic when present with complement. This damage may decrease alveolar surfactant and cause focal alveolar collapse proceeding to pulmonary fibrosis in some cases of pulmonary sarcoidosis.

In vitro restoration of T cell responses in tuberculosis and augmentation of monocyte effector function against Mycobacterium tuberculosis by natural inhibitors of transforming growth factor beta

We examined the capacity of the naturally occurring inhibitors of transforming growth factor beta (TGF-beta), decorin and latency associated peptide (LAP), to reverse depressed T cell functions in peripheral blood mononuclear cells (PBMCs) from patients with pulmonary tuberculosis (TB) in vitro and to counteract the suppressive properties of TGF-beta on mycobacterial replication in blood monocytes (MN) in vitro. T cell blastogenesis in response to purified protein derivative (PPD) in PBMCs of TB patients that were cocultured with decorin or LAP reached levels comparable to those observed in healthy tuberculin-responsive control subjects. Decorin and LAP were as effective as neutralizing antibody to TGF-beta in correcting depressed T cell proliferation. Coculture of PBMCs from healthy PPD reactive individuals with neutralizing antibody to TGF-beta, decorin, or LAP did not affect T cell blastogenesis. Levels of interferon-gamma in cultures of PPD-stimulated PBMCs from patients with TB increased by more than 2-fold in the presence of maximal concentrations of either of the inhibitors of TGF-beta, whereas TGF-beta immunoreactivity declined to background levels. Coculture with optimal concentrations of decorin or LAP also led to reductions in mycobacterial growth in MN infected with Mycobacterium tuberculosis (MTB) in vitro by 51% and 62%, respectively, when compared with cells left untreated. In parallel, levels of immunoreactive TGF-beta in MTB-infected MN cultures containing decorin or LAP decreased to background levels. These data indicate that the naturally occurring inhibitors of TGF-beta, decorin and LAP, efficiently abrogate the suppressive effects of TGF-beta in PBMCs of TB patients and in MN infected with MTB in vitro. Therefore, these agents may be considered as adjuncts to antituberculous chemotherapy, and may be particularly useful in treatment of TB that is unresponsive to conventional chemotherapy.

Inhibition of acid sialidase by inorganic sulfate

Sulfated glycosaminoglycans are known to inhibit mammalian acid-active sialidase. Although the inhibition depends clearly on the presence of sulfate groups on these macromolecules, there was no information on the intrinsic inhibitory potency of inorganic sulfate. In this study, we demonstrate that inorganic sulfates inhibit acid-active Mu-Neu5Ac sialidase of U937 cells. This inhibition was found to be reversible and it appeared to be of the mixed competitive type. Sulfate-induced inhibition was also observed in other cells as well as with other substrates such as sialyl lactose and bovine mixed brain gangliosides. We conclude that the intrinsic inhibitory potency of sulfate groups may be significantly involved in the inhibition of acid-active sialidase by sulfated glycosaminoglycans. In addition, inorganic sulfate by its apparent potency to selectively inhibit acid sialidases might constitute an interesting tool for the characterisation of the minor forms of sialidases occurring in mammalian cells.

Binding of serum autoantibodies to sialidase-treated tracheal epithelial cells. Determination of autoantibodies isotypes in normal and influenza virus infected guinea pig sera

Cultured epithelial cells isolated from guinea pig trachea were treated with Vibrio cholerae sialidase. The treatment was not cytotoxic and resulted in membrane desialylation as assessed by measurement of sialic acids released, along with an increased fixation of the galactose-specific lectin peanut agglutinin. After incubation in serum from normal guinea pigs, membrane-bound immunoglobulins were detected using peroxidase-labelled antibodies. Sialidase-treated cells bound significantly more IgM than controls (P < 0.0005), whereas binding of IgG was not significantly different between treated and untreated cells (0.1 < P < 0.375); IgA were never detected. In influenza-infected guinea-pigs, as assessed by reactivity with peanut agglutinin, the tracheal and lung epithelium, as well as alveolar cells were hyposialylated. In these animals, the level of serum IgG autoantibodies capable to bind sialidase treated cultured cells increased, while the level of IgM autoantibodies did not change. These autoantibodies may participate in cellular dysfunctions and modified bronchoreactivity that occur during infection of the respiratory tract by sialidase-producing microorganisms, either through activation of the complement system, or subsequently to their reaction with cells expressing membrane complement and/or Fc receptors.

The effect of leukocyte depletion on pulmonary M2 muscarinic receptor function in parainfluenza virus-infected guinea-pigs

1. Parainfluenza infections of the airways cause dysfunction of inhibitory M2 muscarinic receptors on the pulmonary parasympathetic nerves. To distinguish the direct effects of virus from the effects of virus-induced airway inflammation on M2 muscarinic receptor function, guinea-pigs were depleted of leukocytes by pretreating with cyclophosphamide (30 mg kg-1, i.p. daily for 7 days) after which they were infected with parainfluenza virus type 1 (Sendai virus). 2. Guinea-pigs were anaesthetized, tracheotomized, and ventilated. The vagus nerves were isolated and cut, and the distal ends were electrically stimulated causing bronchoconstriction. In control animals, pilocarpine (1-100 micrograms kg-1, i.v.) inhibited and gallamine (0.1-10 mg kg-1, i.v.) potentiated vagally-induced bronchoconstriction by stimulating or blocking M2 muscarinic receptors on the vagus. These effects of pilocarpine and gallamine were almost completely lost in virus-infected animals, demonstrating loss of M2 receptor function. 3. Cyclophosphamide depleted peripheral blood leukocytes and inhibited the virus-induced influx of inflammatory cells into the lung. Depletion of leukocytes protected M2 receptor function from viral infection in some, but not all, guinea-pigs tested. 4. Among infected animals that had been depleted of leukocytes, the viral content (expressed as the log of the number of tissue culture infectious doses per g lung tissue) of those that retained normal M2 receptor function was 4.29 +/- 0.05 (mean +/- s.e. mean), while the viral content of those that lost M2 receptor function despite leukocyte depletion was 5.45 +/- 0.20 (P = 0.011). Thus the viral content of the lungs in which M2 receptor function was lost was 16 times greater than that of the lungs in which M2 receptor function was preserved. Viral content correlated with the inhibition of vagally-mediated bronchoconstriction after the maximum dose of pilocarpine (100 Microg kg-1; r2 = 0.81, P =0.0004).5. In antigen-challenged animals, inhibitory M2 muscarinic receptor function is restored when positively charged inflammatory cell proteins are bound and neutralized by heparin. However, heparin(2000 micro kg-1, i.v.) did not reverse virus-induced loss of M2 muscarinic receptor function, even in those guinea-pigs with a lower viral titer.6. Because leukocyte depletion protected M2 muscarinic receptor function only in animals with mild viral infections, it appears that viruses have both an indirect, leukocyte-dependent effect on M2 receptors and, in animals with more severe infections, a leukocyte-independent effect on M2 receptors. The failure of heparin to restore M2 receptor function demonstrates that the leukocyte-dependent loss of M2 receptor function is not mediated by positively charged inflammatory cell proteins.

Initial characterization of human thymocyte sialidase activity: evidence that this enzymatic system is not altered during the course of T-cell maturation

1. The sialidase activity of human thymocyte was examined by a fluorogenic assay. 2. These studies revealed that human thymocyte sialidase activity is essentially acid-active and membrane-bound since 59.6% and 33% of the total activity was recovered in the lysosome-enriched and microsomal fractions, respectively. 3. A weak activity was also detected in the cytosolic fraction. 4. However, the acidic optimum pH of this soluble sialidase was at variance with the general concept of mammalian soluble sialidases which are known to be optimally active at more neutral pH. 5. This acidic soluble sialidase seems to be a general characteristic of the human T-cell lineage since examination of mature circulating T-cells revealed that they contain a soluble sialidase activity similar to that observed in thymocytes. 6. Analysis of mature and immature thymocyte subpopulation obtained by differential PNA agglutination indicated that this enzymatic system was not altered during the course of thymic maturation. 7. These results suggest that unlike in T-cell activation where changes in the level of sialidase activity were shown to influence the extent of cell surface sialylation and thereby the cell physiology, this enzymatic system seems not to be involved in the fluctuation of cell surface sialic acid content observed during thymic maturation.

Alveolar macrophage surface carbohydrate expression is altered in interstitial lung disease as determined by lectin-binding profiles

Cell-surface-associated glycoconjugates play important roles in cellular functions such as antigen presentation and cell adhesion, functions that may be modulated in patients with interstitial lung disease. Because carbohydrate residues can be recognized by specific lectins, we designed our study to establish baseline data for bronchoalveolar-lavage-derived cells from normal volunteers and to compare the lectin-binding properties of these cells with cells recovered from patients presenting with interstitial lung disease. Cells were obtained from patients with idiopathic pulmonary fibrosis (n = 10), patients with sarcoidosis (n = 20), and patients receiving amiodarone without evidence of clinical lung disease (n = 10) as well as from normal volunteers (n = 8). To determine the pattern of cell-surface glycoconjugate expression on alveolar macrophages (AM), we used a panel of 21 fluorochrome-coupled plant lectins and employed flow cytometry to determine their binding to AM. The labeling profiles of AM were found to be highly reproducible for normal subjects. At the lectin concentrations used for this study, some lectins showed very little binding to AM and some displayed intermediate binding, but the majority of the lectins labeled nearly all AM in samples. Fluorescence intensity varied characteristically for cells labeled with different lectins, providing further refinement and permitting discrimination beyond that provided by data restricted to percent of labeling. AM from patients with interstitial lung disease showed increased binding for the plant-derived lectins PNA, UEA-I, BSL-I, VVL, and SJA compared with AM from normal subjects, being most augmented for AM from patients with idiopathic pulmonary fibrosis. Because peripheral blood monocytes from normal subjects show a higher percentage of labeling with PNA, UEA-I, SJA, and BSL-I than did AM, the increased expression of binding sites for these four lectins by AM from patients with interstitial lung disease may reflect the influx of immature blood monocytes and/or the emergence of a proinflammatory macrophage phenotype. This study demonstrated heterogeneous expression of surface carbohydrate residues by AM and blood monocytes from normal subjects and alterations in carbohydrate receptor expression in interstitial lung disease. Lectin-binding properties may prove useful, therefore, in the evaluation of mononuclear phagocyte populations in interstitial lung disease, especially by the identification of functional subsets and/or changed activation states.

Effect of inflammatory cell mediators on M2 muscarinic receptors in the lungs

Acetylcholine released from vagal nerve endings constricts airways by stimulating M3 muscarinic receptors on the airway smooth muscle. At the same time, released acetylcholine feeds back onto inhibitory M2 muscarinic autoreceptors on the nerve endings, limiting further release of acetylcholine. Loss of function of these M2 receptors increases vagally-mediated bronchoconstriction after viral airway infections, exposure to ozone, or antigen inhalation. Viral infections may decrease M2 receptor function by inducing inflammation or via direct damage to the receptors as a result of cleavage of sialic acid residues by viral neuraminidase. Inflammation appears to be critical in the loss of M2 receptor function after ozone exposure. Antigen-induced loss of M2 receptor function can be reversed acutely by administering the poly-anionic substances heparin or poly-l-glutamate, possibly by binding and neutralizing positively charged eosinophil proteins. Such positively charged eosinophil proteins, particularly major basic protein, may be acting as endogenous inhibitors at the M2 receptors, as can be demonstrated in in vitro ligand binding studies.

Effect of desialylation on the biological properties of human plasminogen

There are two major isoenzymes of plasminogen (Pg) in human plasma, designated Pg1 and Pg2. Both Pg forms have an identical primary structure, but differ in their extent of glycosylation. Removal of the oligosaccharide chains alters the normal physiological function of the zymogen and decreases the circulation time of both Pg glycoforms. Recent studies in our laboratory demonstrated that Pg2, with one carbohydrate chain, binds to the surface of U937 monocytoid cells considerably better than Pg1, with two carbohydrate chains, indicating a major role for the carbohydrate chains as determinants for differential binding to the cell surface [Gonzalez-Gronow, Grenett, Fuller & Pizzo (1990) Biochim. Biophys. Acta 1039, 269-276]. In this report we provide evidence that removal of terminal sialic acid from the Thr345-linked oligosaccharide chain of Pg2 is accompanied by the appearance of spontaneous amidolytic and fibrinolytic activity in the single-chain zymogen. Kinetic data demonstrate that asialo-Pg hydrolyses peptide substrates approximately 10% as efficiently as Pm. In addition, the change in carbohydrate content also alters Pg binding to U937 cells. Asialo-Pg binds to U937 cells with a decreased capacity but with a greater affinity than native Pg. Furthermore, asialo-Pg does not compete with native Pg for cell binding. These studies directly demonstrate that the oligosaccharide chains contribute to the heterogeneity observed in the physicochemical and biological properties of Pg1 and Pg2.

Transforming growth factor beta (TGF-beta) in inflammation: a cause and a cure

As we continue to explore the biology of TGF-beta in the network of cells and mediators contributing to host defense, the mechanisms controlling whether the pro- or antiinflammatory effects of this peptide prevail will be unraveled. Understanding these basic mechanisms may offer new approaches for identifying agonists and/or antagonists and in which circumstances their use might be appropriate. The striking differences between local and systemic administration of this cytokine reaffirm that the functional consequences of any biologic mediator must be considered in context (9) and, furthermore, suggest avenues of therapeutic application (Table III). In summary, the central role of TGF-beta in normal and aberrant host defense has become indisputable.

Effect of transforming growth factor beta on postoperative adhesion formation and intact peritoneum

Transforming growth factor beta (TGF beta) is an extremely potent chemoattractant for macrophages, mononuclear leukocytes, and fibroblasts. It also acts as a potent stimulant for collagen and fibronectin synthesis and inhibits epithelial cell growth. TGF beta plays an important role in healing many types of wounds, but its role in peritoneal adhesion formation is not known. These studies were performed to determine if TGF beta could affect postoperative wound healing in a rat model. In the first experiment, 20 rats were divided into two groups and received either 2 micrograms TGF beta or control diluent IP daily for 5 days after surgical injury to the uterine horns. The severity of the adhesions were graded 2 weeks postoperatively using a score of 0-3. The TGF beta group showed a higher adhesion score at 2 weeks compared to control, 2.9 +/- 0.34 and 1.6 +/- 0.61, respectively (P less than 0.001). On H&E stained sections of the adhesions, there was an increase in the number of both inflammatory cells and fibroblasts in the TGF beta-treated animals. A comparison trial of bone-derived TGF beta (a gift from Collagen Corporation, Palo Alto, CA) versus recombinant TGF beta (a gift from Oncogen, Seattle, WA) versus control using the same protocol as above showed that both sources of TGF beta were more effective in promoting postoperative adhesions when compared to controls, and there was no difference between TGF beta groups, 3.0 +/- 0 for both TGF beta groups, and 2.2 +/- 0.91 for control (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Control of transforming growth factor-beta activity: latency vs. activation

Transforming growth factor-beta is a pluripotent regulator of cell growth and differentiation. The growth factor is expressed as a latent complex that must be converted to an active form before interacting with its ubiquitous high affinity receptors. This conversion involves the release of the mature growth factor through disruption of the non-covalent interactions with its pro-peptide or latency associated peptide. The mechanisms for this release in vivo have not been fully characterized but appear to be cell specific and might involve processes such as acidification or proteolysis. Although several factors including transcriptional regulation, receptor modulation and scavenging of the active growth factor have been implicated, the critical step controlling the biological effects of transforming growth factor-beta may be the activation of the latent molecule.

Sialidase in the guinea pig pulmonary parenchyma. Increased activity in the cytosolic and microsomal subcellular fractions after stimulation with Bacillus Calmette Guérin

The sialidase activity was assayed in the guinea pig pulmonary parenchyma after removal of bronchoalveolar cells by washing. After differential centrifugation of the crude tissue homogenate, sialidase activities were measured in the subcellular fractions using the fluorogenic substrate 2-(4-methylumbelliferyl)-alpha-D-N-acetylneuraminate. Sialidase activities were found in the lysosomal-enriched (17,000 x g pellet), in the microsomal (105,000 x g pellet) and in the cytosolic (105,000 x g supernatant) fractions. Microsomal and lysosomal forms of sialidase had an optimum activity at pH 3.6-3.8, whereas the optimum for the cytosolic form was pH 4.6. The activity of all three forms was inhibited by Cu2+, whereas 1 mM Zn2+ and 0.5 mM Ca2+ activated the lysosomal and the cytosolic forms, respectively. In the crude homogenate taken from lungs of Bacillus Calmette Guérin-(BCG-) stimulated guinea pigs, the sialidase activity was increased by 43% (p = 0.025) 3 weeks after the end of the treatment. The cytosolic (+246%) and microsomal (+51%) sialidase activities were significantly increased, whereas the lysosomal sialidase activity was not changed significantly by BCG stimulation.

An enzyme-linked lectin assay for sialidase

A procedure for the detection of low activities of sialidase (= neuraminidase) is described. Natural substrates for sialidase (human erythrocytes, fetuin or gangliosides) were coated onto the wells of microplates and incubated at 37 degrees C with the enzyme. Sialidase-induced desialylation of these natural substrates unmasks saccharides that are specifically recognized by the peanut agglutinin lectin (PNA). The use of a peroxidase-conjugated PNA (Po-PNA) allowed the binding of the lectin to the desialylated substrate to be quantified. The amount of bound Po-PNA correlated directly with the amount of sialic acid released from the substrate, and therefore with the sialidase activity. With this method, it was possible to detect sialidase activity associated with bacteria, myxoviruses and cells from higher organisms. This method may have important clinical implications as the use of ELISA allows automation and concurrent analysis of numerous samples.

Immunoregulatory role of transforming growth factor beta (TGF-beta) in development of killer cells: comparison of active and latent TGF-beta 1

Using recombinant DNA technology, we have generated Chinese hamster ovary (CHO) cell lines that synthesize latent transforming growth factor beta 1 (TGF-beta 1) to study immune regulation by TGF-beta 1. In vitro, latent TGF-beta 1 synthesized by transfectants or added exogenously as a purified complex after activation inhibited CTL generation to a similar extent as seen with acid-activated recombinant human (rHu) TGF-beta 1. In vivo, serum from nu/nu mice bearing CHO/TGF-beta 1 tumors contained significant levels of latent TGF-beta 1 in addition to depressed natural killer (NK) activity in spleens which paralleled that seen in C3H/HeJ mice treated with acid-activated rHuTGF-beta 1. rHuTGF-beta 1 treatment of mice receiving heart allografts resulted in significant enhancement of organ graft survival. Because of possible regulated tissue-specific activation, administration of latent rather than active TGF-beta may provide a better route to deliver this powerful immunosuppressive agent in vivo.

Glycosidase activities in alveolar macrophages from guinea pigs stimulated with a glyco-proteic complex extracted from Klebsiella pneumoniae

An increased resistance of laboratory animals to pulmonary infections following per os administration of a glyco-proteic complex extracted from Klebsiella pneumoniae has been reported. This was associated with an increased phagocytic capacity of alveolar macrophages (AM). In this report, the effect of treating guinea pigs with this extract on the alveolar macrophage (AM) glycosidase machinery has been studied. AM were collected by bronchoalveolar lavage, the cells were pelleted by centrifugation and AM were purified by adherence on plastic dishes. Sialidase, beta-galactosidase, beta-glucuronidase and N-acetyl-beta-D glucosaminidase activities were measured in the AM homogenate. In order to evaluate an extracellular release of these enzymes, they were also assayed in the cell free lavage fluid. Lactic dehydrogenase (LDH) activity was assayed as a control for cell lysis. In treated animals, the total number of cells as well as the number of AM increased by 25% (ns). The protein concentration was slightly reduced in the cell homogenate and unchanged in the lavage fluid. The only significant change was a decreased sialidase activity, in AM homogenate (p less than or equal to 0.01) and in lavage fluids (ns). The LDH activity was not increased in the lavage fluids.

Modifications of sialidase activity during the monocyte-macrophage differentiation in vitro

Human mononuclear cells were isolated from peripheral blood by centrifugation over Ficoll Hypaque, followed by adherence to plastic dishes. Monocyte-derived macrophages were obtained after culture for 3 or 5 days of the adherent cells in RPMI medium containing 20% heat-inactivated foetal calf serum. The sialidase activities were assayed in the whole homogenate using sodium 4-methyl-umbelliferyl-alpha-D-neuraminate as substrate, at various pHs, ranging from 3.6 to 6. The in vitro differentiation of monocytes into macrophages from day 0 up to day 5 was accompanied by a significant (P less than or equal to 0.01) increase in the sialidase activity on both a per-cell (+360%) and a per-mg protein in the homogenate (+125%) basis.

Heterogeneity among human mononuclear phagocytes in their secretion of lysozyme, interleukin 1 and type-beta transforming growth factor: a quantitative analysis at the single-cell level

Human mononuclear phagocytes have the remarkable capacity to secrete a wide range of products. The reverse hemolytic plaque assay was used to visualize and quantify the secretion of lysozyme, interleukin 1 or type-beta transforming growth factor by individual monocytes and macrophages. With this sensitive immunoassay, the release of these products by either freshly isolated monocytes, macrophages derived from monocytes in vitro, or activated peritoneal macrophages was detected in both the presence and absence of secretagogues. When coupled with immunocytochemistry for EBM/11, a monoclonal marker for human cells of the monocyte/macrophage cell lineage, functional heterogeneity was evident both in the amount of lysozyme, interleukin 1 or type-beta transforming growth factor released per cell, and in the number of EBM/11+ cells which secreted detectable levels of these products at any one time. In addition, there was a size-dependent heterogeneity among human monocytes and culture-derived macrophages in their ability to secrete interleukin 1 or lysozyme, respectively. We conclude that the secretory activity of individual mononuclear phagocytes is markedly heterogeneous.

Role for carbohydrate structures in TGF-beta 1 latency

Transforming growth factor-beta (TGF-beta) (reviewed in refs 1-3) is a family of molecules that are made up as disulphide-bonded dimers of at least three different types of homologous polypeptides. The active molecules are cleaved from the C termini of precursors. TGF-beta 1, like other forms of TGF-beta, is synthesized and secreted in a latent high relative molecular mass form (L-TGF-beta 1) from which active TGF-beta 1 can be released by transient and probably unphysiological acidification. The latent complex from human platelets contains one dimeric TGF-beta 1 molecules, which is noncovalently associated with a disulphide-bonded complex of one dimeric remnant of the precursor and a single molecule of the so-called TGF-beta 1 binding protein (TGF-beta 1-BP). We report here that enzymatic removal in vitro of the carbohydrate structures in the remnant of the TGF-beta 1 precursor produces biologically active TGF-beta 1 from the latent complex, suggesting that carbohydrate structures are of importance in rendering TGF-beta 1 inactive in the complex in vivo.