Anti-Inflammatory Activity of Immunoglobulin G Resulting from Fc Sialylation

Immunoglobulin G (IgG) mediates pro- and anti-inflammatory activities through the engagement of its Fc fragment (Fc) with distinct Fcg receptors (FcgRs). One class of Fc-FcgR interactions generates pro-inflammatory effects of immune complexes and cytotoxic antibodies. In contrast, therapeutic intravenous gamma globulin and its Fc fragments are anti-inflammatory. We show here that these distinct properties of the IgG Fc result from differential sialylation of the Fc core polysaccharide. IgG acquires anti-inflammatory properties upon Fc sialylation, which is reduced upon the induction of an antigen-specific immune response. This differential sialylation may provide a switch from innate anti-inflammatory activity in the steady state to generating adaptive pro-inflammatory effects upon antigenic challenge.

Flagellasialin: a novel sulfated 2,9-linked polysialic acid glycoprotein of sea urchin sperm flagella

A novel alpha2,9-linked polysialic acid (polySia)-containing glycoprotein of sea urchin sperm flagella was identified and named "flagellasialin." Flagellasialin from Hemicentrotus pulcherrimus shows a diverse relative molecular mass on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of 40-80 kDa. Flagellasialin is a 96-amino acid, threonine-rich, heavily O-glycosylated (80-90% by weight) glycoprotein with a single transmembrane segment at its C-terminus and no apparent cytosolic domain. Of 12 extracellular Thr residues, eight are O-glycosylated and three are nonglycosylated. Flagellasialin is highly expressed in the testis but cannot be detected in the ovary. The amino acid sequences of flagellasialin from three sea urchin species (H. pulcherrimus, Strongylocentrotus purpuratus, and Strongylocentrotus franciscanus) are identical, but some species differences exist in the three core glycan structures to which the sulfated alpha2,9-linked polyNeu5Ac chain is linked. Finally, the treatment of sperm with a specific antibody against the alpha2,9-linked polyNeu5Ac structure results in the elevation of intracellular Ca(2+) and inhibition of sperm motility and fertilization, implicating flagellasialin as a regulator of these critical processes.

Identification of 9-O-acetyl-N-acetylneuraminic acid in normal canine pre-ocular tear film secreted mucins and its depletion in Keratoconjunctivitis sicca

O-Acetylated sialic acids have been reported in many sialoglycoproteins where they mediate a variety of immune and other biological events. We have previously demonstrated that the protective mucus barrier on the surface of the canine eye contains sialoglycoproteins. We have also investigated the occurrence of O-acetylated sialic acids in these ocular mucins. Mucus aspirated from the surface of normal dog eyes and those with keratoconjunctivitis sicca (KCS) was fractionated into three pools by density gradient centrifugation. Sialic acids comprised 0.6-0.9% of the dry weight of the mucins isolated. The sialic acid profile in these pools was examined using HPLC. O-Acetylated sialic acids, mainly Neu5,9Ac2, were detected in normal animals and made up 10-30% of the total sialic acids detected. A doubling of the sialic acid content was found in KCS mucins, but the level of 9-O-acetylated sialic acid was reduced below 4% of total. Histological analysis of conjunctival tissue from normal and KCS dogs showed the presence of sialic acids, detected with the alpha(2-6) sialic acid-specific lectin Sambucus nigra, in the goblet cells and corresponding to the staining pattern for MUC5AC, the major ocular-secreted mucin gene product. In KCS animals a disruption of the normal pattern of conjunctival goblet cells was seen with preservation of the pattern of lectin binding observed in normal animals. Thus the data demonstrate the presence of mono-O-Acetylated sialic acids in normal canine ocular mucins and a loss of this population of sialic acids in dry eye disease in spite of a significant increase in total sialic acids in KCS mucin.

Topooptical investigations and enzymatic digestions on tissue-isolated amyloid fibrils

Chemical and biochemical analysis of isolated amyloid fibrils reveals the presence of different classes of proteins which are often related to distinct clinical forms of amyloidosis and are useful to classify the amyloid deposits. In this study, enzymatic digestions using hyaluronidase, chondroitinase AC and B, neuraminidase, and chemical extractions using mild acid hydrolysis with hydrochloric and sulfuric acid, were used to control the specificity of various topooptical reactions. The disappearance of intense staining after these extraction methods indicates that tissue-isolated amyloid fibrils contain sialic acids and glycosaminoglycans (GAGs). We conclude that topooptical reactions are the most sensitive methods to detect conformational changes in the non-fibrillar component of amyloid deposits and tissue-isolated amyloid fibrils.

Case report: amyloid tumors in a case of non-secretory multiple myeloma

Multiple myeloma (MM) is a neoplastic disorder characterized by proliferation of a single clone of plasma cells derived from B cells, which proliferates in the bone marrow and frequently invades the adjacent bone, producing skeletal destruction that results in bone pain and fractures. Patients with MM can furthermore present with anemia, hypercalcemia and renal failure. Non-secretory multiple myeloma (NSMM) is characterized by the absence of a monoclonal (M) protein in both the serum and urine. The reported incidence is 1-5% of all multiple myeloma cases. Development of amyloid tumors in NSMM has been described in the literature only occasionally. The clinical features of a 49-year-old female patient with NSMM and amyloid tumors in the breast, lung and rib are presented in this report. Conventional histology, Congo red staining with and without potassium permanganate pretreatment, aldehyde bisulfite-toluidine blue (ABT) reaction, sialic acid specific topo-optical reaction, toluidine blue topo-optical reaction as well as immunohistochemistry were performed. An attempt is made to explain the lack of monoclonal immunoglobulins in the serum and urine, although extensive organ amyloidosis of AL type (kappa-light chains) has been found. It is assumed that the plasmocytic plasma cells possess an excretory mechanism, which allows the pathologic immunoglobulins to be secreted either as amyloid proteins polymerizing into amyloid fibrils, or as immunoglobulin fragments that are subject to degradation as soon as they are excreted out of the tumor cell. In this paper, we review the occurrence of amyloid tumors in non-secretory multiple myeloma and, in a single case report, we confirm the existence of carbohydrate residues, including sialic acids and sulfated GAGs, in amyloid deposits.

Identification of disialic acid-containing glycoproteins in mouse serum: a novel modification of immunoglobulin light chains, vitronectin, and plasminogen

Serum glycoproteins are involved in various biologic activities, such as the removal of exogenous antigens, fibrinolysis, and metal transport. Some of them are also useful markers of inflammation and disease. Although the amount of sialic acid increases following inflammation, little attention has been paid to the presence of linkage-specific epitopes in serum, especially the alpha2,8-linkage. In a previous study, we demonstrated that four components in mouse serum contain alpha2,8-linked disialic acid (diSia), based on immunoreactivity with monoclonal antibody 2-4B, which is specific to N-glycolylneuraminic acid (Neu5Gc)alpha2-->(8Neu5Gc alpha2-->)(n-1), n > or = 2 [Yasukawa et al., (2005) Glycobiology, 15, 827-837]. In this study, we purified three components, 30-, 70-, and 120-kDa gp, and identified them as an immunoglobulin (Ig) light chain, vitronectin, and plasminogen, respectively, using matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy analyses. Modifications of these proteins with alpha2,8-linked diSia were chemically confirmed by fluorometric C7/C9 analyses and mild acid hydrolysates-fluorometric anion-exchange chromatography analyses. We also demonstrated that the IgG, IgM, and IgE light chains are commonly modified with alpha2,8-linked diSia. In addition, both mouse and rat vitronectin contained diSia, and the amount of disialylation in vitronectin dramatically decreased after hepatectomy. These results indicate that a novel diSia modification of serum glycoproteins is biologically important for immunologic events and fibrinolysis.

Glycosylation of the severe acute respiratory syndrome coronavirus triple-spanning membrane proteins 3a and M

The severe acute respiratory syndrome coronavirus (SARS-CoV) open reading frame 3a protein has recently been shown to be a structural protein. The protein is encoded by one of the so-called group-specific genes and has no sequence homology with any of the known structural or group-specific proteins of coronaviruses. It does, however, have several similarities to the coronavirus M proteins; (i) they are triple membrane spanning with the same topology, (ii) they have similar intracellular localizations (predominantly Golgi), (iii) both are viral structural proteins, and (iv) they appear to interact with the E and S proteins, as well as with each other. The M protein plays a crucial role in coronavirus assembly and is glycosylated in all coronaviruses, either by N-linked or by O-linked oligosaccharides. The conserved glycosylation of the coronavirus M proteins and the resemblance of the 3a protein to them led us to investigate the glycosylation of these two SARS-CoV membrane proteins. The proteins were expressed separately using the vaccinia virus T7 expression system, followed by metabolic labeling. Pulse-chase analysis showed that both proteins were modified, although in different ways. While the M protein acquired cotranslationally oligosaccharides that could be removed by PNGaseF, the 3a protein acquired its modifications posttranslationally, and they were not sensitive to the N-glycosidase enzyme. The SARS-CoV 3a protein, however, was demonstrated to contain sialic acids, indicating the presence of oligosaccharides. O-glycosylation of the 3a protein was indeed confirmed using an in situ O-glycosylation assay of endoplasmic reticulum-retained mutants. In addition, we showed that substitution of serine and threonine residues in the ectodomain of the 3a protein abolished the addition of the O-linked sugars. Thus, the SARS-CoV 3a protein is an O-glycosylated glycoprotein, like the group 2 coronavirus M proteins but unlike the SARS-CoV M protein, which is N glycosylated.

Topo-optical visualization reactions of carbohydrate-containing amyloid deposits in the respiratory tract

Staining with Congo red according to is the most commonly used method for the demonstration of amyloid, but structures other than amyloid can give false-positive results. To overcome this problem, introduced an aqueous Congo red staining with gum arabic as the mounting medium, which we have used in this and previous publications. Most histochemical studies on amyloid deposits to date have concentrated on conventional methods including staining with thioflavine, sirius red, alcian blue, methyl and crystal violet. In this study, we used topo-optical reactions with thiazine dyes on both the light and polarization microscopic level to establish the structure, distribution and location of carbohydrate components that occur within amyloid deposits, especially in the respiratory tract. Topo-optical staining reactions for the qualitative analysis of carbohydrate components in amyloid deposits included (1) reactions that identify the carbohydrate residues, (2) reactions that detect sialic acids and, (3) methods that visualize glycosaminoglycans. In conclusion, a comparison of consecutive serial sections stained with Congo red, aldehyde bisulfite toluidine blue reaction, sialic acid-specific topo-optical reaction, toluidine blue topo-optical reaction and chemically intensified basophilic reaction showed correlative staining patterns and anisotropic effects, corresponding to a close pathomorphological relationship between amyloid fibrils, periodate reactive carbohydrates, including sialic acids, and glycosaminoglycans.

Analysis of monosaccharides, fatty constituents and rare O-acetylated sialic acids from gonads of the starfish Asterias rubens

A previous study (Bergwerff et al., Biochimie 74 (1992) 25-37) reported that sialic acids present in Asterias rubens gonads were essentially composed of 8-methyl-N-glycolylneuraminic acid (Neu5Gc8Me), a large part of it being acetylated in position 9. Using GC/MS of heptafluorobutyrate derivatives (Zanetta et al., Glycobiology 11 (2001) 663-676) on the chloroform/methanol soluble and insoluble fractions, we showed that most sialic acids were found in the latter and demonstrated that all sialic acids were derived from N-glycolylneuraminic acid, most of them being 8-methylated, but that the majority were also acetylated in position 4 or 7 (or both positions). GC/MS analyses of the constituents liberated using acid-catalysed methanolysis verified that major glycoprotein-bound glycans were N-linked and of the gluco-oligomannosidic type. Major fatty acids were poly-unsaturated (especially C20:4) and long-chain bases were C22:1 phytosphingosine and C22:2 6-hydroxysphingenine. Major monosaccharides found in the chloroform/methanol extract (quinovose and fucose) were derived from steroidal saponins.

High-purity lineage selection of embryonic stem cell-derived neurons

The derivation of somatic cell types from pluripotent and self-renewing embryonic stem (ES) cells offers attractive prospects for basic research, compound development, and regenerative medicine. A key prerequisite for biomedical applications of ES cells is the ability to differentiate and isolate defined somatic cell populations at high purity. In this study, we explore the potential of the Talpha1- enhanced green fluorescent protein (EGFP) transgene and polysialic acid (PSA)-neural cell adhesion molecule (NCAM) as lineage selection markers for the derivation of ES cell-derived neurons. Upon controlled in vitro differentiation, ES cells engineered to express EGFP under control of the Talpha1-tubulin promoter exhibited exclusive transgene expression in neurons. Similarly, PSA-NCAM expression during the early stages of ES cell differentiation was restricted to neuronal progeny. Talpha1- EGFP- and PSA-NCAM-positive neurons comprised both inhibitory and excitatory phenotypes. Compared to Talpha1-EGFP, the expression of PSA-NCAM was initiated at slightly earlier stages of neural differentiation. FACSorting of Talpha1-EGFP-positive cells and immunopanning of PSA-NCAMexpressing cells yielded neuronal populations at purities up to 99.6% and 96.9%, respectively. These findings depict Talpha1-EGFP and PSA-NCAM as suitable markers for high-purity selection of early ES cell-derived neurons.

Structure of an acidic polysaccharide from the agar-decomposing marine bacterium Pseudoalteromonas atlantica strain IAM 14165 containing 5,7-diacetamido-3,5,7,9-tetradeoxy-L-glycero-L-manno-non-2-ulosonic acid

The structure of an acidic polysaccharide from Pseudoalteromonas atlantica strain 14165 containing 5,7-diacetamido-3,5,7,9-tetradeoxy-L-glycero-L-manno-non-2-ulosonic acid (di-N-acetylpseudaminic acid, Pse5Ac7Ac) has been elucidated. The polysaccharide was studied by 1H and 13C NMR spectroscopy, including 2D experiments, along with sugar and methylation analyses. After a selective hydrolysis a modified polysaccharide devoid of its side chain could be isolated. It was found that the polysaccharide has pentasaccharide repeating units with following structure: [structure: see text].

A re-evaluation of plasma sialic acid determination using the periodate resorcinol method versus the enzymatic method

The concentration of plasma sialic acid was estimated using the modified chemical method and the more sensitive enzymatic method in 20 subjects with impaired glucose tolerance and 20 control subjects. The mean sialic acid concentration values of the control subjects and subjects with impaired glucose tolerance using the enzymatic method were 1.747 +/- 0.047 and 2.583 +/- 0.070 mmole/l and 1.753 +/- 0.067 and 2.591 +/- 1.02 mmole/l for the chemical method. The intra-assay coefficient of variation for the control subjects and for the subjects with impaired glucose tolerance were 1.963% and 1.583%, respectively, for the enzymatic assay and 2.728% and 2.431%, respectively, for the chemical assay. The inter-assay coefficient of variation for the control subjects and for the subjects with impaired glucose tolerance were 2.686% and 2.723% for the enzymatic assay, and 3.819% and 3.95% for the chemical assay. Since the values do not differ significantly, the chemical assay is a cost effective method that can be used in large epidemiological studies.

Clinical significance of total and lipid bound sialic acid levels in oral pre-cancerous conditions and oral cancer

BACKGROUND

Altered glycosylation of glycoconjugates is among the important molecular changes that accompany malignant transformation. The purpose of our study was to investigate clinical usefulness of circulatory levels of total and lipid bound sialic acid for early diagnosis and management of oral cavity cancer patients.

METHODS

Blood samples were collected from 41 untreated oral cancer patients, 20 patients with oral pre-cancerous conditions (OPC) and 20 healthy subjects. Serum sialic acid (total and lipid bound) levels were measured spectrophotometrically.

RESULTS

Serum levels of total and lipid bound sialic acid were significantly elevated (P < 0.001) in untreated oral cancer patients as compared to healthy individuals as well as patients with OPC. Multivariate analysis documented that the progressive rise in total and lipid bound sialic acid was significantly associated (P = 0.0001 and 0.039, respectively) with stage of malignant disease.

CONCLUSION

The data revealed significant elevations in sialic acid levels in oral cancer patients and suggested potential utility of these parameters in diagnosis as well as determining clinical stage of the malignant disease.

Localization of sulfated sialic acids in the dentinal tubules during tooth formation in mice

Lectin-like properties of the major enamel protein amelogenin suggest that it binds to glycoconjugates in dentinal tubules released at the dentin-enamel junction (DEJ) during enamel formation. Therefore, a detailed mapping of glycosylation in dentinal tubules during tooth formation was undertaken using histochemistry and lectin-binding assays. The tubular content exhibited sialidase-susceptible gamma-metachromasia with Toluidine Blue (pH 2.5) and staining with Alcian Blue (pH 1.0). The presence of sulfate groups was confirmed by benzidine reactions (Bracco-Curti's and tetrazonium assays). Alpha2,3-, alpha2,6- and alpha2,8-sialidases entirely abolished staining with the benzidine reactions. The presence of sialic acids in dentinal tubules was confirmed with the Bial's reaction and sialidase-susceptible binding of Limax flavus lectin suggesting that sialic acids are the major sulfated sugars in the glycoconjguates. Immunostaining with the monoclonal antibody 5-D-4 before and after treatment with chondroitin-4- and chondroitin-6-sulfatase confirmed the presence of keratan sulfate (KS), a sialylated proteoglycan, in dentinal tubules. We suggest that sulfated sialic acids are part of the KSs. The sulfated glycoconjugates are also found in dentin and the DEJ but not in predentin suggesting that amelogenin binds to the sialoconjugate during enamel formation.

Nasal and frontal sinus mucosa of the adult dog contain numerous olfactory sensory neurons and ensheathing glia

Olfactory glial cells have been the focus of much recent research interest because of their possible future use as cellular transplants in repair of spinal cord injury. Although olfactory glial cells can be collected from the olfactory bulb for in vitro culture, alternative sites would be preferable for safer surgical access. This study was designed to investigate the distribution of olfactory sensory neurons and olfactory glial cells within the canine peripheral olfactory system. Using immunohistochemistry and electron microscopy on perfused tissue we demonstrate that olfactory sensory neurons are found in both the caudal nasal and the frontal sinus epithelia. Olfactory ensheathing glia were found in the mucosa at both these sites implying that surgical access for harvesting cells for transplantation would be straightforward.

LC/MS Characterization of Meningococcal Depolymerized Polysaccharide Group C Reducing Endgroup and Internal Repeating Unit

Hydrogen peroxide has been used to cleave the native Neisseria meningiditis polysaccharide (PS) from mega-Dalton molecular weight to a smaller size (approximately 20 kDa) depolymerized polysaccharide. The polysaccharide was examined after partial peroxide depolymerization to verify the presence of the carboxyl group at position 1 and the intactness of the internal sialic acid repeating units. The reducing end group of meningococcal polysaccharide type C was also examined after derivatization by L-tyrosine hydrazide. Partial peroxide depolymerization did not result in loss of the position 1 carboxyl group at the reducing end of the polysaccharide. In addition, no loss of structural integrity was noted for the internal sialic repeat units.

Distribution of sialic acids in the milk of spanish mothers of full term infants during lactation

OBJECTIVES

The protective effect of human milk against infection is well known. Several non-immunologic components, including complex carbohydrates, have been described. The present study was undertaken to determine the sialic acid distribution in different milk fractions (complex carbohydrates).

METHODS

Milk samples from 12 Spanish women at three different lactational stages (colostrum, transitional milk and mature milk) were analyzed. Total and glycoprotein-bound, oligosaccharide-bound, casein-bound, and lipid-bound sialic acids were determined.

RESULTS

Sialic acids from human milk are mainly bound to oligosaccharides and only a small amount is present bound to glycoproteins or in the free form. All the fractions analyzed showed a similar trend: sialic acids decrease rapidly along lactation. Casein-bound sialic acid does not follow this trend. We detected the presence of an O-acetylated species of N-acetylneuraminic acid.

CONCLUSIONS

In human milk from Spanish women we observed slightly different values than those previously reported. This could be a result of population differences but nutritional or methodological aspects can not be discarded.

Hippocampal neurogenesis and PSA-NCAM expression following exposure to 56Fe particles mimics that seen during aging in rats

Exposure to particles of high energy and charge can disrupt the neuronal systems as well as the motor and cognitive behaviors mediated by these systems in a similar fashion to that seen during the aging process. In the hippocampus, adult neurogenesis is affected both by aging and irradiation with ionizing particles. Likewise, the maturation of newly formed cells in this region as measured by PSA-NCAM expression is also altered by the aging process. The present study was designed to investigate the effects of 2.5 Gy of 1 GeV/n (56)Fe particles on neurogenesis using the nuclear proliferation marker 5-bromodeoxyuridine (BrdU and PSA-NCAM expression in the dentate gyrus of rats exposed to whole-body irradiation or simply placed in the chamber without being irradiated. All subjects (n=10) were sacrificed 28 days after the last BrdU injection (50 mg/kg X 3 days) and their brains were processed for immunohistochemistry. Results illustrate a decrease in the number of BrdU-positive cells as well as different distribution of these cells in the dentate gyrus of irradiated animals. Additionally, irradiated subjects show decreased levels of PSA-NCAM expression. These changes are consistent with those found in aged subjects indicating that heavy-particle irradiation is an adequate model for the study of aging.

Purification, characterization of O-acetylated sialoglycoconjugates-specific IgM, and development of an enzyme-linked immunosorbent assay for diagnosis and follow-up of indian visceral leishmaniasis patients

The surface expression of 9-O-acetylated sialic acid (9-OAcSA) is elevated on hematopoietic cells and erythrocytes of visceral leishmaniasis (VL) patients. In this study, we show that VL patients contain elevated levels of IgM antibodies directed against 9-O-acetylated sialoglycoconjugates (9-OAcSG). These antibodies were affinity purified with bovine submaxillary protein as the affinity matrix containing the terminal epitope, 9-OAcSAalpha2-6GalNAc. They also bound to 9-OAcSGs on hematopoietic cells of patients with VL and to epitopes in the cytosol of Leishmania donovani promastigotes. A novel enzyme-linked immunosorbent assay was employed that showed 4-fold higher anti-OAcSG titers in VL patients (n=38), mean +/- S.E.M. being 0.83 +/- 0.09 vs. 0.21 +/- 0.04 detected in normal donors (n=20) and patients with cross-reactive diseases such as malaria (n=4) or tuberculosis (n=4). Assay specificity and sensitivity was 100% and 92%, respectively, whereas positive and negative predictive values were 100% and 90%, respectively. Significantly, anti-OAcSG titers declined 30 days after completion of anti-leishmanial treatment, indicating that monitoring of anti-9-OAcSGs may be a valuable alternative toward increasing the efficiency of diagnosis and follow-up of VL.

Low ionic strength promotes association of circulating modified LDL human blood

The resistance to association of circulating multiply-modified low-density lipoproteins (LDL) isolated from human blood and characterized by a decreased content of sialic acids in comparison with native LDL was studied by analysing light transmission fluctuations. LDL association was stimulated by decreasing environmental ionic strength. It is established that circulating modified LDL are less resistant to association than native LDL. Association of LDL in a medium with low ionic strength was irreversible. Probably, increased capacity to irreversible association determines the atherogenic properties of circulating modified LDL subfraction.

Surface sialic acids taken from the host allow trypanosome survival in tsetse fly vectors

The African trypanosome Trypanosoma brucei, which causes sleeping sickness in humans and Nagana disease in livestock, is spread via blood-sucking Tsetse flies. In the fly's intestine, the trypanosomes survive digestive and trypanocidal environments, proliferate, and translocate into the salivary gland, where they become infectious to the next mammalian host. Here, we show that for successful survival in Tsetse flies, the trypanosomes use trans-sialidase to transfer sialic acids that they cannot synthesize from host's glycoconjugates to the glycosylphosphatidylinositols (GPIs), which are abundantly expressed on their surface. Trypanosomes lacking sialic acids due to a defective generation of GPI-anchored trans-sialidase could not survive in the intestine, but regained the ability to survive when sialylated by means of soluble trans-sialidase. Thus, surface sialic acids appear to protect the parasites from the digestive and trypanocidal environments in the midgut of Tsetse flies.

Immunoenhancing effects of bovine glycomacropeptide and its derivatives on the proliferative response and phagocytic activities of human macrophagelike cells, U937

The immunomodulatory effect of GMP and its derivates on the cell proliferative response of human macrophagelike cell, U937, and its effect on phagocytic activities via incorporation of fluorescence beads were studied. GMP was found to be a potent immunoenhancer at low concentrations, significantly enhancing the proliferation and phagocytic activities of U937. The modulatory function could be radically altered by enzymatic treatments. Pepsin digestion significantly enhanced the degree of cell proliferation and phagocytic activities, whereas trypsin had no significant effect. The immunoenhancing effects decreased significantly after sialidase treatment; however, more than 70% of activity was retained after treatment. GMP with different carbohydrate chains was shown to possess different modulatory capabilities. Sialic acid-rich GMP fractions showed an enhanced response. These findings indicate that both the carbohydrate chains compositions, including the terminal sialic acids and the polypeptide portions of GMP, are essential for the stimulatory effects of GMP on cell proliferation and phagocytic activities of U937.