Natural Immunomodulator Research Articles

Xylose rich heteroglycan from flaxseed gum mediates the immunostimulatory effects on macrophages via TLR2 activation

Immunostimulatory activity of the flaxseed gum neutral fraction (NFG) was investigated. NFG was characterized as a xylose rich heteroglycan through monosaccharide composition analysis, FT-IR, methylation/GC–MS, and 1D/2D-NMR. NFG stimulated NO production and phagocytic activity of macrophages. Secretion of interleukin-6, interleukin-1β, and tumor necrosis factor-α (254.7 pg/mL, 2.5 ng/mL, and 42.9 pg/mL, respectively) was significantly induced by NFG. Mitogen-activated protein kinases of JNK and P38 were activated by NFG with increased phosphorylation of JNK and P38, while NO production was reduced to 6.05 and 4.42 μM by JNK and P38 inhibitor, respectively. Nuclear factor-κB signaling pathway was also activated by NFG with the suppression of IκBα and up-regulation of phosphorylation of IκBα and nuclear factor-κB P65. Toll like receptor-2 was the molecular target of NFG and responsible for the activation of down-stream signaling pathways. Thus, NFG from flaxseed gum may potentially be used as a natural immunomodulator in functional foods.

Extraction of yellow pear residue polysaccharides and effects on immune function and antioxidant activity of immunosuppressed mice

Yellow pear residue polysaccharides were extracted via water bath alcohol precipitation, and the extraction conditions were optimized through the response surface method. The yield of polysaccharides maximized to 56.88 mg/g after extraction at 67.45 °C and material-liquid ratio of 1:34.91 for 3.66 h. The crude polysaccharide was further purified to obtain high-purity polysaccharide LPB-C, it was a kind of pyranoid polysaccharide containing a beta glycosidic bond. It consisted of mannose, glucose, rhamnose and xylose and the molar ratio was 3.3:2.3:10.6:23.2. Then the test mice were grouped, modeled and intragastrically administrated and the immune function and antioxidant capacity in immunosuppressed mice were evaluated. The results showed that the administration of yellow pear residue polysaccharides could markedly improve the immune organ index, carbon clearance ability and earlap swelling rate in immunosuppressed mice, significantly increased the secretion of TNF-α, INF-γ, IL-4 and the activities of CAT, SOD, GSH-Px, and decreased MDA levels in liver, kidney and heart. The present study indicated that yellow pear residue polysaccharides might be used as a potential natural immunomodulator and have great development values in the food and medicine fields.

Вплив мікродобрив та імуномоделюючих препаратів на лабораторну схожість насіння

А bility of seeds to germinate in an environment of high concentration is of great practical importance. Knowledge of seeds ability to germinate in a certain concentration of soil solution can solve the problem of exact seeding rate of particular crop.The results of studies of effect different concentrations of micronutrients of natural acids Avatar-1 carboxylates and immunomodulators (growth stimulant) Iodis-consentrate and Iodis-consentrate + Se on energy of germination and laboratory germination of seeds of cereal crops are presented. Sowing qualities of spring crops (wheat, barley) and winter crops (wheat, triticale) of cereal crops were determined according to the methods of DSTU 4138-2002 in the laboratory Quality of Seeds and Planting Material of Plant Growing Department of the National University of Life and Environmental Sciences of Ukraine.Higher rates of germination energy and laboratory germination of seeds of winter grain cereals were provided by application for pre-sowing treatment of immunostimulants Jodis-consentrate and Jodis-consentrate+ Se.Micro-fertilizer of carboxylates of natural acids Avatar-1 has a positive effect on seeds germination of winter grain cereals.A higher concentration of an aqueous solution leads to suppression of seeds germination of winter grain crops, whereas barley effectively uses water of solutions of increased concentration. Durum wheat, due to high protein content in the grain, germinates more slowly than soft wheat and requires a lower concentration of solution for germination than the soft.

Sarcodon imbricatus polysaccharides protect against cyclophosphamide-induced immunosuppression via regulating Nrf2-mediated oxidative stress

Sarcodon imbricatus, a rare medicinal and edible fungus, has various pharmacological bioactivities. The present study systematically investigated the protective effects of S. imbricatus polysaccharides (SIPS) against cyclophosphamide (CTX)-induced immunosuppression in Balb/c mice model. Compared with the CTX-induced immunosuppressive mice, the spleen and thymus indexes in the mice with 28-day SIPS orally administration were significantly increased, bodyweight loss was alleviated, and the natural killer (NK) cytotoxicity and the proliferative activities of lymphocytes were elevated. SIPS regulated the production of immunoglobulins including IgA, IgG and IgM in the serum and spleen. Notably, SIPS promoted the secretion of interleukin-2 (IL-2), IL-6, IL-10, IL-12 and interferon-γ (IFN-γ) of serum and spleen in CTX-induced immunosuppressive mice. Additionally, SIPS inhibited reactive oxygen species (ROS) levels and increased total antioxidant capacity, including superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) activities of spleen and thymus, as well as enhanced acid phosphatase (ACP) and lysozyme (LZM) levels of thymus in CTX-induced immunosuppressive mice. Histopathological analysis of spleen revealed the protective effect of SIPS against CTX-induced immunosuppression. More importantly, SIPS promoted the expression of nuclear factor-erythroid 2-related factor 2 (Nrf2) and its downstream target genes encoding antioxidant enzymes: SOD1, SOD2, haem oxygenase-1 (HO-1), CAT and quinone oxidoreductase 1 (NQO1). Altogether, SIPS reversed CTX-induced immunosuppression effectively and predominantly through Nrf2-mediated oxidative stress, which provided the useful evidence that SIPS can be served as a novel natural immunomodulator in health foods or medicine.

β-Glucan and Parasites.

SummaryImmunosuppression caused by parasitic infections represents the foremost way by which the parasites overcome or escape the host’s immune response. Glucan is a well-established natural immunomodulator with the ability to significantly improve immune system, from innate immunity to both branches of specific immunity. Our review is focused on the possible role of glucan’s action in antiparasite therapies and vaccine strategies. We concluded that the established action of glucan opens a new window in treatment and protection against parasitic infections.

Nutshell Extracts of Xanthoceras sorbifolia: A New Potential Source of Bioactive Phenolic Compounds as a Natural Antioxidant and Immunomodulator.

The nutshell of Xanthoceras sorbifolia, a waste product in the production of edible oil, is rich in health-promoting phenolic acids. However, the individual constituents, bioactivities, and mechanism of action are largely unknown. In this study, 20 phenolic compounds were characterized in nutshell extract (NE) of X. sorbifolia by gas chromatography-mass spectrometry. Four established in vitro studies showed that NE has significant antioxidant potential. Results in vivo indicated that oral administration of NE effectively ameliorated clinical disease severity of experimental autoimmune encephalomyelitis (EAE) and reduced the neuroinflammation and the central nervous system (CNS) demyelination. The underlying mechanism of NE-induced effects involved decreased penetration of pathogenic immunocyte into the CNS, a reduced production of proinflammatory cytokines and factors, and suppressed differentiation of type 1 T helper and type 17 T helper cells through the Janus kinase/signal transducer and activator of transcription pathway. Taken together, our studies showed that X. sorbifolia nutshell, considered a waste material in the food industry, is a novel source of a natural antioxidant and immunomodulator.

Two complement fixing pectic polysaccharides from pedicel of Lycium barbarum L. promote cellular antioxidant defense

Purification, characterization and biological activities of polysaccharides from Lycium barbarum pedicel were investigated in this study. Two polysaccharides, PLBP-I-I and PLBP-II-I, were obtained from water extracts by anion exchange chromatography and gel filtration. Structural elucidation based on IR, 1H NMR, and 13C NMR spectra indicated that these two fractions were typical pectic polysaccharides, with homogalacturonan and rhamnogalacturonan type I regions and arabinogalactan side chains, and some of the galacturonic acid units were methyl esterified. Both fractions exhibited potent complement fixating activity and pro-antioxidant defense capacity, and those two fractions showed different activities. The higher complement fixation activity was obtained in fraction PLBP-I-I, while the higher pro-antioxidant defense capacity was obtained in fraction PLBP-II-I, which may be due to the structural differences between those two fractions. Thus, the pedicel of L. barbarum could be used as a potential source for natural immunomodulator and antioxidant.

Extraction optimization, characterization, antioxidant and immunomodulatory activities of a novel polysaccharide from the wild mushroom Paxillus involutus

Response surface methodology (RSM) using a Box-Behnken design (BBD) was applied to optimize the extraction of Paxillus involutus polysaccharides. The optimum conditions included an extraction time of 3h, extraction temperature of 79°C and a ratio of liquid to raw material of 43.1mL/g. Under the optimized conditions, the polysaccharides yield was 12.25%. Then, the polysaccharides were purified with DEAE-Cellulose 52 and Sephadex G-100 gel columns, and the fraction denoted as PIP2-1 with a molecular weight of 32kDa was obtained. PIP2-1 was composed of mannose, glucose, galactose, fucose with the mole percentages of 2.8%, 62.2%, 25.4% and 9.6%. The PIP2-1 possessed typical Fourier Transform infrared spectroscopy (FTIR) characterization of polysaccharides. The methylation analysis showed that the PIP2-1 mainly included 1-linked-fuc, 1,3-linked-man, 1-linked-glc, 1,4-linked-glc, 1,6-linked-glc, 1-linked-gal, 1,6-linked-gal, 1,4,6-linked-gal and 1,2,6-gal glycosidic bonds. Furthermore, PIP2-1 showed significant antioxidant activity against hydroxyl radicals (OH), 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH), 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and superoxide radicals. Finally, PIP2-1 significantly enhanced the release of TNF-α and IL-6 in RAW264.7 cells. The results indicated that PIP2-1 could be exploited as a natural antioxidant and immunomodulator for functional food and medical applications.

Immunomodulatory activity of glycodelin: implications in allograft rejection.

Glycodelin is an immunomodulator, indispensable for the maintenance of pregnancy in humans. The glycoprotein induces apoptosis in activated CD4+ T cells, monocytes and natural killer (NK) cells, and suppresses the activity of cytotoxic T cells, macrophages and dendritic cells. This study explores the immunosuppressive property of glycodelin for its possible use in preventing graft rejection. Because glycodelin is found only in certain primates, the hypothesis was investigated in an allograft nude mouse model. It is demonstrated that treatment of alloactivated mononuclear cells with glycodelin thwarts graft rejection. Glycodelin decreases the number of activated CD4+ and CD8+ cells and down-regulates the expression of key proteins known to be involved in graft demise such as granzyme-B, eomesodermin (EOMES), interleukin (IL)-2 and proinflammatory cytokines [tumour necrosis factor (TNF)-α and IL-6], resulting in a weakened cell-mediated immune response. Immunosuppressive drugs for treating allograft rejection are associated with severe side effects. Glycodelin, a natural immunomodulator in humans, would be an ideal alternative candidate.

Glucocorticoids stimulate the contractile activity of lymphatic vessels and lymph nodes

Objective. The lymphatic network participates in the launch and development of an immune response. From an immunological point of view, the lymph flow, provided by active contractions of the lymphatic vessels, is the process of delivering antigens and antigen-presenting cells to the lymph nodes. The purpose of this study is to study the non-genomic effects and mechanisms of action of glucocorticoids, which are natural immunomodulators, on the transport function of lymphatic vessels and lymph nodes. Materials and methods. Bovine mesenteric afferent lymphatic vessels 1.2-1.5 mm in diameter and lymph nodes were used for the study. The contractile activity of isolated lymphatic vessels and capsules of lymph nodes under the action of glucocorticoids in vitro were studied. Agonists and antagonists of signaling pathways were used to determine the mechanisms of action of glucocorticoids on smooth muscle cells. Results and their discussion. Glucocorticoids in therapeutic concentrations increase the tone of lymphatic vessels and lymph nodes, increase in frequency and a decrease the amplitude of phase contractions. It is shown that glucocorticoids stimulate α-adrenoreceptors of smooth muscle cells due to the increase in their affinity. Glucocorticoids activate in the smooth muscle cells the RhoA / ROCK signaling pathway and inhibit the synthesis of endothelial vasodilators - NO and prostacyclin. The revealed changes in the contractile function of lymphatic vessels and lymph nodes under the action of glucocorticoids underlie the modulation of glucocorticoid transport of lymph and the speed of delivery to the lymph nodes of antigens and antigen-presenting cells, i.e. regulation of immune responses. Conclusions. Non-genomic effects and mechanisms of action of glucocorticoids on the contractile function of lymphatic vessels and nodes have been studied. Glucocorticoids activate smooth muscle cells of lymphatic vessels and nodes by stimulating α-adrenoreceptors, and also inhibit the production of NO and prostacyclin.

Purification, structural features and immunostimulatory activity of novel polysaccharides from Caulerpa lentillifera

In this study, four purified fractions (CLGP1, CLGP2, CLGP3 and CLGP4) were prepared from green seaweed Caulerpa lentillifera. They were identified to be a novel kind of xylogalactomanans, differed in molecular weight, monosaccharide composition, and the content of uronic acids and sulfate groups, leading to various ζ-potential, ultrastructure and immunostimulatory activity. Especially, CLGP4 was quite different from the others, as it was found to be a homogeneous heteropolysaccharide composed of Xyl, Man and Gal in a percentage ratio of 1.00:2.15:2.40 with 3877.8kDa. Moreover, CLGP4 contained minor uronic acids (2.37%±0.94%) and the highest sulfate content (21.26%±1.22%). These differences in structural features had an effect on the ζ-potential and ultrastructure of CLGP4, showing rod-, rubble- and ellipsoid-shaped particles with largest negatively charge. In vitro immunostimulatory activity evaluation revealed that all the four fractions significantly stimulated macrophages, but CLGP4 showed more potent immunostimulatory activity due to its stronger function on promoting proliferation of macrophages, enhancing phagocytosis, NO production and acid phosphatase activity in macrophages. Therefore, CLGP4 could be explored as a natural immunomodulator. These results would help a fully exploition of Caulerpa lentillifera polysaccharides recognized as health-improving ingredients in functional foods.

Fucoidans Stimulate Immune Reaction and Suppress Cancer Growth.

Fucoidans are gaining popularity as natural immunomodulators. The aim of this study was to compare the immunological activities or both purified samples and commercially available mixtures containing fucoidan. We evaluated the effects of various samples on phagocytosis, mitogenic response, natural killer (NK) activity, antibody formation and inhibition of breast cancer growth. We found significant immunostimulating activity, but the strength of these effects was different among individual samples. Fucoidans have strong immunostimulating potential, including inhibition of cancer, with isolated samples offering better activity than commercial mixtures.

Hypolipidemic effect of mannans from C. albicans serotypes a and B in acute hyperlipidemia in mice

Mannans, which are biological macromolecules of polysaccharide origin and function as immunomodulators, have been shown to stimulate macrophages in vivo by interaction with the mannose receptor. Thus, they can be used to stimulate macrophages in order to effectively remove circulating atherogenic lipoproteins. Our primary aim was to evaluate the hypolipidemic potential of mannans from C. albicans serotype A (mannan A) and serotype B (mannan B) in a murine model of hyperlipidemia. Mannan A and mannan B were shown to significantly (p<0.05) stimulate both the proliferation (p <0.05) and nitric oxide production of murine peritoneal macrophages in vitro. Pre-treatment of CBA/Lac mice with mannan A prior to induction of hyperlipidemia significantly (p<0.001) reduced serum atherogenic LDL-cholesterol, total cholesterol, and triglycerides. Mannan B exhibited a similar, but more potent, hypolipidemic effect. Electron microscopic analysis of liver revealed a significant (p<0.001) decrease in the volume of lipid droplets when hyperlipidemic mice were pretreated by both mannans. In conclusion, our findings would suggest that both polysaccharide-based biological macromolecules evaluated in the present study, specifically, the natural immunomodulators (mannans A and B), appeared to function as effective lipid-lowering macromolecules, which could potentially serve as adjunct therapy to more conventional hypolipidemic medications such as a statin drug.

Respiratory Tract Infections and the Role of Biologically Active Polysaccharides in Their Management and Prevention.

Respiratory tract infections (RTIs) are the most common form of infections in every age category. Recurrent respiratory tract infections (RRTIs), a specific form of RTIs, represent a typical and common problem associated with early childhood, causing high indirect and direct costs on the healthcare system. They are usually the consequence of immature immunity in children and high exposure to various respiratory pathogens. Their rational management should aim at excluding other severe chronic diseases associated with increased morbidity (e.g., primary immunodeficiency syndromes, cystic fibrosis, and ciliary dyskinesia) and at supporting maturity of the mucosal immune system. However, RRTIs can also be observed in adults (e.g., during exhausting and stressful periods, chronic inflammatory diseases, secondary immunodeficiencies, or in elite athletes) and require greater attention. Biologically active polysaccharides (e.g., β-glucans) are one of the most studied natural immunomodulators with a pluripotent mode of action and biological activity. According to many studies, they possess immunomodulatory, anti-inflammatory, and anti-infectious activities and therefore could be suggested as an effective part of treating and preventing RTIs. Based on published studies, the application of β-glucans was proven as a possible therapeutic and preventive approach in managing and preventing recurrent respiratory tract infections in children (especially β-glucans from Pleurotus ostreatus), adults (mostly the studies with yeast-derived β-glucans), and in elite athletes (studies with β-glucans from Pleurotus ostreatus or yeast).

Neem leaf glycoprotein generates superior tumor specific central memory CD8+ T cells than cyclophosphamide that averts post-surgery solid sarcoma recurrence.

The success of cancer vaccines is limited as most of them induce corrupted CD8+ T cell memory populations. We reported earlier that a natural immunomodulator, neem leaf glycoprotein (NLGP), therapeutically restricts tumor growth in a CD8+ T cell-dependent manner. Here, our objective is to study whether memory CD8+ T cell population is generated in sarcoma hosts after therapeutic NLGP treatment and their role in prevention of post-surgery tumor recurrence, in comparison to the immunostimulatory metronomic cyclophosphamide (CTX) treatment. We found that therapeutic NLGP and CTX treatment generates central memory CD8+ T (TCM) cells with characteristic CD44+CD62LhighCCR7highIL-2high phenotypes. But these TCM cells are functionally impaired to prevent re-appearance of tumors along with compromised proliferative, IL-2 secretive and cytotoxic status. This might be due to the presence of tumor load, even a small one in the host, which serves as a persistent source of tumor antigens thereby corrupting the TCM cells so generated. Surgical removal of the persisting tumors from the host restored the functional characteristics of memory CD8+ T cells, preventing tumor recurrence after surgery till end of the experiment. Moreover, we observed that generation of superior TCM cells in NLGP treated surgically removed tumor hosts is related to the activation of Wnt signalling in memory CD8+ T cells with concomitant inhibition of GSK-3β and stabilisation of β-catenin, which ultimately activates transcription of Wnt target genes, like, eomesodermin, a signature molecule of CD8+ TCM cells.

Inhibition of HeLa cell growth by doxorubicin-loaded and tuftsin-conjugated arginate-PEG microparticles

In order to improve the release pattern of chemotherapy drug and reduce the possibility of drug resistance, poly(ethylene glycol amine) (PEG)-modified alginate microparticles (ALG-PEG MPs) were developed then two different mechanisms were employed to load doxorubicin (Dox): 1) forming Dox/ALG-PEG complex by electrostatic attractions between unsaturated functional groups in Dox and ALG-PEG; 2) forming Dox-ALG-PEG complex through EDC-reaction between the amino and carboxyl groups in Dox and ALG, respectively. Additionally, tuftsin (TFT), a natural immunomodulation peptide, was conjugated to MPs in order to enhance the efficiency of cellular uptake. It was found that the Dox-ALG-PEG-TFT MPs exhibited a significantly slower release of Dox than Dox/ALG-PEG-TFT MPs in neutral medium, suggesting the role of covalent bonding in prolonging Dox retention. Besides, the release of Dox from these MPs was pH-sensitive, and the release rate was observably increased at pH 6.5 compared to the case at pH 7.4. Compared with Dox/ALG-PEG MPs and Dox-ALG-PEG MPs, their counterparts further conjugated with TFT more efficiently inhibited the growth of HeLa cells over a period of 48 h, implying the effectiveness of TFT in enhancing cellular uptake of MPs. Over a period of 48 h, Dox-ALG-PEG-TFT MPs inhibited the growth of HeLa cells less efficiently than Dox/ALG-PEG-TFT MPs but the difference was not significant (p > 0.05). In consideration of the prolonged and sustained release of Dox, Dox-ALG-PEG-TFT MPs possess the advantages for long-term treatment.

Polysaccharides with immunomodulating activity from roots of Gentiana crassicaulis

Two polysaccharides, GCP-I-I and GCP-II-I, were obtained from 100°C water extracts of Gentiana crassicaulis roots by DEAE anion exchange chromatography and gel filtration. The results from methanolysis, methylation, FT-IR and NMR, indicated that these two fractions are typical pectic polysaccharides, with HG and RG-I regions and AG-I/AG-II side chains, and some of the galacturonic acid units of fraction GCP-I-I were methyl esterified. Fractions GCP-I-I and GCP-II-I, both exhibited potent complement fixation, and fraction GCP-I-I was more potent than positive control BPII. The higher complement fixation activity obtained in fraction GCP-I-I may be due to the higher Mw and/or higher amount of AG-II present in fraction GCP-I-I than fraction GCP-II-I. The polysaccharides from G. crassicaulis could be used as a potential natural immunomodulator.

Purification and Partial Structural Characterization of a Complement Fixating Polysaccharide from Rhizomes of Ligusticum chuanxiong.

Rhizome of Ligusticum chuanxiong is an effective medical plant, which has been extensively applied for centuries in migraine and cardiovascular diseases treatment in China. Polysaccharides from this plant have been shown to have interesting bioactivities, but previous studies have only been performed on the neutral polysaccharides. In this study, LCP-I-I, a pectic polysaccharide fraction, was obtained from the 100 °C water extracts of L. chuangxiong rhizomes and purified by diethylaminethyl (DEAE) sepharose anion exchange chromatography and gel filtration. Monosaccharide analysis and linkage determination in addition to Fourier transform infrared (FT-IR) spectrometer and Nuclear magnetic resonance (NMR) spectrum, indicated that LCP-I-I is a typical pectic polysaccharide, with homo-galacturonan and rhamnogalacturonan type I regions and arabinogalactan type I and type II (AG-I/AG-II) side chains. LCP-I-I exhibited potent complement fixation activity, ICH50 of 26.3 ± 2.2 µg/mL, and thus has potential as a natural immunomodulator.

Neutrophils and neutrophil serine proteases are increased in the spleens of estrogen-treated C57BL/6 mice and several strains of spontaneous lupus-prone mice.

Estrogen, a natural immunomodulator, regulates the development and function of diverse immune cell types. There is now renewed attention on neutrophils and neutrophil serine proteases (NSPs) such as neutrophil elastase (NE), proteinase 3 (PR3), and cathepsin G (CG) in inflammation and autoimmunity. In this study, we found that although estrogen treatment significantly reduced total splenocytes number, it markedly increased the splenic neutrophil absolute numbers in estrogen-treated C57BL/6 (B6) mice when compared to placebo controls. Concomitantly, the levels of NSPs and myeloperoxidase (MPO) were highly upregulated in the splenocytes from estrogen-treated mice. Despite the critical role of NSPs in the regulation of non-infectious inflammation, by employing NE-/-/PR3-/-/CG-/- triple knock out mice, we demonstrated that the absence of NSPs affected neither estrogen’s ability to increase splenic neutrophils nor the induction of inflammatory mediators (IFNγ, IL-1β, IL-6, TNFα, MCP-1, and NO) from ex vivo activated splenocytes. Depletion of neutrophils in vitro in splenocytes with anti-Ly6G antibody also had no obvious effect on NSP expression or LPS-induced IFNγ and MCP-1. These data suggest that estrogen augments NSPs, which appears to be independent of enhancing ex vivo inflammatory responses. Since estrogen has been implicated in regulating several experimental autoimmune diseases, we extended our observations in estrogen-treated B6 mice to spontaneous autoimmune-prone female MRL-lpr, B6-lpr and NZB/WF1 mice. There was a remarkable commonality with regards to the increase of neutrophils and concomitant increase of NSPs and MPO in the splenic cells of different strains of autoimmune-prone mice and estrogen-treated B6 mice. Collectively, since NSPs and neutrophils are involved in diverse pro-inflammatory activities, these data suggest a potential pathologic implication of increased neutrophils and NSPs that merits further investigation.

Algerian propolis extracts: Chemical composition, bactericidal activity and in vitro effects on gilthead seabream innate immune responses

Propolis has been used as a medicinal agent for centuries. The chemical composition of four propolis samples collected from four locations of the Sétif region, Algeria, using gas chromatography-mass spectrometry was determined. More than 20 compounds and from 30 to 35 compounds were identified in the aqueous and ethanolic extracts, respectively. Furthermore, the antimicrobial activity of the propolis extracts against two marine pathogenic bacteria was evaluated. Finally, the in vitro effects of propolis on gilthead seabream (Sparus aurata L.) leucocyte activities were measured. The bactericidal activity of ethanolic extracts was very high against Shewanella putrefaciens, average against Photobacterium damselae and very low against Vibrio harveyi. The lowest bactericidal activity was always that found for the aqueous extracts. When the viability of gilthead seabream head-kidney leucocytes was measured after 30 min' incubation with the different extracts, both the ethanolic and aqueous extracts of one of the propolis samples (from Babor) and the aqueous extract of another (from Ain-Abbassa) provoked a significant decrease in cell viability when used at concentrations of 100 and 200 μg ml−1. Furthermore, significant inhibitory effects were recorded on leucocyte respiratory burst activity when isolated leucocytes where preincubated with the extracts. This effect was dose-dependent in all cases except when extracts from a third propolis sample (from Boutaleb) were used. Our findings suggest that some of Algerian propolis extracts have bactericidal activity against important bacterial pathogens in seabream and significantly modulate in vitro leucocyte activities, confirming their potential as a source of new natural biocides and/or immunomodulators in aquaculture practice.