The anticarcinogenic effect of propolis in human lymphocytes culture

Application of an Inter-Species Extrapolation Method for the Prediction of Drug Interactions between Propolis and Duloxetine in Humans

Duloxetine (DLX) is a potent drug investigated for the treatment of depression and urinary incontinence. DLX is extensively metabolized in the liver by two P450 isozymes, CYP2D6 and CYP1A2. Propolis (PPL) is one of the popular functional foods known to have effects on activities of CYPs, including CYP1A2. Due to the high probability of using DLX and PPL simultaneously, the present study was designed to investigate the potent effect of PPL on pharmacokinetics (PKs) of DLX after co-administration in humans. A PK study was first conducted in 18 rats (n = 6/group), in which the plasma concentration of DLX and its major metabolite 4-hydroxy duloxetine (4-HD) with or without administration of PPL was recorded. Population PKs and potential effects of PPL were then analyzed using NONMEM software. Lastly, these results were extrapolated from rats to humans using the allometric scaling and the liver blood flow method. PPL (15,000 mg/day) exerts a statistically significant increase in DLX exposures at steady state, with a 20.2% and 24.6% increase in DLX C m a x , s s and the same 28.0% increase in DLX A U C s s when DLX (40 or 60 mg) was administered once or twice daily, respectively. In conclusion, safety issues are required to be attended to when individuals simultaneously use DLX and PPL at high doses, and the possibility of interactions between DLX and PPL might be noted.

Kolaviron shows anti-proliferative effect and down regulation of vascular endothelial growth factor-C and toll like receptor-2 in Wuchereria bancrofti infected blood lymphocytes

The anti-proliferative effect and down regulation of vascular endothelial growth factor C and toll like receptor-2 by kolaviron on Wuchereria bancrofti infected peripheral blood lymphocytes were investigated. Blood were collected from consenting volunteers in Talata Mafara, Nigeria, between the hours of 10pm to 12am, and microscopically identified for microfilariae. W. bancrofti positive samples were cultured for 72h treated with Doxycycline (2μg/ml) and kolaviron (5μg/ml) in vitro. Mitotic index, expression of vascular endothelial growth factor-C (VEGF-c), toll like receptor-2 (TLR-2) were determined using standard procedures. Mitotic index was significantly (P<0.05) reduced in the kolaviron treated group compared to negative control. Kolaviron also significantly (P<0.05) down regulated the expression of VEGF-c and TLR-2 when compared with the untreated group. In both cases, the effects of kolaviron was not significantly different (P<0.05) to that of doxycycline. Furthermore, strong positive correlations between mitotic index, VEGF-c and TLR-2 expressions were observed. The study suggests that kolaviron rich portion of Garcinia kola exhibited anti-proliferative effect and down regulation of VEGF-c and TLR-2 in W. bancrofti infected blood. Thus, the results from this study might have unravelled the potency of kolaviron in the management of complications associated with lymphatic filariasis.

Antifungal Activity of Propolis Against Yeasts Isolated From Blood Culture: In Vitro Evaluation

BACKGROUND

Due to the failure of available antifungal agents in the treatment of candidemia and the toxic activities of these drugs, a lot of researches are being conducted to develop new nontoxic and effective antifungal agents for optimal control of fungal pathogens. The aim of this study is to evaluate the in vitro antifungal activity of propolis against yeasts isolated from the blood cultures of intensive care unit patients.

METHODS

Seventy-six strains were included in this study. The in vitro antifungal activity of propolis, fluconazole (FLU), and itraconazole (ITR) was investigated by the microdilution broth methods (CLSI guidelines M27-A3 for yeast). The propolis sample was collected from Kayseri, Turkey.

RESULTS

Of the 76 isolates, 33 were identified as Candida albicans while 37 were C. parapsilosis, three were C. tropicalis, and three were identified as C. glabrata. The geometric mean range for MIC (μg/ml) with regard to all isolates was 0.077 to 3 μg/ml for FLU and ITR, and 0.375 to 0.70 μg/ml for propolis. It was shown that propolis had significant antifungal activity against all Candida strains and the MIC range of propolis was determined as 0185 to 3 μg/ml.

CONCLUSION

This study demonstrated that propolis had significant antifungal activity against yeasts isolated from blood culture compared with FLU and ITR. The propolis MIC in azole-resistant strains such as C. glabrata was found lower than the FLU MIC.

Mexican propolis flavonoids affect photosynthesis and seedling growth

As a continuous effort to find new natural products with potential herbicide activity, flavonoids acacetin (1), chrysin (2) and 4',7-dimethylnarangenin (3) were isolated from a propolis sample collected in the rural area of Mexico City and their effects on the photosynthesis light reactions and on the growth of Lolium perenne, Echinochloa crus-galli and Physalis ixocarpa seedlings were investigated. Acacetin (1) acted as an uncoupler by enhancing the electron transport under basal and phosphorylating conditions and the Mg(2+)-ATPase. Chrysin (2) at low concentrations behaved as an uncoupler and at concentrations up to 100 μM its behavior was as a Hill reaction inhibitor. Finally, 4',7-dimethylnarangenin (3) in a concentration-dependent manner behaved as a Hill reaction inhibitor. Flavonoids 2 and 3 inhibited the uncoupled photosystem II reaction measured from water to 2,5-dichloro-1,4-benzoquinone (DCBQ), and they did not inhibit the uncoupled partial reactions measured from water to sodium silicomolybdate (SiMo) and from diphenylcarbazide (DPC) to diclorophenol indophenol (DCPIP). These results indicated that chrysin and 4',7-dimethylnarangenin inhibited the acceptor side of PS II. The results were corroborated with fluorescence of chlorophyll a measurements. Flavonoids also showed activity on the growth of seedlings of Lolium perenne and Echinochloa crus-galli.

Effects of an ethanol extract of Brazilian green propolis on human cytochrome P450 enzyme activities in vitro

Supplement-drug interaction on CYP enzyme activity is occasionally found to cause clinically adverse events, and no report on interactions of propolis is available either in vitro or clinical. In this study, we tried to estimate the risk of an interaction between an ethanol extract of Brazilian green propolis (EEP-B55) and drugs in vitro and in vivo. The activities of CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 were attenuated by EEP-B55 in a concentration-dependent manner, and artepillin C, kaempferide, dihydrokaempferide, isosakuranetin, and kaempferol were estimated to have potential for CYP inhibition. The IC50 values of artepillin C for each CYP were approximately 33-fold higher than its Cmax in the blood of rats after dosing with 5-fold the recommended daily intake of EEP-B55. These findings suggest that liver CYP enzyme activities are not markedly affected by artepillin C at the recommended daily intake of EEP-B55.

Amelioration of renal carcinogenesis by bee propolis: a chemo preventive approach

OBJECTIVE

The present study was designed to investigate the chemo preventive efficacy of bee propolis (BP) against diethylnitrosamine (DEN) initiated and ferric nitrilotriacetate (Fe-NTA) promoted renal carcinogenesis in Wistar rats. Chronic treatment of Fe-NTA induced oxidative stress, inflammation and cellular proliferation in Wistar rats. BP is a resinous material collected by bees from various plants which has been used from centuries in folk medicine.

MATERIALS AND METHODS

Renal cancer was initiated by single intraperitoneal injection of N-nitrosodiethylamine (DEN 200 mg/kg body weight) and promoted by twice weekly administration of Fe-NTA 9 mg Fe/kg body weight for 16 weeks. The chemo preventive efficacy of BP was studied in terms of lipid peroxidation (LPO), renal anti-oxidant armory such as catalase, superoxide dismustase, glutathione S-transferase, glutathione peroxidase, glutathione reductase and glutathione (GSH), serum toxicity markers, cell proliferation, tumor suppressor protein and inflammation markers.

RESULTS

Administration of Fe-NTA enhances renal LPO, with concomitant reduction in reduced GSH content and antioxidant enzymes. It induces serum toxicity markers, viz., blood urea nitrogen, creatinine and lactate dehydrogenase. Chemo preventive effects of BP were associated with upregulation of antioxidant armory and down regulation of serum toxicity markers. BP was also able to down regulate expression of proliferative cell nuclear antigen, cyclooxygenase-2, tumor necrosis factor-alpha and upregulated p53 along with induction of apoptosis. Histopathological changes further confirmed the biochemical and immunohistochemical results.

CONCLUSION

These results provide a powerful evidence for the chemo preventive efficacy of BP against renal carcinogenesis possibly by modulation of multiple molecular pathways.

Molecular mechanism of antiproliferation potential of Acacia honey on NCI-H460 cell line

Lung cancer is one of the leading causes of death worldwide. We investigated the molecular mechanism of antiproliferation potential of Acacia honey on NCI-H460 cells by cell cycle, viability, cytokines, calcium ion and gene expression analysis. Acacia honey inhibited cells proliferation, arrested G0/G1 phase, stimulated cytokines, calcium ion release as well as suppressed p53 and Bcl-2 expression in a dose-dependent manner. We proposed that the molecular mechanism of the antiproliferation potential of Acacia honey on NCI-H460 cell line is due to cell cycle arrest, stimulation of cytokines and calcium ion as well as downregulation of Bcl-2 and p53 genes.

Propolis: a wonder bees product and its pharmacological potentials

Propolis is a natural resinous mixture produced by honey bees from substances collected from parts of plants, buds, and exudates. Due to its waxy nature and mechanical properties, bees use propolis in the construction and repair of their hives for sealing openings and cracks and smoothing out the internal walls and as a protective barrier against external invaders like snakes, lizards, and so forth, or against weathering threats like wind and rain. Bees gather propolis from different plants, in the temperate climate zone mainly from poplar. Current antimicrobial applications of propolis include formulations for cold syndrome (upper respiratory tract infections, common cold, and flu-like infections), wound healing, treatment of burns, acne, herpes simplex and genitalis, and neurodermatitis. Worldwide propolis has a tremendous popularity, but in India the studies over propolis have just started, not extensively reported except few regions of India like Maharashtra, West Bengal, Tamil Nadu, Gujrat, and Madhya Pradesh.

Modulation of radiation-induced and mitomycin C-induced chromosome damage by apigenin in human lymphocytes in vitro

Apigenin (APG), a flavone, is known to exhibit antioxidant, antimutagenic and antitumorigenic activity, both in vivo and in vitro. The aim of this study is to investigate the modulatory effects of APG on human lymphocytes after irradiation with gamma rays (3 Gy) or treatment with the antineoplastic agent, mitomycin C (MMC), in vitro. Cytogenetic biomarkers such as chromosome aberrations (CAs), sister chromatid exchanges (SCEs) and cytochalasin-B blocked micronuclei (CBMN), were studied in blood lymphocytes treated with radiation, or antineoplastic agent (MMC), and APG. Whole blood lymphocytes were cultured in vitro using a standard protocol. No significant differences were found in the frequency of CAs or micronuclei (MN) in human peripheral blood lymphocytes irradiated with gamma rays (3 Gy) and then post-treated with APG. There was an increase in the frequency of SCEs per cell in APG-treated samples compared with the controls. Lymphocytes treated with MMC in the presence of APG exhibited a significant decrease (P < 0.01) in the frequency of SCEs compared with MMC treatment alone. The data for the MN test indicated that APG treatment significantly reduced (P < 0.01) the frequency of MMC-induced MN.

Cytotoxic constituents of propolis inducing anticancer effects: a review

Objectives

Propolis is a honeybee product used extensively in traditional medicine for its antioxidant, anti-inflammatory, immunomodulatory and anticancer effects. Propolis exhibits a broad spectrum of biological activities because it is a complex mixture of natural substances. In this review, the antitumour effects of propolis extracts and its constituents (e.g. flavonoids, terpenes and caffeic acid phenethyl ester) are discussed.

Key findings

The effect of propolis on experimental carcinogenesis is discussed, as well as its possible mechanisms of action against tumours, involving apoptosis, cell cycle arrest and interference on metabolic pathways. Propolis seems to be efficient against different tumour cells both in vitro and in vivo, which suggests its potential in the development of new anticancer drugs.

Summary

Propolis extracts may be important economically and would allow a relatively inexpensive cancer treatment. Preclinical investigations are needed to further elucidate the benefits of propolis and its antitumour properties.

Brazilian propolis-derived components inhibit TNF-α-mediated downregulation of adiponectin expression via different mechanisms in 3T3-L1 adipocytes

BACKGROUND

Previous reports suggest that Brazilian propolis has multiple biological functions and may help to restore adiponectin expression and insulin sensitivity. However, little is known about the molecular mechanisms by which these compounds inhibit the downregulation of adiponectin.

METHODS

The effect of various Brazilian propolis-derived components on inhibition of tumor necrosis factor-α (TNF-α)-mediated downregulation of adiponectin expression in 3T3-L1 adipocytes and molecular mechanism was investigated.

RESULTS AND CONCLUSIONS

Pretreatment with either artepillin C (C3) or its derivative (C4) significantly inhibited TNF-α-mediated downregulation of adiponectin expression in 3T3-L1 adipocytes. Interestingly, C3 strongly activated peroxisome proliferator-activated receptor γ (PPARγ) transcriptional activity. Treatment of adipocytes with C3 resulted in the upregulation of adiponectin and fatty acid-binding protein 4 expression, but C4 did not significantly induce PPARγ transactivation. C4 did, however, inhibit the TNF-α-induced c-Jun-NH(2)-terminal kinase (JNK) signaling that is involved in adiponectin expression. Molecular docking studies based on hPPARγ with C3 and JNK1 with C4 clearly supported our experimental results. These data demonstrate that 1) both C3 and C4 significantly inhibit the TNF-α-mediated downregulation of adiponectin in adipocytes, 2) C3 functions as a PPARγ agonist, and its inhibition of the effect of TNF-α is due to this PPARγ transactivation, and 3) C4 is an effective inhibitor of JNK activation, thus inhibiting the TNF-α-mediated downregulation of adiponectin.

GENERAL SIGNIFICANCE

Brazilian propolis-derived components (C3 and C4) can significantly inhibit TNF-α-mediated downregulation of adiponectin in adipocytes, although they do so via different mechanisms.

Brazilian Propolis Suppresses Angiogenesis by Inducing Apoptosis in Tube-Forming Endothelial Cells through Inactivation of Survival Signal ERK1/2

We recently reported that propolis suppresses tumor-induced angiogenesis through tube formation inhibition and apoptosis induction in endothelial cells. However, molecular mechanisms underlying such angiogenesis suppression by propolis have not been fully elucidated. The aim of this study was to investigate the effects of ethanol extract of Brazilian propolis (EEBP) on two major survival signals, extracellular signal-regulated kinase 1/2 (ERK1/2) and Akt, and to elucidate whether changes in these signals were actually involved in antiangiogenic effects of the propolis. Detection by western blotting revealed that EEBP suppressed phosphorylation of ERK1/2, but not that of Akt. Pharmacological inhibition by U0126 demonstrated that ERK1/2 inactivation alone was enough to inhibit tube formation and induce apoptosis. It was also shown that EEBP and U0126 similarly induced activation of caspase-3 and cleavage of poly ADP-ribose polymerase (PARP) and lamin A/C, all of which are molecular markers of apoptosis. These results indicate that inhibition of survival signal ERK1/2, and subsequent induction of apoptosis, is a critical mechanism of angiogenesis suppression by EEBP.

Correlation between antiangiogenic activity and antioxidant activity of various components from propolis

Propolis possesses various physiological activities. In this study, we examined the antiangiogenic and antioxidant activities of various components from propolis: acacetin, apigenin, artepillin C, caffeic acid phenethyl ester, chrysin, p-coumaric acid, galangin, kaempferol, pinocembrin, and quercetin. The effects of these components were tested on in vitro models of angiogenesis, tube formation and growth of human umbilical vein endothelial cells (HUVECs). Furthermore, these components were evaluated for their antioxidant activities by 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical-scavenging and ferric reducing/antioxidant power (FRAP) assays. Two propolis components, caffeic acid phenethyl ester, and quercetin, possessed strong inhibitory effects on tube formation and on endothelial cell proliferation and, coincidentally, showed strong antioxidant activity. Artepillin C, galangin, and kaempferol also possessed strong antiangiogenic and antioxidant activities to a slightly less degree. In contrast, acacetin, apigenin, and pinocembrin possessed a considerable degree of antiangiogenic activities, although they showed very low antioxidant activities. From these results, we propose that components from propolis such as artepillin C, caffeic acid phenethyl ester, galangin, kaempferol, and quercetin might represent a new class of dietary-derived antioxidative compounds with antiangiogenic activities. These propolis components may have the potential to be developed into pharmaceutical drugs for the treatment of angiogenesis-dependent human diseases such as tumors.

Cytogenetic effects of nine Helichrysum taxa in human lymphocytes culture

Helichrysum Mill. (Asteraceae) species have been used in folk medicine for thousands of years in the world. The in vitro cytogenetic effects in human lymphocytes of nine Helichrysum taxa used in Turkey folk medicine were investigated. Blood samples were obtained from healthy donors, non-smoking volunteers, which were incubated and exposed to increasing concentrations of methanol extracts of Helichrysum taxa (0.01, 0.05, 0.1, 0.5 and 1 mg/mL). The inhibitory effects of H. stoechas (L.) Moench subsp. barrelieri (Ten.) Nyman, H. armenium DC. subsp. armenium, H. armenium DC. subsp. araxinum (Kirp.) Takht., H. plicatum DC. subsp. plicatum, H. compactum Boiss. and H. artvinense P.H.Davis & Kupicha on the mitotic index and replication index indicate that these taxa can have genotoxic and mutagenic effects. They should therefore not be used freely in alternative medicine although their antiproliferative activity may suggest anticarcinogenic properties. Increase effects of H. stoechas subsp. barrelieri, H. armenium subsp. armenium, H. armenium subsp. araxinum, H. chasmolycicum P.H.Davis, H. plicatum subsp. plicatum, H. compactum and H. artvinense on the micronucleus rates showed that these taxa can have genotoxic and carcinogenic effects.

Immunomodulatory effects of Turkish propolis: changes in neopterin release and tryptophan degradation

In most of the diseases which are considered to benefit from propolis, cellular immune reaction is activated, neopterin levels in body fluids are increased and enhanced tryptophan degradation is observed. In this study, the immunomodulatory effects of six Turkish propolis samples were evaluated by using the in vitro model of peripheral blood mononuclear cells (PBMC). Concentrations of neopterin, tryptophan, kynurenine and pro-inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) were determined and also the viability of the cells was checked with trypan blue and MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] test. In PBMC treated with mitogen phytohaemagglutinin, neopterin production and tryptophan degradation by enzyme indoleamine 2,3-dioxygenase (IDO) as well as release of cytokines was significantly enhanced and upon treatment with propolis extracts all these effects were dose-dependently suppressed. Results show an immunomodulatory effect of propolis extracts which includes down-regulation of IDO activity. IDO enzyme is considered to play an important role in the development of immunodeficiency and neuropsychiatric symptoms in patient with chronic inflammation. The suppression of tryptophan degradation by propolis extracts may therefore be related with some of its beneficial health properties in humans.

In vitro safety evaluation and anticlastogenic effect of BacoMind on human lymphocytes

OBJECTIVE

BacoMind (BM) is a standardized extract of Bacopa monnieri, which belongs to the family Scrophulariaceae and is a creeping annual plant found throughout the Indian subcontinent. It has been used by Ayurvedic medicinal practitioners in India for almost 3000 years and is classified as a medharasayana, a substance which improves memory and intellect. With the widespread traditional use as well as scientific validation of Bacopa monnieri for nootropic activity, a bioactive-rich unique phytochemical composition-BacoMind was developed from B. monnieri for use as a cognition and memory enhancing agent. The present study aimed to investigate the in vitro toxicity of this formulation of BacoMind on human lymphocytes and to rule out its possible contribution to mutagenicity.

METHODS

In the present investigation the active ingredients present in BM were identified and quantified by high performance liquid chromatography (HPLC) and high performance thin-layer chromatography (HPTLC). Antioxidant and anticlastogenic properties of BM were studied in vitro with and without metabolic activation. Doses of BM were chosen on the basis of mitotic index (MI) and cytokinesis-block proliferation index (CBPI). Clastogenicity assays were performed at 31.2 microg/mL, 62.5 microg/mL, and 125 microg/mL, while the Salmonella reverse mutation assay (Ames test) was performed at doses of 61.72, 185.18, 555.55, 1666.67, and 5000.00 microg/plate.

RESULTS

HPLC and HPTLC analysis of BM revealed the presence of bacoside A3, bacopaside I, bacopaside II, jujubogenin isomer of bacopasaponin C, bacosine, luteolin, apigenin, bacosine, and beta-sitosterol D glucoside. BM demonstrated significant antioxidant activity. The number of chromosomal aberrations and the frequency of micronuclei induced by BM were not statistically significant up to a dose of 62.5 microg/mL. A subsequent dose of 125 microg/mL prior to metabolic activation induced mild clastogenicity, but it was found to be biologically insignificant as this effect was not seen post metabolic activation. BM also demonstrated a dose-dependent protection against the clastogens used in this study using the above tests for clastogenicity. Maximum protection was observed in presence of metabolic activation. Moreover, BM demonstrated no mutagenic effect on the tested strains, as observed in the Ames test.

CONCLUSION

BM protected human lymphocytes against various clastogens. BM also exhibited high antioxidant activity which might be responsible for the observed protective effects against the clastogens since the used clastogens are known to induce their clastogenic effects via production of oxidative radicals.

Suppression of tumor-induced angiogenesis by Brazilian propolis: Major component artepillin C inhibits in vitro tube formation and endothelial cell proliferation

Propolis, a resinous substance collected by honeybees from various plant sources, possesses various physiological activities such as antitumor effects. We have previously shown that propolis of Brazilian origin was composed mainly of artepillin C and that its constituents were quite different from those of propolis of European origin. In this report, we examined an antiangiogenic effects of Brazilian propolis and investigated whether artepillin C was responsible for such effects. In an in vivo angiogenesis assay using ICR mice, we found that the ethanol extract of Brazilian propolis (EEBP) significantly reduced the number of newly formed vessels. EEBP also showed antiangiogenic effects in an in vitro tube formation assay. When compared with other constituents of EEBP, only artepillin C was found to significantly inhibit the tube formation of HUVECs in a concentration-dependent manner (3.13-50microg/ml). In addition, artepillin C significantly suppressed the proliferation of HUVECs in a concentration-dependent manner (3.13-50microg/ml). Furthermore, artepillin C significantly reduced the number of newly formed vessels in an in vivo angiogenesis assay. Judging from its antiangiogenic activity in vitro and in vivo, we concluded that artepillin C at least in part is responsible for the antiangiogenic activity of EEBP in vivo. Artepillin C may prove useful in the development of agents and foods with therapeutic or preventive activity against tumor angiogenesis.

Enrichment and isolation of endosulfan degrading and detoxifying bacteria

In the present study, degradation of endosulfan by a mixed culture isolated from a pesticide-contaminated soil was studied in batch experiments. After two weeks of incubation, the mixed culture was able to degrade 73% and 81% of alpha and beta endosulfan respectively. Endodiol was identified by GC/MS as degradation intermediate. The toxicity studies of endosulfan before and after degradation were carried out using micronucleus assay on human polymorphonuclear cells. The findings suggested that the metabolism of endosulfan isomers by the mixed culture was accompanied by significant reduction in the toxicity. Studies were also carried out to quantify the degradation potential of the individual species in the mixed bacterial culture. Two cultures identified by 16S rRNA as Stenotrophomonas maltophilia and Rhodococcus erythropolis were found to be responsible for majority of the degradation by the mixed culture. S. maltophilia showed better degradation efficiency compared to that by R. erythropolis. This is the first report of endosulfan degradation using the above-mentioned organisms.

Adjuvant effect of green propolis on humoral immune response of bovines immunized with bovine herpesvirus type 5

Despite recent technological advances in vaccine production, most vaccines depend on the association with adjuvant substances. In this study, propolis, which has been attracting the attention of researchers due to its bioactive properties, was evaluated as an immunological adjuvant. The association of 40mg/dose of an ethanolic extract of green propolis with an inactivated oil vaccine against bovine herpesvirus type 5 (BoHV-5), resulted in a significant increase (P<0.01) in the neutralizing antibody levels, comparing to the bovines that received the same vaccine without propolis. Besides, propolis increased the percentage of animals with high antibody titers (above 32). Phenolic compounds such as artepillin C (3,5-diprenyl-4-hydroxycinnamic acid) and the derivatives of cinnamic acid besides other flavonoid substances were abundant in the propolis extract used, and they could be the main substances with adjuvant action. The effect of the green propolis extract on the humoral immune response can be exploited in the development of new vaccines.