Dietary sugars inhibit biologic functions of the pattern recognition molecule, mannose-binding lectin

doi:10.4236/oji.2011.12005

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Vol.1, No.2, 41-49 (2011)

doi:10.4236/oji.2011.12005

Open Journal of Immunology

Dietary sugars inhibit biologic functions of the pattern

recognition molecule, mannose-binding lectin

Kazue Takahashi1, Wei-Chuan Chang1, Patience Moyo1, Mitchell R. White2, Parool Meelu3,

Anamika Verma2, Gregory L. Stahl4, Kevan L. Hartshorn2, Vijay Yajnik3*

1Program of Developmental Immunology, Department of Pediatrics, Massachusetts General Hospital, Harvard Medical School, Bos-

ton, USA;

2Department of Medicine, Boston University School of Medicine, Boston, USA;

3Gastrointestinal Unit, Massachusetts General Hospital, Harvard Medical School, Boston, USA;

*Corresponding Author: ktakahashi1@partners.org

4Center for Experimental Therapeutics and Reperfusion Injury, Department of Anesthesiology, Perioperative and Pain Medicine,

Harvard Institute of Medicine, Harvard Medical School, Boston, USA.

Received 17 August 2011; revised 1 September 2011; accepted 9 September 2011.

ABSTRACT

Mannose-binding lectin (MBL), a mammalian le-

ctin, is a pattern recognition molecule of the in-

nate immune system and recognizes carbohy-

drates that are exposed on pathogens. In this

study, we observed that fructose down regulates

MBL-mediated innate immune mechanisms ag-

ainst both influenza A Virus (IAV) and Staphylo-

coccus aureus. These mechanisms include the

lectin complement pathway and coagulation en-

zyme-like activities on both pathogens. Further-

more, fructose also reduces MBL-mediated pha-

gocytosis of S. aureus and IAV and MBL-medi-

ated IAV infection to epithelial cells. In contrast,

sucrose inhibits MBL-mediated immune mecha-

nisms agai nst S. aureus but not IAV. Together, our

studies show that dietary sugars, in particular

fructose, negatively regulate the innate immu-

nity against viral and bacterial pathogens.

Keywords: Manno s e-Binding Lectin; Fructose;

Influenza A Virus; Staphylococcus Aureus; Com-

plement; Coagulation

1. INTRODUCTION

The innate immune system represents the first line of

host defense against pathogens. It is widely accepted that

in the lumen of our intestines, the innate immune system

is constantly interacting with the microbiota [1,2]. This

interaction is tightly regulated and is essential for both

immune tolerance and immunity against pathogens [3,4].

How our nutrition affects host-microbiome interactions

remains unknown but an increase risk of infection is

observed in patients with diabetes and obesity. These

diseases have been linked to excess consumption of

fructose and fatty foods [5,6]. Fructose, in the form of

high fructose corn syrup, along with sucrose is the main

dietary sugars in our diet [7]. How dietary sugars affect

human disease is an important question that remains

unanswered. A human study in 1973 showed that dietary

sugar intake, but not starch intake, dramatically reduced

bacterial phagocytosis [8]. Although the precise mecha-

nisms of this observation have not been understood,

these observations support the idea that dietary sugars

influence immune functions.

The innate immune system like the adaptive immune

system utilizes both cellular and humoral pathways.

Cellular defense includes epithelial cells and phagocytes,

such as macrophages and neutrophils [9]. Cell surface

receptors on innate immune cells together with soluble

lectins recognize pathogens by specific pathogen-asso-

ciated molecular patterns (PAMPs) and therefore termed

pattern recognition molecules [10]. MBL, a serum pat-

tern recognition molecule, is primarily synthesized in the

liver and in small quantity by the small intestinal epithet-

lial cells [11-14]. MBL was also identified as an opsonin

critical for bacterial (and yeast) phagocytosis [15,16]. In

addition, it is critical for defense against viruses as MBL

is identical to inhibitor found in serum and caused cal-

cium-dependent viral neutralization [17,18]. Thus, mo-

lecular patterns from virus, bacteria and yeast are recog-

nized by MBL.

Pattern recognition by MBL results in activation of

innate immune cascades. For example, MBL activates

complement via the lectin pathway, which is mediated

by MBL-associated serine protease (MASP) 1-3 [19,20].

MASPs are homologous to serum proteins C1r and C1s

K. Takahashi et al. / Open Journal of Immunology 1 (2011) 41-49

that activate the classical complement pathway although

MASPs evolutionally predate C1r and C1s [21]. MBL/

MASP complex also initiates coagulation via throm-

bin-like activity [22-24]. Human MBL gene has poly-

morphisms, producing low and dysfunctional MBL,

which have been associated with increased infection

susceptibilities as reviewed [25]. Clinical observations in

human MBL deficiency were confirmed in an animal

model using MBL null mice. These mice have increased

infection susceptibility against certain pathogens and

reconstitution with exogenous MBL rescues the phenol-

type [26-29].

IAV and S. aureus are common human pathogens that

are recognized by innate immune molecules, including

MBL [30]. IAV is an RNA virus whose surface is envel-

oped with glycoproteins containing neuraminidase and

hemagglutinin, which have glycosylation sites [31]. IAV

infection could results in fatal complications, even in

individuals who are appeared to be healthy [32,33]. S.

aureus is a Gram positive bacteria present on mucosa

and skin of healthy individuals [32,34,35]. Although

normally innocuous, it may cause serious infections and

can develop severe complications leading to much high-

er morbidity and mortality [36]. This bacterial in- fection

has increased problem with rapid emergence of methicil-

lin-resistant S. aureus [37]. In addition, S. aureus can

co-infect with influenza virus resulting in increased

mortality during influenza epidemics [39].

In this study, we investigated the effects of dietary

sugars and its effect on innate immunity against common

human pathogens, IAV and S. aureus. We observed that

fructose negatively regulate MBL-mediated innate im-

mune functions against both IAV and S. aureus using

well established in vitro experimental design that reca-

pitulates environment present in the intestinal lumen and

in blood. These findings represent an important ad-

vancement in our understanding the complex interaction

between diet and human health.

2. MATERIALS AND METHODS

2.1. Preparation of IAV and S. Aureus

Both pathogens were prepared as previously described

[28,40]. Briefly, IAV strain A/Philippine 82 (H3N2) was

grown in the chorioallantoic fluid of chicken eggs and

purified on a discontinuous sucrose gradient. Virus

stocks were dialyzed against PBS and aliquots were

stored at –80˚C. HA titers were determined by titration

with human type O, Rh- red blood cells (RBCs) in PBS.

Fluorescent foci counts (ffc) were determined by Madin-

Darby canine kidney (MDCK) cell infection assay as

previously described [41]. S. aureus was grown in Co-

lumbia media with 2% NaCl and used at mid log phase

and cfu was determined by culture on tryptic soy agar

plates [28].

2.2. MBL Binding Assay

This assay was performed using previously described

methods with a minor modification [27]. Briefly, 96 as-

say plates were coated with mannan (1 g, Sigma, MO),

IAV (1000 HA–1) or S. aureus (Reynolds CP-5+, 5 × 106 cfu)

in 50 l of a bicarbonate buffer, pH 9.5 and blocked with

BSA. The pates were added with indicated concentra-

tions of recombinant human MBL (MBL, a gift from

Enzon Pharmaceuticals. A concentration of stock was 1

mg/ml) in 50 μl and incubated at room temperature. Af-

ter rinsing, bound MBL was detected by mouse anti-

hMBL monoclonal Ab (3F8) [42] followed by alka-

line-phosphatase conjugated anti-mouse Ab (Promega,

WI) and pNTP substrate (Sigma, MO). Reaction was

read at OD 415 nm using SpectraMax M5 (Molecular

Devices, CA). For sugar inhibition experiments, indi-

cated concentrations of sugars were mixed together with

MBL at 1 μg/ml. Binding was expressed as OD415

reading. These assays were performed in triplicates and

repeated at least twice. Representative data was shown.

2.3. Mouse Sera

MBL knockout (KO) mouse sera were used to provide

MASPs [22]. Mouse sera were stored in the –80˚C freezer.

All animal experiments were performed under a protocol

approved by the Subcommittee on Research Animal Care

at Massachusetts General Hospital, Boston, MA.

2.4. Assays of the Lectin Complement

Activity and Thrombin-Like Activity

The lectin pathway assay was performed with a minor

modification of previously described method [28]. 96

well plates were prepared as in the binding assay. After

wash and blocking, wells were incubated with various

concentration of MBL with or without 1% MBL KO sera

and incubated at room temperature. After wash, the wells

were incubated with human C4 (Sigma, MO) and incu-

bated at 37˚C. After wash, the wells were incubated with

rabbit anti-hC4c Ab (Dako, CA) followed by alkaline

phosphatase-conjugated anti-rabbit Ab and then with

pNTP. The plates were read at 415 nm and the results

were expressed as U/ml. Pooled human sera with known

MBL concentration (State Sera Institute, Denmark) was

used to generate a standard curve on mannan-coated

wells.

Thrombin-like activity was performed as previously

described [22]. Briefly, 384 wells were coated as in the

binding assay. After wash, the wells were incubated with

K. Takahashi et al. / Open Journal of Immunology 1 (2011) 41-49

4343

various concentrations of MBL with or without 1% MBL

KO sera. After wash, wells were incubated with rhoda-

mine 110-thrombin substrate R22124 (Invitrogen, CA)

in TBS-CaCl2 and read at 500 nm excitation/520 nm

emission using the SpectraMax M5. The results were

expressed as arbitrary units (AU).

For sugar inhibition on mannan, indicated concentra-

tions of various sugars were mixed with MBL 1 g/ml

with or without MBL KO sera. Sugars tested were man-

nan, N-acetyl-D-glucosamine (GlcNAc), D-fructose, and

sucrose (all sugars are from Sigma, MO). For sugar in-

hibition on IAV and S. aureus, sugars at final concentra-

tion of 10 mg/ml was mixed with MBL 1 g/ml. Inhibi-

tory activities were expressed by % inhibition that was

calculated by the formula: [(Activity by MBL) – (Activ-

ity by MBL + sugars)] × 100 ÷ (Activity by MBL). In

the formula, MBL was replaced with “MBL + MBL KO

sera” for the lectin complement pathway and throm-

bin-like activity.

These assays were performed in triplicates and re-

peated at least twice and representative data was shown.

2.5. Uptake and Binding of IAV and

S. Aureus by Phagocytes

Assays were performed as previously described

[28,43,44]. Briefly, resident peritoneal macrophages of

C57B/6J (Jackson Laboratories, MI) mice were obtained

by peritoneal lavage and re-suspended in HBSS. In the

total 50 l reaction volume, 1 × 105 peritoneal macro-

phages were mixed with FITC-labeled S. aureus (FITC-

S. aureus) with MBL at 10 g/ml and with or without

fructose or galactose at 10 mg/ml. The mixture was in-

cubated on ice for 10 min and then further incu- bated

for 20 min at 37˚C.

Neutrophils from healthy volunteer donors were iso-

lated to greater than 95% purity by using dextran pre-

cipitation, followed by a Ficoll-Hypaque gradient sepa-

ration for removal of non-nuclear cells and hypotonic

lysis to eliminate contaminating erythrocytes [40]. In the

total 100 l reaction volume, 5 × 105 neutrophils were

pretreated at 37˚C for 30 min and then were further in-

cubated for 1 h at 37˚C with FITC-IAV with MBL at 10

g/ml and with or without fructose or galactose at 10

mg/ml [44].

Flow cytometry assays were performed on a FAC-

SCalibur™ (BD Biosciences) with and without addition

of 0.04% trypan blue, which quenches extracellular flu-

orescence, representing binding [28,44]. Results were

analyzed using CELLQuest™ software. Results were

expressed as % of MBL-mediated binding and uptake of

FITC-S. aureus (mean fluorescent × % total) of triplicate

samples.

2.6. IAV Neutralizing Activity Assay (Focus

Assay)

This assay was performed using MDCK cells as in 2.1.

IAV was preincubated with MBL at 1 g/ml with or

without fructose at 10 mg/ml. These mixtures were in-

cubated with MDCK cells to determine IAV infection

(ffc). The assay was repeated 5 times and all data were

combined.

2.7. Statistical Anal ysis

All data were analyzed by Student t-tests to “compare

mean of each pair” using JMP software (SAS institute

Inc., NC). P values less than 0.05 was considered to be

significant.

3. RESULTS

3.1. Fructose and Sucrose Inhibit Biologic

Functions of MBL: Studies on Mannan

Mannan is an established MBL ligand derived from

yeast and in the presence of MASPs, it can activate both

complement and thrombin pathways [22]. In this study,

we used MBL KO sera as a source for MASPs and re-

combinant human MBL (Enzon Biochemicals). As sho-

wn in Figures 1(A)-(B), MBL bound to mannan and

activated the lectin complement pathway and throm-

bin-like activity, in a dose dependent manner.

We investigated effects of dietary sugars on MBL-

mannan interaction and subsequent MBL-mediated bio-

logic functions. Fructose inhibited MBL-mannan inter-

action as determined by ELISA (Figure 2(A)). Fructose

at 10 mg/ml inhibited the MBL-mannan binding by 82%,

which was greater than observed by GlcNAc, 54% (data

not shown). Furthermore, fructose inhibited the lectin

complement pathway and thrombin-like activities in a

dose dependent manner. Its inhibitory effect on biologic

function was detectable even at lower concentrations of

0.4 mg/ml and 2 mg/ml (Figure 2) and comparable to

that of mannan at a concentration of 10 mg/ml for both

the lectin complement and thrombin-like activities (Fig-

ures 2(B)-(C)).

Sucrose also inhibited these activities in a dose de-

pendent manner although it did not inhibit MBL-mannan

binding (Figure 2). Compared to fructose, the inhibitory

effect on the lectin complement pathway activity was

significantly lower, which was only 53% inhibition at a

concentration of 10 mg/ml (Figure 2(B)). In contrast,

sucrose inhibition of thrombin-like activity was over all

comparable to that of fructose and reached a plateau,

66% and 65% inhibition at 2 mg/ml and 10 mg/ml, re-

spectively (Figure 2(C)).

K. Takahashi et al. / Open Journal of Immunology 1 (2011) 41-49

Figure 1. Recombinant human MBL (MBL)-

mediated functions and sugar inhibition aga-

inst mannan. (A) Binding. (B) C4 deposition.

Based on these experiments, fructose IC50 for binding,

the lectin complement pathway and thrombin-like activi-

ties were 22 mM, 5.5 mM and 5.5 mM, respectively,

while sucrose IC50 were > 11 mM, 2.8 mM and 2.6 mM.

In contrast to these dietary sugars, dextran, which is a

polyglucose and is similar to starch, did not inhibit

binding and the lectin complement pathway activation of

MBL on mannan even at 10 mg/ml (data not shown).

3.2. Fructose Inhibits Biologic Functions of

MBL: Studies on IAV

MBL bound to IAV in a dose dependent manner, con-

firming that MBL recognizes IAV (Figure 3(A)) [45,46].

MBL-IAV binding was inhibited by 8% and 14% by

mannan and fructose, respectively, while sucrose did not

show inhibitory effect (Figure 3(B)). To compare the ef-

fects of fructose, mannan was used as a positive control

in IAV studies. Despite the low level inhibition of

MBL-IAV binding, mannan significantly inhibited the

Figure 2. (A)-(C) Sugar inhibition assays of binding, the lectin

complement pathway, and thrombin-like activity, respectively.

Data were expressed as mean ±SEM, which were smaller than

sizes of symbols. *p < 0.0005.

lectin complement activation and thrombin-like activi-

ties, by 87% and 84% inhibition, respectively (Figures

3(C)-(D)). Accordingly, fructose (10 mg/ml) also sig-

nificantly inhibited the lectin complement and throm-

bin-like activities, by 88% and 75%, respectively (Fig-

ures 3(C)-(D)). Sucrose also showed weak inhibition on

thrombin-like activity but not on the lectin complement

activation (Figure 3(D)). Thus, fructose but not sucrose

inhibited MBL-mediated biologic functions, the lectin

complement and thrombin-like activities, by 5-fold

compared with binding inhibition.

MBL, an opsonin up regulates phagocytosis of patho-

gens. We reasoned that since fructose influences hu-

moral arm of innate immunity, it may also disrupt cellu-

lar arm as well. To study IAV uptake we designed two

experiments. First, we observed that MBL-mediated

uptake of FITC-IAV by human neutrophils was signifi-

cantly inhibited by 37% in the presence of fructose at 10

mg/ml (Figure 3(E)). However, the MBL-mediated viral

uptake was not inhibited by galactose, which is not an

MBL ligand (Figure 3(E )) [47,50]. Second, fructose also

K. Takahashi et al. / Open Journal of Immunology 1 (2011) 41-49

4545

Figure 3. MBL-mediated functions and sugar inhibition

against IAV. (A) MBL-binding to IAV. Sugar inhibition of

binding (B), C4 deposition (C), and thrombin-like activity (D).

(E) Phagocytosis assays of FITC-IAV by human neutrophils.

Fruct and Gal indicated fructose and galactose, respectively. (F)

IAV neutralizing assay. Data were expressed as mean ± SEM,

and represent p < 0.05, p < 0.001 and p < 0.0005, respectively.

inhibited MBL’s IAV neutralization activity, which is

determined by infectivity of IAV to epithelial cells

(MDCK) as IAV infection increased when fructose was

added (Figure 3(F)). Taken together, these results dem-

onstrated that fructose down-regulated MBL-mediated

viral phagocytosis and viral neutralization.

3.3. Fructose and Sucrose Inhibit Biologic

Functions of MBL: Studies on S. Au-

reus

Similar to against IAV, MBL bound to S. aureus, in a

dose dependent manner (Figure 4(A)). MBL-binding

was minimally inhibited only 5% - 6% by either mannan

(positive control ligand) or dietary sugars, fructose or su-

crose (Figure 4(B)). Despite the negligible-level binding

Figure 4. MBL-mediated functions and sugar inhibition

against S. aureus. (A) MBL-binding to S. aureus. Sugar inhibi-

tion assays of binding, (B) C4 deposition, (C) and throm-

bin-like activity, (D) Binding, (E) and phagocytosis, (F) assay

of FITC-S. aureus by macrophages. Fruct and Gal indicated

fructose and galactose, respectively. Data were expressed as

mean ± SEM, some of which were smaller than symbols.

*represents p < 0.0005.

inhibition, all sugars, even sucrose (all at 10 mg/ml) sig-

nificantly inhibited the lectin complement activation and

thrombin-likeactivities, in between the range of 39% -

66% and 24% - 36%, respectively (Figures 4(C)-(D)).

Once again, compared with binding inhibition, these

sugars’ inhibitory effects were 5 - 10 fold greater on the

lectin complement activation and thrombin-like active-

ties.

Regarding FITC-S. aureus binding to Regarding FIT

C-S. aureus binding to macrophages, it was signify-

cantly inhibited by 60% in the presence of fructose

(Figure 4(E)). Similarly, MBL-mediated phagocytosis

of FITC-S. aureu s was significantly inhibited by 60% in

the presence of fructose (Figure 4(F)). However, these

activeties were not inhibited by galactose, which is not

K. Takahashi et al. / Open Journal of Immunology 1 (2011) 41-49

an MBL ligand (Figures 4(E)-(F)) [47,50]. Taken to-

gether, these data demonstrated that fructose negatively

regulated MBL-mediated anti-bacterial cellular functions.

4. DISCUSSION

Binding of pattern recognition molecules to pathogens

is a crucial step to initiate a variety of subsequent sig-

naling cascades in innate immunity, the first line of host

defense mechanisms. These mechanisms include the

lectin complement pathway activation and thrombin-like

activities [48,49]. The results of the current study dem-

onstrate that MBL initiates these activities on common

human pathogens. A highly significant and clinically

relevant finding from this study is striking inhibitory

effects by fructose and some extent by sucrose on these

innate immune functions, as we summarize our findings

in Figure 5(a).

Using functional in vitro assays, we demonstrate that

both fructose and sucrose are MBL recognition mole-

cules, and are similar to other MBL recognition mole-

cules, namely, D-mannose and GlcNAc [47,50,51]. Our

findings support recent report that fructose-lysine bound

to MBL and formed complexes with MASP [52]. These

two dietary sugars show differential kinetics in inhibi-

tion of MBL-ligand binding, suggesting that there may

be specific molecular residues that govern these interac-

tions. The importance of dietary sugar interaction with

MBL is underscored by our studies on two common pa-

thogens. Using both viral and bacterial pathogen binding

to MBL, we demonstrate that dietary sugars, specifically

fructose has a dramatic negative consequence. Mannan,

fructose and sucrose had similar low level, inhibition of

MBL binding to immobilized pathogens. However, the

biologic pathways, activation of the lectin complement

pathway and coagulation, downstream of MBL are sig-

nificantly down regulated, particularly in presence of

sucrose and fructose. Using an established bacterial and

viral phagocytosis assay we show that fructose neutral-

izes pathogen entry into phagocytes, such as macro-

phages and neutrophils, the primary cell defense in in-

nate immunity.

Differential effects of two dietary sugars were also

observed on MBL biologic function. We note that su-

crose has minimal influence on MBL-IAV (viral) inter-

actions (Figure 5(a)). This is in contrast to MBL-S.

aureus (bacterial) and MBL-mannan (fungal) interac-

tions (Figure 5(a)). It is possible that diet high in su-

crose may not affect viral innate immunity but could

influence both anti-fungal and anti-bacterial host defense.

MBL functions as an opsonin, which is a key function of

MBL-mediated anti-bacterial defense mechanism [28,53,

54]. As expected, fructose reduced MBL-mediated pha-

gocytosis of IAV and S. aureus, suggesting that fructose

reduces not only MBL-mediated humoral functions (ac-

tivation of complement and coagulation) but also

MBL-mediated cellular response. Our previous study

has demonstrated that the latter is required to reduce

bacterial growth against S. aureus [28]. On the contrary,

dextran, which is poly-glucose and is a similar to starch,

did not inhibit MBL-associated functions, such as bind-

ing and the lectin complement activation. Our finding

may partly explain the study in 1973, showing that bac-

terial phagocytosis by phagocytes isolated from healthy

volunteers was dramatically reduced by intake of dietary

sugars, including fructose, but was unaffected by starch

intake [8].

Our results also suggest that dietary sugars, in par-

ticular fructose has negative effect on innate immunity in

a dose dependent manner. Therefore, it is conceivable

that dietary sugars at low concentrations may not have

any pathological consequence. It has been observed that

in fructose fed rat, fructose concentration in the hepatic

portal vein reaches to 0.4 mg/ml, which significantly

inhibited MBL-mediated biologic functions in our study

[55]. Consumption of these dietary sugars, more so for

fructose, has skyrocketed in recent years and has been

linked to a recent increase in metabolic disease, includ-

ing diabetes and obesity [5-7]. It is also know that dia-

betic patients have increased susceptibility to infection

[6], which has been attributed to a poor circulation in

these patients. Our findings would suggest that those

dietary sugars might also be responsible by directly re-

ducing innate immune functions as blood fructose levels

reportedly increase after fructose consumption in diabe-

tes [56]. Therefore, one can speculate that intake of high

levels of dietary sugar may induce a similar situation to

MBL deficiency, which has been associated with infec-

tion susceptibility [25].

Coagulation, which is mediated by thrombin, is not

generally thought to be microbicidal, nevertheless it is a

primitive innate immune host defense mechanism, par-

ticularly in invertebrates that do not have phagocytes.

For example, tachylectins in horseshoe crab clots lipopoly-

saccharide and -glucan (PAMPs of Gram negative bacteria

and fungi, respectively), providing innate immune pro-

tection [57]. Clotting may also contain pathogen inva-

sion locally, thereby preventing systemic dissemination

of pathogen. Our recent study demonstrates that MBL

KO mice, which are susceptible to IAV and S. aureus

infection, have reduced clotting ability [22]. One can

speculate that elevated fructose in diabetic patients may

reduce local coagulation, in allowing easy pathogen es-

cape into the host. We propose that dietary sugars, in

particular high dose of fructose weakens the innate im-

mune protection, which is initiated by pattern recogni-

tion molecules, including MBL (Figure 5(b)). It is also

conceivable that pattern recognition molecules may play

K. Takahashi et al. / Open Journal of Immunology 1 (2011) 41-49

4747

Figure 5. (a) The summary of the findings from this investigation are presented in a table form showing

the differential effects of sugar on MBL-pathogen interaction. Note: LC, the lectin complement pathway;

Coag, coagulation. Level of inhibition is presented as follows: –no effect; +/–marginal; + low; ++ in-

termediate; and +++ high. ND indicates not done. (b) The potential mechanism for the observed inhibi-

tion of innate immune mechanisms by fructose, which down regulates MBL-mediated anti-microbicidal

activities, including activation of complement, coagulation and phagocytosis. Fructose can be replaced

with sucrose, depending on its concentration and pathogen.

roles in maintaining healthy commensal microbiota by

fending off pathogenic bacteria [58,59]. In turn, the

healthy microbiota would stimulate and strengthen the

innate immune defense mechanisms. Diet can also affect

defense mechanisms. Diet can also affect microbiota

composition in mice underscoring the tight link between

diet and metabolism of intestinal bacteria [60]. Thus,

elucidating the relationships between diet, microbiota

and innate immune system will be central to our under-

standing of human health

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5. ACKNOWLEDGEMENTS

We would like to thank Enzon pharmaceuticals for providing MBL.

The study was in part, supported by UO1 AI074503, R21 AI077081

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