The pathogenesis of Ebola hemorrhagic fever

Ebola virus causes lethal hemorrhagic disease in humans, yet there are still no satisfactory biological explanations to account for its extreme virulence. This review focuses on recent findings relevant to understanding the pathogenesis of Ebola virus infection and developing vaccines and effective therapy. The available data suggest that the envelope glycoprotein and the interaction of some viral proteins with the immune system are likely to play important roles in the extraordinary pathogenicity of this virus. There are also indications that genetically engineered vaccines, including plasmid DNA and viral vectors expressing Ebola virus proteins, and passive transfer of neutralizing antibodies could be feasible options for the control of Ebola virus-associated disease.

Plasminogen-binding activity of neuraminidase determines the pathogenicity of influenza A virus

When expressed in vitro, the neuraminidase (NA) of A/WSN/33 (WSN) virus binds and sequesters plasminogen on the cell surface, leading to enhanced cleavage of the viral hemagglutinin. To obtain direct evidence that the plasminogen-binding activity of the NA enhances the pathogenicity of WSN virus, we generated mutant viruses whose NAs lacked plasminogen-binding activity because of a mutation at the C terminus, from Lys to Arg or Leu. In the presence of trypsin, these mutant viruses replicated similarly to wild-type virus in cell culture. By contrast, in the presence of plasminogen, the mutant viruses failed to undergo multiple cycles of replication while the wild-type virus grew normally. The mutant viruses showed attenuated growth in mice and failed to grow at all in the brain. Furthermore, another mutant WSN virus, possessing an NA with a glycosylation site at position 130 (146 in N2 numbering), leading to the loss of neurovirulence, failed to grow in cell culture in the presence of plasminogen. We conclude that the plasminogen-binding activity of the WSN NA determines its pathogenicity in mice.

Sudden death due to cardiovascular disorders: a review of the studies on the medico-legal cases in Tokyo

The Tokyo Metropolitan Government has a medical examiner system, in which all cadavers classified as "unusual death" in the city of Tokyo should be examined, and if necessary, autopsied to determine the cause of death. Of about 10,000 unusual deaths examined per year, two thirds are usually determined to have died of natural causes. The most common cause of sudden natural death is ischemic heart disease, especially acute myocardial infarction. Pathological examination, however, proves acute myocardial ischemia in only one third of autopsies. Subarachnoid hemorrhage and intracerebral hemorrhage, acute myocarditis and cardiomyopathies and aortic dissection/aneurysm as well as pulmonary thromboembolism are frequent causes of death in medical examiner cases. Both pathological and socio-medical problems associated with these diseases are discussed.

Elevation of plasma free PAI-1 levels as an integrated endothelial response to severe burns

To clarify the role of plasminogen activator inhibitor type 1 (PAI-1) in postburn hypercoagulation, we assayed the plasma levels of tissue-type plasminogen activator (t-PA) antigen, total PAI-1 antigen, and total t-PA-PAI-1 complex in 15 burned patients. The total body surface area of the burn injury ranged from 30 to 80%. Serial blood samples were collected from 12 to 168 h following the thermal injury. The plasma t-PA level and the free PAI-1 level increased significantly in the immediate postburn period, and the percent increase in the latter over the values in the healthy controls was much greater than that of the former. The ratio of the concentrations of t-PA-PAI-1 complex to free PAI-1 decreased throughout the 7 postburn days. The fact that the decreases in this ratio clearly showed no dissociation of the euglobulin fraction suggests that the postburn hypofibrinolysis occurred as a result of increased synthesis of PAI-1. On the other hand, changes in several parameters of the coagulation or fibrinolysis system and in plasma thrombomodulin showed that postburn hypercoagulability is associated with secondary hyperfibrinolysis with no evidence of vascular endothelial injury. The paradoxical coexistence of postburn hyper- and hypofibrinolysis is a good reflection of the character of PAI-1, which is a biphasic protein that is both a functional protein and an acute phase reactant. Thus, increased synthesis of PAI-1 may not enhance postburn hypercoagulability to create a coagulation-dominant type of disseminated intravascular coagulation severe enough to trigger multiple organ dysfunction syndrome. In conclusion, increased synthesis of PAI-1 in the initial postburn period reflects an integrated endothelial response to burn stress, and because it is a functional protein, the concentration of free PAI-1 antigen may be an important index for predicting secondary consumption coagulopathy.

The profibrinolytic enzyme subtilisin NAT purified from Bacillus subtilis Cleaves and inactivates plasminogen activator inhibitor type 1

In this report, we demonstrate an interaction between subtilisin NAT (formerly designated BSP, or nattokinase), a profibrinolytic serine proteinase from Bacillus subtilis, and plasminogen activator inhibitor 1 (PAI-1). Subtilisin NAT was purified to homogeneity (molecular mass, 27.7 kDa) from a saline extract of B. subtilis (natto). Subtilisin NAT appeared to cleave active recombinant prokaryotic PAI-1 (rpPAI-1) into low molecular weight fragments. Matrix-assisted laser desorption/ionization in combination with time-of-flight mass spectroscopy and peptide sequence analysis revealed that rpPAI-1 was cleaved at its reactive site (P1-P1': Arg(346)-Met(347)). rpPAI-1 lost its specific activity after subtilisin NAT treatment in a dose-dependent manner (0.02-1.0 nm; half-maximal effect at approximately 0.1 nm). Subtilisin NAT dose dependently (0.06-1 nm) enhanced tissue-type plasminogen activator-induced fibrin clot lysis both in the absence of rpPAI-1 (48 +/- 1.4% at 1 nm) and especially in the presence of rpPAI-1 (78 +/- 2.0% at 1 nm). The enhancement observed in the absence of PAI-1 seems to be induced through direct fibrin dissolution by subtilisin NAT. The stronger enhancement by subtilisin NAT of rpPAI-1-enriched fibrin clot lysis seems to involve the cleavage and inactivation of active rpPAI-1. This mechanism is suggested to be important for subtilisin NAT to potentiate fibrinolysis.

Real-time radiology--new concepts for teleradiology

We propose two new concepts for teleradiology: 'real-time radiology' and 'seamless operation of a workstation to view images from both local and remote hospitals'. In this paper, we describe an experimental real-time radiology system with a new multimedia diagnostic workstation, which has been established under teleradiology concepts and can be used for cooperative diagnosis by interchanging radiographic images bilaterally in real-time during an audio-visual discussion. The clinical evaluation of real-time radiology using a newly developed diagnostic workstation demonstrated the system to be practical and routinely available to enhance the radiological diagnostic quality of teleradiology.

Effects of cilnidipine on lipids, lipoproteins and fibrinolytic system in hypertensive patients

Sixteen Japanese patients of both sexes aged 46-78 years with essential hypertension were studied at the cardiac clinic of the Department of Cardiology, Shizuoka General Hospital, Shizuoka, Japan. Serum lipids, lipoproteins, plasma fibrinolytic parameters, renin and noradrenaline were determined before and after 3 months of cilnidipine treatment. Systolic and diastolic blood pressures and heart rate were reduced while renin and noradrenaline levels remained unchanged after cilnidipine treatment. Total cholesterol and tissue plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1) and t-PA-PAI-1 complex were reduced. Changes in the other lipids, lipoproteins and fibrinolytic parameters were not significant after cilnidipine treatment. A negative correlation was found between low-density lipoprotein cholesterol and t-PA antigen levels after cilnidipine treatment. In conclusion, cilnidipine was effective for the treatment of hypertension and did not cause reflex tachycardia in Japanese patients. Cilnidipine treatment produced a beneficial lipid profile (decrease in total cholesterol), but did not show a consistent effect on fibrinolytic parameters in hypertensive patients. The metabolic interaction between beneficial lipid changes and fibrinolysis will be of value to better our understanding of the antiatherogenic effects of cilnidipine treatment in hypertensive patients.

Tissue-type plasminogen activator is involved in the process of neuronal death induced by oxygen-glucose deprivation in culture

Effect of tissue-type plasminogen activator (tPA) on oxygen-glucose deprivation (OGD) was studied in cultured cortical neurons prepared from tPA gene knockout (tPA-KO) and wild-type (Wt) mice. Three hours of OGD induced 45% and 23% of neuronal death in Wt and tPA-KO mice, respectively. Neuronal death in tPA-KO mice was increased to 42% by additional tPA. Six hours of OGD induced 80% and 40% of neuronal death in Wt and tPA-KO mice, respectively, whereas the addition of tPA increased to 62% in tPA-KO mice. These results suggest that tPA is directly involved in the process of neuronal death induced by ischemia-mimic stress without involving vascular or circulatory components.

Dissociation of systemic and hippocampal modulation of rat locomotor activity by 5-HT(2C) receptors

In the present study, the ability of 5-hydroxytryptamine(2C) (5-HT(2C)) receptors in the hippocampus to enhance locomotor activity in rats was investigated by local infusion. Intraperitoneal injection of the selective 5-HT(2C) antagonist SB 242084 (1 mg/kg) significantly increased rats motor activity, while the effects of non-selective 5-HT(2C) agonist m-chlorophenylpiperazine (m-CPP, 10 mg/kg; i.p.) on motor activity were lower than those of the control group. In the day hours, the local infusion of non-selective 5-HT(2C) agonist, m-CPP (1.0 mM) into the bilateral hippocampus via microdialysis probes increased locomotor activity in contrast with intraperitoneal injection. This increase was completely reversed by the combined infusion of the selective 5-HT(2C) antagonist SB 242084 (100 mM). In the night hours, the local infusion of SB 242084 (100 mM) into the bilateral hippocampus significantly inhibited the nocturnal hyperactivity, which was reversed by the combined infusion of m-CPP. The present study demonstrates that the 5-HT(2C) receptors in the hippocampus act to increase rat locomotor activity.

Involvement of RNase G in in vivo mRNA metabolism in Escherichia coli

BACKGROUND

Escherichia coli rng gene (previously called cafA) encodes a novel RNase, named RNase G, which is involved in the 5' end-processing of 16S rRNA. In rng mutant cells, a precursor form of 16S rRNA, 16.3S rRNA, is accumulated. Here we report a role of RNase G in the in vivo mRNA metabolism.

RESULTS

We found that rng:cat mutant strains overproduced a protein of about 100 kDa. N-terminal amino acid sequencing of this protein showed that it was identical to the fermentative alcohol dehydrogenase, the product of the adhE gene located at 28 min on the E. coli genetic map. The level of adhE mRNA was significantly higher in the rng:cat mutant strain than that in its parental strain, while such differences were not seen in other genes we examined. A rifampicin-chase experiment revealed that the half-life of adhE mRNA was 2.5-fold longer in the rng:cat disruptant than in the wild-type.

CONCLUSION

These results indicate that, in addition to rRNA processing, RNase G is involved in in vivo mRNA degradation in E. coli.

Mouse Mx2 protein inhibits hantavirus but not influenza virus replication

The antiviral potential of Mx2 protein remains unknown, because the Mx2 gene in commonly used strains of laboratory mice is nonfunctional. Our previous study showed that functional Mx2 protein in some feral-origin strains was induced upon interferon treatment, was localized in the cytoplasm, and inhibited vesicular stomatitis virus replication. In the present study, we have demonstrated that the embryonic fibroblastic cells from a feral-origin strain (SPR) expressed 74 kDa Mx2 protein, which prevented the accumulation of viral transcripts and proteins of hantaviruses when the Mx2 gene was constitutively expressed in transfected Vero cells. Furthermore, the cells showed significantly lower titers of the virus than control cells. In contrast, influenza virus replication was not affected by the expression of Mx2 protein in the Vero cells.

The differential effect of angiotensin II and angiotensin 1-7 on norepinephrine, epinephrine, and dopamine concentrations in rat hypothalamus: the involvement of angiotensin receptors

Angiotensin 1-7 has been recently claimed the active member of the angiotensins' family. In the present study we compared the effect of angiotensin II and angiotensin 1-7 on the concentration of dopamine, serotonin, epinephrine, and norepinephrine and some of their metabolites in the rat hypothalamus, where the levels of angiotensins are particularly high. Intracerebroventricular injection of angiotensin II, but not angiotensin 1-7, time-dependently elevated the levels of both epinephrine (p < 0.05) and norepinephrine (p < 0.05) in the hypothalamus and both effects could be prevented by intracerebroventricular injection of either AT(1) (candesartan), AT(2) (PD123319) or AT(1-7) (A-779) receptor antagonist. Neither angiotensin II nor angiotensin 1-7 produced any changes in the level of dopamine, dihydroxyphenylacetic acid, homovanilic acid, serotonin, 5-hydroxyindoleacetic acid, or tryptophan at any time point in comparison with the control groups. However, AT(1) but not AT(2) receptor blockade, unmasked the stimulatory effect of angiotensin 1-7 on dopamine concentration in the hypothalamus. Thus, angiotensin II and its active metabolite angiotensin 1-7 regulate selectively, albeit differentially, adrenergic, noradrenergic and dopaminergic systems in the hypothalamus, the effects that involve AT(1), AT(2) and AT(1-7) angiotensin receptors.

Bezafibrate attenuates the overexpression of plasminogen activator inhibitor-1 messenger RNA by a combination of mono-unsaturated fatty acid and insulin in hepG2 cells

The effects of bezafibrate (PPAR alpha activator) and troglitazone (PPAR gamma activator) on the expression of plasminogen activator inhibitor type-1 (PAI-1) in HepG2 cells were investigated. Exposure of the cells for 24 hours to either oleic acid or insulin showed no obvious effects on PAI-1 synthesis, whereas the combination of the two agents induced a 2.3-fold increase in PAI-1 synthesis, which was accompanied by a 3-fold increase in both the 2.2 kb and 3.2 kb forms of PAI-1 mRNA. This up-regulation of PAI-1 synthesis was attenuated by bezafibrate in a dose-dependent manner (1-100 microM) with 30% reversal at 100 microM. In contrast, troglitazone further stimulated PAI-1 synthesis to 140% of the level obtained in the presence of both oleic acid and insulin. This attenuation by bezafibrate and enhancement by troglitazone required the presence of both oleic acid and insulin. It is interesting that PAI-1 expression was affected so differently by these two PPAR activators.

Infectivity-enhancing antibodies to Ebola virus glycoprotein

Ebola virus causes severe hemorrhagic fever in primates, resulting in mortality rates of up to 100%, yet there are no satisfactory biologic explanations for this extreme virulence. Here we show that antisera produced by DNA immunization with a plasmid encoding the surface glycoprotein (GP) of the Zaire strain of Ebola virus enhances the infectivity of vesicular stomatitis virus pseudotyped with the GP. Substantially weaker enhancement was observed with antiserum to the GP of the Reston strain, which is much less pathogenic in humans than the Ebola Zaire and Sudan viruses. The enhancing activity was abolished by heat but was increased in the presence of complement system inhibitors, suggesting that heat-labile factors other than the complement system are required for this effect. We also generated an anti-Zaire GP monoclonal antibody that enhanced viral infectivity and another that neutralized it, indicating the presence of distinct epitopes for these properties. Our findings suggest that antibody-dependent enhancement of infectivity may account for the extreme virulence of the virus. They also raise issues about the development of Ebola virus vaccines and the use of passive prophylaxis or therapy with Ebola virus GP antibodies.

Ebola virus glycoprotein: proteolytic processing, acylation, cell tropism, and detection of neutralizing antibodies

Using the vesicular stomatitis virus (VSV) pseudotype system, we studied the functional properties of the Ebola virus glycoprotein (GP). Amino acid substitutions at the GP cleavage site, which reduce glycoprotein cleavability and viral infectivity in some viruses, did not appreciably change the infectivity of VSV pseudotyped with GP. Likewise, removal of two acylated cysteine residues in the transmembrane region of GP showed no discernible effects on infectivity. Although most filoviruses are believed to target endothelial cells and hepatocytes preferentially, the GP-carrying VSV showed greater affinity for epithelial cells than for either of these cell types, indicating that Ebola virus GP does not necessarily have strong tropism toward endothelial cells and hepatocytes. Finally, when it was used to screen for neutralizing antibodies against Ebola virus GP, the VSV pseudotype system allowed us to detect strain-specific neutralizing activity that was inhibited by secretory GP (SGP). This finding provides evidence of shared neutralizing epitopes on GP and SGP molecules and indicates the potential of SGP to serve as a decoy for neutralizing antibodies.

Mucosal vaccination against influenza: protection of pigs immunized with inactivated virus and ether-split vaccine

Effective vaccinations against swine influenza reduce the economic loss of pig industries, and also may minimize the possibility of emergence of new pandemic viruses, since pigs are intermediate hosts to generate reassortant viruses among avian and mammalian influenza viruses. In this study, we showed that intranasal immunization of pigs with formalin-inactivated or ether-split influenza vaccine (A/Aichi/2/68) induced virus-specific IgG, IgM, and IgA antibodies in their nasal secretions and sera, resulting in complete protection from virus challenge. Antibody response to the challenge virus was not observed in the immunized pigs, suggesting that the replication of the virus in the primary targets, respiratory epithelial cells, was inhibited. The present results indicate that intranasal immunization of pigs with inactivated vaccines is effective to control swine influenza, and also provide a good model, as well as a mouse model, to evaluate an intranasal application of influenza vaccine for humans.

Importance of GlcUAbeta1-3GalNAc(4S,6S) in chondroitin sulfate E for t-PA- and u-PA-mediated Glu-plasminogen activation

Chondroitin sulfate E (CSE) markedly enhanced plasminogen activation by tissue plasminogen activators (t-PAs) and urinary plasminogen activator (u-PA) in vitro; in the presence of 10 microg/ml of CSE, the potentiation factors of single chain of t-PA, two chain of t-PA and u-PA were 400, 140 and 130, respectively. Though the potentiation activity of CSE gradually decreased when it was depolymerized by chondroitinase ABC, the specific disaccharide from CSE still showed significant activity. Glycosaminoglycan (GAG) from sea cucumber, which possesses a very similar core structure to CSE, but has additional sulfated fucose branches exhibit very weak activity. These results suggested that the minimal structural requirement in CSE to enhance plasminogen activation by plasminogen activators is GlcUAbeta1-3GalNAc(4S,6S) and that additional branching sugars abolish the activity.

Downregulation of beta1 integrins by Ebola virus glycoprotein: implication for virus entry

Filoviruses, including Ebola virus, are cytotoxic. To investigate the role of the Ebola virus glycoprotein (GP) in this cytopathic effect, we transiently expressed the GP in human kidney 293T cells. Expression of wild-type GP, but not the secretory form of the molecule lacking a membrane anchor, induced rounding and detachment of the cells, as did a chimeric GP containing its ectodomain and influenza virus hemagglutinin transmembrane-cytoplasmic domain. These results indicate that the GP ectodomain and its anchorage to the membrane are required for GP-induced morphologic changes in host cells. Since cell rounding and detachment could be associated with reduced levels of cell adhesion molecules, we also studied the expression of integrins, which are major molecules for adhesion to extracellular matrices, and found that the beta1 integrin group is downregulated by the GP. This result was further extended by experiments in which anti-beta1 monoclonal antibodies or purified integrins inhibited the infectivity of vesicular stomatitis virus pseudotyped with the GP. We suggest that integrins, especially the beta1 group, might interact with the GP and perhaps be involved in Ebola virus entry into cells.

Fatal cardiovascular injuries to the unbelted occupant associated with airbag deployment: two case-reports

We present two forensic autopsy cases of unbelted occupants associated with the airbag deployment in motor vehicle collisions. Both victims suffered from cardiovascular injuries which were the cause of death. Case 1: A 50-year-old man sustained a contusion on the left anterior chest with rib fractures and laceration of the intrapericardial inferior vena cava, the right ventricle, and the right pleuropericardium. Case 2: A 40-year-old man sustained multiple rib fractures, sternal fracture, and the rupture of the right ventricle. Autopsies and vehicle examinations revealed that both victims' chest seemed to strike the steering wheel through the deployed airbag. Therefore, we determined that the source of blunt impact force is the steering wheel through the airbag rather than airbag deployment only. In light of these two cases, we learned that the steering wheel should be considered as the blunt impact force inducing cardiovascular injuries even in cases in which the airbag has been deployed.

Brain net unidirectional uptake of alpha-[14c]methyl-L-tryptophan (alpha-MTrp) and its correlation with regional serotonin synthesis, tryptophan incorporation into proteins, and permeability surface area products of tryptophan and alpha-MTrp

The uptake and trapping constants for labeled tryptophan (Trp) via the serotonin (5-hydroxytryptamine; 5-HT) metabolic pathway and for the incorporation of Trp into proteins, and alpha-[14C]methyl-L-tryptophan (alpha-MTrp) were measured. Measurements were done in rats treated with either saline or probenecid (200 mg/kg). In addition, the blood-brain barrier (BBB) permeability surface area products for Trp (PS(T)) and alpha-MTrp (PSalpha) were measured in normal rats. The results suggest that, in both groups of rats, there is a highly significant correlation (p < 0.05; Pearson Product Moment Correlation (PPMC) between the brain uptake and trapping constants for alpha-MTrp and those of Trp via the 5-HT metabolic pathway, but there is no significant correlation (p > 0.05; PPMC) between either of these constants and the PS products of either compound. There is also no significant correlation (p > 0.05; PPMC) between the constant for the Trp incorporation into proteins with any of the other parameters. For all parameters, except Trp incorporation into proteins (alpha-MTrp is not incorporated into proteins), there was a highly significant correlation (p < 0.001) between the quantities measured for Trp and alpha-MTrp. The data presented here strongly suggests that the brain uptake and trapping of alpha-MTrp relates to brain 5-HT synthesis, and does not relate to the BBB transport or protein incorporation of Trp. On the basis of these results, as well as those previously reported, we concluded that trapping (unidirectional uptake) of alpha-MTrp can be converted to the 5-HT synthesis rates in the brain. From this also follows that labeled alpha-MTrp is a good tracer for in vivo evaluation of the brain 5-HT synthesis.

Functional importance of the coiled-coil of the Ebola virus glycoprotein

Ebola virus contains a single glycoprotein (GP) that is responsible for receptor binding and membrane fusion and is proteolytically cleaved into disulfide-linked GP1 and GP2 subunits. The GP2 subunit possesses a coiled-coil motif, which plays an important role in the oligomerization and fusion activity of other viral GPs. To determine the functional significance of the coiled-coil motif of GP2, we examined the effects of peptides corresponding to the coiled-coil motif of GP2 on the infectivity of a mutant vesicular stomatitis virus (lacking the receptor-binding/fusion protein) pseudotyped with the Ebola virus GP. A peptide corresponding to the C-terminal helix reduced the infectivity of the pseudotyped virus. We next introduced alanine substitutions into hydrophobic residues in the coiled-coil motif to identify residues important for GP function. None of the substitutions affected GP oligomerization, but some mutations, two in the N-terminal helix and all in the C-terminal helix, reduced the ability of GP to confer infectivity to the mutant vesicular stomatitis virus without affecting the transport of GP to the cell surface, its incorporation into virions, and the production of virus particles. These results indicate that the coiled-coil motif of GP2 plays an important role in facilitating the entry of Ebola virus into host cells and that peptides corresponding to this region could act as efficient antiviral agents.

Structure of the infected cell protein 0 gene of canine herpesvirus

The canine herpesvirus infected cell protein 0 (CICP0) gene was sequenced. The CICP0 gene was transcribed as a 1.4 kb mRNA from the end of the unique long region nearby the internal repeat during early phase of productive infection of the virus. An open reading frame of the gene encodes a polypeptide of 333 amino acids. The RING finger domain and acidic transcriptional activation domain were found at the N-terminus and within the middle region in the deduced amino acid sequence, respectively, suggesting that the CICP0, like the ICP0 of herpes simplex virus 1, is a transactivating protein.

Recognition of N-glycolylneuraminic acid linked to galactose by the alpha2,3 linkage is associated with intestinal replication of influenza A virus in ducks

The hemagglutinin (HA) of H3 human influenza viruses does not support viral replication in duck intestine despite its avian origin. A Leu-to-Gln mutation at position 226 and a Ser-to-Gly mutation at position 228 in the HA of human A/Udorn/307/72 (H3N2) permit a reassortant virus [human Udorn HA, with all other genes from A/mallard/New York/6750/78 (H2N2)] to replicate in ducks. To understand the molecular basis of this change in host range restriction, we investigated the receptor specificity of duck influenza viruses as well as of human-duck virus reassortants. The results indicate that the recognition of a glycoconjugate moiety possessing N-glycolneuramic acid (NeuGc) linked to galactose by the alpha2,3 linkage (NeuGcalpha2,3Gal) is associated with viral replication in duck intestine. Immunofluorescence assays with NeuGcalpha2,3Gal-specific antiserum detected this moiety primarily on the crypt epithelial cells of duck colon. Such recognition, together with biochemical evidence of NeuGc in crypt cells, correlated exactly with the ability of the virus to replicate in duck colon. These results suggest that recognition of the NeuGcalpha2,3-Gal moiety plays an important role in the enterotropism of avian influenza viruses.