Dog Erythrocytes Research Articles

The Molecular Basis for the Absence ofN-Glycolylneuraminic Acid in Humans

N-Glycolylneuraminic acid (NeuGc) is abundantly expressed in most mammals, but it is not detectable in humans. The expression of NeuGc is controlled by cytidine monophospho-N-acetylneuraminic acid (CMP-NeuAc) hydroxylase activity. We previously cloned a cDNA for mouse CMP-NeuAc hydroxylase and found that the human genome contains a homologue. We report here the molecular basis for the absence of NeuGc in humans. We cloned a cDNA for human CMP-NeuAc hydroxylase from a HeLa cell cDNA library. The cDNA encodes a 486-amino acid protein, and its deduced amino acid sequence lacks a domain corresponding to the N-terminal 104 amino acids of the mouse CMP-NeuAc hydroxylase protein, although the human protein is highly identical (93%) to the rest of the mouse hydroxylase protein. The N-terminal truncation of the human hydroxylase is caused by deletion of a 92-base pair-long exon in human genomic DNA. The human hydroxylase expressed in COS-7 cells exhibited no enzymatic activity, and a mouse hydroxylase mutant, which lacks the N-terminal domain, was also inactive. A chimera composed of the human hydroxylase and the N-terminal domain of the mouse hydroxylase displayed the enzyme activity. These results indicate that the human homologue of CMP-NeuAc hydroxylase is inactive because it lacks an N-terminal domain that is essential for enzyme activity. The absence of NeuGc in human glycoconjugates is due to a partial deletion in the gene that encodes CMP-NeuAc hydroxylase.

Adenosine triphosphate causes vasospasm of the rat femoral artery.

Adenosine 5'-triphosphate (ATP) causes vasoconstriction by activation of P2-purinoceptors on vascular smooth muscle cells. Erythrocytes contain ATP at a concentration (1.6 mmol/L) that contracts smooth muscle. Previous studies of hemoglobin solutions did not assess whether the vasoactivity was caused by ATP rather than or in addition to hemoglobin. It was hypothesized that the hemolysis of erythrocytes that occurs after subarachnoid hemorrhage releases ATP in concentrations that cause vasospasm. Thirty-eight rats were randomly assigned to undergo placement of one of the following compounds in a silastic elastomer cuff around each femoral artery: 1) agarose gel (n = 8); 2) dog erythrocyte hemolysate (n = 8); 3) purified human hemoglobin (Hemolink; Hemosol, Inc., Toronto, Canada; n = 8); 4) ATP (n = 8); or 5) clotted autologous blood (n = 6). The amounts of hemoglobins and adenine nucleotides in the compounds were measured by spectrophotometry and high pressure liquid chromatography. Hemolysate, purified hemoglobin, and ATP were mixed with agarose gel to create an artificial clot. Rats were killed and fixed by perfusion at physiological blood pressure 7 days after perivascular cuff and spasmogen placement. Vasospasm was assessed by image analysis of cross sections of fixed femoral arteries. Arteries were assessed for histopathological changes on 3-point scales. There was significant variance in arterial diameters among groups (mean diameter +/- standard deviation: agarose gel, 0.29 +/- 0.06; purified hemoglobin, 0.28 +/- 0.04; hemolysate, 0.24 +/- 0.05; ATP, 0.25 +/- 0.05; clotted blood, 0.24 +/- 0.01; P < 0.05, analysis of variance, n = 11-20). Animals exposed to clotted blood, hemolysate that contained ATP, or ATP, developed vasospasm, whereas purified hemoglobin and agarose did not cause vasospasm. Endothelial proliferation and perivascular inflammation were more severe (P < 0.05) in arteries exposed to clotted blood, purified hemoglobin, and hemolysate. These results suggest that ATP may be a vasospastic substance released by erythrocyte hemolysis. The concentration of ATP in impure solutions of hemoglobin is too low to account for the vasoactivity of these solutions. The discrepancy between arterial narrowing and histopathological changes suggests that either histopathological changes may not be an important correlate of arterial vasospasm or that other substances are important in vasospasm.

Metabolic findings in the erythrocytes of cardiopathic and anaemic dogs

Few data are available on the activities of canine erythrocyte enzymes and on 2,3 diphosphoglycerate (2,3DPG) concentrations in pathological conditions other than heritable erythrocyte defects. Because some diseases might affect erythrocyte metabolism and oxygen transport, we evaluated these parameters in 10 healthy dogs and in dogs with symptomless dirofilariosis (n = 9), mild (n = 13) and severe (n = 8) cardiac failure, and haemolytic anaemia (n = 8). To evaluate possible membrane damage, the osmotic fragility of the red cells was measured. No haematological abnormalities were found in the dogs with mild cardiopathy or in those with symptomless dirofilariosis. Severe anaemia and neutrophilic leucocytosis were found in the dogs with haemolytic anaemia and, to a lesser degree, in those with severe heart failure. In dogs with these two diseases, elevated values obtained were, respectively: pyruvate kinase (PK) 17.5 +/- 10.3 U/g haemoglobin (Hb) (P < 0.001) and 11.6 +/- 7.5 U/g Hb (P < 0.01); glucose-6-phosphate dehydrogenase (G6PDH) 8.9 +/- 5.4 U/g Hb (P < 0.001) and 5.6 +/- 4.2 U/g Hb; 2,3DPG 21.8 +/- 4.9 U/g Hb (P < 0.001) and 22.5 +/- 4.1 U/g Hb (P < 0.001). The increased 2,3DPG concentrations may have been due to diminished oxygen availability but the observed enzymatic changes were attributed mainly to the presence of young red blood cells: there was a positive correlation between nucleated red blood cells and PK activity, G6PDH activity and 2,3DPG concentration and a negative correlation between mature erythrocytes and PK activity, G6PDH activity and 2,3DPG concentration. This was supported by the derivative curve of the fragiligram, which showed two or three peaks corresponding to different erythrocyte populations and by the negative correlation between the maximum haemolytic NaCl concentration and the reticulocyte number. The measurement of PK and G6PDH activity and of the 2,3PG concentration, together with information provided by the fragiligram, would seem to be of value in defining the clinico-haematological picture in clinical heart diseases and haemolytic anaemia.

Biochemical characterization of canine blood group antigens: immunoprecipitation of DEA 1.2, 4 and 7 and identification of a dog erythrocyte membrane antigen homologous to human Rhesus

Despite the clinical significance of the canine blood group antigens, relatively little is known of the biochemistry of these molecules. In this study the canine blood group antigens DEA (dog erythrocyte antigen) 1.2, 4 and 7 were immunoprecipitated from red blood cells (RBC) bearing the corresponding blood group, and molecular weights of 85 kD (DEA 1.2), 32–40 kD (DEA 4) and 53–66 kD (DEA 7) assigned. DEA 1.2 and DEA 4 each appeared as a single band, whereas DEA 7 comprised three distinct bands (53, 58 and 66 kD). Polyclonal antisera specific for two peptides derived from the sequence of the human Rhesus blood group (Rh30A-C and Rh50A-C) were used in western blotting against carine and human erythrocyte membranes. The Rh30A-C antiserum identified a band of molecular weight 32 kD in both human and canine RBC, and the antiserum specific for Rh50A-C identified a band of 38–60 kD in human membranes and of 40–53 kD in canine RBC. This finding is consistent with conservation of areas of the Rhesus protein sequence between human and canine erythrocytes.

Interactions between Fusobacterium necrophorum hemolysin, erythrocytes and erythrocyte membranes

The interactions between the hemolysin of Fusobacterium necrophorum subsp. necrophorum, erythrocytes and erythrocyte membranes were studied as an attempt to determine the initial characteristics leading to hemolysis. The spectrum of erythrocyte sensitivity indicated that horse, dog and mouse erythrocytes were highly sensitive whereas those of cattle, sheep, goat and chicken were insensitive to the hemolysin. Binding of hemolysin to horse and dog erythrocytes or their ghosts was more pronounced than to those of cattle and sheep as detected by a decrease of hemolytic activity from hemolysin preparations. The kinetics of hemolysis revealed that lysis is preceded by a prelytic phase characterized by binding of hemolysin to erythrocytes. Treatment of horse erythrocytes with hemolysin at various temperatures prior to incubation at 37°C also revealed that this binding prelytic phase is temperature independent. This was followed by a temperature dependent lytic stage since erythrocytes pretreated with hemolysin and incubated at 4°C showed no hemolysis. An inverse relation was found between erythrocyte concentration and hemolytic activity suggesting a multiple-hit mechanism of hemolysis.

Effects of photodegradation of nifedipine on dog erythrocyte membranes

We studied the effects of nifedipine (NF) on UV-induced photohemolysis of erythrocytes in vitro. A suspension in physiologic saline of crythrocytes separated from the venous blood sample freshly obtained from a dog was prepared and used. NF is a photolabile agent, and this drug was extremely sensitive to the long wavelength (365 nm) of UV light. The most abundant photodegradation product was a nitroso-derivative which changed into a lactam-derivative in the dog erythrocyte suspension with or without irradiation. NF itself showed protective effects against photohemolysis of erythrocytes caused by 365 nm of UV light as well as hypotonic hemolysis. But NF enhanced the degree of photohemolysis under oxygen condition. The photohemolysis enhanced by NF was reduced by thiobarbituric acid, indicating an oxidative stress by a radical intermediate of NF to photohemolysis. On the other hand, the nitroso-derivative reacted with erythrocyte hemoglobin spectroscopically to change into the lactam-derivative. It is considered that NF is a phototoxic agent to cause photohemolysis by producing a radical intermediate with oxygen and unknown species of hemoglobin degraded with the nitroso-derivative of nifedipine photoproduct.

Cardiac Stimulatory, Cytotoxic and Cytolytic Activity of Extracts of Sea Anemones

Sea anemones belonging to four families were examined for their cardiac stimulatory, cytotoxic and cytolytic activities. Aqueous extracts of eleven species, Anthopleura elegantissima (Brandt), A. xanthogrammica (Brandt), Corynactis californica (Carlgren), Epiactis prolifera (Verrill), Metridium senile (L), Pachycerianthus fimbratus, Stomphia didemon (Siebert), Urticina coriacea (Cuvier), U. crassicornis (O. F. Muller), U. lofotensis (Danielson) and U. piscivora (Sebens and Laakso), were tested. All extracts except P. fimbratus, showed dose dependent positive inotropic and chronotropic activity and elicited potent lytic action on erythrocytes of rat, guinea pig and dog. Electron microscopic examination of rat erythrocytes treated with U. piscivora extract revealed significant structural damage to the membranes. The toxicological effects of the extracts were assessed on the basis of mortality, expressed as LD 50. Of all the extracts tested only that of U. lofotensis was toxic when given intraperitoneally, w...

Rate of uptake of CO by hemoglobin in pig erythrocytes as a function of PO2.

This study was initiated to obtain data on the rate of carbon monoxide (CO) uptake (theta CO) by hemoglobin in pig erythrocytes to derive, in a later study, the pulmonary capillary blood volume (Qc) in pigs from the Roughton-Forster relationship. Blood from five different female pigs was used. The theta CO, the milliliters of CO taken up by 1 ml of whole blood per minute per Torr CO tension, was determined on each blood sample with a continuous-flow rapid-mixing apparatus and double-beam spectrophotometry at 37 degrees C and pH 7.4 at four or five different PO2 values. Because the individual regression lines of theta CO vs. PO2 were not significantly different, a common regression equation was calculated: 1/theta CO = 0.0084 PO2 + 0.63. The slope of this regression line is significantly steeper than the reported slopes of regression lines for human and dog erythrocytes measured under the same conditions. Our results revealed that calculation of Qc in pigs by using theta CO values for human or dog erythrocytes would result in an underestimation of 51 and 50%, respectively.

Effect of P2-purinoceptor antagonists on hemolysate-induced and adenosine 5'-triphosphate-induced contractions of dog basilar artery in vitro.

To test the hypothesis that the vasoactive effects of hemolysate of dog erythrocytes on dog basilar artery in vitro are caused by adenosine 5'-triphosphate (ATP). Dog erythrocyte hemolysate was assayed for ATP by high-pressure liquid chromatography. Dog basilar arteries were cut into rings and studied under isometric tension to determine the effects of the P2-purinoceptor antagonists suramin, pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid, and reactive blue 2 on contractions induced by hemolysate, prostaglandin F2 alpha (PGF2 alpha), KCl, uridine 5'-triphosphate, and ATP. Dog erythrocyte hemolysate contained 34 mumol/L of ATP. Hemolysate produced concentration-dependent contractions of dog basilar artery. Suramin (100 mumol/L) significantly inhibited contractions to hemolysate, ATP, and uridine 5'-triphosphate but not to PGF2 alpha and KCl (P < 0.05). Pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid (100 mumol/L) caused a small but significant reduction of the contractions to hemolysate and did not affect contractions to PGF2 alpha and KCl. Reactive blue 2 (30 mumol/L) produced significant inhibition of contractions to hemolysate and PGF2 alpha but did not affect contractions to KCl. These findings suggest that ATP mediates a smooth muscle contractile response of hemolysate on dog basilar artery. Because erythrocyte cytosol is known to be important in the pathogenesis of vasospasm, these results suggest that ATP may contribute to the vasoconstriction that occurs in vasospasm.

IgG subclasses of canine anti-erythrocyte, antinuclear and anti-thyroglobulin autoantibodies

A panel of monoclonal antibodies (mAbs) reactive with the four canine IgG subclasses (IgGI, IgG2, IgG3 and IgG4) was used to investigate the activity of IgG subclasses in autoimmune responses to erythrocytes, nuclear antigens and thyroglobulin in dogs with autoimmune disease. mAbs specific for canine IgGl and IgG4 were able to agglutinate normal dog erythrocytes coated with purified canine IgG containing each of the four subclasses. IgGl autoantibodies were demonstrated on the surface of erythrocytes from seven dogs with Coombs'-positive autoimmune haemolytic anaemia and IgG4 autoantibodies were also present in two of these cases. Serum antinuclear antibody was shown in nine dogs to be predominantly of IgGl, IgG3 and IgG4 subclasses with only one of the dogs also producing an IgG2 antinuclear antibody. The IgG subclass profile of antinuclear antibodies differed between dogs with polyarthritis and dogs with other systemic disease. In six dogs with hypothyroidism, thyroglobulin autoantibodies of subclasses IgGI, IgG2 and IgG4 predominated, but one dog also produced significant levels of IgG3 thyroglobulin autoantibodies. The mAbs are widely applicable to the study of the pathogenesis of canine autoimmune disease.

Reconstitution of calyculin-inhibited K-Cl cotransport in dog erythrocyte ghosts by exogenous PP-1.

Osmotic swelling of dog and other mammalian erythrocytes activates Cl-dependent K transport, K-Cl cotransport. This activation can be abolished by nanomolar concentrations of calyculin, a potent inhibitor of serine-threonine protein phosphatases. Therefore, K-Cl cotransport is probably activated by dephosphorylation by a type 1 and/or type 2A protein phosphatase (PP-1 and PP-2A, respectively). This was tested directly by incorporating exogenous protein phosphatases into resealed ghosts made from dog erythrocytes previously exposed to calyculin. K-Cl cotransport was nearly completely inhibited in the ghosts. Incorporation of PP-1 reconstituted K-Cl cotransport. Maximal reconstitution was up to 90% of the control flux in the ghosts and 0.1 U PP-1/ml lysate gave half-maximal reconstitution of cotransport. In contrast, PP-2A had no effect. This result with PP-1 provides direct evidence that K-Cl cotransport is activated by PP-1 in dog erythrocytes. Half-maximal activation of K-Cl cotransport required approximately 180 molecules of PP-1 per ghost.

Metabolism in the erythrocytes of dogs with low and high glutathione concentrations

Metabolism of the erythrocytes of high potassium and high glutathione (HK-high GSH), high potassium and low GSH (HK-low GSH) and normal low potassium and low GSH (LK-low GSH) dogs were studied with respect to the levels of enzymes associated with GSH synthesis and metabolism, and the capacity of the cells to regenerate GSH. HK-high GSH dogs were found to have significantly higher levels of hexokinase (Hx) and γ-glutamylcyclotransferase (GCT) than low GSH groups. The rate of GSH regeneration was much greater in high GSH dogs than in those of low GSH groups, and there is a positive correlation between GSH level and its, regeneration rate. Glutathione-S-transfer-ase (GST) activity was high in both HK-high GSH and HK-low GSH cells. There were no significant differences in the activities of γ-glutamyl cysteine synthetase (GCS), glutathione synthetase (GSHS) and glutathione reductase (GR) among these three groups. Our results indicate that GSH levels and Hx activity influence GSH regeneration rate, and the GSH levels also affect GST activity.

Toxic effects of the novel protein UPI from the sea anemone Urticina piscivora

UpI is a basic protein, with molecular mass (approximately 28 kDa) and a pI > 9.4, isolated from the sea anemone Urticina piscivora. It is a potent cardiac stimulatory protein with the partial amino acid sequence D1ENEN5LYGPN10ENKAK15AKDLT20AGASY25LTKEA30GCTKL35QAGCT40MYQAY45N [1]. The toxic effects of UpI and the crude extract from which it was isolated have been investigated on three tumour cell lines: KB, L1210, and HEL 299 cells. UpI, however, was less potent on each cell line than the crude extract. Since previous experiments had shown extracts of U. piscivora to be haemolytic on erythrocytes of rat, guinea pig and dog, the haemolytic action of UpI was investigated. It was found to be a potent haemolysin on erythrocytes of rat, guinea pig, dog, pig and human, causing haemolysis on erythrocytes of each species tested at concentrations as low as 10(-10) M. Haemolysis was inhibited in a concentration-dependent manner by the phospholipid sphingomyelin but not cholesterol. Using scanning electron microscopy, it is now being shown that UpI produces significant structural damage to membranes of erythrocytes from rat and guinea pig. It proved to be a potent ichthyotoxin. These data suggest that sea anemone toxin not only possess different pharmacological activities but that UpI, one of the active constituents, could be responsible for the different pharmacological effects exhibited by the crude extract.

An acute hemolytic transfusion reaction caused by dog erythrocyte antigen 1.1 incompatibility in a previously sensitized dog

An acute hemolytic transfusion reaction caused by dog erythrocyte antigen 1.1 incompatibility in a previously sensitized dog

D-glucose transport and glycolytic enzyme activities in erythrocytes of dogs, pigs, cats, horses, cattle and sheep

The activities of D-glucose transport ( D-GT) and the glycolytic enzymes hexokinase ( HK) and pyruvate kinase ( PK), were measured in the erythrocytes of dogs, pigs, cats, horses, cattle and sheep. The erythrocytes of dogs had the highest activities of D-GT, HK and PK, significantly higher than the activities in the erythrocytes of the herbivores. The activities of D-GT and HK in cat erythrocytes were significantly lower than in those of dogs. The differences between the activities of D-GT in the erythrocytes of the different species followed the differences in activities of HK but not those in the activities of PK or in the blood glucose concentrations. It is considered that the activity of HK provides a convenient measurement of the relative rates of glucose oxidation in erythrocytes.

IV3à(NeuGcà2-8NeuGc)-Gg4Cer Is Restricted to CD4+ T Cells Producing Interleukin-2 and a Small Population of Mature Thymocytes in Mice

Monoclonal antibody YK-3 was established by immunization with IV3 alpha (NeuGc alpha 2-8NeuGc)-Gg4Cer (GD1c-(NeuGc-NeuGc-)), and its epitope was determined to be NeuGc alpha 2-8NeuGc alpha 2-3Gal beta 1. Thin layer chromatography immunostaining with YK-3 detected only GD1c-(NeuGc-NeuGc-) among the gangliosides of mouse thymocytes and splenocytes. Immunohistochemical staining with YK-3 visualized the medulla of mouse thymus and T cell-dependent areas of mouse spleen and mesenteric lymph nodes. Two-color flow cytometry demonstrated that GD1c (NeuGc-NeuGc-) was expressed on a quarter of CD3+ mature thymocytes and strongly expressed on three quarters of CD4+ T cells in the spleen, lymph nodes, and peripheral blood but not on CD8+ T cells or B cells. GD1c (NeuGc-NeuGc-)-positive cells and negative cells were separated by panning with YK-3 on Petri dishes into adherent and nonadherent fractions. Following stimulation with concanavalin A, adherent cells, predominantly GD1c (NeuGc-NeuGc-)+, produced more interleukin-2 (IL-2) and markedly less interleukin-4 (IL-4) than nonadherent cells. This conclusion is supported by data obtained by lysis of cells by YK-3 and complement. These data indicate that the cell surface expression of GD1c (NeuGc-NeuGc-) is restricted to a small number of mature thymocytes and a subset of CD4+ T cells, which produce abundant IL-2 and very little IL-4, suggesting that GD1c(NeuGc-NeuGc-) is an excellent marker for mouse naive T or T helper 1-like cells in vivo.

Pathogenesis of Trypanosoma evansi infection in dogs and horses: hematological and clinical aspects

Trypanosoma evansi caused severe anemia in horses and pronounced leukopenia in dogs, both naturally infected. The horses presented microcytic normochromic anemia and the dogs showed microcytic hypochromic anemia. The clinical signs observed were fever, anemia, edema of the legs and lower parts, weakness and inappetence. Light microscopic studies demonstrated that Trypanosoma evansi produced several alterations in erythrocytes of dogs and horses. These pathologic changes included vacuolation, acanthocytes, dacrocytes, codocytes, microspherocytes and bizarre shapes. Mature erythrocyte were observed adhered to trypanosomes. Erythrophagocytosis was also demonstred.

Post-Transfusions-Lebensdauer und Verträglichkeit von Hydroxyethylstärke(HES)-kryokonservierten Erythrozyten – Erfahrungen am autologen Transfusionsmodell Hund

Experiments were carried out with dog erythrocytes as an animal model for human erythrocytes. Caused by hemolysis 30% of the erythrocytes formerly cryopreserved with hydroxyethyl starch (HES) (200000/0.5; 12,5%) could not be labeled with &lt;sup&gt;51&lt;/sup&gt;Cr. All the cryopreserved labeled erythrocytes showed the same in vivo survival as labeled fresh red cells. After autologous substitution of 10% of the dog’s blood by the HES cryopreserve, the HES plasma level decreased, following a first-order kinetics with t&lt;sub&gt;½&lt;/sub&gt; = 4 h. Concerning the blood flow behavior, a transient reduction by the cryopreserved erythrocytes was seen, while the HES had adverse as well as beneficial effects. By further improvement the preserve should become suitable for clinical application.

Immunologic characteristics of anti-erythrocyte membrane antibody produced in dogs during Babesia gibsoni infection.

Serum anti-erythrocyte membrane (RBCm) antibodies and anti-RBCm antibodies eluted from erythrocytes of Babesia gibsoni-infected dogs were examined for immunologic characteristics by immunoblotting analysis. Serum anti-RBCm antibodies of the dogs before and after the experimental inoculation with parasitized erythrocytes reacted with cytoskeletal (bands 1, 2, 2.1, 4.1, 4.2 and 5) and transmembrane structural (band 3) proteins of either self or non-self RBCm. Anti-RBCm antibodies eluted from erythrocytes of B. gibsoni-infected dogs reacted with bands 3 and 4.2 of self and non-self RBCm.

Cloning, sequencing, and viscometric adhesion analysis of heat-resistant agglutinin 1, an integral membrane hemagglutinin from Escherichia coli O9:H10:K99

The gene encoding a mannose-resistant hemagglutinating protein was cloned from Escherichia coli O9:H10:K99. The hemagglutinin is different from two other mannose-resistant hemagglutinins in this strain, K99 and F41. The agglutinin, named heat-resistant agglutinin 1 (HRA1) since heating to 70 degrees C does not destroy its aggregative properties, strongly agglutinates human, pig, and dog erythrocytes, shows little or no affinity towards cow and chicken erythrocytes, but agglutinates human colon adenocarcinoma 201 (COLO 201) cells. The hra1 gene present on the recombinant plasmid pETE1 was localized by subcloning, and its nucleotide sequence was determined. The gene consists of a 792-bp open reading frame coding for a putative protein of 29 kDa with a predicted N-terminal secretory signal sequence. HRA1 shares no significant identity with data base protein sequences. HRA1 is strongly associated with the bacterial membrane, resisting sonication and isolation attempts based upon standard adhesin purification techniques. N-terminal sequencing of a unique 25-kDa band present in polyacrylamide gels of outer membrane preparations of bacteria harboring pETE1 correlated with the predicted N-terminal amino acid sequence of HRA1 after cleavage of the signal peptide. A viscometric agglutination assay sensitive to the strength of bacterial adhesion shows that the agglutination mediated by bacteria expressing HRA1 is weaker than that of bacteria bearing the F41 adhesin, probably because of the high-molecular-weight, multivalent nature of the latter adhesin. Our observations suggest that HRA1 is a monomeric outer membrane agglutinin.