Changes in immunologic properties of group A RBCs during treatment with an A-degrading exo-alpha-N-acetylgalactosaminidase.

BACKGROUND: Blood group A RBCs theoretically can be converted to universal-donor group O cells by incubation with alpha-N-acetylgalactosaminidase (A-zyme). The purpose of this study was to compare the extent of A-zyme treatment required to abolish several immunologic responses of group B or O recipients to group A RBCs. STUDY DESIGN AND METHODS: A(1) RBCs were incubated for 2 hours at 37 degrees C in buffer alone (control) or with 0.1 to 5.0 units (U) of A-zyme per mL of packed cells. They were then tested for 1) immune adherence (% rosetting) and activation of monocytic cells (% erythrophagocytosis, TNFalpha production), 2) activation of immune hemolysis, and 3) hemagglutination with Dolichos biflorus lectin and pooled human anti-A serum. RESULTS: A 2-hour incubation with < or =5.0 U of A-zyme per mL of packed cells abolished monocytic cell adherence and phagocytosis of group A(1) RBCs coated with IgG(3) A MoAb. Epitopes of A binding to IgG(3) anti-A A005 MoAb and BG-2 MoAb differed in A-zyme sensitivity. TNFalpha production in group B or O whole blood in response to the addition of A(1) cells varied, but it essentially was abolished when group A cells were treated with 0.1 to 1.0 U of A-zyme per mL of packed cells. A epitopes mediating immune hemolysis and hemagglutination with D. biflorus lectin were also cleaved by <5 U of A-zyme per mL of packed cells. In contrast, hemagglutination with polyclonal anti-A typing serum was diminished by only 1 to 2 serial titer dilutions. CONCLUSION: A epitopes mediating immune hemolysis and immune adherence to and activation of monocytic cells are highly sensitive to A-zyme cleavage, as compared to those mediating hemagglutination with monoclonal and polyclonal anti-A.

Purification and characterization of blood group A-degrading isoforms of alpha-N-acetylgalactosaminidase from Ruminococcus torques strain IX-70.

To cleave blood group A immunodeterminants from erythrocytes (Hoskins, L. C., Larson, G., and Naff, G. B. (1995) Transfusion 35, 813-821), we purified and characterized alpha-N-acetylgalactosaminidase (EC 3.2.1.49) activity from culture supernatants of the human fecal bacterium Ruminococcus torques strain IX-70. Three isoforms separated during hydrophobic interaction chromatography. Hydroxyapatite chromatography further resolved the most hydrophilic, isoform I, into isoforms IA and IB. The most hydrophobic, isoform III, differed from IA and IB by a more acidic pH optimum, greater heat resistance, greater sensitivity to alkylating agents, and anomalous retardation during gel filtration chromatography. Isoform IB differed from IA and III in N-terminal amino acid sequence and in sensitivity to EDTA inhibition. Each cleaved nonreducing alpha(1-->3)-N-acetylgalactosamine residues from human blood group A and AB mucin glycoproteins, Forssman hapten, and blood group A lacto series glycolipids. The apparent molecular mass of denatured isoform subunits of IA, IB, and III-PII (158, 173, and 201 kDa, respectively) bore no integer relationship to the apparent molecular mass of the native isoforms (265, 417, and 530 kDa), but the latter bore a ratio of 1.96:3.09:3.93 to the weight-average apparent molecular mass of native IA (135 kDa), suggesting that the isoforms are multimers of a 135-kDa sequence. Isoforms IA and III-PII had an identical N-terminal amino acid sequence which showed homologies to the N-terminal sequence of sialidases produced by Bacteroides fragilis SBT3182, another commensal enteric bacterium.

Mucin degradation in human colon ecosystems. Isolation and properties of fecal strains that degrade ABH blood group antigens and oligosaccharides from mucin glycoproteins.

We previously reported that the oligosaccharide chains of hog gastric mucin were degraded by unidentified subpopulations numbering approximately 1% of normal human fecal bacteria. Here we report on the enzyme-producing properties of five strains of mucin oligosaccharide chain-degrading bacteria isolated from feces of four healthy subjects. Four were isolated from the greatest fecal dilutions yielding mucin side chain-degrading activity in culture, and thus were the numerically dominant side chain-degrading bacteria in their respective hosts. Three were Ruminococcus strains and two were Bifidobacterium strains. Two Ruminococcus torques strains, IX-70 and VIII-239, produced blood group A- and H-degrading alpha-glycosidase activities, sialidase, and the requisite beta-glycosidases; these strains released greater than 90% of the anthrone-reacting hexoses from hog gastric mucin during growth in culture. The Bifidobacterium strains lacked A-degrading activity but were otherwise similar; these released 60-80% of the anthrone-reacting hexoses but not the A antigenic structures from hog gastric mucin. Only Ruminococcus AB strain VI-268 produced blood group B-degrading alpha-galactosidase activity, but this strain lacked beta-N-acetylhexosaminidases to complete degradation of B antigenic chains. When this strain was co-cultured with a strain that produced beta-N-acetylhexosaminidases, release of hexoses from blood group B salivary glycoprotein increased from 50 to greater than 90%, and bacterial growth was enhanced. The glycosidases required for side chain degradation were produced by these strains in the absence of mucin substrate, and a substantial fraction of each activity in stationary phase cultures was extracellular. In contrast, none of 16 other fecal Bacteroides, Escherichia coli, Streptococcus faecalis, and Bifidobacterium strains produced ABH blood group-degrading enzymes; other glycosidases produced by these strains were predominantly cell bound except for extracellular beta-N-acetylhexosaminidases produced by the five S. faecalis strains. We conclude that certain Bifidobacterium and Ruminococcus strains are numerically dominant populations degrading mucin oligosaccharides in the human colon due to their constitutive production of the requisite extracellular glycosidases including blood group antigen-specific alpha-glycosidases. These properties characterize them as a functionally distinct subpopulation of normal human enteric microflora comprised of specialized subsets that produce blood group H antigen-degrading glycosidases alone or together with either blood group A- or B-degrading glycosidases.

Mucin degradation in human colon ecosystems. Evidence for the existence and role of bacterial subpopulations producing glycosidases as extracellular enzymes.

Recent work indicates that subpopulations of human fecal bacteria, averaging approximately 1% of the total viable fecal flora, degrade the oligosaccharide side chains of hog gastric mucin, which structurally resembles human epithelial mucins. Here we report studies to determine whether degradation of mucin oligosaccharides is related to glycosidase production by bacteria growing in anaerobic fecal cultures. Triplicate cultures containing hog gastric mucin were inoculated with serially diluted feces from each of seven healthy subjects. When the stationary growth phase was attained, mucin oligosaccharide degradation and both cell-bound and extracellular activities of four glycosidases were measured in each culture. Cell-bound beta-d-galactosidase, beta-N-acetylglucosaminidase, and sialidase were present in bacteria growing at all levels of fecal inocula, including 10(-11) g. In contrast, extracellular activities were present in every culture inoculated with 10(-4)-10(-7) g feces, but were diminished or absent in cultures inoculated with 10(-8)-10(-11) g feces. Bacterial autolysis was an unlikely cause of extracellular glycosidase activity, since p-nitrophenyl-alpha-l-fucosidase remained cell bound in cultures at every level of fecal inoculum. Degradation of mucin oligosaccharides was associated with extracellular, but not with cell-bound beta-d-galactosidase, beta-N-acetylglucosaminidase, and sialidase. Among the seven subjects, the estimated most probable numbers (MPN) of fecal bacteria producing extracellular beta-d-galactosidase, beta-N-acetylglucosaminidase, and sialidase ranged from 10(6)-10(10)/g dry fecal wt, were comparable to the MPN of mucin-degrading bacteria, and were significantly smaller than the MPN of total fecal bacteria. We interpret these findings as evidence for the existence of bacterial subpopulations in the normal fecal flora that produce extracellular glycosidases, and that these subpopulations have a major role in degrading the complex oligosaccharides of mucin in the gut lumen.

Degradation of blood group antigens in human colon ecosystems. I. In vitro production of ABH blood group-degrading enzymes by enteric bacteria.

Human feces contain enzymes produced by enteric bacteria that degrade the A, B, and H blood group antigens of gut mucin glycoproteins. We have studied their production in fecal cultures to determine if such cultures can be a source for enzyme purification and to explore how blood group antigen-degrading enzymes are adapted in individual human colon ecosystems. They were present in fecal cultures from each of 27 healthy subjects, including ABH nonsecretors. Heat-sensitive obligate anaerobes are their major source. From 39 to 85% of the total enzyme activity produced by growing cultures was extracellular. Commercial hog gastric mucin and salivary glycoproteins, including Lea saliva which lacks A, B, and H antigens, enhance production of A-, B-, and H-degrading activity in anaerobic fecal cultures irrespective of the glycoprotein's blood group specificity. There is evidence that the host's ABO blood type and secretor status affects the specificity of blood group-degrading enzymes produced by his fecal bacteria in vitro. Thus, fecal inocula from B secretors incubated with hog gastric mucin (A and H specificity) or with Lea saliva produced greater levels of B-degrading than A- or H-degrading activity, and inocula from A secretors in similar media produced greater levels of A-degrading than B- or H-degrading activity. Blood group-degrading enzymes produced in fecal cultures are glycosidases and not proteases. The B-degrading enzyme cleaves the B antigenic determinant alpha-D-galactose from the oligosaccharide side chains of mucin glycoproteins with B specificity. Anaerobic fecal cultures containing blood group substances are a feasible source for purifying blood group antigen-degrading enzymes. Prior adaptation to blood group antigens in the gut mucins of type A and type B secretors affects the specificity of the enzymes produced in vitro.

Degradation of blood group antigens in human colon ecosystems. II. A gene interaction in man that affects the fecal population density of certain enteric bacteria.

The autosomal dominant ABH secretor gene together with the ABO blood type gene control the presence and specificity of A, B, and H blood group antigens in human gut mucin glycoproteins. Certain obligate anaerobes in feces produce extracellular antigen-specific glycoside structures. We estimated the populations of these bacteria in feces of 22 healthy subjects by determining the greatest dilution of feces that yielded A, B, or H blood group-degrading enzyme activity after 24 h incubation in anaerobic cultures. Comparatively small populations of fecal bacteria produce blood group-degrading enzymes; their estimated populations were 10(8) per g or less in 21 subjects. Fecal populations of B-degrading bacteria were stable over time, and their population density averaged 50,000-fold greater in blood group B secretros than in other subjects. We present evidence that the greater fecal populations of B-degrading bacteria in B secretors is due in part to a competitive nutritional advantage gained by their ability to enzymatically cleave the B antigenic determinant alpha-D-galactose from gut mucins of B secretors. Fecal populations of bacteria producing A and H antigen-degrading enzyme activities were comparable in all subjects to the fecal population of B-degrading bacteria in B secretors. The large populations of fecal anaerobes may be an additional source of A antigen substrate for A-degrading bacteria; thus, antigens cross-reacting with A antigen were detected on cell walls of anaerobic bacteria from 3 of 10 cultures inoculated with 10(-10) g feces. Bacteria producing B-degrading activity likely represent a separate population from those producing A- or H-degrading activity since their fecal populations differed numerically in 14 subjects. These findings suggest that adaptation of blood group-degrading enzymes to mucin structures in human colon ecosystems is chiefly by mutation-selection of comparatively small populations of constitutive enzyme-producing strains rather than by substrate induced enzyme synthesis in many strains.