A further cold agglutinin, F1, recognizing a N-acetylneuraminic acid-determined antigen

Characterization of blood group ABO(H)-active gangliosides in type AB erythrocytes and structural analysis of type A-active ganglioside variants in type A human erythrocytes

Several monosialogangliosides containing the type A-active epitope have been detected in type A erythrocytes on immunological analysis with a monoclonal antibody, and three of them were purified by repeated silica bead column chromatography and by scraping from the TLC plate. Two of these A-active gangliosides were characterized by methylation analysis by GC/MS, negative SIMS, MALDI-TOF/MS, proton nuclear magnetic resonance spectroscopy, and immunological assays, and their structures were concluded to be as follows. A-active ganglioside I:A-active ganglioside II:The reactivity of the purified gangliosides to the anti-A monoclonal antibodies (mAbs) exhibited enhancement after removal of the sialic acid. Therefore, the sialic residue has been shown to inhibit the binding to the terminal A-active epitope through the formation of an immune complex. To confirm the presence of A- (including S-A-I, -II and -III) and B-active gangliosides, the reactivity of anti-A and -B mAbs were investigated using total gangliosides from type A, -B and -AB erythrocytes on TLC plate. The results were that the gangliosides from types A and AB showed positive reaction to anti-A mAbs, whereas in the anti-B mAbs binding the gangliosides from types B and AB were positive. Thus, it revealed that A-active gangliosides were present in type A and -AB, and B-active gangliosides in types B and AB. As there was no difference in respective gangliosides on type AB erythrocytes of 22 individuals, both A- and B-active gangliosides are equally present in type AB erythrocytes. The biological significance of these A- and B-active ganglioside variants remains vague at present. As these molecules exhibit different reactivities to the anti-A mAbs, it is very likely that they can regulate the antigenicity of the A-epitope on the cell surface.

Characterization of I/F1 glycoprotein as a receptor for Mycoplasma pneumoniae

Serologic evidence of anti-I and anti-Fl cold agglutinins occurring in mycoplasma infections led to the isolation of I/Fl glycoprotein from human erythrocyte membranes. Mycoplasma pneumoniae bound to purified I/Fl glycoprotein in a dose-dependent fashion depending on sialylated carbohydrate determinants. This was shown by the decreased binding of mycoplasmas to either sialidase-treated I/Fl glycoprotein (dot blot analysis) or sialidase-treated erythrocytes (hemagglutination test). Structural properties of the receptor for optimal binding could be explored by hemagglutination inhibition assays. Glycophorins were excluded as receptors. These results indicate that Fl (and I) antigens are receptors for M. pneumoniae.

Neolacto (type-2 chain)-sialoautoantigens recognized by human cold agglutinins

The antigens Fl and Vo, recognized by cold agglutinins, are protease-resistant differentiation antigens like I and i antigens. In contrast to Ii, Fl and Vo are sialidase-susceptible antigens like the protease-resistant Gd antigens. Because I/i antigens are branched/linear type-2 (poly-N-acetyllactosamine or neolacto series) chains which are cleaved from red cells by endo-beta-galactosidase, the effect of the enzyme on Fl, Vo and Gd antigens was studied. Fl and Gd antigens, previously shown to be sialylated branched (Fl), and linear and branched (Gd) type-2 sequences, were not inactivated on red cells by the enzyme, whereas Vo antigenicity was completely abolished. The data suggest that Vo antigen is expressed on sialylated linear poly-N-acetyllactosamine sequence.

Cold agglutination

Autoantibodies against red cells optimally reacting at 0 degree C, ie, CA, are normally found with low titers in the serum of human adults. High-titer CA may be induced by certain infectious agents, including M pneumoniae, EBV, CMV, and rubella virus, or may develop on the basis of chronic (malignant) B cell lymphoproliferation. The main clinical manifestation of cold agglutination is AIHA. Antigens and antibodies of cold agglutination are the best characterized reaction partners of a human autoimmune process. CA may recognize I and i antigens, which are lipid- and protein-linked branched and linear N-acetyl-lactosamine chains, respectively. They are precursors of the ABH blood group antigens and are converted into H by fucosylation. An alternative substitution by sialylation creates Gd, Fl, and probably Vo/Li antigens. CA with anti-Pr and anti-Sa specificities recognize 0-glycans with immunodominant sialyl groups on glycophorins. Several Pr subspecificities can be identified by chemically modified sialyl groups on glycophorins. Because CA in chronic lymphoproliferation are monoclonal antibodies, structure-specificity-interrelations of the antibodies could be identified by primary structure analyses of the N-terminal variable regions of H and L chains and by studies on CA idiotypes. Interrelations between distinct CA specificities and particular infectious agents could explain cold agglutination as a response to receptors for the agents or to the binding sites of antibodies against the agents. Interrelations also existing between certain CA isotypes (Ig classes and L chain types) and CA specificities could be a basis for the elucidation of the enigmatic etiology of chronic (malignant) monoclonal cold agglutination.

A cold agglutinin: Om

An IgM kappa cold agglutinin reacted with cord blood as well as with adult red blood cells (RBC). The agglutinin reacted strongly with papainized and neuraminidase (RDE)-treated RBC. It resembled anti-Me cold agglutinin in these serological findings. However, the activity of this agglutinin against RBC was markedly decreased in the presence of human milk. The data suggest that the agglutinin is directed against a new glycolipid antigen common to human RBC, termed Om antigen.

Coexisting anti-I and anti-F1/Gd cold agglutinins in infections by Mycoplasma pneumoniae

192 sera containing cold agglutinins of apparent anti-I specificity were reinvestigated for concomitant cold agglutinins (CA) against sialic acid-dependent antigens. 35 cases of additional anti-F1 and 3 cases of additional anti-Gd were detected. 53% of cases with coexisting anti-I and anti-F1/Gd CA had a clinical diagnosis of pneumonia, in 39% IgM antibodies against Mycoplasma pneumoniae could be demonstrated. Since F1 and Gd antigens are identical with the structures identified as receptors for M. pneumoniae, the findings support the hypothesis that postinfectious CA are directed against the receptor of the infectious agent.

Li cold agglutinin: a further antibody recognizing sialic acid-dependent antigens fully expressed on newborn erythrocytes

The cold agglutinin anti-Li recognizes a sialic acid-dependent antigen fully expressed only on newborn red cells. Although it resembles anti-i in all aspects except for its nonreactivity with neuraminidase-treated red cells, it is entirely different from anti-i, since sialic acid is not involved in i antigenic determinants.

Autoimmune hemolytic anemia by coexisting anti-I and anti-Fl cold agglutinins

In association with atypical pneumonia, a patient developed acute severe autoimmune hemolytic anemia. Hemoglobin temporarily was only 7.0 g/100 ml, so that the patient needed red blood cell (RBC) transfusion. Hemolysis was found to be caused by high titer cold agglutinins (CA), which occurred transiently during the acute period of the disease. CA of two different specificities, anti-I and anti-Fl, were demonstrated in the patient's serum. Antibodies of the two specificities were clearly separated by absorption/elution experiments using neuraminidase (RDE)-treated RBC. They were distinguished by serologic means: Both anti-I and anti-Fl react more strongly with adult RBC than with newborn and i adult RBC; in contrast to anti-I, anti-Fl does not agglutinate RDE-treated cells. Inhibition experiments showed that I-active substances prepared from papainized RBC exhibited both I and Fl antigenic activity. By RDE-treatment of I-active substances, Fl-activity was markedly reduced, while I-activity was increased.

Cold agglutinin Vo. An IgM lambda monoclonal human antibody recognizing a sialic acid determined antigen fully expressed on newborn erythrocytes

An IgM lambda cold agglutinin reacted preferentially with newborn (i cord) and i adult erythrocytes. The whole serum of patient Vo and the antibody isolated by warm elution reacted moderately with native and neuraminidase-treated red cells but strongly with papainized red cells. Papainization of erythrocytes enhanced markedly the susceptibility of the corresponding antigen not only to antibody binding but also to the action of neuraminidase, indicating that sialic acid is the immunodominant component of the cryptic antigen. The cold agglutinin Vo is the first example of a human monoclonal antibody recognizing a sialic acid-dependent, developmentally regulated antigen fully expressed on newborn erythrocytes.

Simultaneous occurrence of anti-F1 and anti-I cold agglutinins in a patient's serum

The second example of anti-F1 cold agglutinins recognizing a developmentally regulated antigen like I is described. The antibody occurred transiently and simultaneously together with an anti-I cold agglutinin. Although anti-F1 and anti-I specificities are entirely different, the data on the biochemistry of F1 and I antigenic determinants provide an explanation for the simultaneous occurrence of anti-F1 and anti-I cold agglutinins in connection with a poly- or oligoclonal autoimmune response.

The reactivities of human erythrocyte autoantibodies anti-Pr2, anti-Gd, Fl and Sa with gangliosides in a chromatogram binding assay

The thin layer chromatogram binding assay was used to study the reaction of several natural-monoclonal autoantibodies which recognize sialic acid-dependent antigens of human erythrocytes. Immunostaining of gangliosides derived from human and bovine erythrocytes was achieved with four autoantibodies designated anti-Pr2, anti-Gd, Sa and Fl, each of which has a different haemagglutination pattern with untreated and proteinase-treated erythrocytes and with cells of I and i antigen types. From the chromatogram binding patterns of anti-Pr2 with gangliosides of the neolacto and the ganglio series, it is deduced that this antibody reacts best with N-acetylneuraminic acid when it is alpha 2-3- or alpha 2-6-linked to a terminal Gal(beta 1-4)Glc/GlcNAc GlcNAc sequence and to a lesser extent when it is alpha 2-3-linked to a terminal Gal(beta 1-3)GalNAc sequence or to an internal galactose and when it is alpha 2-8-linked to another, internal N-acetylneuraminic acid residue. The other three antibodies differ from anti-Pr2 in their lack of reaction with glycolipids of the ganglio series. They react with the NeuAc(alpha 2-3)Gal(beta 1-4)Glc/GlcNAc sequence as found in GM3 and in glycolipids of the neolacto series, but show a preference for the latter, longer sequences. Thus all four antibodies react with sialylated oligosaccharides containing i type (linear) and I type (branched) neolacto backbones. Fl antibody differs from the other three in its stronger reaction with branched neolacto sequences in accordance with its stronger agglutination of erythrocytes of I rather than i type. The four antibodies show a specificity for N-acetyl- rather than N-glycolyl-neuraminic acid.

Reaction of anti-Gd, anti-Fl and anti-Sa cold agglutinins with p erythrocytes

Among four anti-Gd cold agglutinins two showed a slight preferential reaction with p erythrocytes, two did not. Anti-Fl and anti-Sa cold agglutinins, sharing some serologic characteristics with Gd antibodies, showed no preferential reactions with p cells. The findings point to different fine specificities of monoclonal anti-Gd cold agglutinins.

Characterization of an epitope (determinant) structure in a developmentally regulated glycolipid antigen defined by a cold agglutinin Fl, recognition of alpha-sialosyl and alpha-L-fucosyl groups in a branched structure

The antibody Fl shows preferential reactivity with adult erythrocytes over newborn erythrocytes, and its reactivity is abolished by sialidase treatment of the erythrocyte. The antibody was found to recognize binary determinants linked to the branched lacto-N-isooctaosylceramide (formula; see text) The presence of an N-acetylneuraminyl group at one end and L-fucosyl group at the other end is essential for the reactivity of the antibody. A substitution at the penultimate D-galactosyl residue of one of the chains with an alpha-D-(1 leads to 3)-linked 2-acetamido-2-deoxygalactosyl or galactosyl group did not inhibit the reactivity of the antibody. The new blood group A- and B-active, branched gangliosides are also isolated and characterized.