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

Multifarious roles of sialic acids in immunity

Sialic acids are a diverse family of monosaccharides widely expressed on all cell surfaces of vertebrates and so-called "higher" invertebrates, and on certain bacteria that interact with vertebrates. This overview surveys examples of biological roles of sialic acids in immunity, with emphasis on an evolutionary perspective. Given the breadth of the subject, the treatment of individual topics is brief. Subjects discussed include biophysical effects regulation of factor H; modulation of leukocyte trafficking via selectins; Siglecs in immune cell activation; sialic acids as ligands for microbes; impact of microbial and endogenous sialidases on immune cell responses; pathogen molecular mimicry of host sialic acids; Siglec recognition of sialylated pathogens; bacteriophage recognition of microbial sialic acids; polysialic acid modulation of immune cells; sialic acids as pathogen decoys or biological masks; modulation of immunity by sialic acid O-acetylation; sialic acids as antigens and xeno-autoantigens; antisialoglycan antibodies in reproductive incompatibility; and sialic-acid-based blood groups.

Significance of carbohydrate components of cell surfaces

This article is focused on a family of carbohydrate structures which are (a) target antigens of autoantibodies and (b) onco-developmental antigens which change during embryonic development, cell differentiation, maturation and oncogenesis. Among the carrier molecules of these saccharide structures is the receptor for epidermal growth factor. Perturbation of these structures on the isolated receptor enhances autophosphorylation of the receptor glycoprotein. This suggests that the carbohydrate chains may be part of a growth regulatory network which may be 'tuned' or perturbed via interactions with endogenous lectins or by adhesins of infective agents. Certain sialylated forms of these oligosaccharide structures serve as receptors for a pathogen of man, Mycoplasma pneumoniae which, following infection, elicits anti-erythrocyte autoantibodies. These autoantibodies are directed against the backbone domain of the carbohydrate receptor and are therefore anti-receptor antibodies. These observations suggest that complex formation between the adhesins of infective agents and specific saccharides of host-cell membranes may be a 'new' mechanism for eliciting autoantibodies.

Relapsing sensorimotor neuropathy with ophthalmoplegia, antidisialosyl antibodies, and extramembranous glomerulonephritis

A 72-year-old man presented with oculomotor dysfunction, subacute relapsing sensorimotor neuropathy, elevated erythrocyte sedimentation rate, IgM monoclonal paraprotein, cold agglutinins, and antidisialosyl IgM antibodies, features previously described by the acronym CANOMAD (chronic ataxic neuropathy with ophthalmoplegia, M protein, agglutination, and disialosyl antibodies). The patient also had extramembranous glomerulopathy associated with this syndrome. Treatment with corticosteroids improved both the neuropathy and glomerulopathy. This case suggests that the spectrum of neuropathy associated with monoclonal gammopathy may be broader than originally believed.

Neuropathie ataxiante associée à des anticorps anti-gangliosides disialylés : description de nouvelles formes cliniques et biologiques

INTRODUCTION

Polyneuropathies associated with IgM monoclonal gammopathy were recently recognized. Antibodies can react with glycoproteins such as myelin associated glycoprotein (MAG), or gangliosides containing one sialosyl epitope such as GM1 or several sialosyl epitopes (polysialyted gangliosides) including GD2, GD3, GT1b, GT1a, GQ1b.

METHODS

We report on three patients presenting oculomotor dysfunction, chronic sensitive ataxic polyneuropathy, high sedimentation rate, IgM monoclonal paraprotein of unknown signification and antidisialosyl IgM antibodies and for two of them cold agglutinins. Such features have been previously described under the acronym "CANOMAD" (chronic ataxic neuropathy with ophthalmoplegia, M protein, agglutination and disialosyl antibodies).

RESULTS

One of the patients presents extramembranous glomerulopathy and severe motor disability associated with this syndrome. The pathophysiology of the glomerulopathy seems to be linked with the polyneuropathy. Patients were treated either by intravenous immunoglobulin, corticosteroids or cyclophosphamid. Response to treatment differs in the three cases and there is currently no consensus.

CONCLUSION

Our study demonstrates that spectrum of polyneuropathy associated with monoclonal polyneuropathy may be larger than originally described.

A somatically mutated human antiganglioside IgM antibody that induces experimental neuropathy in mice is encoded by the variable region heavy chain gene, V1-18

IgM paraproteins associated with autoimmune peripheral neuropathy and anti-Pr cold agglutinins react with sialic acid epitopes present on disialylated gangliosides including GD1b, GT1b, GQ1b, and GD3. A causal relationship between the paraprotein and the neuropathy has never been proven experimentally. From peripheral blood B cells of an affected patient, we have cloned a human hybridoma secreting an antidisialosyl IgM mAb, termed Ha1, that shows identical structural and functional characteristics to its serum counterpart. Variable region analysis shows Ha1 is encoded by the same VH1 family heavy chain gene, V1-18, as the only other known anti-Pr antibody sequence and is somatically mutated, suggesting that it [correction of is] arose in vivo in response to antigenic stimulation. In the rodent peripheral nervous system, Ha1 immunolocalizes to dorsal root ganglia, motor nerve terminals, muscle spindles, myelinated axons, and nodes of Ranvier. After intraperitoneal injection of affinity-purified antibody into mice for 10 d, electrophysiological recordings from the phrenic nerve-hemidiaphragm preparation demonstrated impairment of nerve excitability and a reduction in quantal release of neurotransmitter. These data unequivocally establish that an antidisialosyl antibody can exert pathophysiological effects on the peripheral nervous system and strongly support the view that the antibody contributes to the associated human disease.

Anti-Pr cold agglutinins recognize immunodominant alpha 2,3- or alpha 2,6-sialyl groups on glycophorins

Anti-Pr agglutinins (CAs) with the subspecificities anti-Pr1h, -Pr1d, -Pr2, -Pr3h, -Pr3d, -PrM and anti-Sa CAs recognize immunodominant N-acetylneuraminic acid (NeuN Ac) groups of tetra and/or trisaccharides (O-glycans) of glycophorin. These O-glycans are sialylated in alpha 2,3- and/or alpha 2,6-linkages. Sa and most Pr antigens have been inactivated by alpha 2,3-specific sialidases. Antigenicity was reconstituted on desialylated glycophorin by alpha 2,3-specific Gal beta 1,3GalN Ac-sialyltransferase indicating that alpha 2,3-linked NeuN Ac groups are the immunodominant components of Sa and most Pr antigens. Some Pr antigens were resistant to alpha 2,3-specific sialidase and were not reconstituted by alpha 2,3-specific Gal beta 1,3GalN Ac-sialyltransferase, which indicates that alpha 2,6-linked NeuN Ac group represents an immunodominant component of some Pr antigens.

Monoclonal IgM cold agglutinins with anti-Pr1d specificity in a patient with peripheral neuropathy

A patient with a demyelinating sensory motor polyneuropathy secondary to IgM paraproteinaemia is reported. The paraprotein binds to the gangliosides GD1b, GT1b, GQ1b and GD3, all of which contain disialosyl groups with the sequence NeuAc alpha 2-8NeuAc alpha 2-3Gal. The paraprotein also acts as a cold agglutinin recognising the sialic-acid-dependent Pr1d antigenic determinant of the red cell membrane glycophorins. In this and in similar cases that have been reported, the coexistence of anti-Pr cold agglutinins and peripheral neuropathy suggest that they might be the causative agents of the disease.

Peripheral neuropathy associated with monoclonal IgM anti-Pr2 cold agglutinins

A patient with a chronic, large fibre sensory neuropathy had an immunoglobulin M lambda monoclonal paraprotein reactive at titres in excess of 1/10(5) with NeuNAc(alpha 2-8)NeuNAc(alpha 2-3)Gal configured disialosyl groups present on the gangliosides GD1b, GT1b, GQ1b, and GD3. The paraprotein showed weaker reactivity with GD1a, GM3, and LM1 but no reactivity with GM2, GM1, or asialo-GM1. In addition, the paraprotein had cold agglutinating activity with anti-Pr2 specificity, Pr2 being an antigenic determinant on membrane glycoproteins or glycolipids in erythrocytes or both. A large fibre sensory neuropathy with monoclonal anti-disialosyl antibodies is an increasingly recognised form of paraproteinaemic neuropathy.

Anti-Sa cold agglutinin of IgA class requiring plasma-exchange therapy as early manifestation of multiple myeloma

The case of a patient (Col) with multiple myeloma presenting as chronic cold agglutinin (CA) syndrome is reported. The CA (Col) was a monoclonal IgA/k paraprotein which recognizes an antigen fully expressed in adult and newborn erythrocytes, sialidase sensitive and partially resistant to proteases. Hemagglutination-inhibition studies showed that immunodominant N-acetylneuraminic acid bound alpha 2-->3 to O-glycans of glycophorins represents the CA(Col) epitope. These serological and biochemical findings fit with the anti-Sa specificity, of which only two previous examples are known. The clinical manifestations of CA (Col) were characterized by marked acrocyanosis, generalized livedo reticularis, and incapacitating dyspnea, but only mild hemolysis. Plasma-exchange therapy was effective in quickly removing the CA and relieving the associated clinical manifestations, but such benefit was only temporary. This is the first reported example of anti-Sa CA of IgA isotype and the first case of IgA CA syndrome treated by plasma exchange.

Ataxic polyneuropathy and anti-Pr2 IgM kappa M proteinemia

A case of ataxic neuropathy associated with IgM kappa M proteinemia is reported. Double filtration plasmapheresis effectively treated the neuropathy. The IgM kappa antibody had anti-Pr2 cold agglutinin activity. We demonstrated reactivities of the IgM kappa antibody to sialosyl paragloboside, sialosyl lactosaminyl paragloboside, GT1b, GD1a, GD1b, GM3 and GD3 on high-performance thin-layer chromatography immunostaining and enzyme-linked immunosorbent assay, which is previously unreported antigenic specificity of the M proteins in cases of paraproteinemic neuropathy. IgM M protein with anti-Pr2 cold agglutinin activity may play a pathogenetic role in peripheral nerve demyelination, because the target antigens of the M protein are present in myelin and possibly in endothelial cells of the peripheral nervous system.

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.

Relationship of variable region genes expressed by a human B cell lymphoma secreting pathologic anti-Pr2 erythrocyte autoantibodies

To study the biology of cold agglutinin disease we previously established EBV-transformed B cell clones isolated from a patient with splenic lymphoma of an early plasmacytic cell type and immune hemolysis due to an anti-Pr2 cold agglutinin. These clones had an aberrant chromosomal marker identical to the patient's B cell lymphoma and each secreted IgMk anti-Pr2 similar to the pathologic autoantibody in the serum of the patient. In this study, we have further investigated the Pr2-specific autoimmune response through nucleotide sequencing of VH and VL region genes. We have shown that the seven clones share the same VDJ/VJ gene segments and junctional elements confirming their clonal origin. The VH sequences were 88% homologous to a VHI germline gene while the VL sequences were 97% homologous to a VkIII germline gene. Only 4 somatic mutations (3 silent and 1 conservative) were found in greater than 5,000 bp sequenced, suggesting that a low mutation rate existed. Based on a tumor mass of 10(12) cells and a minimum of 40 divisions, we estimated the somatic mutation rate to be 4.45 x 10(-5) m/bp/d. This somatic mutation rate is similar to those estimated for acute lymphocytic leukemia (pre-B cell) and chronic lymphocytic leukemia (intermediate B cell), but significantly lower than the mutation frequency in follicular lymphomas (activated B cell). We propose that the difference in somatic mutation frequency of a B cell tumor may be related to the stage of B cell differentiation. In addition, the low mutation frequency observed in the Pr2-specific B cell tumor may also reflect, in part, selection by autoantigen to conserve sIg structure and specificity.

Sialo-oligosaccharide receptors for Mycoplasma pneumoniae and related oligosaccharides of poly-N-acetyllactosamine series are polarized at the cilia and apical-microvillar domains of the ciliated cells in human bronchial epithelium

The occurrence and distribution of the sialo-oligosaccharide receptors (sialosyl-I and sialosyl-i) for Mycoplasma pneumoniae as well as other related oligosaccharide structures of poly-N-acetyllactosamine type, and their short-chain analogs based on galactose linked beta 1-4 or beta 1-3 to N-acetylglucosamine (Gal beta 1-4GlcNAc or Gal beta 1-3GlcNAc, respectively) were investigated in the human bronchial epithelium by histochemistry by using sequence-specific monoclonal antibodies and lectins. Among the mature epithelial cells, only ciliated cells were found to express the long-chain antigens, whereas mucus-secreting cells contained the short-chain antigens associated with mucus globules. The long-chain oligosaccharides were found to be highly polarized at the luminal aspects of the ciliated cells where the branched structures (I and sialosyl-I antigens) were detected both at the apical-microvillar border and on the cilia, but the linear structures (i, sialosyl-i, and VIM-2 antigens) were detected exclusively at the apical-microvillar border. These observations provide the first in situ visualization of the receptor structures for M. pneumoniae at the primary site of infection. The lack of sialo-oligosaccharide receptors in secretory cells and the mucus they produce provides a biochemical basis for evasion by this microorganism of the secreted mucus barrier.

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.

Comparative biochemical and genetic characterization of clonally related human B-cell lines secreting pathogenic anti-Pr2 cold agglutinins

To study the biology of cold autoimmune hemolytic anemia, Epstein-Barr virus (EBV)-transformed B-cell clones were established from a patient with splenic lymphoma associated with immune hemolysis due to an anti-Pr2 cold autoantibody. Studies were performed comparing the cold autoantibody present in culture supernatants of these cell lines to the pathogenic cold autoantibodies present in the patient's plasma. Cytogenetic studies of splenic lymphocytes demonstrated an abnormal karyotype (51XX, +3, +9, +12, +13, +18). After EBV transformation, eight clones secreting IgM, kappa anti-Pr were isolated; each clone had the same abnormal karyotype as above. DNA isolated from the clones and spleen was analyzed by Southern blot hybridization with JH, C mu, and C kappa probes; identical gene rearrangements were seen in each case. Anti-Pr antibodies, isolated from culture supernatant and serum were compared by isoelectric focusing (IEF) and demonstrated similar banding patterns. Distinctive binding patterns, however, were observed in 2/8 clones, suggesting structural differences. Adsorption studies with red blood cells further showed that the observed IEF banding patterns were solely due to anti-Pr cold autoantibody. With a thin-layer chromatography method, the biochemical determinants recognized by the cold autoantibodies were defined as glycolipids containing Neu Ac alpha 2-3Gal beta 1-4Glc sequences. The data demonstrate that the autoantibodies of the EBV-transformed B-cell lines were similar to the pathogenic monoclonal serum autoantibody in both structure and specificity. These clonal cell lines may thus serve to further study the biology of human B-cell lymphomas with defined autoantibody specificity.

A human monoclonal IgM kappa cold agglutinin recognizing oligosaccharides with immunodominant sialyl groups preferentially at the blood group M-specific peptide backbone of glycophorins: anti-PrM

A kappa-monotypic IgM high titer cold agglutinin reacting like anti-Pr at low, like anti-M at higher temperatures, is described. It recognizes tetra- and/or trisaccharides with immunodominant sialyl groups on glycophorins A, B, C like anti-Pr. Its affinity to the oligosaccharides is, however, approximately 10-fold increased when they are attached to the M-specific peptide backbone of glycophorin A. The antibody, termed anti-PrM, occurred in a blood group MN patient with chronic cold agglutinin disease and caused autoimmune hemolytic anemia.

Detection of blood group type glycosphingolipid antigens on thin-layer plates using polyclonal antisera

The conditions for binding of antibodies to glycosphingolipids separated on a thin-layer plate have been optimized for polyclonal antisera. The method has a broad detection range with low background staining. Examples are shown for the detection of blood group A and B active glycosphingolipids.

Antibody response of rabbits to nerve ending gangliosides. Analysis of antibody specificity by liposome lysis and lysis inhibition assays

Rabbits were immunized with nerve ending fraction prepared from guinea pig brain. Serum antibodies to total gangliosides were followed by enzyme-linked immunosorbent assay; their titers were highest at 2 to 3 weeks after immunization and some rabbits showed a response to reinjections. Specific reactivities of the antibodies against each molecular species of gangliosides were analyzed by liposome lysis assay and liposome lysis inhibition assay. Antibody responses were detected against GM1, GD1b, GM3 and GM2, but not against GD1a and GT1b. Natural and immune antibodies to the asialo glycolipids and to galactosylceramide were also observed.

Glycosphingolipid carriers of carbohydrate antigens of human myeloid cells recognized by monoclonal antibodies

Six monoclonal antibodies with known specificities for the carbohydrate antigens i, X or Y, and seven anti-myeloid antibodies (determinants unknown) selected for their differing reaction patterns with human leucocytes were tested in chromatogram binding assays for reactions with myeloid cell glycolipids derived from normal human granulocytes and chronic myelogenous leukemia cells. Antigenicities were found exclusively on minor glycolipids which were barely or not at all detectable with orcinol-sulphuric acid stain. Among these, a neutral glycosphingolipid bound the anti-i antibody Den and chromatographed as the ceramide octasaccharide, Gal beta 1----4GlcNac beta 1----3Gal beta 1----4GlcNac beta 1----3Gal beta 1----4GlcNAc beta 1----3Gal beta 1----4Glc-Cer. Several species of neutral glycosphingolipids with six to more than ten monosaccharides were detected which carry the X antigen and others the Y antigen: Gal beta 1----4(Fuc alpha 1----3)GlcNAc and Fuc alpha 1----2Gal beta 1----4(Fuc alpha 1----3)GlcNAc, respectively. In addition, three new types of carbohydrate specificities were detected among the myeloid cell glycolipids. Two were associated with neutral glycolipids: the first, recognised by anti-myeloid antibodies VIM-1 and VIM-10, was expressed on a distinct set of glycolipids with six or more monosaccharides, and the second, recognized by VIM-8, was expressed on glycolipids with more than ten monosaccharides. The third specificity, recognised by the anti-myeloid antibody VIM-2, was expressed on slow migrating sialoglycolipids with backbone structures of the poly-N-acetyllactosamine type that are susceptible to degradation with endo-beta-galactosidase. Thus, we conclude that the i and Y antigens occur among the glycolipids of normal myeloid and chronic myelogenous leukemia cells and that a high proportion of hybridoma antibodies raised against differentiation antigens of myeloid cells are directed at carbohydrate structures.

Evidence for sialylated type 1 blood group chains on human erythrocyte membranes revealed by agglutination of neuraminidase-treated erythrocytes with Waldenström's macroglobulin IgMWOO and hybridoma antibody FC 10.2

Haemagglutination studies have been performed with untreated and neuraminidase-treated human erythrocytes of the three Lewis antigen types Le(a-b-), Le(a+b-) and Le(a-b+) using two monoclonal antibodies, IgMWOO and FC 10.2, which were previously shown to recognize the type 1 based blood group chains: Gal beta 1----3GlcNAc beta 1----3Gal beta 1----4Glc/GlcNAc (for explanation of abbreviations see table IV legend). Both antibodies behaved as cold agglutinins with neuraminidase-treated but not with untreated erythrocytes of the three Lewis antigen types. Neuraminidase-treated erythrocytes of i antigen type were similarly agglutinated. This haemagglutination was specifically inhibited by the type 1 based milk oligosaccharide lacto-N-tetraose. Thus, there is strong evidence for the occurrence of sialylated type 1 chains on human erythrocyte membranes of I and i antigen types. In addition, evidence for the presence of type 1 chains which are both sialylated and fucosylated was obtained by (1) haemagglutination of Le(a+b-) erythrocytes with the monoclonal antibody 19.9; (2) increased haemagglutination of neuraminidase-treated erythrocytes with anti-H antibodies of Bombay serum; (3) increased haemagglutination of neuraminidase-treated Le(a+b-) cells with anti-Lea antibodies, and (4) the appearance of Lea antigen activity on neuraminidase-treated erythrocytes of Le(a-b+) type.

Interaction of Mycoplasma pneumoniae with erythrocyte glycolipids of I and i antigen types

The role of sialoglycolipids (gangliosides) as receptors for the human pathogen Mycoplasma pneumoniae was investigated by using purified gangliosides of known carbohydrate structures as inhibitors of the binding of 51Cr-labeled erythrocytes to sheet cultures of M. pneumoniae. We found that sialoglycolipids with long carbohydrate backbones of the poly-N-acetyllactosamine type were more potent inhibitors of M. pneumoniae binding than those with short carbohydrate chains. This is in accord with earlier inhibition data for glycoproteins and oligosaccharides. Thus, the inhibitory activity of a fraction of bovine erythrocyte gangliosides containing long backbone structures of I antigen type was approximately 200 times greater than that of the short chain gangliosides GM3 and GT1b. The binding of M. pneumoniae to erythrocytes of I and i antigen types was found to be comparable, indicating that M. pneumoniae in its adhesive specificity may not distinguish between the branched carbohydrate backbones of I type and the linear structures of i type. Thus, the production of autoantibodies to the backbone structures of I type rather than i type after infection with this agent may simply reflect a greater abundance of branched carbohydrate receptors of I type on the surface of host cells with which the mycoplasma forms immunogenic complexes.

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.

Species differences in the expression of carbohydrate differentiation antigens on mammalian blood cells revealed by immunofluorescence with monoclonal antibodies

Following recent observations using monoclonal antibodies that carbohydrate structures behave as differentiation antigens of man and mouse, we have made a preliminary survey of the expression of 8 monoclonal antibody-defined carbohydrate antigens on blood cell smears of man, baboon, mouse, rat, rabbit, pig, and dog. There are considerable species differences in the patterns of antigen expression. However, certain generalizations can be made as follows: the i and I antigens, associated with linear and branched carbohydrate chains consisting of repeating N-acetyl-lactosamine sequences (Gal beta 1-4GlcNAc, termed Type-2 backbone sequences) are widely distributed among granulocytes and lymphocytes of all the species studied, and on erythrocytes, monocytes, and platelets of some of them. Substantial amounts of Type-1 backbone sequences (Gal beta 1-3GlcNAc) may occur on rabbit lymphocytes. The N-acetylneuraminic acid-containing antigens, Pr2 and Gd, are also expressed to varying degrees on blood cells. On the other hand, antigens based on mono- and difucosylated N-acetyllactosamine, termed SSEA-1 (or X-hapten) and C14 (or Y-hapten) are predominantly granulocyte/monocyte-associated antigens. The former antigen is expressed in overt form only on untreated human granulocytes but occurs in cryptic state, masked by sialic acid, on human monocytes, and on the granulocytes and monocytes of baboon, rabbit, and dog but not on those of mouse, rat, and pig. The latter antigen is expressed on human granulocytes and on neuraminidase-treated monocytes and granulocytes of dog. Lymphocytes of dog are unusual in their expression of C14 antigen, in cryptic state, masked by sialic acid residues. Although the physiological roles of these various carbohydrate structures, in vivo, are not yet known, they seem excellent candidates as determinants of species and cell-type differences in susceptibilities to infective agents.