The presence of the Ii blood group system on human platelets

New Insights in the Pathogenesis and Therapy of Cold Agglutinin-Mediated Autoimmune Hemolytic Anemia

Autoimmune hemolytic anemias mediated by cold agglutinins can be divided into cold agglutinin disease (CAD), which is a well-defined clinicopathologic entity and a clonal lymphoproliferative disorder, and secondary cold agglutinin syndrome (CAS), in which a similar picture of cold-hemolytic anemia occurs secondary to another distinct clinical disease. Thus, the pathogenesis in CAD is quite different from that of polyclonal autoimmune diseases such as warm-antibody AIHA. In both CAD and CAS, hemolysis is mediated by the classical complement pathway and therefore can result in generation of anaphylotoxins, such as complement split product 3a (C3a) and, to some extent, C5a. On the other hand, infection and inflammation can act as triggers and drivers of hemolysis, exemplified by exacerbation of CAD in situations with acute phase reaction and the role of specific infections (particularly Mycoplasma pneumoniae and Epstein-Barr virus) as causes of CAS. In this review, the putative mechanisms behind these phenomena will be explained along with other recent achievements in the understanding of pathogenesis in these disorders. Therapeutic approaches have been directed against the clonal lymphoproliferation in CAD or the underlying disease in CAS. Currently, novel targeted treatments, in particular complement-directed therapies, are also being rapidly developed and will be reviewed.

Clinical immunology of chronic cold agglutinin disease

We studied clinical and immunological characteristics of 15 patients with chronic cold agglutinin disease (CAD). Mean age at disease debut was 68 years for female and 67 years for male patients. The patients had no signs of other autoimmune diseases. All patients had V(H)4-34 encoded IgM kappa cold agglutinins (CA) in high titre. In five patients IgM increased significantly with advancing disease. Seven patients had reduced concentrations of lymphocytes, largely of CD4 and CD8 T cells. Percentages of NK cells (CD56) and B cells (CD19) were increased in seven and three patients, respectively. In six out of nine patients a clonal expansion of kappa positive B cells was found. Serum C3 was decreased in nine patients and C4 was decreased in 11 patients, six of whom had reduced CH50. Such data indicate that patients with CAD experience a continuous low-grade complement consumption. Five patients had experienced increased haemolysis during infections. After addition of active complement to patient sera in vitro, six sera showed increased haemolytic activity. Our results indicate that some patients with CAD have a relative deficit of complement in their serum and that an increase of complement production occurs during an acute phase reaction which enhances haemolysis. Our data also indicate that both CA titre and thermal amplitude are important characteristics when predicting complement activation and clinical course in CAD.

Coexistence of erythrocyte agglutination and EDTA-dependent platelet clumping in a patient with thymoma and plasmocytoma

For 8 years, EDTA-dependent pseudothrombocytopenia was observed in a 55-year-old woman with a history of rheumatoid arthritis who had undergone surgery for lymphoepithelial thymoma 11 years earlier. The clinical picture was characterized by the presence of platelet clumps and antiplatelet antibodies of the IgM class. With the recent appearance of a solitary extramedullary plasmocytoma in the right retrobulbar region and the detection of an IgGlambda monoclonal gammopathy, blood examination also revealed erythrocyte agglutinates alongside the platelet clumps and the presence of a cold IgG antibody with antiI specificity. Both phenomena were observed in vitro when the sample temperature declined to 20 degrees C to 25 degrees C, but not at 37 degrees C. While the EDTA-dependent antiplatelet antibodies did not appear to be chronologically correlated with the patient's diseases, the cold antierythrocyte autoantibodies were strictly related to the plasmocytoma and the IgGlambda monoclonal component in serum. To our knowledge, this is the first description of an association between EDTA-dependent platelet and erythrocyte agglutinates, with a clinical picture of pseudothrombocytopenia and pseudoerythrocytopenia due to cold agglutinins.

Evans' syndrome as a presenting manifestation of atypical paroxysmal cold hemoglobinuria

Paroxysmal cold hemoglobinuria is a rare and potentially life-threatening acquired hemolytic anemia occurring either as an acute transient anemia following several different viral syndromes, or in a chronic idiopathic form. Episodic hemolysis in paroxysmal cold hemoglobinuria is usually associated with a biphasic (Donath-Landsteiner) IgG cold-reactive complement-fixing autohemolysin with anti-P specificity. Paroxysmal cold hemoglobinuria has not previously been associated with malignancy nor has it been clearly shown to be steroid-responsive. This report describes a patient with steroid-responsive autoimmune hemolytic anemia and immune thrombocytopenia (Evans' syndrome) associated with oat cell carcinoma of the lung and a unique biphasic anti-IgM autohemolysin. This case extends the spectrum of biphasic antibody-mediated immune cytopenias and widens both the clinical and the serologic definition of paroxysmal cold hemoglobinuria.

Quantitative determination of platelet surface alloantigens using a monoclonal probe

A monoclonal antibody with specificity for the Fc portion of IgG was used to determine the number of IgG alloantibody molecules bound at saturation to alloantigens of the PlA1 and HLA systems on normal human platelets. In preliminary studies, it was found that the number of cell-bound IgG molecules recognized by this probe correlates well with the number measured by electroimmunoassay, an independent measure of alloantibody binding. PlA1-positive platelets could be divided into two groups binding 34,000-43,000 or 19,000-24,000 alloantibody molecules. Family studies and studies with a cytolytic assay showed that the former group is homozygous and the latter heterozygous for PlA1. Because the number of glycoprotein IIIa (GPIIIa) molecules carrying the PlA1 determinant on the surface of normal platelets is thought to be about 40,000, these findings suggest that each GPIIIa molecule carries one PlA1 determinant. The number of class I HLA molecules expressed on normal platelets was considerably smaller than the number of PlA1 determinants, ranging from 4400 to 10,000 (HLA-A2), 870 to 8400 (Bw4), and 1300 to 5800 (Bw6). Preliminary analysis indicates that stronger or weaker expression of Bw4 and of Bw6 correlates with certain "private" HLA-B determinants carried on the HLA-B molecule as found in previous studies using an indirect method to measure alloantigen density. These findings appear to explain why antibodies reactive with platelet-specific antigens such as PlA1 react more strongly with platelets than HLA-specific antibodies in most serologic tests. The weak expression of HLA determinants on platelets of some subjects may account for the less than perfect correlation between in vitro compatibility tests and post-transfusion platelet survivals observed in most studies.

A naturally occurring, warm-reactive macroglobulin specific for papain-treated human platelets: preliminary characterization

Sera from 28 of the 113 normal children and adults (25%) studied were found to contain an immunoglobulin capable of causing complement-dependent lysis of normal platelets treated with small quantities of papain. This factor reacts equally well at 4 degrees C and at 37 degrees C with a determinant induced on platelets from normal subjects by treatment with papain or bromelain, but not by trypsin, chymotrypsin, or neuraminidase. It does not bind to red cells treated with any of these enzymes. The site(s) for which the factor was specific could not be induced on platelets from six patients with type I Glanzmann's thrombasthenia (lacking glycoproteins IIb and IIIa), in contrast to platelets from each of 20 normal donors. Isolation and characterization of the factor has been difficult because of its intolerance to chemical and physical manipulation. In 11 of the 20 individuals studied, however, it was found to have the properties of an IgM immunoglobulin. The factor appears to be different from any previously described, naturally occurring human immunoglobulin. It has not yet been shown to be associated with any disease state, but in the presence of complement, it is capable of causing profound damage to platelets previously subjected to minimal proteolysis, and the possibility that it can provoke platelet destruction in some conditions deserves further study.

Heterogeneous distribution of antigens on human platelets demonstrated by fluorescence flow cytometry

We have used fluorescence flow cytometry to analyse cell-to-cell variability in the density of platelet ABH, Ii, Lewis, P, P1A1, Bak,a and HLA class I antigens. Human IgG and IgM antibodies were used in a two-stage assay with goat FITC-conjugated antihuman IgG (H&L) antibody as the label, followed by single cell analysis of 10 000 platelets per sample using a 256-channel fluorescence flow cytometer (Becton-Dickinson FACS Analyser). Computer analysis of fluorescence intensity histograms for mean and peak channel and coefficient of variation shows that the degree of heterogeneity in platelet antigen density varies with each particular blood group. The broad fluorescence distribution curves with oligosaccharide antigens (CVs: A = 53, B = 40, I = 44, Lea = 40, P = 40) indicate that these antigens possess a greater variability in the number of sites per cell compared to the more homogeneous distribution of P1,A1 BaK,a and HLA (CVs: P1A1 = 24, HLA = 30). These findings may partly account for the mechanism by which transfusion of ABO-incompatible platelets results in a biphasic survival curve, with a period of early rapid removal of those platelets with a high density of antigen sites, followed by a relatively normal survival curve for those platelets that possess only a few or no antigen sites. In contrast, P1A1 and HLA sites are less variable in number from one platelet to another in a given donor, and immune-mediated removal would be more likely to approximate a single exponential curve.

Biochemical characterisation of A blood group activity on human platelets

A butanol extraction procedure has been used to isolate the blood group A antigen determinants from platelet membranes and to determine their biochemical structure-glycolipid and/or glycoprotein. The blood group A serological activity was found to reside entirely in the butanol (organic) fraction. When this fraction was analyzed by thin-layer chromatography, the A-inhibitory activity was found to comigrate with extracts of erythrocyte type Aa, Ab and Ac variant structures. The results of this study indicate that the ABO blood group A determinants on human platelets are glycolipid, similar in structure to glycolipid A determinants on erythrocytes.

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.