Monoclonal antibodies against antigens of the human platelet surface: preparation and properties

A functional platelet fibrinogen receptor with a deletion in the cysteine-rich repeat region of the beta(3) integrin: the Oe(a) alloantigen in neonatal alloimmune thrombocytopenia

This report describes a new low-frequency alloantigen, Oe(a), responsible for a case of neonatal alloimmune thrombocytopenia (NAIT). In a population study none of 600 unrelated blood donors was an Oe(a) carrier. By immunochemical studies the Oe(a) antigen could be assigned to platelet glycoprotein (GP) IIIa. Sequencing of GPIIIa complementary DNA from an Oe(a) (+) individual showed deletion of a lysine residue at position 611 (DeltaLys(611)). Analysis of 20 Oe(a) (-) and 3 Oe(a) (+) individuals showed that the DeltaLys(611) form of GPIIIa was related to the phenotype. Anti-Oe(a) reacted with the DeltaLys(611), but not with the wild-type isoforms on stable transfectants expressing GPIIIa, indicating that DeltaLys(611) directly induces the expression of Oe(a) epitopes. Under nonreducing conditions the Pro(33)DeltaLys(611) variant migrated with a slightly decreased molecular weight compared to the Pro(33)Lys(611) isoform suggesting that DeltaLys(611) has an influence on the disulfide bonds of GPIIIa. The Pro(33)DeltaLys(611) GPIIIa could undergo conformational changes and bind to fibrinogen in a similar manner as the Pro(33)Lys(611) isoform. No difference was found in the tyrosine phosphorylation of pp125(FAK), suggesting that DeltaLys(611) has no effect on integrin function. In contrast to all other low-frequency antigens, the DeltaLys(611) isoform was associated with the HPA-1b, but not with the high frequency HPA-1a allele. Comparison with GPIIIa DNA from nonhuman primates indicated that the HPA-1a allele represents the ancestral form of GPIIIa. It can be assumed that the Oe(a) form did arise as a result of a mutational event from an already mutated GPIIIa allele.

Human Endothelial Cells in Culture and In Vivo Express on Their Surface All Four Components of the Glycoprotein Ib/IX/V Complex

The platelet glycoprotein Ib (GpIb) complex is composed of four polypeptides: the disulfide-linked GpIbα and GpIbβ and the noncovalently associated GpIX and GpV. GpIbα contains binding sites for von Willebrand factor and for thrombin and mediates platelet adhesion to the subendothelium under conditions of high shear stress. We have previously shown the presence of GpIbα and GpIbβ mRNA and protein in cultured human umbilical vein endothelial cells (HUVECs) as well as the presence of GpIbα mRNA and protein in tonsillar endothelium. We, therefore, probed ECs for the presence of the other components of the GpIb/IX/V complex. We have identified the presence of GpIX and GpV mRNA in cultured HUVEC monolayers. The sequence of HUVEC GpIX cDNA was identical to the previously published human erythroleukemia (HEL) cell GpIX cDNA sequence. Two species of GpV mRNA, one of 3 kb and one of 4.4 kb, were found in HUVECs, whereas HEL cells displayed only the 4.4-kb species and the megakaryocytic cell line CHRF-288 contained only the 3-kb species. We previously showed that EC GpIbα protein is identical in molecular weight to platelet GpIbα. HUVEC GpIbβ, in contrast to its platelet counterpart, has a molecular weight of 50 kD and forms a correspondingly larger disulfide-bonded complex with EC GpIbα. The molecular weights of GpIX and GpV were 22 and 88 kD, respectively, identical to the corresponding platelet polypeptides. Furthermore, we have identified all four components of the complex in tonsillar vessels. Using flow cytometry, we have established that all four polypeptides of the GpIb/IX/V complex are expressed on the surface membranes of cultured HUVECs and adult aortic ECs. Furthermore, using two-color fluorescence, we have shown that all ECs expressing GpIbα also express GpIX and GpV on their surface. The ratio of GpIbα:GpIX:GpV is 1:1:0.5, which is identical to the ratio present in platelets. None of the polypeptides of the GpIb complex could be identified on the surface of human smooth muscle cells or lymphocytes. The presence of all members of the GpIb complex in the EC membrane suggests that this complex may play a role in endothelial function in vivo.

Human Endothelial Cells in Culture and In Vivo Express on Their Surface All Four Components of the Glycoprotein Ib/IX/V Complex

The platelet glycoprotein Ib (GpIb) complex is composed of four polypeptides: the disulfide-linked GpIbα and GpIbβ and the noncovalently associated GpIX and GpV. GpIbα contains binding sites for von Willebrand factor and for thrombin and mediates platelet adhesion to the subendothelium under conditions of high shear stress. We have previously shown the presence of GpIbα and GpIbβ mRNA and protein in cultured human umbilical vein endothelial cells (HUVECs) as well as the presence of GpIbα mRNA and protein in tonsillar endothelium. We, therefore, probed ECs for the presence of the other components of the GpIb/IX/V complex. We have identified the presence of GpIX and GpV mRNA in cultured HUVEC monolayers. The sequence of HUVEC GpIX cDNA was identical to the previously published human erythroleukemia (HEL) cell GpIX cDNA sequence. Two species of GpV mRNA, one of 3 kb and one of 4.4 kb, were found in HUVECs, whereas HEL cells displayed only the 4.4-kb species and the megakaryocytic cell line CHRF-288 contained only the 3-kb species. We previously showed that EC GpIbα protein is identical in molecular weight to platelet GpIbα. HUVEC GpIbβ, in contrast to its platelet counterpart, has a molecular weight of 50 kD and forms a correspondingly larger disulfide-bonded complex with EC GpIbα. The molecular weights of GpIX and GpV were 22 and 88 kD, respectively, identical to the corresponding platelet polypeptides. Furthermore, we have identified all four components of the complex in tonsillar vessels. Using flow cytometry, we have established that all four polypeptides of the GpIb/IX/V complex are expressed on the surface membranes of cultured HUVECs and adult aortic ECs. Furthermore, using two-color fluorescence, we have shown that all ECs expressing GpIbα also express GpIX and GpV on their surface. The ratio of GpIbα:GpIX:GpV is 1:1:0.5, which is identical to the ratio present in platelets. None of the polypeptides of the GpIb complex could be identified on the surface of human smooth muscle cells or lymphocytes. The presence of all members of the GpIb complex in the EC membrane suggests that this complex may play a role in endothelial function in vivo.

The phenotype of L-CFU and its correlation with the immunological characteristics of the blast cell population in AML

The membrane phenotype of AML clonogenic cells (L-CFU) was analyzed in 19 AML patients using an in vitro culture technique after a complement-mediated lysis assay employing a panel of six monoclonal antibodies (McAb) -HLA-DR, FMC56 (CD9), FMC27 (CD9), CD14, CD15, CD41a-. Our results show that L-CFU has a heterogeneous but immature phenotype lacking on the expression of differentiation antigens (CD14, CD15, CD41a). In addition, we observed that the L-CFU phenotype is different from that of the whole blast cell population. Interestingly, L-CFU showed a higher expression of HLA-DR antigens with respect to their progeny. Upon analyzing whether the L-CFU phenotype was related to both the morphological and immunological features of AML blast cells, it was observed that, while there is no correlation with the FAB classification, there was a partial relationship between the immunological phenotype of AML blast cells and that of L-CFU. Accordingly, the more immature AML cases showed a more differentiated L-CFU phenotype (HLA-DR+, CD9+, FMC27+) when compared with cases with a more mature blast cell phenotype. These results suggest that those AML cases with a relatively immature myeloblastic phenotype may arise from a progenitor cell that has undergone partial differentiation and that is unable to acquire myeloid differentiation antigens, while those AML cases with mature blast cells might emerge from a very early L-CFU that has the capacity to undergo a greater degree of differentiation.

Long-term treatment results for acute megakaryoblastic leukaemia patients: a multicentre study

The prognosis and long-term results of a group of 57 acute megakaryoblastic leukaemia (M7-AML) patients was analysed from a multicentre perspective. Ages ranged from 4 to 83 years, median 49 years; 30 were males and 27 were females. The median follow-up time was 7 months, range 1-24 months. Early exits occurred in 12 cases, their median age being 71 years. Forty-five patients were treated with combined aggressive chemotherapy (CT) (n = 26) or low-dose cytarabine (LD-AraC) (n = 19). The following results were obtained with combined CT or AraC, respectively. Complete remission (CR) rates were 73% and 84%, 12-month survival (SV) were 37% and 26%, 24-month SV were 12% and 11%, median SV 10 and 4 months, and relapse rates (RR) were 68% and 94%. These differences were not statistically significant. Irrespective of the treatment modality, the results were better for children (n = 10) than for adults (n = 35): RR rates were 90% and 74%, median SV: 7 and 5 months, 12-month SV: 40% and 22%, 24-month SV; 30% and 9%, and RR: 78% and 81%, respectively; these differences also were not statistically significant. In addition, a literature review of 42 patients from 18 previous reports is presented, including seven cases treated with allogeneic bone marrow transplantation (BMT). The best results were obtained with BMT: 12 and 24 month SV was 86% and the RR was 0%. On the above-mentioned basis, we feel that children and young adults with M7-AML should be offered BMT. In patients over 60 years old or not eligible for aggressive chemotherapy or BMT, an interesting possibility would be the use of LD-AraC which allows a high CR rate, followed by a classical consolidation regimen in order to prevent early relapses.

A method for identifying megakaryocytic and erythroid cells by a combined immunocytochemical and cytochemical stain

The effectiveness of immunoperoxidase staining for platelet glycoprotein IIb/IIIa coupled with cytochemical staining for hemoglobin has been evaluated as a dual staining technique for identifying lineage-specific characteristics of the megakaryocytic and erythroid series in cells of the same hemopoietic tissue preparation. A sequence of staining was established which produced a circumferential brown stain around cells of the megakaryocytic series, and a diffuse yellow to orange stain in the cytoplasm of cells of the erythroid series. Each staining reaction possessed a high degree of specificity and sensitivity which enabled the combined stain to provide a convenient means for establishing the megakaryocytic and erythroid nature of individual cells in hematological specimens where classification cannot be achieved with certainty on morphological grounds.

Induced differentiation of K562 leukemia cells: a model for studies of gene expression in early megakaryoblasts

The K562 leukemia cell line has been extensively used in studies of erythroid differentiation but it has been less well appreciated that treatment of K562 cells with the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) leads to loss of their erythroid properties and to acquisition of several megakaryoblastoid characteristics. These include synthesis and surface expression of glycoprotein IIIa, an increase in platelet peroxidase positivity, enhancement of thromboxane A2 receptors, and increased cell volume and DNA ploidy. TPA-treated K562 cells also synthesize and secrete platelet derived growth factor (PDGF), transforming growth factor beta 1 (TGF beta 1), urokinase-plasminogen activator (u-PA) and its specific inhibitor, type 1 plasminogen activator inhibitor (PAI-1). Induction of all these proteins, which have also been found in platelet granules (u-PA on platelet surface receptors) occurs at the level of mRNA accumulation. Therefore, in addition to facilitating studies and cloning of genes specific for erythroid differentiation, the K562 cells offer a tool to approach early steps of megakaryoblast commitment and differentiation. Observations made with the K562 cell line and several other leukemia cell lines co-expressing erythroid and megakaryocyte markers suggest that the erythroid and megakaryocyte lineages diverge from a common bipotent precursor cell.

Leukocytes in the graft bed associated with corneal graft failure. Analysis by immunohistology and actuarial graft survival

Immunohistochemical staining analysis using monoclonal antibodies was performed on 107 recipient corneas removed at graft. There were significantly more infiltrating cells bearing one or more of the leukocyte-common antigen, class II major histocompatibility complex antigens, various myeloid-lineage markers, and a peripheral T cell marker, in the graft beds of those recipients who subsequently lost a corneal graft than there were in the graft beds of those for whom the outcome was successful. The hypothesis that large numbers of leukocytes in the recipient graft bed would be correlated with subsequent graft failure was examined by actuarial graft survival analysis. Recipients whose corneas contained fewer than 50 leukocyte-common antigen-positive cells/mm2 of corneal stroma showed a 3-year actuarial graft survival of 83%, compared with 39% in those whose corneas contained more than 50 such cells/mm2. The corneal leukocyte count was a particularly useful prognostic indicator of outcome in those patients judged clinically to be at risk of graft failure.

Leukaemoid reaction with megakaryocytic features in newborns with Down's syndrome

A leukaemoid reaction was observed in 3 newborns with Down's syndrome. Thrombocytopenia was present in 2, requiring platelets transfusions in 1, and red cell transfusions were necessary in 2 patients. Blast cells characterization by specific monoclonal antibodies showed a prevalence of megakaryoblasts in all 3 cases. This feature was confirmed in 2 of them by the demonstration of platelet peroxidase (PPO) activity under transmission electron microscopy (TEM). A spontaneous remission of the leukaemoid picture was observed after 2-3 months. However, in 1 case a relapse of the myeloproliferative disorder with the same features of the blast cell population was diagnosed after 16 months. Chemotherapy with low-dose Ara-C, started because of a relevant clinical involvement, induced a complete remission.

Philadelphia chromosome positive essential thrombocythemia evolving into lymphoid blast crisis

The Philadelphia chromosome with the classic translocation t(9;22) was detected in all metaphases of a patient with essential thrombocythemia who presented without hematologic signs of chronic myeloid leukemia (CML). After 12 months of treatment with hydroxyurea followed by 6 months of busulfan, the disease transformed into lymphoid blast crisis with the immunophenotype of pre-pre-B cells frequently seen in lymphoid blast crisis of CML. This progression was not associated with karyotypic evolution because lymphoblasts contained only the Philadelphia chromosome. Further clinical course in this patient confirmed the development of a Philadelphia chromosome positive stem cell with predominantly megakaryocytic committment through partially megakaryocytic/lymphoid differentiation to purely lymphoid committment, a previously unreported transformation.

The expression of mature myeloid cell differentiation markers in acute leukemia

Cells from 82 patients with leukemia in acute phase (40 ANLL, 1 AUL, 36 ALL, 5 CGL in blast crisis) were studied for the expression of mature cell markers of the major nonlymphocytic cell lineages (monocytes, granulocytes, erythrocytes and platelets) using monoclonal antibodies. In addition, cells were examined for the presence of HLA-A, B, C antigens, Ia antigens and common ALL antigen, as well as Fc receptors capable of binding murine immunoglobulins. Approximately one-third of ANLL specimens lacked any of the mature-cell differentiation markers studied. These were always in the relatively undifferentiated morphological subgroups (M1 and M2). Some of the specimens in these groups also expressed little or no HLA-A, B, C and/or Ia antigen. Of the lineage-specific MAb, FMC32 and FMC34, which bind to monocytes, and monocytes plus granulocytes respectively, gave the most interesting results. Together with the anti-CALLA antibody J5, they contributed to the differential diagnosis of ANLL and ALL. In addition they detected phenotypic heterogeneity within the FAB types of ANLL, particularly the M1 and M2 groups. Binding of murine IgG2a and IgG3 antibodies, apparently via Fc receptors, was commonly observed with ANLL cells. This is a potentially serious source of "false positives" in studies using murine MAb with human leukemic cells.

Heterogeneity of TdT+, HLA-DR+ acute leukaemia: immunological, immunocytochemical and clinical evidence of lymphoid and myeloid origin

15 cases of acute leukemia (AL) displaying a TdT+, HLA-DR+ phenotype were studied; surface immunoglobulins, T cell markers and the common acute lymphoblastic leukaemia (c-ALL) antigen were negative, as were peroxidase and non-specific esterase cytochemical reactions. All cases were extensively investigated by conventional immunofluorescence (IF) and immunoperoxidase (IP), with a panel of monoclonal antibodies (MoAb), using both light and electron microscopy, and for ultrastructural myeloperoxidase (MPO). 8 cases, which were OKB2+, BA1+, B4+, J5- and BA2- by IF, expressed the J5 antigen in IP. These cases were therefore re-classified as ALL with a weak expression of the C-ALL antigen. The other 7 cases showed an OKB2-, BA1-, B4+, BA2+ phenotype at IF and were also positive for 1 or more anti-myeloid MoAb. These features were confirmed by IP study. 4 patients also presented ultrastructural positivity to MPO. These cases were considered as proliferations of early precursor cells capable of expressing both myeloid and lymphoid features. This study, while demonstrating the heterogeneity of TdT+, HLA-DR+ AL, suggests that the cell origin of many cases may be defined by extensive immunotyping at both IF and IP level. The prognostic and therapeutic implications of these findings are discussed, also in view of the poor prognosis often observed in the more undifferentiated cases of AL.

Expression of the non-T ALL-associated p24 antigen on leukaemic blasts from patients with ANLL

Leukaemic cells from the peripheral blood of 90 patients with acute leukaemia (54 non-lymphocytic (ANLL) 36 lymphocytic (ALL)) have been examined for the presence of the platelet/ALL-associated p24 membrane antigen by indirect immunofluorescence and flow cytometry using monoclonal antibody FMC8. Cells from 28 of the ANLL patients and 24 of the ALL patients expressed the antigen. In many specimens, both ANLL and ALL, blast cell populations were heterogeneous with respect to FMC8 binding. In ANLL, FMC8-positive cells were observed in specimens from a range of morphological subtypes. Proteolytic stripping/resynthesis experiments demonstrated that the antigen was synthesized by ANLL cells, not passively acquired. Immunoprecipitation and electrophoretic analysis of the antigen from NP40 lysates of 125I surface labelled cells from a patient with acute monoblastic leukaemia confirmed that the epitope identified by FMC8 was present on a peptide of the same molecular weight (p24) as that observed on ALL cells.

Surface marker analysis in acute myeloid leukaemia and correlation with FAB classification

The immunological phenotype of blast cells in 102 patients with acute myeloid leukaemia (AML) was analysed with a panel of 20 monoclonal antibodies and the enzyme terminal transferase, and correlated with the FAB classification. Although a partial correlation between these two approaches could be observed, almost every morphological group contained patients from more than one immunological phenotype. The M1 and M5a leukaemias showed the most undifferentiated phenotype, often lacking in specific myelomonocytic antigens. The M3 formed a uniform group defined as My7+, Ia-, FMC8+, a phenotype which was also observed in two cases of the microgranular variant. The granulocytic (CDw15) and monocytic (CDw14) antibodies crossreacted with some M5b and M2 leukaemias, respectively. Compared with M5a, the M5b leukaemias showed a large increase in the expression of CDw14 antigen, confirming the validity of the morphological differentiation. Glycophorin-A was present in four out of five M6 leukaemias. TdT activity was demonstrated in 10% of AML cases, with a higher incidence among the monocytic variants: M4 and M5-. Eleven AML were considered as unclassifiable according to the FAB criteria and in seven of them a megakaryoblastic cell population (GP IIb/IIIa+, GPIb+) was demonstrated; this confirms the need to include the subgroup of megakaryoblastic leukaemias within the AML. Finally, a possible immunological classification for AML is proposed.

A rapid, simple method for leukemia immunophenotyping using air-dried blood and bone marrow smears

This paper describes a modification of the peroxidase technique by which immunophenotyping may be carried out on routinely air-dried blood and bone marrow (BM) smears. The method is simple and quick, requires no special equipment, can be performed on fresh or stored specimens and gives a standard of morphological detail equal to that of routine blood films. With a monoclonal anti-HLA-DR antibody as a prototype, it was possible to demonstrate reliably, the presence of positively and negatively stained cells of appropriate morphological types in the peripheral blood of leukemia patients. Although only about one-third of antibodies tested were effective with the technique, we identified monoclonal antibodies capable of demonstrating myelomonocyte, granulocyte, monocyte, pan-leukocyte, transferrin, platelet, pan-T, 'cALLA plus B cell' and other antigens. However, we have not yet found antibodies able to identify T cell subsets, nor to distinguish 'common' acute lymphoblastic leukemia from its rare B-cell counterpart. With these limitations the method is suitable for routine use alongside cytochemistry in the differential diagnosis of leukemias and lymphomas.

The nature of blast cells in myelodysplastic syndromes evolving to acute leukaemia

The blast cells from nine patients with an overt acute leukaemia following a previous myelodysplastic syndrome (MDS) are analyzed with a panel of monoclonal antibodies as well as by morphological and cytochemical criteria. By integrating the results obtained with these three approaches the leukaemia in 6 patients was assessed as myeloid-granulocytic and/or monocytic-, in two as mixed- megakaryoblastic/myeloid- and in one as lymphoid. A good correlation between morphology, cytochemistry and immunological markers was observed in 7 out of the 9 cases. In three cases a noteworthy percentage of J5+ cells was detected. The exceptional finding of lymphoid as well as megakaryocytic and myeloid transformations suggests that the target cell for these leukaemias could be a pluripotent stem cell.

Immunochemical characterization of a new platelet specific monoclonal antibody and its use to demonstrate the cytoskeletal association of the platelet glycoprotein IIb-IIIa complex

We describe the production and characterization of a monoclonal antibody specific for platelets. This antibody reacts strongly with human and primate platelets, but does not recognise human monocytes, polymorphonuclear leucocytes, lymphocytes, erythrocytes, leukaemic nor fibroblast cell lines, nor rodent platelets. Immunoprecipitation studies using radiolabelled platelet membrane proteins showed that the monoclonal antibody binds to the platelet membrane glycoprotein IIb-IIIa complex. Affinity chromatography using immobilized monoclonal antibody allows purification of the antigen, but also co-purifies the cytoskeletal proteins actin and myosin. Our results demonstrate immunochemically that although the GP IIb-IIIa complex is an external structure, it is connected through the cell membrane to the microfilament system.

Purification and preliminary characterization of the glycoprotein Ib complex in the human platelet membrane

Human platelet glycoprotein Ib (GP Ib) is a major integral membrane protein that has been identified as the platelet-binding site mediating the factor VIII/von Willebrand-factor-dependent adhesion of platelets to vascular subendothelium. Recent evidence suggests that GP Ib is normally complexed with another platelet membrane protein, GP IX. In this study, human platelet plasma membranes were selectively solubilized with a buffer containing 0.1% (v/v) Triton X-100. The GP Ib complex (GP Ib plus GP IX) was purified to homogeneity in approximately 30% yield by immunoaffinity chromatography of the membrane extract using the anti-(glycoprotein Ib complex) murine monoclonal antibody, WM 23, coupled to agarose. GP Ib and GP IX were subsequently isolated as purified components by immunoaffinity chromatography of the GP Ib complex using a second anti-(glycoprotein Ib complex) monoclonal antibody, FMC 25, coupled to agarose. As assessed by dodecyl sulphate/polyacrylamide gel electrophoresis, purified GP Ib was identical to the molecule on intact platelets and had an apparent relative molecular mass of 170 000 under nonreducing conditions and 135 000 (alpha subunit) and 25 000 (beta subunit) under reducing conditions. GP IX had an apparent Mr of 22 000 under both nonreducing and reducing conditions. Purified Gb Ib complex and GP Ib inhibited the ristocetin-mediated, human factor VIII/von Willebrand-factor-dependent and bovine factor VIII/von Willebrand-factor-dependent agglutination of washed human platelets suggesting the proteins had been isolated in functionally active form. GP Ib alpha had a similar amino acid composition to that previously reported for its proteolytic degradation product, glycocalicin. The amino acid compositions of GP Ib beta and GP IX were similar but showed marked differences in the levels of glutamic acid, alanine, histidine and arginine. The N-termini of GP Ib alpha and GP IX were blocked; GP Ib beta had the N-terminal sequence, Ile-Pro-Ala-Pro-. On crossed immunoelectrophoresis, both GP Ib and GP IX were found to occur in the same immunoprecipitin arc(s) whether the platelets had been solubilized in the absence or presence of the calcium-dependent protease inhibitor, leupeptin. Binding studies in platelet-rich plasma indicated a similar number of binding sites (means +/- SD) for three anti-(glycoprotein Ib complex) monoclonal antibodies: AN 51, epitope on GP Ib alpha (22 000 +/- 2700, n = 3), WM 23, epitope on GP Ib alpha (21 000 +/- 3400, n = 3), FMC 25, epitope on GP IX (20 100 +/- 2700, n = 3), and FMC 25 (Fab')2 (27 100 +/- 800, n = 2).(ABSTRACT TRUNCATED AT 400 WORDS)

Murine monoclonal antibodies and human alloantisera specific for HLA inhibit monocyte phagocytosis of anti-D-sensitized human red blood cells

Evidence is presented that monoclonal antibodies (mAb) against some human major histocompatibility complex (MHC) gene products and human sera containing HLA antibodies strongly inhibit immune phagocytosis of anti-D-sensitized red blood cells by human monocytes. w6.32HL, a mAb against a monomorphic class I antigen of high cell surface density, revealed the strongest inhibition among mAb reactive with MHC class I products. mAb with preferential reactivity for monomorphic and polymorphic DR and DQ epitopes (L203, L227, IIIE3, Tü22, Genox 3.53 and IV12) were noninhibitory. Definite inhibition was also apparent with a mAb against DRw52/MT2 (I-LR2) and with an antibody to class II antigens of high cell surface density (2MC3). Human sera containing HLA antibodies showed strong inhibition of immune phagocytosis up to a dilution of 1/1000. This inhibition could not be abrogated by platelet absorption. This indicates that human sera inhibiting immune phagocytosis may comprise at least two types of antibodies: cytotoxic HLA-specific antibodies which may or may not be inhibitory, and inhibitory antibodies against monocytic antigens not necessarily cytotoxic. These latter antibodies may recognize HLA DR or another as yet undefined gene product within, or closely associated to, the human MHC.

Characterization of blast cells in chronic granulocytic leukaemia in transformation, acute myelofibrosis and undifferentiated leukaemia. II. Studies with monoclonal antibodies and terminal transferase

A panel of 19 monoclonal antibodies (McAb) and the enzyme terminal transferase (TdT) have been applied to the characterization of poorly differentiated blasts from 50 patients with chronic granulocytic leukaemia (CGL) and myelofibrosis in blast crisis (BC), acute myelofibrosis and undifferentiated leukaemia. These cells were also extensively studied by transmission electron microscopy (TEM) (see Polli et al, 1985a). McAb against platelet glycoproteins (GP) showed a high specificity for megakaryoblasts, in particular those reactive with the GPIIb/IIIa complex (J15) and GPIIIa (C15 and C17), which were positive in a higher proportion of blasts than the McAb to GPIb (AN51 and FMC25). Findings with these anti-platelet McAb paralleled those of the platelet-peroxidase (PPO) reaction in 76% of cases studied simultaneously. The PPO reaction was always positive in cases in which two or more of the McAb were reactive with the blast cells. The differences observed suggest, nevertheless, that PPO is more sensitive for megakaryoblasts than the McAb and that this TEM technique should be reserved for cases which are negative with the platelet specific McAb. Of the McAb against myeloid antigens used in this series OKM1 was positive in 50% of cases but the others failed to demonstrate early features of differentiation in myeloblasts and monoblasts. In only three cases were erythroid precursors demonstrated by TEM and these were the only ones reactive with a McAb to glycophorin-A (LICR LON/R10). TdT and the McAb J5 helped in the identification of lymphoblasts which were seen as a 'pure' proliferation in 23% of CGL-BC and as part of blast cell mixtures in another 17% of cases. The McAb reactive to haemopoietic precursor cells (RFB1, FMC8 and OKIa), on the other hand, were of no practical value for the classification of blast cell types. The lineage specificity of several of the McAb used in this study, confirmed by TEM, suggest that these reagents are valuable tools for the characterization of immature blast cells.

A monoclonal antibody GR2110 reactive with a P24 antigen present in a subgroup of acute lymphoid leukemias

A monoclonal antibody IgG1K against a P24 antigen has been obtained. This antigen is present on a subgroup of non-T-ALL and platelets. GR2110 monoclonal antibody was produced by immunizing with a CALL (CALLA+, Ia+, IgS-, E-, T3-) This P24 antigen is absent in normal T-lymphocytes, monocytes, mitogen-activated T-cells; weakly expressed on B-cells and granulocytes and negative with several cell lines, except with KM3. GR2110 monoclonal antibody was tested with chronic and acute human leukemias. It was positive only with some CALL, NULL ALL, B-ALL and negative with B-CLL, T-CLL, T-cell lymphoma, Hairy cell leukemia, AML, T-ALL. The immunoprecipitation of 125I-labeled cell membrane with the monoclonal antibody and SDS-PAGE analysis revealed a 24 kD molecular weight polypeptide. The comparison of GR2110 and FMC 8 in capping experiments and cellular reaction patterns, showed that both antibodies react with the same molecule but probably with different epitopes.

Analysis of chemical and biochemical properties of membrane molecules in situ by analytical flow cytometry with monoclonal antibodies

Methods are described for analysing chemical and biochemical properties of membrane antigens against which monoclonal antibodies are available. The methods are based on gentle manipulation of whole viable cells and quantitative flow cytometric fluorescence analysis of the effect of such treatment on monoclonal antibody binding. Proteolytic enzymes, glycosidases, inhibitors of biosynthesis and various mild chemical treatments have been used to derive information on the chemical nature of individual membrane antigens, their insertion in the membrane, and their turnover. The nature of the particular epitope detected by a monoclonal antibody may be probed in a similar way.

Method for the simultaneous labelling of terminal deoxynucleotidyl transferase (TdT) and membrane antigens

A method for the simultaneous labelling of terminal deoxynucleotidyl transferase (TdT) and membrane antigens is described. TdT is visualised in the cell nucleus with the peroxidase-antiperoxidase (PAP) method, and the immunogold method is used in combination with monoclonal antibodies against membrane antigens. The morphology of the labelled cells is well preserved for analysis by light microscopy and the preparations obtained can be kept permanently. This method is useful for the analysis of mixed cell proliferations, particularly in leukaemias.