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Several monoclonal antibodies (MAbs) directed to blood group P1 (Gal alpha 1-4Gal beta 1-4GlcNAc beta-O) and Pk (Gal alpha 1-4Gal beta 1-4Glc beta-O) determinants were produced with high efficiency by using synthetic neoglycoproteins as immunogens. The specificity of IgM and IgG1 MAbs was characterized by binding to defined oligosaccharides and glycoconjugates. Antibodies that bound equally well to P1 and Pk determinants and to Gal alpha 1-4Gal beta 1-O-derivatives were obtained, together with others that showed selective recognition of the entire trisaccharide chain. Selected antibodies were shown to be useful as reagents for detection of the blood group P antigens in glycolipid extracts of erythrocytes and on the surface of erythrocytes of different P phenotypes, demonstrated both by radioimmune assays and hemagglutination. Six IgM MAbs directed to the Pk determinant bound selectively to Burkitt lymphoma cells and 2 of these antibodies (424/3D9 and 424/6A2) could be used as auxiliary reagents in immunofluorescence for diagnosis and classification of B-cell lymphomas and leukemias using flow cytometric analysis. Eight normal individuals and 37 patients with lymphoma or leukemia were studied. Tumor cells of 2/2 patients with "Burkitt-like" lymphoma, 1 patient with centroblastic lymphoma and 2 patients with acute leukemia were strongly stained for the Pk antigen. The staining patterns for differentiation markers classified the tumor cells to a developmental stage closely related to the Burkitt cell type.