Relationship between bacterial binding to lymphocytes and clinical features in chronic lymphocytic leukemia

Interaction of Fusobacterium nucleatum 191 with human peripheral blood lymphocytes

Fusobacterium nucleatum is frequently isolated in high numbers from the subgingival plaque of patients with periodontal diseases. Adherence of these bacteria to several host tissues is lectin-like in that it is inhibited by galactose, lactose, and N-acetyl-galactosamine. Since F. nucleatum has the capacity to activate human peripheral blood lymphocytes, the purpose of this study was to determine whether F. nucleatum adheres to lymphocytes and, if so, to determine whether lectin-like interactions facilitate lymphocyte activation. Adherence of F. nucleatum strain 191 to lymphocytes was confirmed by agglutination assays, scanning electron microscopy, and by using fluorescein- or [3H]-labeled bacteria. Saturation of adherence was reached at about 35 bacteria per lymphocyte. F. nucleatum adhered to greater than 90% of the lymphocytes, and adhered in higher numbers to B cell-enriched subpopulations than to T cell-enriched subpopulations. Adherence was inhibited by N-acetyl-galactosamine, lactose greater than galactose, alpha- and beta-methyl galactoside, but not by 100 mM glucose, mannose, N-acetyl-glucosamine, or other sugars tested. Lymphocytes underwent mitogenesis when preincubated with bacteria and washed to remove weakly adherent and non-adherent bacteria. Mitogenesis induced by low concentrations of F. nucleatum was reduced, but not completely eliminated, by N-acetyl-galactosamine. However, N-acetyl-galactosamine had no effect on mitogenesis induced by preincubation with high concentrations of bacteria. These results suggest that adherence of F. nucleatum facilitates activation of lymphocytes, particularly at low concentrations of bacteria.

Characterization and biological implications of membrane lectins in tumor, lymphoid and myeloid cells

Complex carbohydrates and sugar receptors at the surface of eukaryotic cells are involved in recognition phenomena. Membrane lectins have been characterized, using biochemical, biological and cytological methods. Their biological activities have been assessed using labeled glycoproteins or neoglycoproteins. Specific glycoproteins or neoglycoproteins have been used to inhibit their binding capacity in both in vitro and in vivo experiments. In adults, lymphoid and myeloid cells as well as tumor cells grow in a given organ and eventually migrate and home in another organ; these phenomena are known as the homing process or metastasis, respectively. In specific cases, membrane lectins of endothelial cells recognize cell surface glycoconjugates of lymphocytes or tumor cells, while membrane lectins of lymphocytes and of tumor cells recognize glycoconjugates of extracellular matrices or of non-migrating cells. Therefore, membrane lectins are involved in cell-cell recognition phenomena. Membrane lectins are also involved in endocytosis and intracellular traffic of glycoconjugates. This property has been demonstrated not only in hepatocytes, fibroblasts, macrophages and histiocytes but also in tumor cells, monocytes, thyrocytes, etc. Upon endocytosis, membrane lectins are present in endosomes, whose luminal pH rapidly decreases. In cells such as tumor cells or macrophages, endosomes fuse with lysosomes; it is therefore possible to target cytotoxic drugs or activators, by binding them to specific glycoconjugates or neoglycoproteins through a linkage specifically hydrolyzed by lysosomal enzymes. In cells such as monocytes, the delivery of glycoconjugates to lysosomes is not active; in this case, it would be preferable to use an acid-labile linkage. Cell surface membrane lectins are developmentally regulated; they are present at given stages of differentiation and of malignant transformation. Cell surface membrane lectins usually bind glycoconjugates at neutral pH but not in acidic medium: their ligand is released in acidic specialized organelles; the internalized ligand may be then delivered into lysosomes, while the membrane lectin is recycled. Some membrane lectins, however, do bind their ligand in relatively acidic medium as in the case of thyrocytes. The presence of cell surface membrane lectins which recognize specific sugar moieties opens the way to interesting applications: for instance, isolation of cell subpopulations such as human suppressor T cells, targeting of anti-tumor or anti-viral drugs, targeting of immunomodulators or biological response modifiers.

Fluorescent bacterial rosetting of lymphocyte subpopulations. II. Identification of human lymphocyte subpopulations

In a previous study, fluorochrome-labelled bacteria were found to be a very objective tool to investigate human lymphocyte heterogeneity with regard to bacterial rosette formation. The application of these assay systems (mono-, double- and anti-Ig/bacterial rosetting test) to identify lymphocyte subpopulations is given.

Binding of bacteria from the genus Brucella to human B lymphocytes

In previous studies, we have shown that various lymphocyte subpopulations bind different strains of bacteria of different genera and species. Among these bacteria was a strain of Brucella melitensis which bound to all human B lymphocytes. To determine whether the binding of B. melitensis to human B lymphocytes was strain, species, or genus characteristic, we tested the binding of B. melitensis, Brucella abortus, Brucella ovis, Brucella suis, Brucella canis and Brucella neotomae to human normal and leukemic B lymphocytes. The binding of different Brucella species to B lymphocytes was determined by single- and double-labeling experiments in which a strain of Escherichia coli, coated with anti-light chain antibodies, was used as a marker for B cells. As in previous experiments, we found that B. melitensis and antibody-coated E. coli bound to the same cells. Also, we found that all the other species of bacteria tested bound to the B lymphocytes, normal or leukemic. B. ovis and B. neotomae, which are not human pathogens, bound to fewer B lymphocytes than did the human pathogens B. abortus, B. melitensis, B. suis, and B. canis. Furthermore, we found that the quality of rosettes formed by the nonpathogenic bacteria with the lymphocytes, i.e., the number of bacteria per lymphocytes, was lower than that of pathogenic Brucella species. We conclude that all of the Brucella species tested have the ability to bind to human B lymphocytes, but that only those which are human pathogens bind firmly to all B lymphocytes and may be used as reliable markers for these cells. We also suggest that the binding of Brucella species to B lymphocytes may have some bearing on the pathogenesis of brucellosis in humans.

The use of bacteria as markers of leukemic lymphocytes and for the isolation of natural killer cells

Human lymphocyte subpopulations as well as leukemic lymphocytes can be identified and enumerated in blood smears by using bacteria that bind spontaneously to lymphocytes or by using bacteria to which antibodies are chemically coupled. The mechanism of natural binding of bacteria to lymphocytes was shown to involve a lectin on the lymphocyte surface and a carbohydrate on the bacteria. Also, we found that natural killer (NK) cells can be separated by negative selection using monolayers of bacteria. A subpopulation of T cells, identified by their binding of B. globigii, was shown to be suppressors for NK cells.