ABSTRACT
Malignant B cells from chronic lymphocytic leukemia (B-CLL) patients have a long survival in vivo, although, in culture, they spontaneously die by apoptosis. Here, we analyzed the capacity of accessory leukocytes to modulate apoptosis of B-CLL cells in vitro. To this end, we performed long-term cultures using total mononuclear cells (TMC) from B-CLL patients and TMC depleted from monocytes, NK cells and T lymphocytes (B-CLL cells). In all the patients studied (n = 25) the presence of accessory leukocytes markedly prolonged the survival of B-CLL cells. The anti-apoptotic effect was exerted by monocytes and, to a lesser degree, NK cells, partially through the release of soluble factors. Indeed, accessory leukocytes separated from leukemic cells by semipermeable membranes were still able to prolong B-CLL cell survival. By flow cytometric analysis we found that the protective effect of non-malignant cells was associated with delayed down-regulation of Bcl-2 expression on leukemic cells. By contrast, the expression of Fas and Fas ligand proteins was unchanged in most samples. Our findings suggest that monocytes and NK cells, by delaying leukemic cell apoptosis, may play a role in B-CLL cell accumulation in vivo.
Subject(s)
Apoptosis/drug effects , Leukemia, Lymphocytic, Chronic, B-Cell/pathology , Leukocytes, Mononuclear/physiology , Aged , Aged, 80 and over , B-Lymphocytes/drug effects , B-Lymphocytes/pathology , Biological Factors/metabolism , Biological Factors/pharmacology , Cell Communication , Coculture Techniques , Down-Regulation , Fas Ligand Protein , Humans , Killer Cells, Natural/metabolism , Killer Cells, Natural/physiology , Leukemia, Lymphocytic, Chronic, B-Cell/blood , Leukemia, Lymphocytic, Chronic, B-Cell/etiology , Leukocytes, Mononuclear/metabolism , Membrane Glycoproteins/biosynthesis , Middle Aged , Monocytes/metabolism , Monocytes/physiology , Proto-Oncogene Proteins c-bcl-2/metabolism , fas Receptor/biosynthesisABSTRACT
In the present study we examined the effect of immune complexes (IC) on the survival of chronic lymphocytic leukaemia (B-CLL) B cells. Our results showed that either precipitating IC (pIC), Ab-coated erythrocytes (E-IgG) or heat-aggregated IgG (aIgG) significantly inhibited spontaneous apoptosis of B-CLL cells, as well as that induced by fludarabine, chlorambucil or dexamethasone. After depletion of T lymphocytes, monocytes and NK cells, incubation with IC was no longer able to delay B-CLL cells apoptosis, suggesting that prevention of apoptosis depends on IC interaction with accessory leucocytes. The release of IFNgamma by non-malignant cells upon activation with IC was responsible, to some extent, for IC effects as shown by the fact that neutralizing anti-IFNgamma MoAb partially prevented their ability to inhibit B-CLL cells apoptosis. The observation that treatment with IC resulted in increased expression of HLA-DR on B-CLL cells suggests that inhibition of apoptosis is associated with cellular activation.
