Bice Perussia

Immune interferon: a pleiotropic lymphokine with multiple effects

Immune (gamma) interferon (IFN-γ) is produced during an immune response by antigen-specific T cells and probably also by natural killer (NK) cells recruited by the T cell-product interleukin 2 (IL-2). IFN-γ was discovered and originally measured on the basis of its anti-viral activity, but its complex anti-cellular activities probably reflect its biological role more clearly. In this review, Giorgio Trinchieri and Bice Perussia discuss some aspects of the biology of IFN-γ, its pleiomorphic anti-cellular effects and its ability to modulate cellular responses to other regulatory factors.

Antibody-dependent cytotoxicity mediated by natural killer cells is enhanced by castanospermine-induced alterations of IgG glycosylation.

Inhibitors of glycosylation and carbohydrate processing were used to probe the functional consequences of specific, differential alterations in glycosylation of monoclonal IgG secreted by hybridoma clones. Neither the absence of glycosylation nor the presence of atypical oligosaccharides significantly influenced binding of the monoclonal antibody to the cell surface antigen recognized. However, lymphocyte-mediated antibody-dependent cytotoxicity was enhanced significantly, as compared to native (unmodified) IgG-sensitized target cells, when target cells were sensitized with IgG bearing the atypical oligosaccharides induced metabolically by castanospermine, N-methyldeoxynojirimycin, deoxymannojirimycin or monesin, but not by swainsonine. The enhanced cytotoxicity was mediated by natural killer cells but not by monocytes or interferon-activated polymorphonuclear leukocytes. By contrast, antibody-dependent cytotoxicity mediated by activated polymorphonuclear leukocytes against target cells sensitized with the IgG glycosylation phenotypes induced by swainsonine and tunicamycin, but not by castanospermine, was decreased in comparison to cytotoxicity against target cells sensitized with native IgG. The enhanced lymphocyte-mediated cytotoxicity was Fc receptor-dependent. A panel of monoclonal antibodies directed against different human tumor target cells was used to demonstrate that the castanospermine-induced IgG phenotype generally enhanced antibody-dependent tumoricidal activity mediated by natural killer cells. However, differences in lymphocyte response to an alteration in IgG glycosylation were observed.

Binding of platelets to human monocytes: A source of artifacts in the study of the specificity of antileukocyte antibodies

A serious and often ignored source of artifacts when testing the specificity of antibodies is the contamination of leukocyte preparations with platelets which subsequently adhere to monocytes. The presence of Ca2+ chelating agents or acetylsalicylic acid in the washing buffers inhibits adhesion of platelets to monocytes, thus permitting an accurate distinction among antibodies that are specific for monocytes, platelets or both. The analysis of the specificity of various new or recently described monoclonal antibodies reactive with these cell types is reported here.

Regulation of hematopoiesis by T lymphocytes and natural killer cells

T lymphocytes and natural killer (NK) cells exert both stimulatory and suppressive effects that regulate growth and differentiation of hematopoietic cells. Activated T and NK cells have been demonstrated in different pathological states of bone marrow failure and are proposed to play a role in the pathogenesis of the disease. T and NK cells have also been shown to be responsible for bone marrow graft rejection in both allogeneic and syngeneic donor/recipient combinations. Lymphocytes can regulate hematopoietic cell growth by direct cellular contact or by releasing soluble factors, such as colony-stimulating factors, immune interferon, lymphotoxin, and tumor necrosis factor, active on hematopoietic precursor cells.

Differential susceptibility of type III erythrocytes of paroxysmal nocturnal hemoglobinuria to lysis mediated by complement and perforin

Previous reports have suggested that a 65 kDa membrane protein, termed homologous restriction factor (HRF), in addition to protecting erythrocytes (E) against lysis by homologous complement (C), may also be involved in protecting cytolytic lymphocytes against lysis mediated by a pore-forming protein (PFP/perforin), one of their own lytic mediators. Here, we used HRF-deficient type III E of patients with paroxysmal nocturnal hemoglobinuria (PNH) to study their susceptibility to lysis mediated by homologous C and perforin, and compared it with lysis of HRF-bearing control or PNH type I E. We show that type III E of PNH patients are indeed more susceptible to lysis mediated by homologous C than control or type I E, but they are as susceptible to perforin-mediated lysis as type I E. In addition, all human E (type I or III) tested here are equally susceptible to lysis mediated by either human (homologous) or murine (heterologous) perforin. By immunoblot analysis, we confirm that type III E, in contrast to type I E, were deficient in the 65 kDa HRF. These results support the notion that homologous species restriction is seen in the C- but not in the lymphocyte perforin-system and argue against an active participation of HRF in protecting cells from perforin-mediated lysis.

PHENOTYPIC CHARACTERIZATION OF HUMAN NATURAL KILLER AND ANTIBODY-DEPENDENT KILLER CELLS AS AN HOMOGENEOUS AND DISCRETE CELL SUBSET

Publisher Summary This chapter focuses on phenotypic characterization of human natural killer (NK) and antibody-dependent killer (K) cells as a homogeneous and discrete cell subset. NK cells have been identified until now along with null lymphocytes (non-B, non-T) characterized by the presence of surface receptors for the Fc fragment of IgG (IgG-FcR) and, on a proportion of them, of receptors for sheep erythrocytes. The NK cell can be morphologically identified as a large granular lymphocyte (LGL). Antibody-dependent killer cells bear the same surface receptors and have the same morphology as NK cells. In this study, a panel of monoclonal antibodies was used to examine the antigenic characteristics of NK and K cells. The reactivity of monoclonal antibodies with NK and K cells was analyzed using three methods. The results suggest that eighty to ninety percent of the cytotoxic effector cells express the antigen recognized by either OKT11A or OKM1/B43.4, and the majority of them express both antigens. The lack of one of the two antigens in some cytotoxic cells is more likely because of a quantitative heterogeneity in the distribution of the markers in a single subpopulation, than to the existence of NK cell subsets.

Regulation of Activation and Proliferation of Human Natural Killer Cells

Human peripheral blood lymphocytes from all healthy donors are able to lyse in vitro a variety of target cells, including normal, tumor-derived and virus-infected cells, in the absence of previous sensitization against target cell antigens (1). Although lymphocytes from different donors show a large variability in their cytotoxic ability, the rank of cytotoxicity against different target cell lines depends on the susceptibility of the cell lines to the cytotoxic cells and not on the individual variations among lymphocyte donors. Unlike specific cytotoxicity mediated by cytotoxic T cells, this natural cytotoxicity is not restricted by antigens of the major histocompatibility complex (HMC). The human target cell line most used as a target, the myeloerythro leukemic K562 line, expresses neither class I nor class II MHC antigens. The effector cells responsible for this spontaneous cytotoxicity have been defined natural killer (NK) cells and morphologically identified as large granular lymphocytes (LGL). LGL are light density medium- to large-sized lymphocytes characterized by abundant cytoplasm, indented nucleus and few distinct azurophilic granules (2). Separation of lymphocytes on Percoli gradients has been extensively used to obtain enriched preparations of LGL (3). Although this technique was instrumental for much of our advanced knowledge of NK cell biology. LGL preparations obtained with Percoli gradients are not pure NK cells and the contaminant cell types, even if present in a low proportion, have often been responsible for artifactual results and erroneous attributions of functions to NK cells.

Control of Hematopoietic Progenitor Cells by Natural Killer Cells

In adult animals and in physiological conditions, hematopoiesis occurs only in the bone marrow and in lymphoid organs, and it is not observed in organs such as liver or spleen, sites of fetal hematopoiesis. Precursor cells committed to erythroid and myeloid hematopoietic lineages originate from pluripotent stem cells and, through several cycles of cell division, give rise to terminally differentiated cells.(1) The entire process of hematopoiesis is regulated by the equilibrium between the self-renewal capability of the stem cell and the commitment to differentiate along one or more hematopoietic lineages. The maintenance of this equilibrium underlies the hematopoietic homeostasis necessary for the continuous production of the different types of hematopoietic cells required in physiological conditions. The regulation of hematopoiesis is also sufficiently flexible to enable hematopoietic organs to respond effectively to pathological situations (e.g., during bleeding or infections) requiring a rapidly increased production of a particular blood cell type.

Fc Receptor-Ligand Interaction Induces Activation of Human Natural Killer Cells

Interaction of NK cells with Sepharose-linked anti-Fc receptor (FcR, CD16 antigen) antibodies inhibits their ability to mediate both spontaneous and antibody-dependent cytotoxicity, whereas bivalent anti-CD16 antibodies enhance spontaneous cytotoxicity. Treatment of cultured NK cells with Sepharose-linked anti-CD16 antibodies induces expression of IL-2 and transferrin (Tf) receptors and of 4F2 antigens and this effect is enhanced in the presence of IL-2 during treatment. Analogously, treatment of NK cells with the anti-CD16 antibodies or immune complexes synergizes with IL-2 in inducing production of IFNγ and TNF. The combined treatment of NK cells with IL-2 and anti-CD16 antibodies induces cytoplasmic accumulation of mRNA transcripts for IL-2R and for the two lymphokines. Nuclear run-on experiments show that gene transcription is induced by the two stimuli. These data indicate that FcR are specialized molecules on NK cell surface that mediate signal transduction upon ligand binding. These effects may be similar to those induced in NK cells upon target cell recognition.