A cloned cell with NK function resembles basophils by ultrastructure and expresses IgE receptors

Natural killer (NK) cells are defined by their ability to lyse certain tumour cells in vitro without previous exposure to them, and have been postulated as effectors of immune surveillance against spontaneous neoplasms. Because they kill some non-neoplastic lymphoid cells, they may also have a role in immunoregulation. NK cell activity resides in a small proportion of normal mouse spleen cells (less than 5%) that have been difficult to characterize completely. They may represent a heterogeneous group of effector cells whose precise relationship to other myelopoietic or immunological cells has remained obscure. We have previously described a cloned mouse cell line (Cl. Ly 1-2-NK-1+/11) with the functional characteristics of natural killer cells activated by interferon or other factors. We now find that this cloned line, like basophils and mast cells, expresses high-affinity plasma membrane receptors (Fc epsilon R) specific for IgE antibody. In addition, the clone contains cytoplasmic granules similar by ultrastructure to those of basophils of the mouse and other species. Our findings indicate that cells sharing morphological and biochemical features of basophilic granulocytes can mediate NK lysis.

[Production of secondary T-killers]

Restimulation of lymphocytes on the 8th day of mixed lymphocyte culture (MLC) and cultivation on the monolayer of syngeneic macrophages are accompanied by an increase in the DNA synthesis, which rises negligibly within the first 24 hours, reaches maximum after 48 hours and then drops. After reexposition with alloantigen lytic activity of lymphocytes reaches the level of initial culture within the first 24 hours and in the 48-72 hours following increases 2-4-fold. On the 11th-12th days of MLC secondary T-killers transform to medium-size and small lymphocytes whose cytoplasm shows the signs of activation of the secretory apparatus on interaction with target-cells. It is assumed that secondary antigenic stimulus in vitro induces the differentiation of T-killers that correspond with immune lymphocytes isolated after immunization in vivo.

Direct analysis of individual killer T cells: susceptibility of target cells to lysis and secretion of hydrolytic enzymes by CTL

Direct identification, enumeration and biological characterization of cytolytic T lymphocytes (CTL) complementing the chromium release test had allowed us to propose a mechanism for T-cell mediated cytotoxicity (T-CMC). One CTL without accessory cells is able to lyse a specific target. Binding which allows cell contact (E-T doublets), should activate effector CTLs and render target cells susceptible to lysis. Secretion of hydrolytic enzymes localized at the CTL-target junction accounts for the lethal hit given by CTLs to susceptible targets. This hypothesis that the resulting cell lesion is identified with an alteration of the lipid bilayer membrane had been confirmed by single killer cell study. Furthermore, we have proposed that phospholipase enzymes are involved in the membrane alterations, since susceptible targets bound to effector cells (conjugates) were lysed in a much higher yield in the presence of phospholipase. Membrane cell lesion determined by hydrolytic enzyme (phospholipase) could represent a basic general mechanism for other cellular or molecular mediated processes.

The nature of piecemeal necrosis in chronic active hepatitis

On the basis of histological studies, it is proposed that the type of liver-cell death in piecemeal necrosis is apoptosis. The characteristic inconspicuousness of apoptosis explains why the mode of hepatocyte elimination in piecemeal necrosis has hitherto remained obscure. Cell-mediated immune attack induces apoptosis, not classical necrosis, and the occurrence of apoptosis in piecemeal necrosis links the observed morphological changes in chronic active hepatitis with the other evidence for an autoimmune pathogenesis. It is significant that apoptosis does not evoke inflammation or fibroplasia. In attempting to elucidate the cause of the fibrosis that accompanies progression to cirrhosis in chronic hepatitis, it may thus be more relevant to study the effect on fibroblasts of substances liberated during lymphocyte-hepatocyte interactions than the death of the hepatocytes.

The mechanism of K-cell (antibody-dependent) mediated cytotoxicity. III. The ultrastructure of K cell projections and their possible role in target cell killing

The cytotoxic interaction between lymphoid K cells from normal rat spleen and antibody-coated P815 mastocytoma cells has been studied in conditions under which the number of cytolytic events occurring at the time of observation was at a maximum. Electron micrographs of material fixed during the first 15 min after contact between the target and effector cells had been initiated by centrifugation showed that the K cells produce long projections which push deeply into the P815 cells, causing infoldings of the plasma membrane and distortion of the nucleus. The plasma membranes of the effector and target cells, and the nuclear membrane, remain intact. Subsequently the target cells undergo violent cytoplasmic blebbing (zeiosis) which is the first stage of cell lysis. The evidence for the hypothesis that projections from lymphoid K cells develop as a result of contact between receptors on the K cell surface and antibody bound to the target cell, and that the projections are involved in the cytotoxic mechanism is discussed.

[Is the process of localized lysosomal exocytosis responsible for the cytolytic action of killer T-lymphocytes?]

In this paper, we formulate the hypothesis that in the process of target cell lysis a lysosomal enzyme regurgitation, performed by killer cells at the level of the target effector junction, accounts for the target lesion which precedes the lysis (lethal hit). This process of exocytosis, similar to the one described previously in polymorphonuclear neutrophils is supported by cytological studies performed directly on identified killers isolated by micromanipulation. Light and electron microscopy observations confirm a previous report which describes the effector cells rich in lysosomal bodies. In addition, when a killer cell is associated with a target cell to form a conjugate, lysosomes are concentrated near the cell junction and, after incubation at 37 degrees C, acid phosphatases may be detected at the junction. Lysosomal enzyme exocytosis explains why target lysis needs an effector target binding to occur and also the other conditions required for any exocytosis process such as Ca++ in the medium, integrity of the microtubular apparatus, a low level of cyclic AMP and energy dependancy.

Human peripheral Nullymphocytes: ultrastructural aspects of the "K" cell effect against a melanoma target cell

A null cell fraction was isolated from human peripheral blood by Ficoll density gradient centrifugation followed by removal of mononuclear phagocytes, passage through Ig-antiIg columns and sedimentation of E-rosette forming T cells. In contrast to the T cell fraction in the Null cell population exhibited cytotoxic activity against antibody-sensitized human melanoma target cells (ADCC reaction). This activity could be attributed to a low affinity Fc-receptor bearing cells present in the Null cell preparation. At the ultrastructural level in 2 h ADCC reaction most tumor cells were surrounded by up to 10 lymphoid cells which showed narrow junctions with parallel plasma membranes and local evaginations of lymphoid cells into recessus of the target melanoma cells. The mononuclear cell type found in close contact with the antibody-sensitized target cells had the following morphological criteria: 8 to 10 mu diameter, irregular nucleus, discrete rough endoplasmic reticulum, isolated ribosomes, cytoplasmic organelles concentrated under a ruffling membrane in the contact area with the tumor cell.