Influence of Vindesine on the Lytic Phase of Mouse Natural Cytotoxicity Against Human Leukemic Cells

Vindesine (VDS), a structural analogue of Vinca Alkaloids, was found to increase the NK-mediated cytolytic effects of mouse lymphocytes against human K562 target cells in a 18-hr assay. Pretreatment of effector or target cells with the drug did not affect substantially the NK reaction. The phenomenon has been detected using splenocytes of either congenitally a-thymic or conventional euthymic mice of different strains. Effector lymphocytes deprived of cells adherent to plastic surface or to nylon-wool column were still competent for drug-mediated increase of NK function. It is suggested that modification of the membrane make-up of effector or target cells re-versibly induced by VDS, would promote higher NK-mediated cytolytic effects.     

Increase of natural killer (NK) activity of mouse lymphocytes following in vitro treatment with cytosine-arabinoside

The in vitro influence of cytosine-arabinoside (Ara-C) on mouse NK activity was studied treating effector cells, target cells or effector and target mixture with graded concentrations of the drug. Ara-C increased the NK efficiency of mouse splenocytes without enhancing the susceptibility of target cells or the cytolytic events when added to effector-target mixture. This phenomenon was confirmed with splenocytes collected from congenitally athymic (nude) or conventional donors of different ages, untreated or depressed or boosted for NK activity by various agents. In addition Ara-C increased the NK activity of spleen cells of nude mice deprived of nylon-adherent cells, and did not affect suppressor cells capable of inhibiting the lytic phase of NK process. The drug was able to significantly augment the binding ability of spleen cells to the NK-sensitive YAC-1 target. It was concluded that Ara-C would increase the efficiency of natural cytotoxicity presumably through a direct influence on effector lymphocytes.     

Natural killer lymphocytes: "null cells" no more

Natural Killer (NK) lymphocytes were initially described as potent effector cells that, unlike T lymphocytes, were able to kill targets in the absence of a priori stimulation and without specific recognition mechanisms. Over the past ten years however, it has been clearly demonstrated that NK cell function is regulated by a number of surface receptors that bind specific ligands expressed by target cells. Some of these receptors display inhibitory functions and recognize MHC class I molecules expressed by normal autologous cells that, as a consequence, are spared from indiscriminate NK-mediated killing. Other receptors are involved in NK cell activation against allogeneic cells or cells that, upon viral infection or tumor transformation, down-regulate MHC Class I expression. Altogether these data provide important advances toward the understanding of the complexity of the molecular mechanisms that regulate NK-mediated functions.     

C-reactive protein is involved in natural killer cell-mediated lysis but does not mediate effector-target cell recognition.

Anti-CRP and complement treatment of human peripheral blood lymphocytes significantly reduces natural killer (NK) cell-mediated cytotoxicity to K562 target cells as well as to MOLT-4 target cells. Although not all activity is eliminated by treatment of effector cells with antibody and complement, the reduction of NK function indicates that C-reactive protein (CRP) is present on a significant proportion of NK cells. Higher concentrations of anti-CRP or anti-CRP F(ab')2 fragments also reduce NK function; this suggests that CRP is not only present on these effector cells but may also play a role in NK-mediated killing. We initially suspected that CRP-ligand interactions might be involved in effector-target cell recognition. Several lines of evidence suggest that this is not the case. While F(ab')2 anti-CRP will block NK function, Fab anti-CRP will not, suggesting that the NK response is not impaired when surface CRP (S-CRP) is blocked but is only inhibited when the S-CRP is cross-linked and modulated. Neither CRP-C polysaccharide complexes (CRP-CPS) nor concentrations of CPS ranging from 0.1 microgram/ml to 200 micrograms/ml have any effect on NK cell-mediated killing. Treatment of target cells with a ligand for CRP or CRP prior to co-culture with NK effectors does not augment NK function. Single cell assays clearly demonstrate that high concentrations of anti-CRP have no effect on the formation of effector-target cell conjugates. Although these concentrations of anti-CRP do not block effector-target cell conjugation in the single cell assay, they do block the killing of conjugated target cells. In total, this evidence strongly suggests that although CRP appears to be involved in NK-mediated killing, it is not involved in effector-target cell-mediated recognition.     

Laminin inhibits the recognition of tumor target cells by murine natural killer (NK) and natural cytotoxic (NC) lymphocytes.

Tumor cells sensitive to lysis by murine natural killer (NK) or natural cytotoxic (NC) cells were shown to bind laminin. They bound 125I-labeled laminin in a time- and concentration-dependent manner, and binding of the radioactive laminin was inhibited by excess cold laminin. In the presence of laminin, cell-cell aggregation occurred. Murine tumor cells not sensitive to NK/NC-mediated killing bound much less laminin, and laminin did not induce aggregation of these cells. The addition of exogenous laminin to NK or NC cytotoxicity assays reduced target lysis in a dose-related manner. Reduction of lysis was due to an inability of NK/NC cells to bind to the targets. Target cells pretreated with laminin were reduced in their ability to cold-target compete for NK-mediated lysis of untreated target cells. These effects were unique to laminin. The control proteins (fibronectin and thyroglobulin) had no effect on NK activity. Finally, inhibition of cytolytic activity by laminin appeared to be specific for NK/NC cells. Laminin had no effect on cytolysis mediated by alloimmune cytotoxic T lymphocytes regardless of whether the targets did or did not bind laminin.     

Multiple natural killer cell-activating signals are inhibited by major histocompatibility complex class I expression in target cells

Several lines of evidence indicate that major histocompatibility complex class I molecules expressed by target cells can prevent natural killer cell (NK) lysis, possibly by engaging inhibitory receptors expressed by NK cells. On the other hand it is likely that NK cells must be activated to lysis by the recognition of unidentified NK target structures on target cells. To investigate the relationship between positive activation of NK cells by NK target structures versus inhibition by target cell class I molecules, we have examined various NK/target cell interactions for which the expression of inhibitory class I molecules by the target cells is known. The results suggest that specific properties of the target cell other than the absence of class I expression are necessary to activate NK-mediated lysis. Furthermore, different effector cell populations, i.e. freshly isolated versus interleukin-2 activated NK cells, differ in their capacity to kill class I-deficient lymphoblast target cells. In general, class I-deficient target cells that are resistant to direct lysis by a given NK population can be lysed by the NK cells when the reaction is mediated by antibody-dependent cellular cytotoxicity (ADCC). Most significantly, all types of NK-mediated lysis of lymphoblasts, of tumor cells and of almost any target by ADCC can be inhibited by appropriate class I gene expression in the target cell. These results suggest a model in which lysis by NK cells must be triggered by any one of a set of distinct target cell ligands, but that all of these signals can be overruled by class I-mediated inhibition.     

Natural Killer Cells may be the Only Cells in Normal Mouse Lymphoid Cell Populations Endowed with Cytolytic Ability for Antibody-Coated Tumour Target Cells

Mouse normal lymphoid cells were analysed as to their ability to perform in three cytolytic systems: Ability to act as 'natural killer', NK, cells against a NK sensitive tumour target, YAC; as effector cells against IgG-coated 815 cells, or to function as effector cells against IgG-coated CRBC. NK activity and ADCC against the IgG-coated P815 cells were found to vary in parallel as affected by age, organ distribution and genotype of the effector cells. On the other hand, ADCC against CRBC was largely carried out by effector cells distinct from those functioning as NK cells or in ADCC against P815. Temperature pretreatment schedules at 37 degrees C showed both NK cells and ADCC ability against P815 to be highly sensitive on contrast to ADCC against CRBC. Likewise, inoculation of Corynebacterium parvum intraperitoneally will lead to reduction in ADCC ability against CRBC but increase in ADCC against P815 and NK activity. Blocking experiments using 'cold' inhibitor cells in the cytolytic assays indicated that NK cells and effector cells against IgG-coated P815 cells are the very same cells. We thus conclude that NK cells in the mouse also have the ability to express K cell activity against IgG-coated tumour target cells. In fact, our data suggest that the NK cells may be the only cell type in the mouse equipped with cytolytic potential for antibody-coated murine nucleated cells     

Rat natural killer cell and cytotoxic T cell lysis of H-2-negative murine embryonal carcinoma cells

H-2-lacking murine embryonal carcinoma (EC) cells have been proposed as universal targets for natural killer (NK) effectors from different species because their killing appeared to be uncomplicated by potential T cell effector mechanisms (Stern, P. L. et al., Int. J. Cancer 1981. 27:679). While some previous studies had shown that murine cytotoxic T cells were unable to lyse EC cells, rat T killers are shown here to be active against these targets and to be distinguishable from NK cells. Percoll density fractionation of rat peripheral blood lymphocytes enriches in parallel for NK-mediated lysis of both EC or YAC target cells. These NK cells unlike T cells, do not mediate lectin-dependent and cell-mediated cytotoxicity (LDCC) of NK-insensitive target cells. This procedure is thought to reveal the total cytolytic potential of stimulated T cell populations, regardless of specificity. In contrast to previous results with mice, we found that allogeneically primed rat cytotoxic T cells can kill murine EC cells in LDCC and, further, that rat cytotoxic T cells, generated by stimulation with mouse spleen cells in vitro, can lyse murine EC cells directly. This demonstration of T cell lysis of EC cells suggests that either there is a novel mechanism of lysis operating without requirement for major histocompatibility complex (MHC) structures, or EC cells express some hitherto unidentified MHC-like structures on their cell surface.     

The two‐pore domain K2P channel TASK2 drives human NK‐cell proliferation and cytolytic function

Natural killer (NK) cells are a subset of cytotoxic lymphocytes that recognize and kill tumor‐ and virus‐infected cells without prior stimulation. Killing of target cells is a multistep process including adhesion to target cells, formation of an immunological synapse, and polarization and release of cytolytic granules. The role of distinct potassium channels in this orchestrated process is still poorly understood. The current study reveals that in addition to the voltage‐gated K_V1.3 and the calcium‐activated K_Ca3.1 channels, human NK cells also express the two‐pore domain K₂P channel TASK2 (TWIK‐related acid‐sensitive potassium channel). Expression of Task2 varies among NK‐cell subsets and depends on their differentiation and activation state. Despite its different expression in TASK2^highCD56^brightCD16^? and TASK2^lowCD56^dimCD16⁺ NK cells, TASK2 is involved in cytokine‐induced proliferation and cytolytic function of both subsets. TASK2 is crucial for leukocyte functional antigen (LFA‐1) mediated adhesion of both resting and cytokine‐activated NK cells to target cells, an early step in killing of target cells. With regard to the following mechanism, TASK2 plays a role in release of cytotoxic granules by resting, but not IL‐15‐induced NK cells. Taken together, our data exhibit two‐pore potassium channels as important players in NK‐cell activation and effector function.     

Kinetic Analysis of K+ Ion Channel Functio in Lymphokine-Activated Killer (Lak) Cells'

Abstract

K⁺ ion channels of lymphocytes have been implicated in cellular differentiation, activation and cytolytic functions. We previously demonstrated that K⁺ channel blockers modulate lytic activity of CTLs and LAK cells. In the present study, we define and quantitate the inhibitory effects of ion channel blockers on the lytic process using kinetic analysis of lysis. The K⁺ channel blocker, 4-aminopyridine, the neuroendocrine monoamine, serotonin, its agonist, quipazine, and the Ca⁺⁺ dependent K⁺ channel blocker, quinidine were found to non-competitively inhibit the lytic process in a dose-dependent manner. These compounds inhibit lytic activity by causing a decrease in the maximum velocity (Vmax) by which LAK cells lyse tumor targets. These ion channel blockers did not alter effector or target cell viability or the binding of LAK cells to tumor cells. The inhibitory effects occurred at the effector cell level, since pre incubation of LAK effector cells resulted in a dose-dependent decrease in Vmax which was related to a slower rate of target cell lytic programming (k₂) by the LAK effector cells. Modulation of LAK cell lytic function occurs at a post-binding step, perhaps in the generation or release of the lytic signal.     

p40, a novel surface molecule involved in the regulation of the non-major histocompatibility complex-restricted cytolytic activity in humans

Four monoclonal antibodies (mAb) termed NKTA255, NKTA72, 1F1 and 1B1 were selected on the basis of their ability to inhibit the cytolytic activity of natural killer (NK) cell clones against P815 target cells. These mAb selectively reacted with normal or tumor cells of hematopoietic origin and displayed a cellular distribution similar to that of CD45 or CD11a/CD18 antigens. Immunoprecipitation experiments showed that they reacted with molecules with an apparent molecular mass of 40 kDa under both reducing and nonreducing conditions (“p40” molecules), thus differing from CD45 or CD11a/CD18 antigens as well as from the “inhibitory” receptors for HLA class I molecules (i.e. p58, CD94 and NKB1 molecules). Double-immunofluorescence analysis of peripheral blood mononuclear cells allowed the identification of three distinct populations on the basis of the fluorescence intensity of cells stained with anti-p40 mAb. p40^bright cells were homogeneously HLA-DR-positive, p40^medium cells were HLA-DR-negative but co-expressed CD56 antigens, while p40^dull cells were all CD3⁺. Anti-p40 mAb strongly inhibited the lysis of K562 target cells, mediated by fresh NK cells, as well as the lysis of P815 target cells by NK or T cell clones. In addition, in redirected killing assays, anti-p40 mAb strongly reduced the anti-CD16 mAb-induced cytolytic activity of NK cell clones. On the contrary, they did not inhibit either the anti-CD3 or anti-T cell receptor mAb-mediated cytolytic activity of T cell clones or the lysis of allogeneic phytohemagglutinin blasts mediated by specific cytolytic T cell clones. The p40-induced inhibition of the NK cytotoxicity required optimal cross-linking, as anti-p40 mAb could inhibit the lysis of Fcγ receptor (FcγR)-positive but not of FcγR-negative target cells. In addition, (Fab')₂ fragments of anti-p40 mAb failed to inhibit the lysis of FcγR-positive target cells. In conclusion, p40 molecules represent a new type of inhibitory surface molecule that appears to play a general regulatory role in the NK-mediated cytolysis.     

Induction of Natural Killer Cell Activity and Allocytotoxicity in Human Peripheral Blood Lymphocytes after Mixed Lymphocyte Culture

The K-562 tumour cell is a highly susceptible target for natural killer (NK) cell lysis by lymphocytes of human peripheral blood. We have studied the antigenic relationship between the recognition sites for lysis of lymphoid and various tumour target cells by cytolytic T lymphocytes (CTL) and NK cells induced in mixed lymphocyte cultures (MLC). The characteristics of these two effector cell types have also been investigated. It was demonstrated that fresh NK cells lose their NK lytic activity when cultured alone. Cell lines not susceptible to lysis by fresh NK cells are lysed by MLC-induced NK cells. There is no antigenic relationship between the recognition sites for the alloreactive T lymphocytes and MLC-generated NK cells expressed on the lymphoid target cells and the tumour target cells, respectively. The MLC-generated alloreactive T cells and NK cells are not identical. The MLC-generated NK cells are different from the fresh NK cells present in the peripheral blood.     

A Comparative Analysis of Cell Surface Markers on Murine NK Cells and CTL Target-Effector Conjugates

The rosetting of sheep erythrocytes (SRBC) coated with non-haemagglutinating monoclonal antibodies rather than conventional haemagglutinating antisera revealed readily detectable FcR on most splenic natural killer (NK) cells since 76% of splenic lymphocytes forming conjugates with YAC also resetted with SRBC coated with high concentrations of monoclonal anti-SRBC antibody of the IgG2b subclass and since Ficoll depletion or enrichment of splenic lymphocytes rosetting with IgG2b-coated SRBC resulted in a corresponding 4-fold decrease or increase in conjugate-forming cells and a 10-fold decrease or increase in NK cytolytic acttvity. NK cells bound much less readily to monoclonal IgG2a and not at all to monoclonal IgGI or IgM, but the degree of binding was directly proportional to the amount of antibody on the erythrocytes and was not isotype-restricted. In addition, immunofluorescent studies revealed that YAC-1-conjugated lymphocytes were Lyt-1^-, Lyt-2^-, partially Thy-1⁺ (60%), asiato-GMI ⁺ (80%), Qa-4⁺ (77%), Qa-5⁺ (79%), and Ly-5⁺ (94%). In comparison, a proportion (39%) of alloimmune peritoneal exudate cells which conjugated with P815–2 also siained by immunofluorescence with anti-asialo GM1 antisera. Most (>90%) P815- conjugated cells were Thy-1⁺, Lyt-2⁺. and a subpopulation of Lyt-l⁺2⁺ conjugates was observed (25 %). Qa-5 and Ly-5 were also expressed on most (two-thirds) cytolytic T lymphocytes (CTL) conjugates, whereas Qa-4 and FcR for IgG2b were not detected. The best phenotypic distinctions between NK cells and CTL were therefore based on the presence or absence of Lyt-2, Qa-4, and FcR for IgG2b on most effector cells. Anti-asialo-GMl or monoclonal anti-Qa-4 and complement treatment greatly diminished both the frequency of NK conjugates and the percentage of conjugates with detectable IgG2b FcR or asialo-GM1. These results confirm that NK cells co-express asialo-GMI and Fc receptors, at the single-celt level, and provide a simple method for greatly enriching NK populations at least 10-fold.     

Serotonin Modulated CA++ Dependent K+ Channels in Alloimmune Effector Cell Lytic Function

Abstract

Potassium channel activity has been implicated in the lytic function of cloned murine effector T lymphocytes (5) and human NK cells (12) as well as in the initiation of the injury process in tumor cells (23). In the present studies, the effects of various K⁺ channel blockers on the cytolytic function of in vivo derived alloimmune lymphocytes towards P815 tumor cells were evaluated. The classical K⁺ channel blocker 4-aminopyridine (4-AP), the naturally occurring monoamine serotonin (5-hydroxytryptamine, 5-HT) and its agonist, quipazine, as well as the Ca⁺⁺ dependent K⁺ channel blocker quinidine were chosen for investigation based on their known ion channel gating properties. These agents, when present in the assay medium, inhibited in a dose dependent manner the lysis of P815 tumor cells as measured by specific ⁵¹Cr release. Preincubation of effector lymphocytes with the various K⁺ channel blockers resulted in greater inhibition of lysis than did the preincubation of target cells. The 5-HT agonist quipazine was of particular interest in that it inhibited the lytic process with equal effectiveness when continuously present in the assay medium or when the effector cells alone were preincubated. Quinidine was used to investigate whether Ca⁺⁺ dependent K⁺ channels were the predominant ion channel involved in the lytic process. When present during the lytic assay, quinidine was similar to quipazine in terms of their dose range at which they inhibited the lytic process. These results indicate that 5-HT sensitive Ca⁺⁺ dependent K⁺ channels are likely to be involved in the delivery of lytic signal (s) by immune effector lymphocytes and suggests that neuroenocrine products may modulate the functional activity of in vivo derived lymphocytes.     

Involvement of transferrin and transferrin receptors in human natural killer effector:target interaction

In this current study one of the determinants of natural killer cell specificity in immunosurveillance against cancer, may be the recognition of transferrin receptors on neoplastic cells by the NK effectors. Human transferrin, when saturated with iron (FeTf), was found to inhibit human natural killer (NK) activity against K562 tumor cells, if included in assay mixtures at physiologically relevant levels. Whereas both FeTf and iron-free transferrin (ApoTf) inhibited initial conjugate formation at the level of the target cell, only FeTf inhibited NK cytolytic activity, as judged by release of chromium from the targets. This suggested a functional role for FeTf on either NK or tumor cells. When either targets or effector lymphocytes were pre-incubated with FeTf, inhibition of killing was strongest when the targets were first exposed to FeTf. The evidence suggested that NK-associated transferrin mediated the interaction with target cells through free target-associated transferrin receptors. The finding that rabbit anti-human transferrin antibody (RaHTf) inhibited killing, when reacted with effector lymphocytes but not with target cells, supported this hypothesis.     

Suppression of Target Cell Proliferation by Natural Killer Cells

The cytolytic effects of natural killer (NK) cells have been extensively studied in recent years. In the present study we have investigated the cytostatic effects of NK cells. Human peripheral blood lymphocytes from healthy volunteers were used as a source of effector cells, and the cell lines K562, U937, U1285, and Molt-4 were used as target cells. Effector cells were enriched for NK cells using Percoll gradients and depleted of NK cells on Percoll gradients or by using Leu-19 antibodies and magnetic beads. By monitoring cell numbers during co-culture of effector cells and K562, it was found that after an initial phase of cell killing for 3 h target cell numbers remained stable during the following 24-48 h. In a microcytotoxicity assay measuring inhibition of uptake of [3H]thymidine, the four target cell types were shown to have different NK sensitivity; inhibition of greater than or equal to 80% was obtained for K562 and U937 at an effector to target cell (E/T) ratio of 30:1, 50% for U1285, and 30% for Molt-4. This inhibition was shown to be partly a direct effect on DNA synthesis for all cell lines, as incorporation of [3H]thymidine was decreased in cocultured target cells compared with an equal number of target cells alone. Inhibition of DNA synthesis was thus not directly related to cell death and was also observed for the Molt-4 cell line that was not killed. A cell division assay, with target cells in agarose and effector cells in a liquid upper layer, showed a decline in the rate of target cell divisions. Effects on the cell cycle were studied on latent-phase cells. It was shown that effector cells delayed the onset of DNA synthesis. This anti-proliferative effect was observed for several days, but cell growth then gradually resumed. The effector cells were identified as CD56-positive large granular lymphocytes (LGL). Double-layer cultures and experiments using effector cell supernatants demonstrated that the growth-inhibitory effect could be mediated by soluble factors, and the production of such factors was stimulated by exposure to a small proportion of target cells (50:1). Studies with specific antibodies indicated that growth inhibition was not mediated by alpha interferon (IFN-alpha) but it was partly mediated by tumour necrosis factor alpha (TNF-alpha). It is concluded that NK cells have a growth-inhibitory effect that is distinct from the cytolytic effect and this activity is probably mediated by several soluble factors including TNF-alpha.     

An inhibitor of cytotoxic functions produced by CD8+CD57+ T lymphocytes from patients suffering from AIDS and immunosuppressed bone marrow recipients

An inhibitor of the cytotoxic functions (ICF) mediated by human immunodeficiency virus (HIV)- or HLA-specific cytotoxic T lymphocytes, natural killer and lymphokine-activated killer (LAK) cells is secreted by CD8⁺CD57^? T lymphocytes, a subset expanded during infection with HIV and after bone marrow transplantation. We previously showed an apparent molecular mass of 20–30 kDa for this soluble glycosylated concanavalin A-binding inhibitor which is distinct from known cytokines. Here, we report a characterization of the mechanism of action of this CD8⁺CD57⁺ ICF. We show that the ICF-induced inhibition of LAK cell cytolytic activity is transient, with a spontaneous recovery of cytolytic potential after 18 h. When testing interactions of ICF with a large set of cytokines we found that the ICF-mediated inhibition of cytotoxic functions is antagonized by two cytokines: recombinant interleukin (rIL)-4 and recombinant interferon (rIFN)-γ. Finally, we show that ICF acts at the level of cytolytic effector cells, where it induces a significant increase of cyclic AMP (cAMP) level. In contrast, no modification of either cell surface antigen expression or of target/effector cell conjugate formation could be evidenced. Addition of rIL-4 and rIFN-γ reverses such an increase of cAMP levels and in parallel restores the cytolytic activity. Altogether, these data demonstrate that the glycoprotein ICF produced by CD8⁺CD57⁺ cells (1) inhibits cell-mediated cytotoxicity by sensitizing cytolytic effector cells to the cAMP pathway, and (2) is part of a cytokine network controlling cell-mediated cytotoxic functions.     

Identification of NKp80, a novel triggering molecule expressed by human NK cells

The ability of NK cells to kill a wide range of tumor or virally infected target cells as well as normal allogeneic T cell blasts appears to depend upon the concerted action of multiple triggering NK receptors. In this study, using two specific monoclonal antibodies [(mAb) MA152 and LAP171], we identified a triggering NK receptor expressed at the cell surface as a dimer of approximately 80 kDa (NKp80). NKp80 is expressed by virtually all fresh or activated NK cells and by a minor subset of T cells characterized by the CD56 surface antigen. NKp80 surface expression was also detected in all CD3- and in 6 / 10 CD3+ large granular lymphocyte expansions derived from patients with lymphoproliferative disease of granular lymphocytes. In polyclonal NK cells, mAb-mediated cross-linking of NKp80 resulted in induction of cytolytic activity and Ca2+ mobilization. A marked heterogeneity existed in the magnitude of the cytolytic responses of different NK cell clones to anti-NKp80 mAb. This heterogeneity correlated with the surface density of NKp46 molecules expressed by different NK clones. The mAb-mediated masking of NKp80 led to a partial inhibition of the NK-mediated lysis of appropriate allogeneic phytohemagglutinin-induced T cell blasts, while it had no effect on the lysis of different tumor target cells, including T cell leukemia cells. These data suggest that NKp80 recognizes a ligand on normal T cells that may be down-regulated during tumor transformation. Molecular cloning of the cDNA coding for NKp80 revealed a type II transmembrane molecule of 231 amino acids identical to the putative protein encoded by a recently identified cDNA termed KLRF1.     

Cytolytic effector function is present in resting peripheral T lymphocytes.

Antigen-specific cytotoxic killer lymphocytes (CTLs) represent one of the major effector functions of the immune system. It is well established that, as a consequence of TCR recognition of the antigen-bearing target cell, resting T lymphocytes develop into fully active antigen-specific CTLs. In contrast, natural killer (NK) cells are immediately lytic upon contact with an appropriate target cell. The lytic machinery of CTLs and NK cells is thought to include the contents of their cytoplasmic granules, in particular the pore-forming protein perforin. Here we report direct cytolytic activity by resting peripheral CD3+CD8+ T cells as a result of TCR-CD3 binding to the target cell; the murine OKT3 hybridoma (anti-human CD3) was used as a target. The cytotoxicity was more pronounced in the CD8+CD45RO+ population, which contains 'memory' T cells, than in the reciprocal CD8+CD45RA+ subset; CD8+CD4- mature thymocytes were non-cytotoxic. The cytolytic potential of these populations correlated with the presence or absence of perforin. The results demonstrate that the cytolytic machinery of T cells develops post-thymically and can be immediately triggered by TCR-CD3 stimulation.     

Augmentation of Cytotoxicity by Splenic Cells of Pregnant or Human Chorionic Gonadotropin-Treated Normal Mice

Abstract

The natural killer (NK) activity, of an allogeneic tumor system, was found to be enhanced by the total splenic population of either pregnant or normal female BALB/c mice treated with human chorionic gonadotropin (HCG). The splenic population of the early pregnant (9-10 days) mice resulted in a statistically significant increase in NK activity over nonpregnant controls at all effector/ target ratios tested. The mid (12-13 days) and the late (15-16 days) pregnant groups also significantly enhanced NK activity above control values at effector/target ratios of 100:1, 50:1 and 25:1. The i.v. administration of carrageenan into pregnant mice abolished the increased NK activity suggesting a putative role for the macrophage in this system. HCG administered to normal female BALB/c mice resulted in enhanced NK activity similar to that seen for the pregnant mice. This augmented NK activity does not appear to be effected by either the number or the timing of HCG administration. The augmentation of NK activity of HCG treated mice was also detected in a syngeneic system utilizing ₅₁Cr labeled M109 tumor target cells and BALB/c effector cells.