Lytic Function Research Articles

Transforming growth factor beta 1 costimulated growth and regulatory function of staphylococcal enterotoxin B-responsive CD8+ T cells.

Transforming growth factor beta (TGF-beta) exhibits diverse effects on growth and differentiation of a wide range of cell types. In the immune system, TGF-beta 1 is a potent inhibitor of T cell proliferation and certain T cell effector functions. However, TGF-beta 1 also enhances growth of T cells, predominantly of naive phenotype, and induces their expression of selected cytokines. We have previously demonstrated that TGF-beta 1 costimulates growth of highly purified murine CD8+ T cells activated by immobilized anti-CD3 Ab. TGF-beta 1-costimulated CD8+ T cells rapidly express a memory phenotype, lose lytic function, and express a mixed cytokine pattern with IL-2, IFN-gamma, and appreciable IL-10, as well as TGF-beta 1. The present work examines the possibility that TGF-beta 1 similarly costimulates response of murine CD8+ T cells to the microbial superantigen staphylococcal enterotoxin B (SEB) and characterizes their effector and regulatory functions. TGF-beta 1 significantly enhances CD8+ T cell proliferation to SEB in the presence of MHC class II-positive APC and TGF-beta 1-primed CD8+ T cells are enriched for SEB-reactive V beta 8+ TCR expression. TGF-beta 1 priming also up-regulates a memory-like CD45RBlowCD44highMEL-14low phenotype. TGF-beta 1 priming inhibits development of SEB-specific lytic effector function by more than 90%. However, TGF-beta 1-primed CD8+ effector T cells express elevated levels of IL-10 and TGF-beta 1, variable IFN-gamma, and undetectable IL-4. Additionally, they exhibit growth inhibitory effector function of SEB-induced proliferation of other CD4+ and CD8+ T cells. Growth inhibition by TGF-beta 1-primed CD8+ T cells is reversed in part by anti-IL-10 Ab. Thus, in the context of SEB response, TGF-beta 1 promotes the outgrowth and induces the effector function of CD8+ T cells that have the capacity to impair T cell clonal growth.

Altered phenotype and function of natural killer cells expressing the major histocompatibility complex receptor Ly-49 in mice transgenic for its ligand.

The Ly-49 molecule has been shown to interact with major histocompatibility complex (MHC) class I molecules, and the lytic function of Ly-49+ natural killer (NK) cells from C57BL/6 (H-2b) mice is inhibited by the recognition of H-2Dd on tumor target cells. Introduction of a Ly-49 ligand, H-2Dd, into C57BL/6 mice did not alter the percentage of Ly-49+ NK cells (13-18%), but it led to three functional effects on this subset. (i) The Ly-49 expression in the positive population was reduced by 30-50% compared to C57BL/6 control mice. (ii) While this Ly-49+ subset (Ly-49lo) in the transgenic mice failed to kill BALB/c concanavalin A (Con A) blasts, which have high H-2Dd expression, it was capable of killing SP2/0 tumor cells, which have low H-2Dd expression. Ly-49+ NK cells (Ly-49hi) from nontransgenic mice failed to kill both of these H-2Dd-expressing target cells. (iii) In the transgenic mice, the Ly-49+ subset acquired the ability to kill C57BL/6 Con A blasts, in contrast to the Ly-49+ NK cells of C57BL/6 mice. We propose a "receptor-calibration" hypothesis, where low receptor density on the effector cells imposed by selection or adaptation to the environment allows higher sensitivity for detection of reduced self-MHC ligands on potential target cells.

In Utero Exposure to Ethanol Affects Postnatal Development of T‐ and B‐Lymphocytes, But Not Natural Killer Cells

The effect of intrauterine exposure to ethanol on lymphocyte development in the neonatal period was studied in C57BI/6J mice. Mice were bred, and then the female mice were assigned to 1 of 3 diet groups, 25% ethanol-derived calories (EDC), pair-fed control, or ad libitum laboratory chow. At birth, all offspring were cross-fostered to surrogate mothers who had been fed laboratory chow. At weekly intervals, the neonatal mice were weighed, and 4 mice from each group were used to assess the development of splenic lymphocytes. The total number of splenocytes was similar in all three groups at each sampling. The number of T-cells, B-cells, and natural killer (NK) cells was measured by flow cytometry. T-cells and NK cells did not vary significantly among the three diet groups. However, the total number of B-cells was decreased for the first 3 weeks of life in the ethanol-exposed animals. The function of the T-cells and B-cells was determined by assessing the response to lipopolysaccharide, pokeweed mitogen, phytohemagglutinin, and concanavalin A. The response to all four mitogens was significantly reduced in the ethanol-exposed animals and did not recover to control levels until 4-5 weeks of life. Ethanol exposure had no significant effect on the kinetics of acquisition of NK lytic function, as assessed by determining the killing of chromium-51 labeled YAC-1 tumor target cells. These data show that prenatal exposure to ethanol causes a transient immunodeficiency in some, but not all compartments of the immune system.

Natural killer cell activity in long-term survivors of testicular cancer. Influence of cytostatic therapy and initial stage of disease.

Patients with testicular cancer can be cured by cisplatin-based chemotherapy in many cases. Thus, concern about possible late toxicities of treatment is warranted. In this investigation, the absolute number of natural killer (NK) cells according to their CD56+ phenotype, NK cell activity, and antibody dependent cellular cytotoxicity (ADCC) were investigated in 29 patients with seminomas or nonseminomatous germ cell tumors (NSGCT) a median of 31 months (range, 5-73 months) after termination of chemotherapeutic treatment. No difference in the absolute number of NK cells, NK cell activity, and ADCC was found between patients with testicular cancer after either standard polychemotherapy consisting of bleomycin, etoposide, and cisplatin (BEP) or monotherapy with carboplatin and healthy control subjects. When patients were analyzed further using multivariate analysis, a significant (P < 0.05) detrimental influence of BEP polychemotherapy versus carboplatin monotherapy on NK cell activity was found. Moreover, NK cell activity also depended significantly (P < 0.05) on the time elapsed after chemotherapy was administered, but normalized with time. Because the absolute number of NK cells was not affected, is was assumed that polychemotherapy induced a functional defect. In a subanalysis of patients with NSGCTs, metastases at diagnosis resulted in a significant (p < 0.05) and persistent stimulation of NK cell activity but not of ADCC. Cytostatic chemotherapy in patients with testicular cancer did not lead to compromised lytic effector cell function as assessed by NK cell activity and ADCC. However, a short, time-dependent reduction was found that also depended on the intensity of chemotherapeutic treatment. This finding related to the observation of a long-lasting stimulus of NK cell activity by initial metastases in patients with NSGCTs.

Thiol supplier N-acetylcysteine enhances conjugate formation between natural killer cells and K562 or U937 targets but increases the lytic function only against the latter

In this in vitro study, an evaluation of the importance of intracellular oxidative balance on cell-mediated cytotoxicity was performed by analyzing the effects of the antioxidant N-acetylcysteine (NAC), a specific thiol supplier, on natural killer (NK) cell-mediated cytotoxicity. The results obtained indicate that an enhancement of target cell (TC) killing can be detected when a pre-exposure of effector cells (EC) to NAC was performed. However, this effect seems to depend upon the TC type used. In fact, the increase of EC activity was detected against the differentiated U937 TC while no changes were detected by the same effectors against K562 cells. The mechanism of this enhancement seems to be ascribable to an increased ability of NAC-exposed NK cells to form conjugates (binding) which, in turn, appears to be due to a specific effect of NAC on actin microfilaments. A role for NAC as a cytoskeleton thiol-modifier contributing to the activation of effector cells can thus be hypothesized.

Infection and inhibition of human cytotoxic T lymphocytes by herpes simplex virus

The effect of herpes simplex virus type 1 (HSV-1) infection on human cytotoxic T-lymphocyte (CTL) lytic function was assessed. All HSV-infected CTL populations tested were significantly inhibited in lysing target cells. The inhibition of CTL lytic function by infection with HSV-1 was independent of T-cell receptor-mediated antigen recognition and did not involve virus-induced shutoff of host protein synthesis, the expression of the HSV-1 transactivation protein, ICP4, or replicating virus. Understanding the functional impairment of CTL following infection with HSV may have important implications for HSV-induced immunosuppression and the mechanism of HSV persistence in immunocompetent hosts.

Restoration of Lytic Function in a Human Natural Killer Cell Line by Gene Transfection

NK cells can recognize and lyse target cells without restriction by the MHC. The molecular interaction responsible for NK cell recognition is poorly understood. It has been frequently suggested that the loss of β 2 integrin in immune competent cells may lead to dysfunction due to inadequate cell-cell interaction. We examined the role of lymphocyte functional adhesion molecule-1 in the function of a human natural killer leukemia cell line, YT-1. A mutant YT-1(-) cell subclone showed an absence of killing activity against a B lymphoma cell line, compared with that against a CD11a/CD18 positive parental cell line. YT-1(+) cells. We found that this loss of cytotoxicity was correlated with lack of surface expression of CD11a/CD18 molecules due to the mutation of the CD18 gene. Using gene transfer experiments, we provide strong evidence demonstrating that CD18 transfection to this mutant NK cell line. YT-1(-), restored the surface expression or CD11a/CD18, and this restoration was accompanied by reexpression of cytotoxic function.

Effective induction of human NK cells with OK-432 and further augmentation of their cytolytic function by rIL-2.

Low concentrations of exogenously added recombinant interleukin 2 (rIL-2) were able to augment OK-432-induced natural killer (NK) cell activity. This kind of augmenting effect depended on the dose of rIL-2 and manifested itself only in PBMC stimulated with OK-432 (OK-MC) followed by rIL-2; augmentation did not happen in the reverse order. The existence of CD16+/CD25+ (IL-2 receptor positive; IL-2R+) and CD57+/CD25+ double positive cells which possess NK cell surface markers in OK-MC markedly increased in a long-term culture (12 days). A strong positive correlation was observed between the IL-2-dependent augmentation of NK activity and the quantitative changes in cell populations that possessed NK cell phenotypes. Treatment of the day-12-OK-MC with monoclonal anti-CD56 antibody plus complement could almost completely abrogate the augmented NK cytotoxicity. Furthermore, this augmenting effect was detectable within 4 hr after addition of rIL-2 at single cell level, suggesting that the effect did not require NK cell's DNA synthesis. Thus it was suggested that OK-432 could promote and upregulate the expression of IL-2 receptor (CD25) on CD56+ NK cell populations. Moreover, it was considered that the interaction of low concentration rIL-2 with IL-2 receptors on OK-432-activated NK cells could augment their lytic function.

Characterization and function of the NKR-P1dim/T cell receptor-alpha beta+ subset of rat T cells.

MHC-unrestricted cytotoxicity is mediated primarily by NK cells. However, some subsets of TCR-alpha beta+ and TCR-gamma delta+ T cells also have the capacity to mediate MHC-unrestricted cytotoxicity, particularly after incubation in high concentrations of IL-2. Currently, it is not known what receptors on T cells are responsible for this activity, nor whether such receptors are the same as those on NK cells. We have recently described a type II integral membrane protein, termed NKR-P1, that is expressed at high levels on rat NK cells (NKR-P1bright). NKR-P1 contains a carbohydrate recognition domain characteristic of C-type (Ca(2+)-dependent) animal lectins and is a representative member of a distinct group of this superfamily. By a variety of criteria, NKR-P1 is linked to a signaling pathway that activates NK cell lytic function. Based on its structure and function, NKR-P1 has been implicated as a candidate molecule involved in or contributing to MHC-unrestricted cytotoxicity. We describe herein the expression of NKR-P1 at low levels on a small subset of rat T cells with an NKR-P1dim/TCR-alpha beta+ phenotype and on a small subset of cells with an NKR-P1dim/TCR-alpha beta- phenotype (presumably containing gamma delta+ T cells). Before incubation with IL-2, the NKR-P1dim subsets of cells lack MHC-unrestricted cytolytic capacity and lack the capacity for reverse antibody-dependent cellular cytotoxicity (rADCC) mediated via NKR-P1. However, culture of NKR-P1dim/TCR-alpha beta+ T cells in IL-2 led to the acquisition of both MHC-unrestricted cytotoxicity and the capacity for rADCC via NKR-P1. NK-like cytolytic function was not found among IL-2-activated NKR-P1-/TCR-alpha beta+ T cells. These data suggest that expression of functional NKR-P1 (i.e., ability to signal rADCC) correlates with and potentially contributes to MHC-unrestricted cytotoxicity.

Requirement of thiol compounds as reducing agents for IL-2-mediated induction of LAK activity and proliferation of human NK cells.

Thiol-related compounds, such as L-cystine, 2-ME or reduced glutathione (GSH), are important in many lymphoid cell activation pathways. We investigated their role in IL-2-generated lymphokine-activated killer (LAK) activity in human NK (CD16+ and/or CD56+) cells. Depletion of GSH and L-cystine, but not L-leucine or glycine, from medium used during culture of NK cells with IL-2 inhibited LAK and proliferative activities, whereas IL-2-independent lytic function of NK cells remained intact. Addition of L-cysteine, 2-ME or GSH, but not methylated analogs of these compounds (which cannot function as proton donors) to L-cystine/GSH-depleted medium restored proliferative response of NK cells and LAK generation. In the presence of L-buthionine-(S,R)-sulfoximine, an inhibitor of GSH synthesis, IL-2-induced LAK activity and proliferation of NK cells in medium without L-cystine and GSH, could be restored, at least in part, by addition of GSH, but not 2-ME or L-cystine. Furthermore, intracellular GSH levels were depressed in cells cultured in L-cystine/GSH-depleted medium but could be restored by the addition of 2-ME. The results suggest that (1) L-cystine or thiol containing compounds such as L-cysteine, 2-ME, or GSH are necessary for effective IL-2-activation of human NK cells, (2) these compounds must be functional proton-donors, i.e., reducing agents, implying regulation of the IL-2 activation pathway by oxidation-reduction, and (3) GSH synthesis is necessary for the activation. Experiments were performed to begin to dissect the redox-sensitive step(s) in LAK development. Depletion of reducing agents had no effect on internalization of rIL-2. In contrast, intracellular granzyme A activity was significantly depressed in NK cells cultured with rIL-2 in L-cystine/GSH-depleted medium compared with those cultured in medium in which L-cystine levels had been replenished. The findings suggest that step(s) in the transduction of the IL-2 signal in NK cells, between the internalization of IL-2 and the maturation of the lytic mechanism, are subject to regulation by oxidation-reduction.

Inhibition of human CTL-mediated lysis by fibroblasts infected with herpes simplex virus.

Previously, we demonstrated that human anti-HSV CTL and allo-antigen-specific CTL were inhibited in lysing their normally sensitive target cells when they were exposed to human fibroblasts (FB) infected with herpes simplex virus (HSV). In this study, the mechanism of inhibition of CTL lytic function by FB infected with HSV-1 (HSV-FB) was studied. CTL exposed to HSV-FB early (2 h) in the infection cycle were inhibited by a mechanism that appears to be distinct from the inhibition of lytic function mediated by HSV-FB at late times (20 h) during the infection cycle. The inhibition of CTL-mediated lysis by FB infected with HSV-1 for 2 h required the expression of ICP4, an immediate-early protein of HSV-1, but not the production of infectious virus or virus-induced shut-off of host protein synthesis. In contrast, the expression of HSV-specific glycoproteins essential for viral infectivity (glycoproteins B, D, H, K, and L), and thus, infectious virus, was required for inhibition of CTL lytic function by FB infected with HSV-1 for 20 h. Further, CTL exposed to FB infected with HSV-1 for 20 h expressed HSV-specific proteins indicating that they were infected with HSV-1. Cell-to-cell spread of HSV-1 appeared to be the major mode of transmission because 1) an insufficient level of HSV-1 was present in the supernatant of HSV-FB to inhibit CTL lytic function; and 2) paraformaldehyde-fixed HSV-FB did not inhibit CTL-mediated lysis. The inhibition of CTL lytic function by HSV-FB may be an important mechanism of HSV-induced immunosuppression, permitting the virus to spread and persist in immunocompetent hosts after primary infection or reactivation of latent HSV.

A novel target cell antigen involved in the NK-like lytic activity of antigen-specific cytotoxic T lymphocytes

Monoclonal antibodies (mAbs) have been derived which identify a target cell antigen involved in human natural killer (NK) cell lysis. The effects of the mAbs on the NK-like cytotoxic activity exhibited by different populations of human cytolytic T cells were examined. The anti-target cell mAbs 1E7 and 18C2 inhibited the lysis of K562 target cells by endogenous NK cells, antigen-specific cytotoxic T lymphocytes (CTL) with NK-like activity, and non-major histocompatibility complex (MHC)-restricted T cells. Cytolysis of K562 target cells was not affected by treatment of the target cells with the anti-class I HLA mAb W6/32. Further, the anti-target cell mAbs had no effect on antigen-specific lysis by the CTL. The mAb W6/32, however, inhibited the antigen-specific killing. Experiments at the single-cell level revealed that the anti-target cell mAbs inhibited the formation of conjugates between the effector cells and K562 tumor cells but had no effect on CTL binding to the antigen-specific target cells. Thus, antigen-specific CTL exhibiting NK-like lytic function appeared to recognize a novel target cell antigen that is distinct from typical MHC antigens and is identical to the target-cell antigen recognized by true NK cells.

Phi X174 E complements lambda S and R dysfunction for host cell lysis.

Hybrid lambda phages which have the E lysis gene of the bacteriophage phi X174 in cis to defective nonsense and deletion alleles of the normal lambda lysis genes S and R have been constructed and shown to be fully competent for plaque-forming ability, which demonstrates that the single-gene, lysozyme-independent lysis system of phi X174 and related phages can serve the lytic function for large complex phages. These hybrid phages are unable to form plaques on a slyD host. Moreover, plaque morphology indicates that in E-mediated lysis the soluble lambda R endolysin can participate in lysis, indicating that the protein E-mediated lesions are not completely sealed off from the periplasm.

Monoclonal antibodies to LFA-I molecule beta-chain promote a rise in the cytotoxic index of effector cells and stimulate their proliferation

Successful interaction of a T cell with antigen (AG) requires, besides a T-cell receptor (TCR), the expression of a number of coreceptor molecules which provide the binding (formation) of the AGMHC protein complex (MHC - main histocompatibility complex) and signal transduction into the cell [8]. Specifically, AG-specific activation involves an adhesive molecule LFA-I (lymphocyte function-associated antigen) which is not directly bound to TC1L This molecule belongs to the family of integrins, heterodimers with non-covalently bound o~- and B-chains. These transmembrane proteins are associated with the cytoplasmic domains of the cytoskeleton. By interacting with the ligand ICAM-I (intercellular adhesion molecule), LFA-I provides an additional adhesive mechanism necessary to the cell for implementing some other interactions such as MHC/AG-receptor, TCR, cytokines, etc. [6]. It is known that in vitro antibodies to LFA-I a-chain suppress a proliferative response in a mixed culture of lymphocytes (MCL) [9], Tcell proliferation in response to phytohemagglutinin (PHA) [4], concanavalin A, production of interleukin-2, and the T-cell-mediated antibody response [13], and also inhibit the lytic function of

The acidic amino-terminal region of herpes simplex virus type 1 alpha protein ICP27 is required for an essential lytic function.

The herpes simplex virus type 1 (HSV-1) alpha protein ICP27 regulates the transition between the delayed-early and late phases of the viral infection. Previous genetic analyses have suggested that the important functional domains of ICP27 map to its carboxyl-terminal half. One striking feature of the primary sequence of ICP27, however, is an extremely acidic region near its amino terminus. To determine whether this region is required for ICP27 function, we deleted the sequences in the ICP27 gene which encode it (codons 12 through 63). In transient expression assays, the deletion mutant was unable to efficiently repress the expression of a cotransfected reporter gene or to efficiently complement the growth of d27-1, an HSV-1 ICP27 null mutant. These results suggested that the acidic region of ICP27 is involved in a regulatory function required for lytic growth. To test this possibility further, we introduced the mutant allele into the HSV-1 genome by marker transfer. Two independently derived isolates of the mutant virus, designated d1-2a and d1-2b, were recovered and analyzed. Both isolates were defective for growth in Vero cells, exhibiting a 100-fold reduction in virus yield compared with the wild-type infection. Vero cells infected with the d1-2 isolates showed a three- to eightfold reduction in viral DNA replication, a moderate reduction in the expression of viral gamma genes, and a delay in the repression of beta genes. The phenotype of the d1-2 isolates differs substantially from the phenotypes of previously isolated ICP27 mutants, which show much more severe defects in viral gene expression. Our results demonstrate that the amino-terminal half of ICP27 participates in its regulatory activities in both infected and transfected cells.

In vitro studies of natural killer cell activity in post traumatic stress disorder patients. Response to methionine-enkephalin challenge.

Attempts to define biological parameters that may be specifically associated with the pathophysiology of post traumatic stress disorder (PTSD) have met with only limited success, reflecting perhaps the practical limitations resulting from the high frequency of comorbidity of this condition with Axis I, II and III psychiatric diagnoses. We now report our studies on natural killer cell activity (NKCA), and the response of this cellular immune function to an in vitro methionine-enkephalin (MET) challenge in a population of Vietnam veterans with PTSD. Due to the characteristics of our PTSD patients, our protocol included four sex-matched, age-comparable control groups: (1) chronic alcoholics, (2) chronic drug abusers excluding alcohol, (3) chronic users of alcohol and other drugs of abuse and (4) drug-free, healthy volunteers. Although these groups did not significantly differ in their "baseline" NKCA, significant findings emerged from their response to preincubation with MET (10(-10), 10(-8) and 10(-6) M; 40:1 effector-to-target cell ratio). To minimize interindividual variations in the expression of NKCA each subject was used as its own control. Whereas peptide challenge resulted in an increase in NK lytic function in a subpopulation of group four (one or more MET concentrations, 8 out of 22 subjects), it produced mixed results in samples from individuals in group 2, and in general failed to elicit NKCA changes in the samples from participants in groups 1 and 3. Nine of the thirteen PTSD patients responded to MET preincubation with decreases in NKCA, which in five of them reached values below 20% of baseline for the three peptide concentrations tested. These findings may suggest that the "stress factor" in Vietnam veterans with PTSD plays a role in downmodulating NK lytic function in response to an in vitro MET challenge, an effect that appears to be potentiated by the use of drugs of abuse other than alcohol. The possible clinical relevance of these findings, including the identification of a subgroup of PTSD patients on the basis of immunological tests such as the one described in this work, deserves further investigation.

Anergized T cell clones retain their cytolytic ability.

CD4+ T cells have been described to have both helper and lytic function. The helper function of Th1 cells in particular can be inactivated by inducing the T cell into a state of nonresponsiveness in which the T cell is no longer capable of producing IL-2 or proliferating in an autocrine way to a conventional antigenic stimulus. To determine whether the lytic ability of Th1 cells can also be rendered nonfunctional upon anergy induction, we induced Th1 clones into a nonresponsive state and tested their ability to lyse target cells in an Ag-specific and MHC class II-restricted manner. We show that cells newly induced into an anergic state were able to lyse target cells nonspecifically. This effect was short-lived and after resting in culture media, the cells regained their ability to lyse target cells in an Ag/MHC-specific manner, and this ability was comparable to normal resting T cells. In contrast, the helper function of these cells remained nonresponsive, and the cells were unable to proliferate or to secrete IL-2 in response to the same antigenic stimulus used for lysis. Therefore, the lytic pathway appears to be regulated separately from the proliferative/lymphokine pathway(s) and is not affected long-term by an anergic stimulus.

Killer cell recruitment and renewal capacity of purified cytolytic and noncytolytic human peripheral blood natural killer cell subsets.

The inability to isolate NK precursors at different stages of development has impeded understanding of the processes involved in NK maturation. The present studies utilize a flow cytometric technique that enables the isolation of operationally defined cell subsets, lytic (killers) and nonlytic conjugate-forming (binders), and nonconjugate-forming (free) cells, within NK-enriched preparations to test whether these might represent cells in different stages of NK development. To characterize both the steps involved in NK maturation and the cells responsible for IL-2 induced proliferation, these purified subsets were analyzed for their killer cell recruitment and renewal capacity. After a 2-h exposure to IFN-alpha or IL-2, induction of lytic function was developed only in the binder subset as detected in the single cell assay. Neither enhancement of killer cell recycling nor induction of binding function among the subsets was observed. However, after an 18-h culture period, with or without rIL-2, killer cells preferentially expressed activation Ag CD69 (Leu-23) and the IL-2R alpha-chain, TAC (CD25). In addition, all cells in contact with K562 targets displayed enhanced expression of these Ag. Killer cells also showed an enhanced capacity to proliferate in response to rIL-2 in a 6-day [3H]TdR incorporation assay. Additional irradiated K562 targets enhanced the proliferative capacity of all the subsets, with only a marginal effect on sorted free cells. Nevertheless, sorted free cells, in addition to binders, developed potent binding and lytic function when tested in the single-cell assay after 4 days of IL-2 culture. The lytic activity of killers was reduced, as compared with freshly isolated killers. The results are consistent with a two-step model for NK maturation, involving the acquisition of lytic function before proliferative capacity, and specific triggering of killer cells through interaction with target cells for induction of a proliferative competent state.

Association of lytic effector cell function with high expression of HER-2 expression in breast cancer patients

Association of lytic effector cell function with high expression of HER-2 expression in breast cancer patients

Bacteriophage lysis: mechanism and regulation.

Bacteriophage lysis involves at least two fundamentally different strategies. Most phages elaborate at least two proteins, one of which is a murein hydrolase, or lysin, and the other is a membrane protein, which is given the designation holin in this review. The function of the holin is to create a lesion in the cytoplasmic membrane through which the murein hydrolase passes to gain access to the murein layer. This is necessary because phage-encoded lysins never have secretory signal sequences and are thus incapable of unassisted escape from the cytoplasm. The holins, whose prototype is the lambda S protein, share a common organization in terms of the arrangement of charged and hydrophobic residues, and they may all contain at least two transmembrane helical domains. The available evidence suggests that holins oligomerize to form nonspecific holes and that this hole-forming step is the regulated step in phage lysis. The correct scheduling of the lysis event is as much an essential feature of holin function as is the hole formation itself. In the second strategy of lysis, used by the small single-stranded DNA phage phi X174 and the single-stranded RNA phage MS2, no murein hydrolase activity is synthesized. Instead, there is a single species of small membrane protein, unlike the holins in primary structure, which somehow causes disruption of the envelope. These lysis proteins function by activation of cellular autolysins. A host locus is required for the lytic function of the phi X174 lysis gene E.