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Atypical protein kinase Cs are the Ras effectors that mediate repression of myogenic satellite cell differentiation.

Oncogenic Ha-Ras is a potent inhibitor of skeletal muscle cell differentiation, yet the Ras effector mediating this process remains unidentified. Here we demonstrate that the atypical protein kinases (aPKCs; lambda and/or zeta) are downstream Ras effectors responsible for Ras-dependent inhibition of myogenic differentiation in a satellite cell line. First, ectopic expression of Ha-RasG12V induces translocation of PKClambda from the cytosol to the nucleus, suggesting that aPKCs are activated by Ras in myoblasts. The aPKCs function as downstream Ras effectors since inhibition of aPKCs by expression of a dominant negative PKCzeta mutant or by treatment of cells with an inhibitor, GO6983, promotes myogenesis in skeletal muscle satellite cells expressing oncogenic Ha-Ras. Arresting cell proliferation synergistically enhances myogenic differentiation only when aPKCs are also inhibited. Thus, the repression of myogenic differentiation in a satellite cell line appears to be directly mediated by aPKCs acting as Ras effectors and indirectly mediated via stimulation of cell proliferation.

Animals↗

Antibodies to synthetic peptide from the residue 33 to 42 domain of c-Ha-ras p21 block reconstitution of the protein with different effectors.

Residues 32 to 40, which are conserved among ras proteins from different species, are likely to participate in interactions with the p21 effector system. With the goal of understanding the structural basis of the regulatory functions of c-Ha-ras p21, we produced rabbit antisera against a synthetic peptide corresponding to amino acids 33 to 42 of the protein. The affinity-purified antibodies interacted specifically with p21 and with the antigenic peptide. The epitope recognized by the antibodies appeared to be centered on threonine 35. The antibodies inhibited both in vitro p21-induced production of cyclic AMP in detergent extracts of RAS-defective yeast membranes and GAP-stimulated GTPase activity. However, monoclonal anti-ras antibodies Y13-259 and Y13-238 were not capable of specifically inhibiting interactions of p21 with these two putative effector proteins. The apparent inhibitory effect of Y13-259 on stimulation of p21 by GAP was due to a greatly reduced rate of exchange of nucleotides in the binding pocket of the protein. These findings provide additional support for the essential role of the residue 32 to 40 domain as the true effector site and further evidence of the involvement of GAP as a cellular effector of ras proteins.

Amino Acid Sequence↗

Interleukin 10 and transforming growth factor beta contribute to the development of experimentally induced allergic conjunctivitis in mice during the effector phase.

AIM: To investigate the involvement of interleukin (IL)10 and transforming growth factor (TGF) beta in the development of experimentally induced allergic conjunctivitis in mice. METHODS: Balb/c mice were actively sensitised with ragweed in alum, and then challenged with ragweed in eye drops after 10 days. 24 h later, the conjunctivas, spleens and blood were collected for histological and cytokine expression analyses, proliferation and cytokine production assays and measurement of immunoglobulin (Ig) levels. Mice developing experimentally induced allergic conjunctivitis were injected intraperitoneally with 200 microg of anti-IL10 or anti-TGF beta antibodies at 0, 2, 4, 6 and 8 days (induction phase treatment) or 500 microg of antibodies 2 h before ragweed challenge (effector phase treatment). Normal rat IgG was used for control injections. RESULTS: Treatment with either anti-IL10 or anti-TGF beta antibodies during the induction phase did not affect eosinophil infiltration into the conjunctiva. By contrast, treatment with either antibody during the effector phase suppressed infiltration. During the effector phase, treatment with anti-TGF beta antibody, but not the anti-IL10 antibody, markedly up regulated proliferation and Th2 cytokine production by splenocytes. IL1alpha levels in the conjunctiva were reduced after treatment with either antibody; in addition, eotaxin and tumour necrosis factor alpha levels were reduced after treatment with antibody to TGF beta. CONCLUSIONS: IL10 and TGF beta do not have immunosuppressive roles in the development of experimentally induced allergic conjunctivitis. Rather, they augment the infiltration of eosinophils into the conjunctiva during the effector phase of experimentally induced allergic conjunctivitis.

Adoptive Transfer↗

Threshold dissociation of thermoregulatory effector responses in febrile rabbits.

When the core temperature stabilizes at a hyperthermic level after iv injection of lipopolysaccharide (LPS), the threshold core temperature for cutaneous vasoconstriction (Thcv) is significantly increased in hot and neutral environments, while the threshold core temperature for shivering (Thsh) is not significantly altered in hot or cold environments but is significantly reduced at thermoneutrality. This type of dissociated threshold alterations of thermoregulatory effector responses seems to be typical for the febrile response of rabbits to LPS. Because the same threshold dissociation can be demonstrated after icv injection of LPS, the systemic and the central effects of LPS in the generation of fever seem to be mediated by identical mechanisms. Prostaglandins of the E series (PGE), one of the mediators considered as important in fever generation, cause parallel increases in Thcv and Thsh when injected icv. This indicates that the mode of action of PGE on the central targets producing hyperthermia differs from that of the ensemble of mediators involved in the generation of LPS fever in rabbits. In rabbits pretreated with aspirin, the threshold dissociation after iv LPS injection still occurs. This indicates that factors other than PGE play an important role in the generation of the threshold dissociation of thermoregulatory effector responses, which is typical for LPS fever. These data indicate also that the states of activity of the thermoregulatory effectors involved in the febrile responses can be altered individually and that the activities of these effectors during LPS fever are quite different from their activities in the control state.

Animals↗

CD8+ T cell effector mechanisms in resistance to infection.

Based on T cell subset depletion studies and the analysis of gene knockout mice, it is evident that CD8(+) T cells contribute to resistance against intracellular infections with certain viral, protozoan, and bacterial pathogens. Although they are known primarily for their capacity to kill infected cells, CD8(+) T cells elaborate a variety of effector mechanisms with the potential to defend against infection. Microbes use multiple strategies to cause infection, and the nature of the pathogenhost interaction may determine which CD8(+) T cell effector mechanisms are required for immunity. In this review, we summarize our current understanding of the effector functions used by CD8(+) T cells in resistance to pathogens. Analyses of mice deficient in perforin and/or Fas demonstrate that cytolysis is critical for immunity against some, but not all, infections and also reveal the contribution of cytolysis to the pathogenesis of disease. The role of CD8(+) T cell-derived cytokines in resistance to infection has been analyzed by systemic treatment with neutralizing antibodies and cytokine gene knockout mice. These studies are complicated by the fact that few, if any, cytokines are uniquely produced by CD8(+) T cells. Thus, the requirement for CD8(+) T cell- derived cytokines in resistance against most pathogens remains to be defined. Finally, recent studies of human CD8(+) T cells reveal the potential for novel effector mechanisms in resistance to infection.

Animals↗

Endogenous effectors of human liver glycogen phosphorylase modulate effects of indole-site inhibitors.

Phosphorylase is regulated by a number of small-molecular-weight effectors that bind to three sites on the enzyme. Recently, a fourth site referred to as the indole-inhibitor site has been identified. Synthetic compounds bind to the site and inhibit activity. However, the effects of these compounds in the presence of other endogenous effectors are unknown. We have determined the effects of four indole derivative glycogen phosphorylase inhibitors (GPI) on recombinant human liver glycogen phosphorylase a activity. The GPIs tested were all potent inhibitors. However, the endogenous inhibitors (glucose, ADP, ATP, fructose 1-phosphate, glucose 6-phosphate, UDP-glucose) and the activator (AMP) markedly reduced the inhibitory effect of GPIs. Consistent with these in vitro findings, the IC50 for the inhibition of glycogenolysis in cells and the liver drug concentration associated with glucose-lowering activity in diabetic ob/ob mice in vivo were also significantly higher than those determined in in vitro enzyme assays. The inhibitory effect of indole-site effectors is modulated by endogenous small-molecular-weight effectors of phosphorylase a activity. However, at higher concentrations (10-30 microM), the GPI effect was dominant and resulted in inhibition of phosphorylase a activity irrespective of the presence or absence of the other modulators of the enzyme.

Adenosine Diphosphate↗

24-hour control of body temperature in rats. I. Integration of behavioral and autonomic effectors.

Some studies suggest that the nocturnal elevation in core temperature (Tc) of the rat is mediated by an elevation in the set point. The role of set point can be assessed if behavioral effectors are measured simultaneously with other thermoregulatory effectors and Tc over a 24-h period. Selected ambient temperature (STa) and motor activity (MA) were measured in rats housed in a temperature gradient system with a 12:12-h photoperiod (lights on 0600 h). Tc and heart rate (HR) were monitored by telemetry. During the light phase, STa, Tc, HR, and MA were relatively stable with values 29.0 degrees C, 37.1 degrees C, 310 beats/min, and 1-2 m/h, respectively. During the light-to-dark transition there were abrupt elevations in Tc, HR, and MA but no change in STa. STa decreased during the dark phase and reached a nadir of 23 degrees C at 0500 h. All variables recovered to basal levels within 3-4 h after the onset of the light phase. Overall, autonomic effectors control the elevation in Tc during the onset of the dark phase while behavioral effectors have little if any role. Behavioral thermoregulation is important in two ways: 1) the selection of cooler Ta values at night to prevent an excess elevation in Tc and 2) a preference for cooler Ta values before the light phase to facilitate the recovery of Tc.

Animals↗

Host lymphodepletion augments T cell adoptive immunotherapy through enhanced intratumoral proliferation of effector cells.

T-cell adoptive immunotherapy for stringent murine tumor models, such as intracranial, s.c., or advanced pulmonary metastases, routinely uses lymphodepletive conditioning regimens before T-cell transfer, like recent clinical protocols. In this study, we examined whether host lymphodepletion is an obligatory component of curative T-cell therapy; we also examined the mechanism by which it augments therapy. Mice bearing intracranial, s.c., or 10-day pulmonary metastases of MCA 205 received total body irradiation conditioning or were nonirradiated before i.v. transfer of tumor-reactive T cells. Total body irradiation was not required for immunologically specific curative therapy and induction of memory provided that a 3- to 12-fold higher T-cell dose was administered. The mechanism involved enhanced intratumoral proliferation of T-effector cells in total body irradiation-conditioned recipients. In this tumor model, intratumoral T(reg) cells were not detected; consequently, intratumoral T-effector cells produced identical amounts of IFN-gamma upon ex vivo antigen stimulation irrespective of total body irradiation conditioning. Thus, host lymphodepletion augments T-cell immunotherapy through enhanced antigen-driven proliferation of T-effector cells, but curative therapy can be achieved in nonconditioned hosts by escalation of T-cell dose. These data provide a rationale for dose escalation of T-effector cells in situations where single or repeated lymphodepletion regimens are contraindicated.

Animals↗

Sequential Immune Activation of Effector T Cells as Biomarkers of Response to Durvalumab in Patients with Locally Advanced NSCLC.

PURPOSE: Durvalumab therapy following concurrent chemoradiotherapy (cCRT) improves progression-free survival (PFS) in patients with unresectable locally advanced non-small cell lung cancer. In this prospective observational study, we evaluated the changes in peripheral blood immune cell counts to elucidate the immunologic mechanisms underlying cCRT and durvalumab therapy. EXPERIMENTAL DESIGN: Peripheral blood mononuclear cell (PBMC) samples were collected at four time points: before cCRT, after cCRT, at the start of durvalumab, and 8 weeks after the start of durvalumab, and analyzed by multicolor flow cytometry. RESULTS: Of the 149 enrolled patients, 115 received durvalumab consolidation therapy after cCRT. The median PFS in the overall population was 24.2 months, and the 3-year PFS rate was 38.9%. PBMC analysis showed an increased effector fraction of CD4+ T cells before and after cCRT but no change in CD8+ T cells. Following durvalumab therapy, the effector fraction ratio of CD8+ T cells (CD62Llow CD8+ T cells) increased and positively correlated with increased CD62Llow CD4+ T cells during cCRT. Patients whose proportion of CD62Llow CD4+ T cells exceeded the threshold for cCRT had better PFS than those below the threshold. Patients whose CD62Llow CD8+ T-cell proportion exceeded the threshold after durvalumab therapy showed prolonged PFS compared with those below the threshold. CONCLUSIONS: cCRT promotes an increase in effector CD4+ T cells, and the subsequent increase in CD8+ T cells following durvalumab therapy prolongs PFS. Peripheral blood effector-type CD4+ and CD8+ T cells are potential biomarkers for evaluating the immune status of patients and predicting treatment efficacy.

Humans↗

Activation of effector cells of experimental allergic encephalomyelitis in Lewis rats: comparison of T-cell lines with primary cultured lymph node cells.

We studied the mechanism of activation of effector cells in experimental allergic encephalomyelitis (EAE) by using T-cell lines (EAE/TL) reactive against guinea pig myelin basic protein generated from in vivo primed lymph node cells (LNC) of Lewis rats. EAE-effector cells are activated in the presence of a specific antigen and antigen-presenting cells (APC) with a compatible Ia antigen. The antigen presentation occurs during the first 18 h. EAE-effector cells cannot be activated by allogeneic stimulator cells, but a nonspecific T-cell mitogen, concanavalin A, can activate the effector cells in the presence of syngeneic as well as allogeneic APC.

Animals↗

Characterization of effector cells responsible for cell-mediated cytotoxicity in patients with carcinoma of the prostate.

In earlier experiments it has been shown that cellular cytotoxicity of patients with prostatic carcinoma (CaP) as measured by cytolysis of EB 33 target cells correlates with the extent of their tumor lesion: a high grade of cytotoxicity was observed only when CaP was confined to gland. In order to define a possible in vivo immunological host-tumor interaction, further characterization of the type of effector cell responsible for in vitro killing has been attempted. Effector cells could be either tumor-specific sensitized T cells, K cells, macrophages or NK cells. Antibody-dependent K-cell activity could most likely be excluded, since autologous and homologous serum did not affect the extent of EB 33 killing when added to the test medium. Further separation of effector cells by nylon wool columns resulted in increased cytolysis of EB 33 target cells. This can be due either to tumor-specific T-cell-mediated mechanisms or to an increased natural killer cell activity, as macrophages and B cells were significantly removed by this measure. Separation of T and NK cells is necessary to ascertain the effector cell responsible for the in vitro killing of tumor cells derived from human CaP.

Adult↗

Characterization of effector cells mediating the augmentation of spontaneous cell-mediated cytotoxicity induced by therapeutic infarction of human renal carcinomas.

Spontaneous cell-mediated cytotoxicity has been shown to be augmented after therapeutic infarction of human renal carcinomas. The effector cell responsible for the enhanced cytotoxicity was characterized by fractionation by adherence to nylon-wool and serum-coated plastic surfaces, density, and reactivity with certain monoclonal antibodies. The effector cell was nonadherent, sedimented in the lighter fractions of a 40-53% discontinuous Percoll gradient, and was not affected by preincubation with OKT 3 antibody selectively blocking cytotoxic T lymphocytes. About 70% of effector cells expressed the HNK-1 and 50% the OKM-1 antigenic markers. Cytotoxicity was high against the NK-sensitive target K-562 and low against the relatively NK-resistant target cell Daudi. These data define the effector cell mediating the increased cell-mediated cytotoxicity induced by infarction of renal carcinomas as a natural killer cell.

Carcinoma, Renal Cell↗

Chemokine CXCL10 promotes atherogenesis by modulating the local balance of effector and regulatory T cells.

BACKGROUND: Studies to define the overall contribution of lymphocytes to lesion formation in atherosclerosis-susceptible mice have demonstrated relatively subtle effects; the use of lymphocyte-deficient mice, however, compromises both the effector and regulatory arms of the immune system. Here, we tested the hypothesis that deletion of CXCL10 (IP-10), a chemokine specific for effector T cells that has been localized within atherosclerotic lesions, would significantly inhibit atherogenesis. METHODS AND RESULTS: Compound deficient Apoe(-/-)/Cxcl10(-/-) mice fed a Western-style diet for either 6 or 12 weeks demonstrated significant reductions in atherogenesis as compared with Apoe(-/-) controls, as assessed by both aortic en face and cross-sectional analyses. Immunohistochemical studies revealed a decrease in the accumulation of CD4+ T cells, whereas quantitative polymerase chain reaction analysis of lesion-rich aortic arches demonstrated a marked reduction in mRNA for CXCR3, the CXCL10 chemokine receptor. Although overall T-cell accumulation was diminished significantly, we found evidence to suggest that regulatory T-cell (Treg) numbers and activity were enhanced, as assessed by increased message for the Treg-specific marker Foxp3, as well as increases in immunostaining for the Treg-associated cytokines interleukin-10 and transforming growth factor-beta1. We also documented naturally occurring Treg cells in human atherosclerotic lesions. CONCLUSIONS: We provide novel evidence for a functional role for the effector T-cell chemoattractant CXCL10 in atherosclerotic lesion formation by modulating the local balance of the effector and regulatory arms of the immune system.

Animals↗

Natural killer cell in systemic lupus erythematosus. Defects in effector lytic activity and response to interferon and interferon inducers.

Spontaneous cytotoxicity mediated by natural killer (NK) cells is impaired in several human diseases including systemic lupus erythematosus (SLE). The precise mechanism(s) by which NK activity is suppressed in patients with SLE is generally unknown. The present study was designed to focus on cellular defects per se in NK cells from patients with SLE. It was observed that the usual enhancing effect of interferon (IF) and IF inducers was markedly impaired in SLE patients. Of 24 SLE patients studied, 17 had significantly decreased NK activity relative to controls. NK activity had a significant negative correlation with clinical activity score (r = -0.56, P less than 0.005) but was not correlated with corticosteroid dose, antinuclear antibody titers, total hemolytic complement (CH50), or sedimentation rate. Furthermore, significant depressions in NK activity correlated with variations in disease activity in six patients followed serially. Depressed NK function could not be reversed by prolonged in vitro incubation at 37 degrees C or with protease treatment. Furthermore, depressed NK activity was not altered by removal of glass adherent cells nor was a suppression of NK activity in normal controls seen by the addition of SLE peripheral mononuclear cells. No reversal of depressed activity to normal levels was seen by the addition of indomethacin nor did the supernatants from SLE cell cultures cause a suppression of normal NK function. NK activity in SLE patients did not respond normally to IF inducers (poly-I:C and concanavalin A) even if the SLE patients had normal NK function. The response of SLE cells to exogenous IF was also impaired. The number of effector-target conjugates was quantitated with several target cells (K562, Yac-1, Fravel) in SLE patients and controls. A significant correlation between the proportion of glass nonadherent mononuclear cells that formed effector-target conjugates with these various targets and the magnitude of NK lysis was observed. However, SLE and normal subjects had equal numbers of effector-target conjugates independent of NK function. Release of a soluble cytotoxic factor was induced with concanavalin A, and was markedly impaired in SLE patients relative to normal controls. Thus, impaired NK cell function in SLE does not appear to be related to cell-mediated suppressive mechanisms or to the deletion of effector cells; rather, the decreased NK activity may be related to an impaired release of a soluble cytotoxic factor.

Adult↗

Prostaglandin E1 inhibits effector T cell induction and tissue damage in experimental murine interstitial nephritis.

Immunosuppressive effects of E-series prostaglandins have been demonstrated in many in vitro assays of immune responsiveness as well as in autoimmune diseases. To explore the mechanisms underlying prostaglandin E1 (PGE1)-associated immunosuppression in autoimmunity, we treated SJL mice immunized to produce immune-mediated interstitial nephritis with PGE1, PGF2 alpha, or vehicle alone. Mice receiving PGE1 treatment do not develop interstitial nephritis, nor do they display delayed-type hypersensitivity (DTH) to the immunizing renal tubular antigen preparation. The observed immunosuppression is critically dependent on PGE1 administration during the period of effector T cell induction. We therefore investigated the effect of PGE1 on the in vitro induction of DTH effector T cells reactive to renal tubular antigens (SRTA). PGE1 inhibits effector T cell induction in a dose-dependent, reversible manner, but has no inhibitory effect on fully differentiated DTH effector cells or SRTA-reactive cell lines. The PGE1 effect is indirect and mediated via nonspecific suppressor lymphokines. This suppression can be overcome by recombinant interleukin 1 (IL-1), which suggests a mechanism related to either diminished IL-1 secretion or target cell sensitivity to IL-1.

Alprostadil↗

Coupling of the adhesive receptor CD11b/CD18 to functional enhancement of effector macrophage tissue factor response.

Initiation and regulation of localized selective proteolysis is an important effector property of cells of macrophage (Mo) lineage. Among such effector responses is the induced expression of tissue factor (TF) by cells of Mo lineage. In characterizing the regulation of the Mo responses that may influence the magnitude of the effector phase of the cellular immune response, we have identified a role for the cell surface adhesive receptor CD11b/CD18 (Mac-1, CR3) to amplify the induced TF response. Occupancy of CD11b/CD18 by MAb as surrogate ligands does not directly initiate a TF response. In contrast, after either T cell-derived cytokine or LPS as initial signals, engagement of CD11b/CD18 by MAb induces a two- to eight-fold functional enhancement of the TF response in murine and human Mo. This pathway of CD11b/CD18 enhancement of this Mo effector response was also confirmed with recognized ligands for CD11b/CD18 by exposure of Mo to immobilized fibrinogen. A quantitative increase of Mo surface expression of TF was validated by flow cytometry. We suggest that engagement of CD11b/CD18 by complementary ligands including adherence to extracellular matrix, and possibly in antigen-driven TH:Mo collaborative responses, results in the transduction of cellular signals that quantitatively enhance the expression of TF per se and thereby enhance the inflammatory component of Mo mediated response.

Animals↗

Inhibition of murine nephritogenic effector T cells by a clone-specific suppressor factor.

We have used a murine model of organ-specific autoimmunity to characterize therapeutic modalities capable of down-regulating the cellular limb of the autoimmune response. Murine interstitial nephritis is an autoimmune disease mediated by tubular antigen-specific CD8+ nephritogenic effector T cells which are delayed-type hypersensitivity (DTH) reactive and cytotoxic to renal epithelial cells. Previous studies have demonstrated that disease can be suppressed with experimentally induced populations of T cells (Ts1 and Ts2 cells) obtained after injection of tubular antigen-coupled splenocytes into syngeneic mice. As the target of Ts2 is the CD8+ effector T cell, we have evaluated its effects on nephritogenic effector T cell clones isolated from diseased animals. Our studies demonstrate that soluble proteins expressed by Ts2 cells (TsF2) specifically abrogate the DTH, cytotoxic, and nephritogenic potential of M52 cells, although T cell receptor and IL-2 receptor expression are unchanged in these unresponsive M52 clones. TsF2-induced inhibition is dependent on new mRNA and protein synthesis. In a cytotoxic clone, M52.26, exposure to TsF2 induces expression of TGF-beta 1 which is, in turn, required for inhibition of cytotoxicity and nephritogenicity. Our studies are consistent with TGF-beta 1 behaving, at least in some T cells, as a nonspecific final effector of clone-specific suppression.

Amino Acid Sequence↗

Expansion of CD7(low) and CD7(negative) CD8 T-cell effector subsets in HIV-1 infection: correlation with antigenic load and reversion by antiretroviral treatment.

The antiviral response of CD8 T cells involves the differentiation of naive T cells into distinct types of effector and memory cells, which may be distinguished by the level of CD7 expression. We have investigated CD8 T cells in adults and children infected with HIV-1 to determine the disease relevance of cell subsets defined by CD7. CD8 T cells from patients infected with HIV-1 displayed profound down-modulation of CD7 expression as compared with healthy subjects, with expansion of both CD7(low) and CD7(negative) effector subsets. Loss of CD7(high) cells correlated directly with HIV-1 load and was particularly pronounced in patients with rapid disease progression. CD8 T cells specific for HIV-1, as well as Epstein-Barr virus (EBV) and cytomegalovirus (CMV) were predominantly found in the CD7(low) effector cell subset. Furthermore, recovery of CD4 counts on antiretroviral therapy was associated with reversion of the skewed CD7 profile in CD8 T cells. Thus, effector CD8 T-cell subsets distinguished by lowered CD7 expression expand in a manner that correlates with the magnitude of HIV-1, EBV, and CMV antigenic challenge and contract in response to successful antiretroviral treatment. The results are discussed in relation to the dual roles of CD7 as a receptor of both costimulation and cell death.

Adult↗