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PubMed2004

Diverse evolutionary mechanisms shape the type III effector virulence factor repertoire in the plant pathogen Pseudomonas syringae.

Many gram-negative pathogenic bacteria directly translocate effector proteins into eukaryotic host cells via type III delivery systems. Type III effector proteins are determinants of virulence on susceptible plant hosts; they are also the proteins that trigger specific disease resistance in resistant plant hosts. Evolution of type III effectors is dominated by competing forces: the likely requirement for conservation of virulence function, the avoidance of host defenses, and possible adaptation to new hosts. To understand the evolutionary history of type III effectors in Pseudomonas syringae, we searched for homologs to 44 known or candidate P. syringae type III effectors and two effector chaperones. We examined 24 gene families for distribution among bacterial species, amino acid sequence diversity, and features indicative of horizontal transfer. We assessed the role of diversifying and purifying selection in the evolution of these gene families. While some P. syringae type III effectors were acquired recently, others have evolved predominantly by descent. The majority of codons in most of these genes were subjected to purifying selection, suggesting selective pressure to maintain presumed virulence function. However, members of 7 families had domains subject to diversifying selection.

Base Composition↗

PubMed2002

Withdrawal of stimulation may initiate the transition of effector to memory CD4 cells.

The initial steps that determine development of memory in CD4 cells are unknown. To distinguish an intrinsic capacity of effectors to become memory cells from contributions of as yet undefined survival factors, we analyzed the effects of withdrawal of signals via TCR, costimulation, and cytokines from Th1 or Th2 primary effectors induced in vitro from TCR-transgenic CD4 cells. Withdrawal of stimulation caused the transition of effectors to resting populations with a memory phenotype that did not undergo division following transfer to normal syngeneic recipients. The return of effectors to rest was accompanied by acquisition of the capacity to function as memory cells in vivo as defined by extended persistence and a more rapid response to Ag in vivo than naive cells in adoptive hosts. Upon challenge with Ag, these in vitro-rested Th1 and Th2 cells were similar to long-term in vivo-rested memory cells, but distinct from in vitro-generated primary effectors and in vivo-restimulated memory effectors by their ability to resist apoptosis. Cessation of stimulation may occur when activated CD4 cells exit lymphoid tissues after priming and transition to memory may be initiated if effectors either fail to gain access to Ag in peripheral tissues where restimulation can lead to activation-induced cell death or do not receive sufficient stimuli to continue a response. Our results suggest that the first stage leading to stable CD4 memory could occur stochastically and independently of instructional processes and as such, the development of memory may be a default pathway when signals that direct responses are not received.

Animals↗

PubMed2002

Proliferation requirements of cytomegalovirus-specific, effector-type human CD8+ T cells.

Two prototypic types of virus-specific CD8(+) T cells can be found in latently infected individuals: CD45R0(+)CD27(+)CCR7(-) effector-memory, and CD45RA(+)CD27(-)CCR7(-) effector-type cells. It has recently been implied that CD45RA(+)CD27(-)CCR7(-) T cells are terminally differentiated effector cells and as such have lost all proliferative capacity. We show in this study, however, that stimulation of CMV-specific CD45RA(+)CD27(-)CCR7(-) T cells with their cognate peptide in concert with either CD4(+) help or IL-2, IL-15, or IL-21 in fact induces massive clonal expansion. Concurrently, these stimulated effector T cells change cell surface phenotype from CD45RA to CD45R0 and regain CCR7, while effector functions are maintained. Our data imply that CD45RA(+)CD27(-)CCR7(-) effector-type T cells contribute to immunity not only by direct execution of effector functions, but also by yielding progeny in situations of viral reinfection or reactivation.

CD8-Positive T-Lymphocytes↗

PubMed2003

CD7 is a differentiation marker that identifies multiple CD8 T cell effector subsets.

The adaptive immune response of human CD8 T cells to invading pathogens involves the differentiation of naive cells into memory and effector cells. However, the lineage relationship between memory and effector cells and the differentiation of CD8 T cells into distinct subsets of effector cell subpopulations are subjects of considerable debate. CD7 identifies three populations of CD8 T cells: CD7 high (CD7(high)), low (CD7(low)), and negative (CD7(neg)) that translate into subsets with distinct functional properties. The CD7(high) subset contains naive and memory cells and the CD7(low) and CD7(neg) subsets contain effector cells. The effector cells can functionally be divided into cytokine-secreting effector CD8 T cells and lytic effector CD8 T cells. These data provide a model of human CD8 T cell differentiation in which specialized distinct subpopulations can be identified by expression of CD7.

Antigens, CD7↗

PubMed2004

Glycoprotein 96 can chaperone both MHC class I- and class II-restricted epitopes for in vivo presentation, but selectively primes CD8+ T cell effector function.

The ability of mature T lymphocytes to develop effector capacity after encounter with cognate Ag is generally dependent upon inflammatory signals associated with infection that induce dendritic cell activation/maturation. These inflammatory signals can derive directly from pathogens or can be expressed by host cells in response to infection. Heat shock proteins (HSPs) are a class of host-derived inflammatory mediators that perform the dual function of both chaperoning MHC class I-restricted epitopes into the cross-presentation pathway of DCs and inducing the activation/maturation of these DCs to allow priming of cognate CD8(+) T cell effector responses. Although the ability of HSPs to elicit effector CD8 cell responses has been well established, their potential to prime CD4 cell effector responses has been relatively unexplored. In the current study we compared the ability of the endoplasmic reticulum-resident HSP gp96 to prime CD4 vs CD8 cells using TCR transgenic adoptive transfer systems and soluble gp96-peptide complexes. As expected, gp96 facilitated the cross-presentation of a class I-restricted peptide and priming of effector function in cognate CD8 cells. Interestingly, gp96 also facilitated the in vivo presentation of a class II-restricted peptide; however, the resulting CD4 cell response did not involve the development of effector function. Taken together, these data suggest that gp96 is an inflammatory mediator that selectively primes CD8 cell effector function.

Animals↗

PubMed2004

An in vitro model for the lepromatous leprosy granuloma: fate of Mycobacterium leprae from target macrophages after interaction with normal and activated effector macrophages.

The lepromatous leprosy granuloma is a dynamic entity requiring a steady influx of macrophages (Mphi) for its maintenance. We have developed an in vitro model to study the fate of Mycobacterium leprae in a LL lesion, with and without immunotherapeutic intervention. Target cells, consisting of granuloma Mphi harvested from the footpads of M. leprae-infected athymic nu/nu mice, were cocultured with normal or IFN-gamma-activated (ACT) effector Mphi. The bacilli were recovered and assessed for viability by radiorespirometry. M. leprae recovered from target Mphi possessed high metabolic activity, indicating a viable state in this uncultivable organism. M. leprae recovered from target Mphi incubated with normal effector Mphi exhibited significantly higher metabolism. In contrast, bacilli recovered from target Mphi cocultured with ACT effector Mphi displayed a markedly decreased metabolic activity. Inhibition by ACT Mphi required an E:T ratio of at least 5:1, a coculture incubation period of 3-5 days, and the production of reactive nitrogen intermediates, but not reactive oxygen intermediates. Neither IFN-gamma nor TNF-alpha were required during the cocultivation period. However, cell-to-cell contact between the target and effector Mphi was necessary for augmentation of M. leprae metabolism by normal effector Mphi as well as for inhibition of M. leprae by ACT effector Mphi. Conventional fluorescence microscopy and confocal fluorescence microscopy revealed that the bacilli from the target Mphi were acquired by the effector Mphi. Thus, the state of Mphi infiltrating the granuloma may markedly affect the viability of M. leprae residing in Mphi in the lepromatous lesion.

Animals↗

PubMed2004

In vivo cyclophosphamide and IL-2 treatment impedes self-antigen-induced effector CD4 cell tolerization: implications for adoptive immunotherapy.

The development of T cell tolerance directed toward tumor-associated Ags can limit the repertoire of functional tumor-reactive T cells, thus impairing the ability of vaccines to elicit effective antitumor immunity. Adoptive immunotherapy strategies using ex vivo expanded tumor-reactive effector T cells can bypass this problem; however, the susceptibility of effector T cells to undergoing tolerization suggests that tolerance might also negatively impact adoptive immunotherapy. Nonetheless, adoptive immunotherapy strategies can be effective, particularly those utilizing the drug cyclophosphamide (CY) and/or exogenous IL-2. In the current study, we used a TCR-transgenic mouse adoptive transfer system to assess whether CY plus IL-2 treatment rescues effector CD4 cell function in the face of tolerizing Ag (i.e., cognate parenchymal self-Ag). CY plus IL-2 treatment not only enhances proliferation and accumulation of effector CD4 cells, but also preserves the ability of these cells to express the effector cytokine IFN-gamma (and to a lesser extent TNF-alpha) in proportion to the level of parenchymal self-Ag expression. When administered individually, CY but not IL-2 can markedly impede tolerization, although their combination is the most effective. Although effector CD4 cells in CY plus IL-2-treated self-Ag-expressing mice eventually succumb to tolerization, this delay results in an increased level of in situ IFN-gamma expression in cognate Ag-expressing parenchymal tissues as well as death via a mechanism that requires direct parenchymal Ag presentation. These results suggest that one potential mechanism by which CY and IL-2 augment adoptive immunotherapy strategies to treat cancer is by impeding the tolerization of tumor-reactive effector T cells.

Adjuvants, Immunologic↗

PubMed2005

TGF-beta 1 attenuates the acquisition and expression of effector function by tumor antigen-specific human memory CD8 T cells.

TGF-beta1 is a potent immunoregulatory cytokine. However, its impact on the generation and effector function of Ag-specific human effector memory CD8 T cells had not been evaluated. Using Ag-specific CD8 T cells derived from melanoma patients immunized with the gp100 melanoma Ag, we demonstrate that the addition of TGF-beta1 to the initial Ag activation cultures attenuated the gain of effector function by Ag-specific memory CD8 T cells while the phenotypic changes associated with activation and differentiation into effector memory were comparable to control cultures. These activated memory CD8 T cells consistently expressed lower mRNA levels for T-bet, suggesting a mechanism for TGF-beta1-mediated suppression of gain of effector function in memory T cells. Moreover, TGF-beta1 induced a modest expression of CCR7 on Ag-activated memory CD8 T cells. TGF-beta1 also suppressed cytokine secretion by Ag-specific effector memory CD8 T cells, as well as melanoma-reactive tumor-infiltrating lymphocytes and CD8 T cell clones. These results demonstrate that TGF-beta1 suppresses not only the acquisition but also expression of effector function on human memory CD8 T cells and tumor-infiltrating lymphocytes reactive against melanoma, suggesting that TGF-beta1-mediated suppression can hinder the therapeutic benefits of vaccination, as well as immunotherapy in cancer patients.

Cell Line, Tumor↗

PubMed2006

T-bet down-modulation in tolerized Th1 effector CD4 cells confers a TCR-distal signaling defect that selectively impairs IFN-gamma expression.

When Th1 effector CD4 cells encounter tolerizing Ag in vivo, their capacity to express the effector cytokines IFN-gamma and TNF-alpha is lost more rapidly than noneffector functions such as IL-2 production and proliferation. To localize the relevant intracellular signaling defects, cytokine expression was compared following restimulation with Ag vs agents that bypass TCR-proximal signaling. IFN-gamma and TNF-alpha expression were both partially rescued when TCR-proximal signaling was bypassed, indicating that both TCR-proximal and -distal signaling defects impair the expression of these two effector cytokines. In contrast, bypassing TCR-proximal signaling fully rescued IL-2 expression. T-bet, a transcription and chromatin remodeling factor that is required to direct the differentiation of naive CD4 cells into IFN-gamma-expressing Th1 effectors, was partially down-modulated in tolerized Th1 effectors. Enforcing T-bet expression during tolerization selectively rescued the ability to express IFN-gamma, but not TNF-alpha. Conversely, expression of a dominant-negative T-bet in Th1 effectors selectively impaired the ability to express IFN-gamma, but not TNF-alpha. Analysis of histone acetylation at the IFN-gamma promoter further suggested that down-modulation of T-bet expression during Th1 effector CD4 cell tolerization does not impair IFN-gamma expression potential through alterations in chromatin structure.

Adoptive Transfer↗

PubMed2006

Three memory subsets of human CD8+ T cells differently expressing three cytolytic effector molecules.

Multicolor flow cytometric analysis for the expression of three effector molecules, i.e., perforin (Per), granzyme A (GraA), and granzyme B (GraB), in human CD8(+) T cells demonstrated that they included five subpopulations, implying the following pathway for the differentiation of CD8(+) T cells: Per(-)GraA(-)GraB(-)-->Per(-)GraA(+)GraB(-)-->Per(low)GraA(+)GraB(-)--> Per(low)GraA(+)GraB(+)-->Per(high)GraA(+)GraB(+). The analysis of the expression of these molecules in the subsets classified by the combination of the expression of CCR7 and CD45RA or by that of CD27, CD28, and CD45RA showed that functional CD8(+) T cell subsets could be partially identified by these phenotypic classifications. However, the functional subsets could be precisely identified by the classification using five cell surface markers or three cell surface markers and three cytolytic molecules. Per(-)GraA(-)GraB(-) and Per(-/low)GraA(+)GraB(-) cells were predominantly found in CCR5(-)CCR7(+) and CCR5(high/low)CCR7(-) subsets, respectively, of CD8(+) T cells expressing the CD27(+)CD28(+)CD45RA(-) phenotype, whereas Per(low)GraA(+)GraB(+) cells were found in the CCR5(low)CCR7(-) subset of those expressing this phenotype and in a part of the CCR5(-/low)CCR7(-) subset of those expressing the CD27(-/low)CD28(-)CD45RA(-/+) phenotype. Ex vivo EBV-specific CD8(+) T cells, which were Per(low/-)GraA(+)GraB(-/+) cells, hardly or very weakly killed the target cells, indicating that these were not effector T cells. These findings suggest that the Per(-)GraA(-)GraB(-), Per(-/low)GraA(+)GraB(-), and Per(low)GraA(+)GraB(+) cells were central memory, early effector memory, and late effector memory T cells, respectively. Per(-/low)GraA(+)GraB(-) cells gained GraB expression after TCR stimulation, indicating that early effector memory T cells could differentiate into late effector and effector T cells. The present study showed the existence of three memory subsets and the pathway for their differentiation.

CD8-Positive T-Lymphocytes↗

PubMed1999

Presence of effector CD8+ T cells in hepatitis C virus-exposed healthy seronegative donors.

CTL responses against multiple hepatitis C virus (HCV) epitopes were detected in 7 of 29 (24.1%) healthy family members (HFM) persistently exposed to chronically HCV-infected patients (HCV-HFM). These precursor CTL were at very low or undetectable frequencies, as determined by limiting dilution analysis. However, when HCV-specific effector CD8+ T cells, freshly isolated from PBMC of HCV-HFM, were assessed by a sensitive enzyme-linked immunospot assay, their frequencies were severalfold higher than those of precursor CTL. These results indicate that the two assays detect two functionally distinct T cell populations and that the effector cells are not assayed by the 51Cr-release assay. Furthermore, the combination of cell depletion and enzyme-linked immunospot analyses showed that the effector cells were confined into a CD8+ CD45RO+ CD28- population. The persistence of effector CD8+ T cells specific for both the structural and nonstructural viral proteins in uninfected HCV-HFM, suggest that: 1) an immunological memory is established upon a subclinical infection without any evidence of hepatitis, in a large cohort of HCV-exposed individuals; 2) because these cells required neither restimulation nor the addition of particular cytokines in vitro for differentiating in effectors, they should be capable of prompt HCV-specific effector function in vivo, possibly providing antiviral protection; and 3) the maintenance of effector T cell responses may be sustained by persisting low-level stimulation induced by inapparent infections.

Adolescent↗

PubMed1975

Specific and nonspecific antitumor immunity. II. Macrophage-mediated nonspecific effector activity induced by BCG and similar agents.

The recently described inhibition of DNA synthesis (IDS) assay, which measures antitumor effector (E) cell function by the quantitation of decreases in tritiated thymidine incorporation of target tumor cells, was used to analyze the nonspecific effector activity of peritoneal exudate cells (PEC) from mice infected intraperitoneally with BCG. These PEC could inhibit growth of and then kill all tumor target (effector to target) cells tested at E/T ratios as low as 1:1. This activity was not due to alterations in media, nor could any activity be shown for cell-free supernatants prepared from active cells. The principal cell type mediating this effector function was the "activated" macrophage-no activity was found in lymphoid or polymorphonuclear leukocytes. Direct effector to target contact was necessary for the cytotoxic reaction. The time course of these effects and comparative 51Cr release data were reported. The removal of the adherent nonspecific effectors from PEC of mice immunized to both BCG and a specific syngeneic tumor revealed a specific cytotoxicity of the remaining lymphoid cells. These results indicated that nonspecific effector activity by "activated" macrophages induced by BCG infection could be a potent antitumor mechanism, at least in vitro, and the IDS assay provided an accurate, reproducible, and quantitative method for measurement of the function of such E cells.

Animals↗

PubMed1990

Proteins as biological effectors.

This chapter presented an overview of the role of proteins as biological effectors. From a simplistic point of view, based solely on comparison of the structural diversity of immunoglobulins, blood coagulation proteins, gonadotropins, growth factors, and antiproteins, it could be concluded that the functional mechanisms of these protein families bear little or no relationship. Despite this enormous divergency in structure-function relationship, there are in fact elements of commonality in their effector roles arising as a direct consequence of the ability of these classes of protein effectors to act as exquisite examples of the processes of biorecognition. All these case histories, and the numerous other familial case studies of protein effectors which could have been employed to illustrate the different functional roles of proteins, owe their biological properties to their primordial protein antecedents which have traversed the harsh wilderness of evolution in biorecognition phenomena and survived to elicit specific effector roles. Dictated by underlying physicochemical constraints, deceived at times by the lulling tones of the siren entropy, and constantly vulnerable to the vagaries of other more pervasive forms of biological networking and information transfer encoded in the genes of virus and invading microorganisms, protein biorecognition in higher life forms, and particularly in mammals, represents the finely tuned molecular avenues for the genome to transfer its information to the next generation. The examples summarized in this chapter illustrate the complex, and in disease states imperfect, functional potential of proteins to be manifested in the jigsaw of biorecognition and be realized in the network of nature's biological effectors. Proteins thus represent a diverse range of effector molecules whose properties are totally dependent on their conformational or topographic status. The three-dimensional structure defines active sites on the molecule through which intermolecular interaction and biorecognition phenomena can occur. The cipher for this surface topography is, of course, coded in the primary amino acid sequence. Much experimental work is being directed in these and other laboratories at elucidating the principles governing the folding of unique peptide sequences into three-dimensional structures. Further advances in the theoretical understanding of the thermodynamics of protein folding as observed by x-ray crystallography, nuclear magnetic resonance and other spectroscopic techniques will greatly aid this quest. In addition, more comprehensive computer-aided algorithms for structure simulation, improved models of protein conformational behavior, and greater insight into the molecular forces which control sequence nucleation will also be required.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗

PubMed2005

[Influence of HSP70 on combined method of hyperthermia and immunologic effector cells to treat cancer].

OBJECTIVE: To investigate hyperthermia enhanced expression of heat shock protein70 (HSP70) in breast cancer drug sensitive cell line MCF7 and multi-drug resistant (MDR) cell line MCF7/ADR, so as to increase cytotoxic activity of immunologic effector cells against the target cells, and to provide an experimental basis for cell immunotherapy based on hyperthermia. METHODS: The immunological effector cells were induced and expanded by cytokines. Breast cancer cell lines MCF7 and MCF7/ADR were treated at 42 degrees C for an hour. Then after being incubated for additional 4 hours, 24 hours and 48 hours, the cells were digested. Flow cytometry (FCM) was used to detect the expression of HSP70 on the target cells. MTT assay was employed to evaluate cell proliferation and the cytotoxic activity of immunologic effector cells against target cells. RESULTS: The expressions of HSP70 in both the target cells had significant difference. The expression of HSP70 in MCF7/ADR cells was higher than in MCF7 cells before hyperthermia. After hyperthermia the expression of HSP70 increased by 6 folds in MCF7/ADR cells, and 22 folds in MCF7 cells and was higher than in MCF7/ADR cells at hour 4. The proliferation inhibition fraction of hyperthermia against MCF7 was significantly lower than that of MCF7/ADR. The cytotoxic activity of immunologic effector cells against MCF7 cells was lower than against MCF7/ADR cells before hyperthermia. After hyperthermia the cytotoxic activity of immunologic effector cells against MCF7 cells rose by 86.23%, and was higher than against MCF7/ADR cells (rose by 30.32%). CONCLUSION: The expression of HSP70 in breast cancer drug sensitive cell line MCF7 and MDR cell line MCF7/ADR were enhanced significantly by hyperthermia. Cytotoxic activity of immunologic effector cells against both the target cells were increased by hyperthermia. The differential expressions of HSP70 in breast cancer drug sensitive cell line MCF7 and MDR cell line MCF7/ADR affect the cytotoxic activity of immunologic effector cells.

Breast Neoplasms↗

PubMed1991

Distinct subsets of accessory cells activate Thy-1+ triple negative (CD3-, CD4-, CD8-) cells and Th-1 delayed-type hypersensitivity effector T cells.

The SJL strain of mice possess a unique developmental delay in the ability to exhibit delayed-type hypersensitivity (DTH) responses after immunization with a wide variety of Ag. Similar to other models of DTH, the adoptive transfer of syngeneic Ag-pulsed macrophages from DTH-responsive mice into these DTH-unresponsive mice results in the activation of Ag-specific, CD4+ DTH effector Th1 T cells. The absence of other defects in APC-dependent immune responses indicate that the macrophages is the sole APC required for the induction of DTH effector T cells in SJL mice. The defect occurs during the sensitization phase of the DTH response; however, it has not been determined whether a Th cell, which is required for the induction of CD4+ DTH effector T cells, was present in the DTH unresponsive SJL mice. In this study, we have determined that the Thy-1+ helper cell is induced upon Ag stimulation of nonresponder mice and present evidence for the existence of an accessory cell distinct from the macrophage that induces CD4+ DTH effector T cells. Our data indicate that CD4+ DTH effector T cells are induced in an Ag-specific and MHC-restricted manner by an adherent macrophage that expresses the Mac-1+, Mac-2-, Mac-3+, I-A+ phenotype. Adoptive transfer of as few as 100 of the Mac-1+, Mac-2-, or Mac-3+ subsets from DTH responsive donors to DTH unresponsive recipients is able to overcome the DTH deficit. The activation of CD4+ DTH effector T cells in the SJL mouse cells also requires a Thy-1+, Lyt-1+, CD3-, CD4-, CD8-, helper cell. In contrast to the Mac-1+, Mac-3+, I-A+ accessory cell, this helper cell requires an adherent, irradiation resistant, accessory cell that expresses the Mac-1+, Mac-2-, Mac-3-, I-A- surface phenotype for activation. Further, the interaction between this accessory cell and the Thy-1+ helper cell is neither Ag-specific nor MHC restricted. This is the first demonstration of an accessory cell requirement for the Thy-1+, Lyt-1+, B220-, CD4-, CD8-, CD3- DTH Th cell. These data indicate that the activation of the triple negative helper cells and subsequent activation of the CD4+ effector T cells are regulated by two distinct macrophage subpopulations.

Animals↗

PubMed2006

[Immunological effector cells enhance apoptosis induced by adriamycin in a multi-drug resistant human breast cancer cell line].

OBJECTIVE: To investigate the effects of immunologic effector cells to enhance apoptosis induced by adriamycin (ADR) in multi-drug resistant human breast cancer cell line MCF7/ADR. METHODS: The immunologic effector cells were induced and expanded by IFN-gamma, McAb CD3, IL-1 and IL-2. The expression of P-glycoprotein (P-gp) and its relation to apoptosis in target cells were detected by TUNEL technique and immunohistochemical staining. Flow cytometry (FCM) was carried out to determine the expression level of human breast cancer related P185 antigen and the positive rate of Annexin V-FITC/PI expression. The subcellular distribution of ADR and Annexin V expression in the target cells were detected by fluorescence microscopy. RESULTS: The immunologic effector cells down-regulated the expression of P185 and P-gp in MCF7/ADR cells. The accumulation and subcellular distribution of ADR in MCF7/ADR cells were increased after co-culture with the immunologic effector cells. After treatment with the immunologic effector cells in combination with ADR, apoptosis rate of the target cells was 10 times higher than that induced by ADR alone, and 13 times higher than that induced by the immunologic effector cells alone. CONCLUSION: Immunologic effector cells can simultaneously down-regulate the expression of P185 and P-gp in MCF7/ADR cell line, and increase the apoptosis rate of MCF7/ADR cells in combination with ADR.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1991

Effector-induced conformational transitions in Ascaris suum phosphofructokinase. A fluorescence and circular dichroism study.

Results of activity and spectral studies using fluorescence and circular dichroism show that AMP and fructose 2,6-bisphosphate (F-2,6-P2) activate Ascaris suum phosphofructokinase through specific and similar conformational changes. Inorganic compounds like (NH4)2SO4 and KH2PO4 also induce structural alterations in the enzyme in a manner different from those caused by AMP and F-2,6-P2. The enzyme is activated by both AMP and F-2,6-P2, in 20 mM phosphate buffer, pH 6.6, with 0.2 mM ATP and 1 mM F-6-P. The Kact values for AMP and F-2,6-P2 are 25 +/- 3 microM and 1.5 +/- 0.2 microM, respectively. Both effectors quench enzyme tryptophan fluorescence in phosphate, pH 6.6, in a concentration-dependent manner. The Kd values determined from the decrease in emission intensity at 342 nm as a function of effector concentration are 24 +/- 3 microM for AMP and 1.00 +/- 0.15 microM for F-2,6-P2, in excellent agreement with the values of Kact. Both effectors also produce dramatic changes in the CD spectrum of the enzyme, in the region from 240 to 190 nm representing the peptide backbone. Secondary structure calculations suggest an increase in the alpha-helical content of the enzyme in the presence of either effector. The Kd values obtained from the concentration dependence of the decrease in ellipticity at 210 nm are 22.8 +/- 5.3 microM and 1.3 +/- 0.2 microM, respectively, for AMP and F-2,6-P2, once again in close agreement with the Kact values for these effectors. The data imply that activation of phosphofructokinase by these effectors is concomitant with structural changes in the enzyme. Further, comparison of the difference CD spectra for the effects of AMP and F-2,6-P2 show that both of them produce similar conformational changes and probably stabilize a similar final activated state of the enzyme. Other hexose phosphate analogues such as fructose 6-phosphate, glucose 1,6-bisphosphate, and fructose 1,6-bisphosphate do not affect the CD spectrum of the enzyme. Ammonium sulfate has no effect on the CD spectrum of the enzyme in phosphate buffer but does cause a significant alteration in the spectrum obtained in Mes. Gel filtration high performance liquid chromatography using a Borosil TSK 400 column shows that the tetrameric state of the native enzyme is not affected by the presence of the effectors.

Adenosine Monophosphate↗

PubMed1985

Network regulation of the immune response: alternative control points for suppressor modulation of effector lymphocytes.

The network theory of the immune response proposed by Jerne has stimulated considerable interest, and a large body of evidence supporting this theory has been produced. However, the structure and function of the immune network have not been precisely defined. In this paper we develop several criteria to compare alternative systems on the basis of function and then examine mathematically the functional significance of two interactions involving suppressor regulation of effector lymphocytes in normal immune responses. The interactions examined in detail are suppressor regulation of the production of effector lymphocytes and suppressor regulation of the clearance of effector lymphocytes. The approach is one that has been used previously to predict and characterize function and design in biochemical and genetic control systems. The results of our analysis suggest that an immune system with suppressor regulation of the production of effector lymphocytes is equal or superior to a system without this form of regulation on the basis of all of the criteria examined in this study. Also, a system with regulation of the clearance of effector lymphocytes can be equal or superior to a system without this form of regulation on the basis of six criteria, but it is inferior to such a system on the basis of one criterion. Furthermore, a system with regulation of both production and clearance of effector lymphocytes is equal or superior to a system without regulation of production on the basis of all of the criteria and can be equal or superior to a system without regulation of clearance on the basis of six criteria, but it is inferior to such a system on the basis of one criterion. Similar conclusions hold for the comparison of systems in which regulation is exerted upon the production or clearance of effector molecules, such as antibodies or free radicals.

Animals↗