Biomedical subjects

C A Hunter

Publications and source records attributed to C A Hunter.

At least 19 recordsLinked to original sources

PubMed2000

Sequence-dependent DNA structure: dinucleotide conformational maps.

We have used a computational model to calculate the potential energy surface for dinucleotide steps in double helical DNA as a function of the two principal degrees of freedom, slide and shift. By using a virtual bond to model the constraints imposed by the sugar-phosphate backbone, twist, roll, tilt and rise can be simultaneously optimised for any given values of slide and shift. Thus we have been able to construct complete conformational maps for all step types. For some steps, the maps agree well with experimental data from X-ray crystal structures, but other steps appear to be strongly perturbed by the effects of context (conformational coupling with the neighbouring steps). The optimised values of twist and roll show sequence-dependent variations consistent with the crystal structure data. The conformational maps allow us to construct adiabatic paths, and hence calculate the flexibility of each step with respect to slide and shift. Again the results agree well with the available experimental assignments of flexibility: YR steps, CA/TG and CG, are the most flexible and RR steps, such as AA, the least flexible.

Base Pairing↗

PubMed2000

Sequence-dependent DNA structure: tetranucleotide conformational maps.

A database of X-ray crystal structures of double helical DNA oligomers has been used to analyse the role of the sugar-phosphate backbone in coupling the conformational properties of neighbouring dinucleotide steps. The base step parameters which are most strongly coupled to the backbone degrees of freedom are slide and shift, and these are the two dinucleotide step parameters which show strong correlations along a sequence: the value of slide follows the values in the neighbouring steps, whereas shift tends to alternate. This conformational coupling is mediated by the shared furanose rings at the step junctions: a change in the value of slide causes a change in the mean value of the same strand 3' and 5'-chi torsion angle, and a change in the mean value of the 3' and 5' sugar pseudo-rotation phase angle, P; a change in the value of shift causes a difference between the same strand 3' and 5'-chi in A-DNA and a difference between the 3' and 5'-P in B-DNA. We have used a database of tetranucleotide X-ray crystal structures to parameterise a simple model for the coupling of slide and shift. Using this junction model together with our dinucleotide step potential energy maps described previously, we can in principle calculate the structure of any DNA oligomer. The parameterisation indicates that the rotational step parameters are accurate to within 5 degrees, and the translational step parameters are accurate to within 0.5 A. The model has been used to study the potential energy surfaces of all possible tetranucleotide sequences, and the calculations agree well with the experimental data from X-ray crystal structures. Some dinucleotide steps are context independent (AA/TT, AT and TA), because the conformational properties of all possible neighbouring steps are compatible. When the conformational properties of the neighbours are not compatible, the behaviour of a step cannot be understood at the dinucleotide level. Thus the conformations of CG, GC and GG/CC are all strongly context dependent. The remaining mixed sequence steps show weakly context-dependent behaviour. The approach allows the calculation of the relative stability and flexibility of tetranucleotide sequences, and the results indicate why TATA is used as an origin of replication. Clear predictions are made about sequences which have not yet been characterised crystallographically. In particular, poly(CCA).poly(TGG) is predicted to have an unusual structure which lies between the C and D-DNA polymorphs.

Base Pairing↗

PubMed2000

The CD40/CD40 ligand interaction is required for resistance to toxoplasmic encephalitis.

Since the CD40/CD40 ligand (CD40L) interaction is involved in the regulation of macrophage production of interleukin 12 (IL-12) and T-cell production of gamma interferon (IFN-gamma), effector cell functions associated with resistance to Toxoplasma gondii, the role of CD40L in immunity to this parasite was assessed. Infection of C57BL/6 mice with T. gondii results in an upregulation of CD40 expression on accessory cell populations at local sites of infection as well as in lymphoid tissues. Splenocytes from C57BL/6 mice infected with T. gondii for 5 days produced high levels of IL-12 and IFN-gamma when stimulated with toxoplasma lysate antigen, and blocking CD40L did not significantly alter the production of IFN-gamma or IL-12 by these cells. Similar results were observed with splenocytes and mononuclear cells isolated from the brains of chronically infected mice. Interestingly, although CD40L(-/-) mice infected with T. gondii produced less IL-12 than wild-type mice, they produced comparable levels of IFN-gamma but succumbed to toxoplasmic encephalitis 4 to 5 weeks after infection. The inability of CD40L(-/-) mice to control parasite replication in the brain correlated with the ability of soluble CD40L, in combination with IFN-gamma, to activate macrophages in vitro to control replication of T. gondii. Together, these results identify an important role for the CD40/CD40L interaction in resistance to T. gondii. However, this interaction may be more important in the control of parasite replication in the brain rather than the generation of protective T-cell responses during toxoplasmosis.

Animals↗

PubMed2000

Blockade of costimulation prevents infection-induced immunopathology in interleukin-10-deficient mice.

Interleukin-10 (IL-10) is associated with inhibition of cell-mediated immunity and downregulation of the expression of costimulatory molecules required for T-cell activation. When IL-10-deficient (IL-10KO) mice are infected with Toxoplasma gondii, they succumb to a T-cell-mediated shock-like reaction characterized by the overproduction of IL-12 and gamma interferon (IFN-gamma) associated with widespread necrosis of the liver. Since costimulation is critical for T-cell activation, we investigated the role of the CD28-B7 and CD40-CD40 ligand (CD40L) interactions in this infection-induced immunopathology. Our studies show that infection of mice with T. gondii resulted in increased expression of B7 and CD40 that was similar in wild-type and IL-10KO mice. In vivo blockade of the CD28-B7 or CD40-CD40L interactions following infection of IL-10KO mice with T. gondii did not affect serum levels of IFN-gamma or IL-12, nor did it prevent death in these mice. However, when both pathways were blocked, the IL-10KO mice survived the acute phase of infection and had reduced serum levels of IFN-gamma and alanine transaminase as well as decreased expression of inducible nitric oxide synthase in the liver and spleen. Analysis of parasite-specific recall responses from infected IL-10KO mice revealed that blockade of the CD40-CD40L interaction had minimal effects on cytokine production, whereas blockade of the CD28-B7 interaction resulted in decreased production of IFN-gamma but not IL-12. Further reduction of IFN-gamma production was observed when both costimulatory pathways were blocked. Together, these results demonstrate that the CD28-B7 and CD40-CD40L interactions are involved in the development of infection-induced immunopathology in the absence of IL-10.

Abatacept↗

PubMed1999

Aluminium hydroxide adjuvant initiates strong antigen-specific Th2 responses in the absence of IL-4- or IL-13-mediated signaling.

Previous studies demonstrate that aluminium hydroxide adjuvant (alum) produces increased Th1 responses in IL-4-deficient mice compared with wild-type animals, although the continued production of IL-5 by spleen cells from these mice also indicates that Th2 responses are induced. In the present study, we demonstrate that alum can induce Th2-associated IL-4 and IL-5 production in the absence of IL-4 signaling in mice deficient in either IL-4Ralpha or Stat6. The Th2 responses observed could not be due to IL-13 as IL-13 responses are also impaired in IL-4Ralpha- and Stat6-deficient mice. We also detected higher levels of IL-4 in IL-4Ralpha gene-deficient, though not Stat6-deficient, mice compared with their wild-type counterparts. The increased levels of IL-4 could be explained by the IL-4R being unavailable to neutralize this cytokine in IL-4Ralpha-deficient mice. While levels of IL-5 production in IL-4Ralpha- or Stat6-deficient mice were similar to IL-4-deficient and wild-type mice, other type 2-associated responses, which are largely or wholly IL-4 dependent, such as the production of IgG1 or IgE Abs, were either reduced or absent. We conclude that alum adjuvants can induce IL-4 production and Th2 responses independently of IL-4 or IL-13, negating the requirement for an early source of IL-4 in the Th2 response induced by this adjuvant.

Adjuvants, Immunologic↗

PubMed1999

The NF-kappa B family member RelB is required for innate and adaptive immunity to Toxoplasma gondii.

The NF-kappa B family of transcription factors are associated with the regulation of innate and adaptive immunity to infection. Infection of C57BL/6 mice with Toxoplasma gondii resulted in up-regulation of NF-kappa B activity that included the NF-kappa B family member RelB. To assess the role of RelB in the regulation of the immune response to this infection, we challenged RelB-deficient mice (RelB-/-) and wild-type (WT) littermate controls with T. gondii. Although WT controls were resistant to T. gondii, RelB-/- mice succumbed 10-15 days after infection. Examination of accessory cell functions associated with resistance to T. gondii revealed that RelB-/- macrophages stimulated with IFN-gamma plus LPS or TNF-alpha produced IL-12 as well as reactive nitrogen intermediates and inhibited parasite replication similar to WT macrophages. Analysis of the systemic responses of RelB-/- and WT mice revealed that infected mice had similar serum levels of IL-12. However, RelB-/- mice challenged with T. gondii produced negligible levels of IFN-gamma and had reduced NK cell activity compared with WT mice. Similarly, splenocytes from uninfected RelB-/- mice stimulated with polyclonal stimuli were deficient in their ability to produce IFN-gamma. Together, our results demonstrate that RelB is essential for the development of innate NK and adaptive T cell responses that lead to the production of IFN-gamma and resistance to T. gondii.

Animals↗

PubMed1999

Role of CD28 in the generation of effector and memory responses required for resistance to Toxoplasma gondii.

CD28 deficient (CD28-/-) mice were used to study the role of costimulation in the T cell-mediated, IFN-gamma-dependent mechanism of resistance to Toxoplasma gondii. These mice were resistant to infection with the ME49 strain of T. gondii. Analysis of the immune response of acutely infected CD28-/- mice revealed that IL-12 was required for T cell production of IFN-gamma and this was independent of the CD40/CD40 ligand interaction. A similar mechanism of IL-12-dependent, CD28/B7 independent production of IFN-gamma by T cells was also observed in wild-type mice. Interestingly, although chronically infected wild-type mice were resistant to rechallenge with the virulent RH strain of T. gondii, chronically infected CD28-/- mice were susceptible to rechallenge with the RH strain. This deficiency in the protective memory response by CD28-/- mice correlated with a lack of IL-2 and IFN-gamma in recall responses and reduced numbers of CD4+ T cells expressing a memory phenotype. Together, our findings demonstrate that CD28 is not required for the development of a protective T cell response to T. gondii, but CD28 is required for an optimal secondary immune response.

Animals↗

PubMed1999

The CD28/B7 interaction is not required for resistance to Toxoplasma gondii in the brain but contributes to the development of immunopathology.

Infection of C57BL/6 mice with Toxoplasma gondii leads to chronic encephalitis characterized by infiltration into the brain of T cells that produce IFN-gamma and mediate resistance to the parasite. Our studies revealed that expression of B7.1 and B7.2 was up-regulated in brains of mice with toxoplasmic encephalitis (TE). Because CD28/B7-mediated costimulation is important for T cell activation, we assessed the contribution of this interaction to the production of IFN-gamma by T cells from brains and spleens of mice with TE. Stimulation of splenocytes with Toxoplasma Ag or anti-CD3 mAb resulted in production of IFN-gamma, which was inhibited by 90% in the presence of CTLA4-Ig, an antagonist of B7 stimulation. However, production of IFN-gamma by T cells from the brains of these mice was only slightly reduced (20%) by the addition of CTLA4-Ig. To address the role of the CD28/B7 interaction during TE, we compared the development of disease in C57BL/6 wild-type (wt) and CD28-/- mice. Although the parasite burden was similar in wt and CD28-/- mice, CD28-/- mice developed less severe encephalitis and survived longer than wt mice. Ex vivo recall responses revealed that mononuclear cells isolated from the brains of chronically infected CD28-/- mice produced less IFN-gamma than wt cells, and this correlated with reduced numbers of intracerebral CD4+ T cells in CD28-/- mice compared with wt mice. Taken together, our data show that resistance to T. gondii in the brain is independent of CD28 and suggest a role for CD28 in development of immune-mediated pathology during TE.

Animals↗

PubMed1999

IL-18 and CD28 use distinct molecular mechanisms to enhance NK cell production of IL-12-induced IFN-gamma.

NK cells play an important role in innate immune resistance, particularly through synthesis of the pro-inflammatory cytokine IFN-gamma. This study compares the abilities of the cytokine IL-18 and the costimulatory cell surface molecule CD28 to enhance IL-12-driven IFN-gamma production by NK cells. Studies with other cytokines (IL-1beta, IL-6, TNF-alpha, IL-15) showed that IL-18 or anti-CD28 treatments were the most efficient inducers of IFN-gamma when combined with IL-12. The ability of IL-18 to enhance IFN-gamma was shown to be dependent on the presence of IL-12. Similarly, although anti-CD28 stimulation alone could enhance IFN-gamma synthesis, this effect was significantly increased in the presence of IL-12. Although neither method of costimulation required de novo protein synthesis for their effects on IFN-gamma mRNA expression, these molecules used distinct mechanisms. Specifically, nuclear run-on analysis revealed that IL-18 in combination with IL-12 enhanced the rate of transcription of the IFN-gamma gene. Conversely, treatment with anti-CD28 plus IL-12 did not significantly up-regulate the rate of transcription of the IFN-gamma gene, but stabilized IFN-gamma mRNA expression within NK cells. These findings illustrate costimulatory pathways that result in potent IFN-gamma responses by NK cells and show that although IL-18 and anti-CD28 can enhance the synthesis of IL-12-driven IFN-gamma, they employ molecular mechanisms that are distinct from one another.

Animals↗

PubMed1999

Anti-TGF-beta treatment promotes rapid healing of Leishmania major infection in mice by enhancing in vivo nitric oxide production.

CB6F1 mice display intermediate susceptibility to Leishmania major infection compared with the highly susceptible BALB/c and resistant C57BL/6 parental strains. During early weeks of infection, these mice develop dominant Th2 type responses to L. major, although they eventually exhibit a Th2 to Th1 switch and spontaneously resolve their infections. In this study, we have examined the effects of either IL-12 or anti-TGF-beta therapy on the immune response and course of disease in chronically infected CB6F1 mice. Local treatment with IL-12 inoculated into the parasitized lesion at 4 wk of infection induced a marked increase in IFN-gamma production but did not result in a significant reduction in numbers of parasite or promote more rapid healing. However, local treatment with an Ab to TGF-beta led to both a decrease in parasite numbers and more rapid healing, despite the fact that such treatment did not significantly alter the pattern of IL-4 and IFN-gamma production. Immunohistochemical studies showed that anti-TGF-beta treatment resulted in increased nitric oxide production within parasitized lesions. Our results suggest that TGF-beta may play an important regulatory role during chronic stages of a L. major infection by suppressing macrophage production of nitric oxide and that, in the absence of TGF-beta, even the relatively low levels of IFN-gamma observed in mice with dominant Th2-type responses are sufficient to activate macrophages to destroy amastigotes within parasitized lesions.

Adjuvants, Immunologic↗

PubMed1999

IL-10 enhances NK cell proliferation, cytotoxicity and production of IFN-gamma when combined with IL-18.

Previous studies have shown that IL-10 inhibits the accessory cell functions required for production of IFN-gamma by T cells and NK cells. Our results show that although IL-10 did not induce the production of IFN-gamma by NK cells, it did enhance the ability of IL-18 to stimulate NK cell production of IFN-gamma. In addition, IL-10 augmented NK cell proliferation and cytotoxic activity when combined with IL-18. However, IL-10 did not affect the ability of IL-12 to stimulate NK cells to produce IFN-gamma or proliferate, but there was an additive effect with IL-12 to increase NK cell cytotoxic activity. Interestingly, the type I IFN, whose receptors (R) are related to the IL-10R, also enhanced the effects of IL-18 on NK cell production of IFN-gamma and NK cell cytotoxicity. The ability of IL-10 to elevate the production of IFN-gamma appeared to be specific for NK cells since IL-10 had no effect on the production of IFN-gamma by Th1 clones stimulated with IL-18 or IL-12 in the presence of a monoclonal antibody specific for CD3. These latter results correlated with lower mRNA levels for the alpha and beta chains of the IL-10R in Th1 cells than observed in NK cells. Thus, the ability of IL-10 and IL-18 to up-regulate NK cell function, but not Th1 cell activity, appears to be based on expression of the IL-10R.

Adjuvants, Immunologic↗

PubMed1998

Inhibition of interferon gamma induced interleukin 12 production: a potential mechanism for the anti-inflammatory activities of tumor necrosis factor.

Inflammation is associated with production of cytokines and chemokines that recruit and activate inflammatory cells. Interleukin (IL) 12 produced by macrophages in response to various stimuli is a potent inducer of interferon (IFN) gamma production. IFN-gamma, in turn, markedly enhances IL-12 production. Although the immune response is typically self-limiting, the mechanisms involved are unclear. We demonstrate that IFN-gamma inhibits production of chemokines (macrophage inflammatory proteins MIP-1alpha and MIP-1beta). Furthermore, pre-exposure to tumor necrosis factor (TNF) inhibited IFN-gamma priming for production of high levels of IL-12 by macrophages in vitro. Inhibition of IL-12 by TNF can be mediated by both IL-10-dependent and IL-10-independent mechanisms. To determine whether TNF inhibition of IFN-gamma-induced IL-12 production contributed to the resolution of an inflammatory response in vivo, the response of TNF+/+ and TNF-/- mice injected with Corynebacterium parvum were compared. TNF-/- mice developed a delayed, but vigorous, inflammatory response leading to death, whereas TNF+/+ mice exhibited a prompt response that resolved. Serum IL-12 levels were elevated 3-fold in C. parvum-treated TNF-/- mice compared with TNF+/+ mice. Treatment with a neutralizing anti-IL-12 antibody led to resolution of the response to C. parvum in TNF-/- mice. We conclude that the role of TNF in limiting the extent and duration of inflammatory responses in vivo involves its capacity to regulate macrophage IL-12 production. IFN-gamma inhibition of chemokine production and inhibition of IFN-gamma-induced IL-12 production by TNF provide potential mechanisms by which these cytokines can exert anti-inflammatory/repair function(s).

Animals↗

PubMed1998

Immune suppression by recombinant interleukin (rIL)-12 involves interferon gamma induction of nitric oxide synthase 2 (iNOS) activity: inhibitors of NO generation reveal the extent of rIL-12 vaccine adjuvant effect.

Recombinant interleukin 12 (IL-12) can profoundly suppress cellular immune responses in mice. To define the underlying mechanism, recombinant murine (rm)IL-12 was given to C57BL/6 mice undergoing alloimmunization and found to transiently but profoundly suppress in vivo and in vitro allogeneic responses and in vitro splenocyte mitogenic responses. Use of neutralizing antibodies and genetically deficient mice showed that IFN-gamma (but not TNF-alpha) mediated rmIL-12-induced immune suppression. Splenocyte fractionation studies revealed that adherent cells from rmIL-12-treated mice suppressed the mitogenic response of normal nonadherent cells to concanavalin A and IL-2. Addition of an inhibitor of nitric oxide synthase (NOS) restored mitogenic responses, and inducible (i)NOS-/- mice were not immunosuppressed by rmIL-12. These results support the view that suppression of T cell responses is due to NO produced by macrophages responding to the high levels of IFN-gamma induced by rmIL-12. When a NOS inhibitor was given with rmIL-12 during vaccination of A/J mice with irradiated SCK tumor cells, immunosuppression was averted and the extent of rmIL-12's ability to enhance induction of protective antitumor immunity was revealed. This demonstrates that rmIL-12 is an effective vaccine adjuvant whose efficacy may be masked by its transient immunosuppressive effect.

Adjuvants, Immunologic↗

PubMed1998

A DNA damage and stress inducible G protein-coupled receptor blocks cells in G2/M.

Cell cycle progression is monitored by highly coordinated checkpoint machinery, which is activated to induce cell cycle arrest until defects like DNA damage are corrected. We have isolated an anti-proliferative cell cycle regulator named G2A (for G2 accumulation), which is predominantly expressed in immature T and B lymphocyte progenitors and is a member of the seven membrane-spanning G protein-coupled receptor family. G2A overexpression attenuates the transformation potential of BCR-ABL and other oncogenes, and leads to accumulation of cells at G2/M independently of p53 and c-Abl. G2A can be induced in lymphocytes and to a lesser extent in nonlymphocyte cell lines or tissues by multiple stimuli including different classes of DNA-damaging agents and serves as a response to damage and cellular stimulation which functions to slow cell cycle progression.

3T3 Cells↗

PubMed1998

Sequence-dependent DNA structure: the role of the sugar-phosphate backbone.

A detailed analysis of the coupling between the conformational properties of the sugar-phosphate backbone and the base stacking interactions in dinucleotide steps of double helical DNA is described. In X-ray crystal structures of oligonucleotides, the backbone shows one major degree of freedom, consisting of the torsion angles chi, delta, zeta and the pseudorotation phase angle, P. The remaining torsion angles (beta, epsilon, alpha and gamma) comprise two less important degrees of freedom. The base stacking interactions show three degrees of freedom: slide-roll-twist, shift-tilt, and rise (which is more or less constant). Coupling is observed between the base and backbone degrees of freedom. The major base stacking mode, slide-roll-twist, is coupled to the major backbone mode, chi-P-delta-zeta. The secondary base stacking mode, shift-tilt, is coupled to epsilon and zeta and to a lesser extent to the chi-P-delta-zeta mode. We show that the length of the backbone, C, given by the same strand C1'-C1' separation, is an excellent single parameter descriptor for the conformation of the backbone and the way in which it is coupled to the base stacking geometry. The slide-roll-twist motion relates to changes in the mean backbone length, C, and the shift-tilt motion to the difference between the lengths of the two backbone strands, DeltaC. We use this observation to develop a simple virtual bond model which describes the coupling of the backbone conformations and the base stacking geometry. A semi-flexible bond is used to connect the same strand C1'-C1' atoms. Analysis of the X-ray crystal structure database, simple geometric considerations and model building experiments all show that this bond is flexible with respect to slide, shift and propeller but rigid with respect to the other 14 local base stacking parameters. Using this simple model for the backbone in conjunction with potential energy calculations of the base stacking interactions, we show that it is possible to predict accurately the values of these 14 base step parameters, given values of slide, shift and propeller. We also show that the base step parameters fall into three distinct groups: roll, tilt and rise are determined solely by the base stacking interactions and are independent of the backbone; twist is insensitive to the base stacking interactions and is determined solely by the constraints of a relatively rigid fixed length backbone; slide and shift are the primary degrees of freedom and cannot be predicted accurately at the dinucleotide level because they are influenced by the conformations of neighbouring steps in a sequence. We have found that the context effect on slide is mediated by the chi torsion angles while the context effect on shift results from a BI to BII transition in the backbone. We have therefore reduced the dimensionality of the dinucleotide step problem to two parameters, slide and shift.

Carbohydrates↗

PubMed1998

Targeted disruption of the bradyzoite-specific gene BAG1 does not prevent tissue cyst formation in Toxoplasma gondii.

Expression of the 30 kDa small heat shock protein BAG1 is restricted to the latent bradyzoite 'tissue cyst' form of Toxoplasma gondii, first appearing approximately 2-3 days after the initiation of bradyzoite differentiation. Although developmental expression of small heat shock proteins has been described for many species, their precise function is unclear. In order to examine the function of BAG1 in T. gondii bradyzoites and its role during parasite differentiation, we have used homologous recombination to produce a knock-out mutant in the cyst-forming strain P(LK), a clonal derivative of ME49. Under tissue culture conditions that stimulate bradyzoite differentiation (alkaline pH), the mutant was found to express several bradyzoite-specific markers with the same kinetics and frequency as the parental strain. Neither enhanced nor decreased susceptibility to stress was observed for the BAG1-deficient mutant. In vivo studies revealed that tachyzoites of the bag1 knock-out mutant were fully able to establish a chronic infection in C57BL/6 mice, producing brain cysts of a size, morphology and frequency indistinguishable from cysts formed by the parental control strain. Brain cysts of the bag1 knock-out mutant contained viable parasites capable of establishing an acute infection after oral administration, demonstrating that conversion of bradyzoites to tachyzoites is also unimpaired. We conclude that BAG1 is not essential for normal function of bradyzoite containing tissue cysts, at least in intermediate host species. This clone of P(LK) was found to be unable to produce oocysts and is therefore unsuitable for studies in cats.

Amino Acid Sequence↗

PubMed1998

Interleukin-12 and interleukin-18 synergistically induce murine tumor regression which involves inhibition of angiogenesis.

The antitumor effect and mechanisms activated by murine IL-12 and IL-18, cytokines that induce IFN-gamma production, were studied using engineered SCK murine mammary carcinoma cells. In syngeneic A/J mice, SCK cells expressing mIL-12 or mIL-18 were less tumorigenic and formed tumors more slowly than control cells. Neither SCK.12 nor SCK.18 cells protected significantly against tumorigenesis by distant SCK cells. However, inoculation of the two cell types together synergistically protected 70% of mice from concurrently injected distant SCK cells and 30% of mice from SCK cells established 3 d earlier. Antibody neutralization studies revealed that the antitumor effects of secreted mIL-12 and mIL-18 required IFN-gamma. Interestingly, half the survivors of SCK.12 and/or SCK.18 cells developed protective immunity suggesting that anti-SCK immunity is unlikely to be responsible for protection. Instead, angiogenesis inhibition, assayed by Matrigel implants, appeared to be a property of both SCK.12 and SCK.18 cells and the two cell types together produced significantly greater systemic inhibition of angiogenesis. This suggests that inhibition of tumor angiogenesis is an important part of the systemic antitumor effect produced by mIL-12 and mIL-18.

Animals↗

PubMed1998

IL-1 alpha and TNF-alpha are required for IL-12-induced development of Th1 cells producing high levels of IFN-gamma in BALB/c but not C57BL/6 mice.

The development of Th1- or Th2-type responses determines the type of immune response that is elicited in response to Ag. Responsiveness to IL-12 is critical for the development of Th1-type CD4+ T cells required for cell-mediated immune responses. Addition of IL-12 to primary cultures of CD4+ T cells stimulated with OVA and splenocytes or dendritic cells resulted in the development of a Th1 phenotype with the capacity to secrete high levels of IFN-gamma upon restimulation with splenic APC. The present study shows that using dendritic cells to present Ag upon restimulation reveals a requirement for additional cofactors, including IL-1 alpha and TNF-alpha, which were provided by spleen cells but not dendritic cells. Furthermore, these cofactors are required for optimal IL-12-induced Th1 development in BALB/c but not C57BL/6 mice. This differential requirement for such cofactors in IL-12-driven Th1 development may play a role in genetic predisposition to Th1 or Th2 responses to infectious agents.

Adjuvants, Immunologic↗