Helper T cell differentiation, inside and out

Endometrial TGF-β, IL-10, IL-17 and autophagy are dysregulated in women with recurrent implantation failure with chronic endometritis

BACKGROUND

Chronic endometritis (CE) is a condition which results in reduced receptivity of embryos by dysregulated lymphocyte subsets, abnormal expression of cytokines, chemokines and other regulatory molecules in the endometrium (EM). Macroautophagy (autophagy), the highly conserved cellular homeostasis pathway, plays an essential role in the development and function of T lymphocytes, and supports T cell lineage stability and survival fitness. The possible relationships between autophagy and local cytokine milieus in repeated implantation failure (RIF) with CE have not been elucidated yet.

METHODS

This case-control study was performed at a large reproductive medicine center between February 2015 and July 2016. Seventy-five recurrent implantation falliure women with CE who had "strawberry aspect" and 75 women with male factor infertility were included. In this study, endometrial expressions of IL-17, IL-10, TGF-β and autophagy related molecules, including LC3-II and mTORC1 were investigated by qRT-PCR, Western blot, immunofluorescence and immunohistochemistry assays.

RESULTS

The expression of IL-17 was significantly higher in patients with CE compared to women with male factor infertility, while the expressions of IL-10 and TGF-β were significantly lower. Moreover, the expression of autophagy (LC3-II) is increased, while the expression of mTORC1 was impaired.

CONCLUSIONS

CE is associated with shifted cytokine milieu towards Th17 over Treg immunity in endometrium through impaired autophagy by decreased mTORC1.

Humanized mouse model for assessing the human immune response to xenogeneic and allogeneic decellularized biomaterials

Current assessment of biomaterial biocompatibility is typically implemented in wild type rodent models. Unfortunately, different characteristics of the immune systems in rodents versus humans limit the capability of these models to mimic the human immune response to naturally derived biomaterials. Here we investigated the utility of humanized mice as an improved model for testing naturally derived biomaterials. Two injectable hydrogels derived from decellularized porcine or human cadaveric myocardium were compared. Three days and one week after subcutaneous injection, the hydrogels were analyzed for early and mid-phase immune responses, respectively. Immune cells in the humanized mouse model, particularly T-helper cells, responded distinctly between the xenogeneic and allogeneic biomaterials. The allogeneic extracellular matrix derived hydrogels elicited significantly reduced total, human specific, and CD4⁺ T-helper cell infiltration in humanized mice compared to xenogeneic extracellular matrix hydrogels, which was not recapitulated in wild type mice. T-helper cells, in response to the allogeneic hydrogel material, were also less polarized towards a pro-remodeling Th2 phenotype compared to xenogeneic extracellular matrix hydrogels in humanized mice. In both models, both biomaterials induced the infiltration of macrophages polarized towards a M2 phenotype and T-helper cells polarized towards a Th2 phenotype. In conclusion, these studies showed the importance of testing naturally derived biomaterials in immune competent animals and the potential of utilizing this humanized mouse model for further studying human immune cell responses to biomaterials in an in vivo environment.

Mining large-scale response networks reveals 'topmost activities' in Mycobacterium tuberculosis infection

Mycobacterium tuberculosis owes its high pathogenic potential to its ability to evade host immune responses and thrive inside the macrophage. The outcome of infection is largely determined by the cellular response comprising a multitude of molecular events. The complexity and inter-relatedness in the processes makes it essential to adopt systems approaches to study them. In this work, we construct a comprehensive network of infection-related processes in a human macrophage comprising 1888 proteins and 14,016 interactions. We then compute response networks based on available gene expression profiles corresponding to states of health, disease and drug treatment. We use a novel formulation for mining response networks that has led to identifying highest activities in the cell. Highest activity paths provide mechanistic insights into pathogenesis and response to treatment. The approach used here serves as a generic framework for mining dynamic changes in genome-scale protein interaction networks.

Mechanisms underlying lineage commitment and plasticity of human γδ T cells

Phenotypic and functional heterogeneity are the hallmarks of effector and memory T cells. Upon antigen stimulation, γδ T cells differentiate into two major types of memory T cells: central memory cells, which patrol the blood and secondary lymphoid organs, and effector memory cells, which migrate to peripheral tissues. γδ T cells display in vitro a certain degree of plasticity in their function that is reminiscent of that which is observed in conventional CD4 T cells. Similar to CD4 T cells, in which a plethora of specialized subsets affect the host response, γδ T cells may readily and rapidly assume distinct Th1-, Th2-, Th17-, T(FH) and T regulatory-like effector functions, suggesting that they profoundly influence cell-mediated and humoral immune responses. In addition to differences in cytokine repertoire, γδ T cells exhibit diversity in homing, such as migration to lymph node follicles, to help B cells versus migration to inflamed tissues. Here, we review our current understanding of γδ T-cell lineage heterogeneity and flexibility, with an emphasis on the human system, and propose a classification of effector γδ T cells based on distinct functional phenotypes.

Interleukin-13 induces T helper type 2 immune responses in OVA-immunized BALB/c mice bearing a T cell lymphoma

T lymphocytes play a crucial role in the regulation of immune responses against the tumour cells. Tumour progression results in dysfunction and inhibition of T cells, which ultimately leads to impairment in the antitumour immune response. The impaired antitumour immune response in the host is represented by the decreased number of T cells and their incomplete and improper function. The immunosuppressive network in tumour-bearing host mediated by tumour cells also leads to the inequities of T cell subsets and imbalance of Th1/Th2 dichotomy. Therefore, in the present study, we sought to investigate the role of tumour progression in the development of T cell phenotype and the involvement of interleukin-13 thereof selecting Dalton's lymphoma (DL) as a tumour model. It was observed that a significant increase in the number of CD4(+) T cell population, whereas a significant decline in the CD8(+) T cells among lymphoid cell population of OVA-immunized DL-bearing BALB/c mice occurs. Similar observation was found following the administration of IL-13 to the normal healthy mice. It was further confirmed that expansion in Th2 type cells among CD4(+) T cell population occurs following the progression of tumour and administration of IL-13 to normal healthy mice by an yet to define mechanism. Therefore, it can be concluded that IL-13 has immense role in polarizing the immune responses by inducing the differentiation of Th2 type of cells.

Regulation of interferon-gamma during innate and adaptive immune responses

Interferon-gamma (IFN-gamma) is crucial for immunity against intracellular pathogens and for tumor control. However, aberrant IFN-gamma expression has been associated with a number of autoinflammatory and autoimmune diseases. This cytokine is produced predominantly by natural killer (NK) and natural killer T (NKT) cells as part of the innate immune response, and by Th1 CD4 and CD8 cytotoxic T lymphocyte (CTL) effector T cells once antigen-specific immunity develops. Herein, we briefly review the functions of IFN-gamma, the cells that produce it, the cell extrinsic signals that induce its production and influence the differentiation of naïve T cells into IFN-gamma-producing effector T cells, and the signaling pathways and transcription factors that facilitate, induce, or repress production of this cytokine. We then review and discuss recent insights regarding the molecular regulation of IFN-gamma, focusing on work that has led to the identification and characterization of distal regulatory elements and epigenetic modifications with the IFN-gamma locus (Ifng) that govern its expression. The epigenetic modifications and three-dimensional structure of the Ifng locus in naive CD4 T cells, and the modifications they undergo as these cells differentiate into effector T cells, suggest a model whereby the chromatin architecture of Ifng is poised to facilitate either rapid opening or silencing during Th1 or Th2 differentiation, respectively.

Regulatory mechanisms of helper T cell differentiation: new lessons learned from interleukin 17 family cytokines

Interleukin 17 (IL-17) family consists of six cytokines in mammals. Among them, IL-17 and IL-17F are expressed by a novel subset of CD4+ helper T (Th) cells and play critical function in inflammation and autoimmunity. On the other hand, IL-17E, also called IL-25, has been associated with allergic responses. Here we summarize recent work by us as well as other investigators in understanding the regulation and function of these three cytokines. From these studies, IL-17 family cytokines may serve as novel targets for pharmaceutical intervention of immune and inflammatory diseases.

Reduced expression of IL-6 and IL-1α mRNAs in secretory phase endometrium of women with recurrent miscarriage

A diverse array of cytokines is implicated in regulating the immune adaptation and endometrial tissue remodelling events that facilitate successful embryo implantation and early placental development. The aim of this study was to evaluate expression of mRNAs encoding a panel of immunoregulatory cytokines in the endometrium of fertile women and women experiencing recurrent miscarriage using highly sensitive, quantitative RT-PCR assays. Endometrial biopsies were collected during the mid-secretory phase of the menstrual cycle from women classified as proven fertile (control; n=12) and women experiencing unexplained recurrent miscarriage (RM; n=9). Reduced IL-6 mRNA and reduced IL-1alpha mRNA were independently associated with recurrent miscarriage. Altered expression was evident after accounting for variation in the composition of endometrial biopsies by normalization of data to epithelial and mesenchymal cell-specific transcripts, cytokeratin-18 mRNA and vimentin mRNA, respectively. The relative abundance of mRNAs encoding LIF, GM-CSF, IFNgamma, IL-1beta, IL-4, IL-5, IL-10, IL-12p40, TNFalpha, TGFbeta1, TGFbeta2 and TGFbeta3 were not altered in recurrent miscarriage tissue. Associations between expression of IL-10, LIF, GM-CSF and TGFbeta2 suggest that regulatory circuits link the transcription of these cytokine genes. Inadequate expression of IL-6 and IL-1alpha mRNAs in endometrial tissue may predispose to recurrent miscarriage through a perturbed maternal immune response, effects on decidual tissue remodeling and angiogenesis, or dysregulated trophoblast differentiation and invasion. Quantitative RT-PCR assays for these cytokines in endometrial biopsies may be a realistic strategy for development of novel diagnostics for predisposition to recurrent miscarriage.

3D computation modelling of the influence of cytokine secretion on Th‐cell development suggests that negative selection (inhibition of Th1 cells) is more effective than positive selection by IL‐4 for Th2 cell dominance

Th-cell development has been suggested to include selective mechanisms in which certain cytokines select either Th1 or Th2 cells to proliferate and grow. The selective theory is based on the observation that Th2 cells secrete IL-4, a cytokine that promotes Th2 development, whereas Th1 cells secrete interferon-gamma (IFN-gamma) that favours Th1 development, and both positive and negative selective influences have been suggested to operate. In this study, we investigate the role of autocrine secretion and utilization of IL-4 by Th2 cells and address the question of whether an activated Th2 cell can be positively selected by IL-4 secreted from other Th2 cells. We present a spatial three dimensional (3D) modelling approach to simulate the interaction between the IL-4 ligand and its IL-4 receptors expressed on discrete IL-4 secreting cells. The simulations, based on existing experimental data on the IL-4 receptor-ligand system, illustrate how Th-cell development is highly dependent on the distance between cells that are communicating. The model suggests that a single Th2 cell is likely to communicate with possible target cells within a range of approximately 100 microm and that an activated Th2 cell manages to fill most of its own IL-4 receptors, even at a low secretion rate. The predictions made by the model suggest that negative selection against Th1 cells is more effective than positive selection by IL-4 for promoting Th2 dominance.

Cytokine and chemokine transcription profile during Mycoplasma pulmonis infection in susceptible and resistant strains of mice: macrophage inflammatory protein 1beta (CCL4) and monocyte chemoattractant protein 2 (CCL8) and accumulation of CCR5+ Th cells

The progression of murine mycoplasma pneumonia is dependent on T cells and other immune cells. The role of cytokines in immunity are complex, and identifying the network of cytokines produced after infection of mice is essential in dissecting the key cytokine cascades involved mycoplasma disease pathogenesis. In the present study, mRNA expression of 143 different cytokines, chemokines, or receptors were evaluated in lung tissues from both susceptible (BALB/c and C3H/HeN) and resistant (C57BL/6) mice after Mycoplasma pulmonis infection. To accomplish this, membrane-based cDNA microarrays were used to monitor changes mRNA expression in lungs. There was a clear association with disease susceptibility and development of cytokine mRNA expression. In addition to proinflammatory cytokines, mRNA expression of an anti-inflammatory cytokine, interleukin-10, increased with disease severity, suggesting an attempt to moderate the severity of the inflammatory response. Furthermore, it is clear that an array of chemokines produced in susceptible mice could contribute to the recruitment and maintenance of inflammatory cells at the site of disease. In support of this, there was an increase in macrophage inflammatory protein 1beta (MIP-1beta; CCL4) and monocyte chemoattractant protein 2 (MCP-2; CCL8) mRNA levels from mycoplasma-infected mice and a corresponding accumulation of CD4+ Th cells expressing the MIP-1beta/MCP-2 receptor, CCR5, in the lungs of mice. Furthermore, MIP-1beta- and MCP-2-producing cells and CD4+ T cells were found to be in close association in pulmonary lesions. Thus, there was a significant cytokine response associated with disease pathogenesis, and these studies provide important leads and insights into ongoing cytokine- and chemokine-mediated processes in this persistent inflammatory disease.

Direct and indirect effects of retinoic acid on human Th2 cytokine and chemokine expression by human T lymphocytes

BACKGROUND

Vitamin A (VA) deficiency induces a type 1 cytokine response and exogenously provided retinoids can induce a type 2 cytokine response both in vitro and in vivo. The precise mechanism(s) involved in this phenotypic switch are inconsistent and have been poorly characterized in humans. In an effort to determine if retinoids are capable of inducing Th2 cytokine responses in human T cell cultures, we stimulated human PBMCs with immobilized anti-CD3 mAb in the presence or absence of all-trans retinoic acid (ATRA) or 9-cis-RA.

RESULTS

Stimulation of human PBMCs and purified T cells with ATRA and 9-cis-RA increased mRNA and protein levels of IL-4, IL-5, and IL-13 and decreased levels of IFN-gamma, IL-2, IL-12p70 and TNF-alpha upon activation with anti-CD3 and/or anti-CD28 mAbs. These effects were dose-dependent and evident as early as 12 hr post stimulation. Real time RT-PCR analysis revealed a dampened expression of the Th1-associated gene, T-bet, and a time-dependent increase in the mRNA for the Th2-associated genes, GATA-3, c-MAF and STAT6, upon treatment with ATRA. Besides Th1 and Th2 cytokines, a number of additional proinflammatory and regulatory cytokines including several chemokines were also differentially regulated by ATRA treatment.

CONCLUSION

These data provide strong evidence for multiple inductive roles for retinoids in the development of human type-2 cytokine responses.

Biodegradable nanoparticle delivery of a Th2-biased peptide for induction of Th1 immune responses

The type of immune response developed against the hepatitis B virus (HBV) is crucial in determining the outcome of the disease. The protective effects of vaccine-induced antibody responses against subsequent exposure to HBV are well-established. After the establishment of chronic HBV infection, cell-mediated immune response is curative while humoral response is detrimental. A therapeutic vaccine that could switch the type of response could lead to disease resolution. Hepatitis B core antigen (HBcAg)(129-140) has been identified as a Th2-biased peptide in H-2(b) mice when it is administered along with complete Freund's adjuvant (CFA). We formulated HBcAg(129-140) along with monophosphoryl lipid A in poly(D,L-lactic-co-glycolic acid) (PLGA) nanoparticles. Naive mice immunized with the nanoparticle formulation developed a strong Th1-type response while mice immunized with the control formulation of CFA and peptide did not. We then primed mice with CFA and peptide to establish a Th2-type immune response before administering the nanoparticle formulation. Mice receiving the nanoparticle formulation being primed with CFA still developed a strong Th1-type response, while mice that received incomplete Freund's adjuvant and peptide instead of nanoparticles did not. The ability of PLGA nanoparticles to alter the type of immune response elicited by a peptide, even in the context of an ongoing immune response, makes PLGA nanoparticles a strong candidate for the formulation of therapeutic vaccines.

In silico simulations suggest that Th‐cell development is regulated by both selective and instructive mechanisms

Th-cell differentiation is highly influenced by the local cytokine environment. Although cytokines such as IL-12 and IL-4 are known to polarize the Th-cell response towards Th1 or Th2, respectively, it is not known whether these cytokines instruct the developmental fate of uncommitted Th cells or select cells that have already been committed through a stochastic process. We present an individual based model that accommodates both stochastic and deterministic processes to simulate the dynamic behaviour of selective versus instructive Th-cell development. The predictions made by each model show distinct behaviours, which are compared with experimental observations. The simulations show that the instructive model generates an exclusive Th1 or Th2 response in the absence of an external cytokine source, whereas the selective model favours coexistence of the phenotypes. A hybrid model, including both instructive and selective development, shows behaviour similar to either the selective or the instructive model dependent on the strength of activation. The hybrid model shows the closest qualitative agreement with a number of well-established experimental observations. The predictions by each model suggest that neither pure selective nor instructive Th development is likely to be functional as exclusive mechanisms in Th1/Th2 development.

NK cells in gamma-interferon-deficient mice suppress lung innate immunity against Mycoplasma spp

The purpose of this study was to examine the 100-fold difference in mycoplasma levels in lungs of gamma interferon knockout (IFN-gamma(-/-)) mice compared to those seen with wild-type BALB/c mice at 3 days postinfection. NK cells secreted IFN-gamma; however, their cytotoxic granule extracts failed to kill mycoplasma. We found a conundrum: the clearance of organisms was as effective in NK-depleted IFN-gamma(-/-) animals as in wild-type mice (with both IFN-gamma and NK cells). NK(+) IFN-gamma(-/-) animals had high mycoplasma burdens, but, after NK-like cell depletion, mycoplasma numbers were controlled. Essentially, IFN-gamma was important in animals with NK-like cells and unimportant in animals without NK cells, suggesting that IFN-gamma counters deleterious effects of NK-like cells. Impairment of innate immunity in IFN-gamma(-/-) mice was not due to NK-like cell killing of macrophages. The increased levels of inflammatory cytokines and neutrophils in lung fluids of NK(+) IFN-gamma(-/-) mice were reduced after NK cell depletion. In summary, in the murine model that resembles chronic human disease, innate immunity to mycoplasma requires IFN-gamma when there are NK-like cells and the positive effects of IFN-gamma counteract negative effects of NK-like cells. When imbalanced, NK-like cells promote disease. Thus, it was not the lack of IFN-gamma but the presence of a previously unrecognized NK-like cell-suppressive activity that contributed to the higher mycoplasma numbers. It appears that pulmonary NK cells may contribute to the immunosuppressive environment of the lung, but when needed, these dampening effects can be counterbalanced by IFN-gamma. Furthermore, there may be instances where perturbation of this regulatory balance contributes to the susceptibility to and severity of disease.

The beneficial helminth parasite?

There is unequivocal evidence that parasites influence the immune activity of their hosts, and many of the classical examples of this are drawn from assessment of helminth infections of their mammalian hosts. Thus, helminth infections can impact on the induction or course of other diseases that the host might be subjected to. Epidemiological studies demonstrate that world regions with high rates of helminth infections consistently have reduced incidences of autoimmune and other allergic/inflammatory-type conditions. Here I review and assess the possible ways by which helminth infections can block or modulate concomitant disease processes. There is much to be learned from careful analysis of immuno-regulation in helminth-infected rodents and from an understanding of the immune status of acutely and chronically infected humans. The ultimate reward from this type of investigation will likely be a more comprehensive knowledge of immunity, novel ways to intervene in the immune response to alleviate autoimmune and allergic diseases (growing concerns in economically developed areas), and perhaps the development of helminth therapy for patients suffering from specific inflammatory, autoimmune or allergic disorders.

Leukemia Inhibitory Factor Is Linked to Regulatory Transplantation Tolerance

BACKGROUND

The specific regulation of allo-tolerance in vivo occurs within a complex microenvironment and involves co-operation between a small proportion of different cell types within the spleen or draining lymph node. By analyzing unmanipulated whole spleen cell populations we have aimed to mimic this in vivo situation to identify critical signaling molecules in regulatory allo-tolerance.

METHODS

We compared the kinetics of cytokine release and induction of signaling proteins in (BALB/c-tolerant)CBA, versus (BALB/c-rejected)CBA, spleen cells after challenge with BALB/c antigen.

RESULTS

The distinguishing features of allo-tolerance were Foxp3 protein expression, LIF release, and increased levels of STAT3. Comparison of isogenic clones of Tr1, Th1, and Th2 cells revealed that only the regulatory Tr1 cells are characterized by both LIF and IL10 release.

CONCLUSIONS

Overall, our findings demonstrate that allo-antigen driven signaling events can be detected within a whole spleen cell population and identify a role for LIF in the regulation of transplantation tolerance in vivo.

Stimulation of Host NKT Cells by Synthetic Glycolipid Regulates Acute Graft-versus-Host Disease by Inducing Th2 Polarization of Donor T Cells

NKT cells are a unique immunoregulatory T cell population that produces large amounts of cytokines. We have investigated whether stimulation of host NKT cells could modulate acute graft-vs-host disease (GVHD) in mice. Injection of the synthetic NKT cell ligand alpha-galactosylceramide (alpha-GalCer) to recipient mice on day 0 following allogeneic bone marrow transplantation promoted Th2 polarization of donor T cells and a dramatic reduction of serum TNF-alpha, a critical mediator of GVHD. A single injection of alpha-GalCer to recipient mice significantly reduced morbidity and mortality of GVHD. However, the same treatment was unable to confer protection against GVHD in NKT cell-deficient CD1d knockout (CD1d(-/-)) or IL-4(-/-) recipient mice or when STAT6(-/-) mice were used as donors, indicating the critical role of host NKT cells, host production of IL-4, and Th2 cytokine responses mediated by donor T cells on the protective effects of alpha-GalCer against GVHD. Thus, stimulation of host NKT cells through administration of NKT ligand can regulate acute GVHD by inducing Th2 polarization of donor T cells via STAT6-dependent mechanisms and might represent a novel strategy for prevention of acute GVHD.

Variability in cytokine production and cell proliferation by mitogen-activated ovine peripheral blood mononuclear cells: modulation by interleukin (IL)-10 and IL-12

T-cell reactivity is typically measured by cell proliferation and/or production of cytokines in response to antigenic/mitogenic stimulation. The choice of assays is more limited in ruminants than rodents, and complicated by the variability inherent in outbred populations. We have measured proliferation and production of interferon-gamma (IFN-gamma) by peripheral blood mononuclear cells (PBMC) from 24 sheep, and compared the responses between sheep, within sheep over several sample points, and also drawn comparisons between the two assays. PBMC derived from different sheep varied by as much as ten-fold in both proliferation and IFN-gamma production, though not necessarily at the same sample time. Thus, there was a poor correlation between the two assays and also considerable variation in the responses from the same animal at different time points. Both parameters could be modulated by exogenous recombinant ovine interleukin (IL)-10 and IL-12, but we were unable to correlate IFN-gamma production with endogenous cytokine production in the assays. These data highlight the importance of assay selection for the measurement of immune responsiveness and also demonstrate the variation that can be expected between sheep and over time.

Conjugated linoleic acids: are they beneficial or detrimental to health?

Conjugated linoleic acids (CLAs) comprise a family of positional and geometric isomers of linoleic acid (18:2n-6; LA) that are formed by biohydrogenation and oxidation processes in nature. The major dietary sources of these unusual fatty acids are foods derived from ruminant animals, in particular dairy products. The main form of CLA, cis-9, trans-11-18:2, can be produced directly by bacterial hydrogenation in the rumen or by delta-9 desaturation of the co-product vaccenic acid (trans-11-18:1) in most mammalian tissues including man. The second most abundant isomer of CLA is the trans-10, cis-12-18:2 form. Initially identified in grilled beef as a potential anti-carcinogen a surprising number of health benefits have subsequently been attributed to CLA mixtures and more recently to the main individual isoforms. It is also clear from recent studies that the two main isoforms can have different effects on metabolism and cell functions and can act through different cell signalling pathways. The majority of studies on body compositional effects (i.e. fat loss, lean gain), on cancer and cardiovascular disease attenuation, on insulin sensitivity and diabetes and on immune function have been conducted with a variety of animal models. Observations clearly emphasise that differences exist between mammalian species in their response to CLAs with mice being the most sensitive. Recent studies indicate that some but not all of the effects observed in animals also pertain to human volunteers. Reports of detrimental effects of CLA intake appear to be largely in mice and due mainly to the trans-10, cis-12 isomer. Suggestions of possible deleterious effects in man due to an increase in oxidative lipid products (isoprostanes) with trans-10, cis-12 CLA ingestion require substantiation. Unresponsiveness to antioxidants of these non-enzymatic oxidation products casts some doubt on their physiological relevance. Recent reports, albeit in the minority, that CLAs, particularly the trans-10, cis-12 isomer, can elicit pro-carcinogenic effects in animal models of colon and prostate cancer and can increase prostaglandin production in cells also warrant further investigation and critical evaluation in relation to the many published anti-cancer and anti-prostaglandin effects of CLAs.

Combining cytokine signalling with T-bet and GATA-3 regulation in Th1 and Th2 differentiation: a model for cellular decision-making

Differentiation of uncommitted T cells into Th1 and Th2 subpopulations depends on both intracellular events controlling expression of transcription factors T-bet and GATA-3 and interactions between cells mediated by cytokines, particularly IL4 and IFNgamma. A great deal is known about the intracellular and extracellular events involved in Th1 and Th2 (Th) differentiation, but how these are integrated in T-cell populations or indeed why extracellular cytokine control is required after a decision has been made at a transcriptional level is not at all understood. We present a mathematical model of CD4+ T-cell differentiation that describes both intracellular and extracellular processes and the interactions between them. It shows how antigen stimulation in conjunction with cytokines and other extracellular signals gives rise to rapid, reversible and mutually exclusive expression of T-bet or GATA-3 due to feedback between the transcription factors and their signalling pathways. After transient signalling by APC, continued Th1 and Th2 differentiation is shown to require cytokine production by the proliferating T cells. Moreover, intercellular communication by T-cell-derived cytokines lowers the threshold of APC signals required for Th differentiation. This provides an explanation for enhanced Th differentiation by pre-existing memory T cells. The model also predicts that Th differentiation can be reversed at the single cell level before commitment by manipulating the cytokine environment. It suggests a mechanism for switching between Th1 and Th2 in the so-called irreversible state that may be developed as a novel therapeutic means of manipulating Th1 and Th2 responses.

IL-4-induced GATA-3 expression is a time-restricted instruction switch for Th2 cell differentiation

An initial activation signal via the TCR in a restricted cytokine environment is critical for the onset of Th cell development. Cytokines regulate the expression of key transcriptional factors, T-bet and GATA-3, which instruct the direction of Th1 and Th2 differentiation, through changes in chromatin conformation. In this study, we investigated the kinetics of IL-4-mediated signaling in a transgenic mouse, expressing human IL-4R on a mouse IL-4alphaR-deficient background. These experiments, allowing induction with human IL-4 at defined times, demonstrated that an IL-4 signal was required at the early stage of TCR-mediated T cell activation for lineage commitment to Th2, along with structural changes in chromatin, which take place in the conserved noncoding sequence-1 and -2 within the IL-4 locus. At later times, however, IL-4 failed to promote efficient Th2 differentiation and decondensation of chromatin, even though GATA-3 was clearly induced in the nuclei by IL-4 stimulation. Moreover, IL-4-mediated Th2 instruction was independent from cell division mediated by initial TCR stimulation. The role of IL-4 signaling may have a time restriction during Th2 differentiation. In late stages of initial T cell activation, the chromatin structure of the IL-4 locus retains condensation state. These results demonstrate that IL-4-induced GATA-3 expression is time-restriction switch for Th2 differentiation.

The upper and lower respiratory tracts differ in their requirement of IFN-gamma and IL-4 in controlling respiratory mycoplasma infection and disease

The purpose of this study is to evaluate the significance of IFN-gamma and IL-4 production in controlling mycoplasma infection and the pathogenesis of disease in the upper and lower respiratory tract. By using IFN-gamma knockout and IL-4 knockout BALB/c mice, we were able to study the contribution of these cytokines in the development of pathogenesis and/or protection in response to mycoplasma respiratory infection, in both the upper and lower respiratory tracts. The loss of either IFN-gamma or IL-4 does not affect disease pathogenesis or mycoplasma organism numbers in the upper respiratory tract. However, in the absence of IL-4, the nasal passages developed a compensatory immune response, characterized by higher numbers of macrophages and CD8(+) T cells, which may be masking detrimental effects due to IL-4 deficiency. This is in contrast to the lower respiratory tract, where the loss of IFN-gamma, but not IL-4, leads to higher mycoplasma numbers and increased disease severity. The loss of IFN-gamma impacted the innate immune system's ability to effectively clear mycoplasma, as the number of organisms was higher by day 3 postinfection. This higher organism burden most likely impacted disease pathogenesis; however, the development of Th2 cell-mediated adaptive immune response most likely contributed to lesion severity at later time points during infection. Our studies demonstrate that the upper and lower respiratory tracts are separate and distinct in their cytokine requirements for generating immunity against mycoplasma infection.

Helper T cell differentiation and the problem of cellular inheritance

The quality of the helper T cell response against antigen can determine the outcomes of infectious, inflammatory, and autoimmune diseases. Mature Th1 and Th2 cell subsets are thought to arise from a common naive progenitor. In these precursor cells, effector cytokine genes appear to exist in a restrictive structure, which is determined by methylation of cytosine bases and higher-order structure of chromatin. The restrictive gene structures appear to be plastic, giving way to more active structures in some daughter cells. Some genetic loci, which are active in naive cells, however, become silenced during terminal differentiation. Both the derepression of silent loci and the silencing of active loci appear to be linked to the process of DNA replication. Future investigation will be directed toward understanding the way in which patterns of gene expression are altered or transmitted during the cell division of helper T lymphocytes.

Immunity and the Animation of the Genome

Expression of genes in the right place at the right time is fundamental to all of life. The ontogeny of effector and memory T cells is a robust example of this important principle. Although lymphocytes represent a late addition in animal evolution, they are serving as an exceptional model system to unlock the mysteries surrounding the way in which the genome is animated. It will be speculated here that further insight into fundamental principles of genome function may arise from study of immunity. Likewise, such information may be key to understanding and altering immunobiology.

Active recruitment of DNA methyltransferases regulates interleukin 4 in thymocytes and T cells

How T cells regulate interleukin 4 (IL-4) expression is not completely understood. We show here that single-positive thymocytes express IL-4, but attenuate GATA-3 expression, recruit DNA methyltransferases (Dnmts) to the Il4-Il13 locus and downregulate IL-4 expression as they mature into T cells. Type 2 polarization blocks Dnmt1 recruitment, enhances histone H3 Lys4 methylation (indicative of accessible chromatin) and initiates DNA demethylation of the locus. Dnmt1-/- CD4 and CD8 T cells derepress IL-4 expression considerably, demethylate DNA and increase H3 Lys4 methylation without affecting GATA-3 expression, demonstrating that Dnmt1 and DNA methylation are essential for proper Il4 regulation. These results indicate that Dnmts, DNA and histone methylation, and transcription factors 'collaborate' to determine appropriate Il4 expression patterns.

Delta1-Notch3 Interactions Bias the Functional Differentiation of Activated CD4+ T Cells

Following activation by antigen, naive CD4+ T helper precursor cells execute distinct genetic programs that result in their differentiation toward the type 1 or type 2 helper T cell (Th1 or Th2) phenotype. Although the differentiation and function of these Th subsets has been well studied, little is known about the contribution to these differentiation events of cell surface receptors other than those for soluble cytokines, such as IL-12 or IL-4. Here, we provide direct evidence that the Delta1 interaction with Notch3 on CD4+ T cells transduces signals, promoting development toward the Th1 phenotype. The positive role of Notch signaling in effector cell differentiation was dose dependent, with high levels of stimulation resulting in reduced T cell activation. Our data revealed a clear contribution of Notch pathways to Th1 versus Th2 fate decisions, while also providing insight into another mechanism for inhibition of CD4+ T cell activation.

Enhanced expression of interferon regulatory factor-1 in the mucosa of children with celiac disease

Celiac disease (CD) is an enteropathy characterized by a Th1-type immune response to the dietary gluten. The transcriptional mechanisms or factors that control Th1 cell development in this condition remain to be elucidated. The aim of this study was to analyze in CD the expression of interferon (IFN) regulatory factor (IRF)-1, a transcription factor that regulates the differentiation and function of Th1 cells. Duodenal biopsies were taken from children with untreated CD and control children, and analyzed for IRF-1 by Southern blotting of reverse-transcriptase PCR products and Western blotting. IRF-1 DNA-binding activity was assessed by electrophoretic shift mobility assay. The effect of gliadin stimulation on IRF-1 induction was investigated in an ex vivo organ culture of treated CD biopsies. Enhanced IRF-1 was seen in untreated CD in comparison with controls. This was evident at both the RNA and protein level. Furthermore, untreated CD samples exhibited stronger nuclear accumulation and DNA-binding activity of IRF-1 than controls. In contrast, IRF-2, a transcriptional repressor that binds the same DNA element and competes with IRF-1, was expressed at the same level in nuclear proteins extracted from both untreated CD and control patients. In explant cultures of treated CD biopsies, gliadin enhanced both IRF-1 RNA and protein. This effect was prevented by a neutralizing IFN-gamma antibody. Furthermore, stimulation of normal duodenal biopsies with IFN-gamma enhanced IRF-1. These data indicate that IRF-1 is a hallmark of the gliadin-mediated inflammation in CD and suggest that IFN-gamma/IRF-1 signaling pathway can play a key role in maintaining and expanding the local Th1 inflammatory response in this disease.

Integrating systemic information at the molecular level: cross-talk between steroid receptors and cytokine signaling on different target cells

An essential event in immune activation is the increase of cytokines in both plasma and immune tissues. Steroid hormones influence several adaptive responses in both health and disease. Cytokines and steroids have an intimate cross-communication in many systems, making possible a satisfactory adaptive response to environmental changes. The ultimate level of integration of the cytokine-steroids cross-talk is the molecular level. We have demonstrated this in four types of cross-talk mechanisms on different cells in which steroids have major roles: (1) The tumor necrosis factor (TNF)-glucocorticoid receptor (GR) transcriptional interaction in cellular targets of TNF-induced cytotoxicity. TNF potentiates the transactivation activity of GR and the priming with TNF increases the protective action of GR on TNF-induced cytotoxicity. (2) The GR-T cell receptor (TCR) antagonism in GR-TCR-induced T cell apoptosis and its modulation by cAMP. cAMP inhibits the TCR-induced apoptosis through a PKA-CREB-dependent mechanism and potentiates glucocorticoid-induced apoptosis by means of a CREB-independent mechanism. (3) The GR influence on Th1-Th2 cytokine expression and differentiation. Glucocorticoids inhibit the induction of GATA-3 and T-bet transcription factors. (4) The influence of ER/Smad-4 signaling cross-communication on prolactinoma pathogenesis. Physical and functional interactions between Smad-4 and estrogen receptors take place in prolactinoma cells, providing a molecular explanation to link the tumorigenic action of these two important players of prolactinoma pathogenesis. The molecular cross-talk between steroids and transcription factors is the mechanism that provides the basis for the outcome of adaptive responses integrating the systemic information provided by hormones and cytokines.

HMG-CoA reductase inhibitors as immunomodulators: potential use in transplant rejection

The benefit of HMG-CoA reductase inhibitors (statins) to the cardiovascular system is now well established and these drugs are being used extensively to treat hypercholesterolaemia clinically. However, as clinical outcomes become available it appears that statins are proving more beneficial than expected and thus it is being proposed that the actions of statins go beyond their ability to lower serum cholesterol levels. The report that statins can interact directly with lymphocyte function-associated antigen (LFA)-1 and prevent it engaging with the intracellular adhesion molecule (ICAM)-1 receptor on T cells is a novel mechanism of statin action and provides convincing evidence that these compounds can regulate biological systems other than by the cholesterol synthesis pathway. Immunosuppression to prevent organ transplant rejection is one application for which statins are currently being assessed. The clinical evidence is conflicting and does not convincingly reflect whether statins are beneficial as immunomodulators. However, in vivo studies investigating the cellular actions of statins have identified two mechanisms by which statins can potentially modulate an in vivo immune response. Firstly, statins regulate inducible class II major histocompatibility complex (MHC) expression on macrophages and endothelial cells. Secondly, statins can inhibit LFA-1 adhesion to ICAM-1 and thus regulate T cell activation. These findings suggest that statins have the potential to regulate an immune response in vivo and that more investigation is essential in order to explain the opposing clinical data.

Pretreatment of donors with interleukin-18 attenuates acute graft-versus-host disease via STAT6 and preserves graft-versus-leukemia effects

Interleukin-18 (IL-18) is a unique cytokine that modulates both T(H)1/T(H)2 responses, but its ability to modulate diseases through induction of T(H)2 cytokines is unclear. It has been shown to play an important role in allogeneic bone marrow transplantation (BMT). Because immune responses of allogeneic BM donors may affect acute graft-versus-host disease (GVHD), we investigated the effect of pretreating BM transplant donors with IL-18 on the severity of acute GVHD using a well-characterized experimental BMT model (BALB/c-->B6). Pretreatment of allogeneic BM transplant donors with IL-18 significantly improved survival (80% vs 0%; P <.001), and reduced clinical, biochemical, and pathologic indices of acute GVHD in BM transplant recipients. IL-18 pretreatment was associated with reduced interferon gamma (IFN-gamma) and greater IL-4 secretion by donor T cells after BMT. Acute GVHD mortality was reduced when IL-18 was administered to donors deficient in IFN-gamma and signal transducer and activator of transcription 4 (STAT4) but not STAT6 signaling molecules, suggesting a critical role for STAT6 signaling in IL-18's protective effect. IL-18 treatment did not alter donor CD8(+) cytotoxic T-lymphocyte (CTL) activity and preserved graft-versus-leukemia (GVL) effects after allogeneic BMT (70% vs 10%; P <.01). Together these data illustrate that pretreatment of donors with IL-18 prior to allogeneic BMT attenuates acute GVHD in a STAT6-dependent mechanism while preserving GVL effects.

Impaired accumulation and function of memory CD4 T cells in human IL-12 receptor beta 1 deficiency

Defects in IL-12 production or IL-12 responsiveness result in a vulnerability to infection with non-viral intracellular organisms, but the immunological mechanisms responsible for this susceptibility remain poorly understood. We present an immunological analysis of a patient with disseminated Salmonella enteritidis and a homozygous splice acceptor mutation in the IL-12Rbeta1-chain gene. This mutation resulted in the absence of IL-12Rbeta1 protein on PBMC and an inability of T cells to specifically bind IL-12 or produce IFN-gamma in response to either IL-12 or IL-23. The accumulation of memory (CD45R0(high)) CD4 T cells that were CCR7(high) (putative central memory cells) was normal or increased for age. Central memory CD4 T cells of the patient and age-matched controls were similar in having a low to undetectable capacity to produce IFN-gamma after polyclonal stimulation. In contrast, the patient had a substantial decrease in the number of CCR7(neg/dull) CD45R0(high) memory CD4 T cells (putative effector memory cells), and these differed from control cells in having a minimal ability to produce IFN-gamma after polyclonal stimulation. Importantly, tetanus toxoid-specific IFN-gamma production by PBMC from the patient was also significantly reduced compared with that in age-matched controls, indicating that signaling via the IL-12Rbeta1-chain is generally necessary for the in vivo accumulation of human memory CD4 T cells with Th1 function. These results are also consistent with a model in which the IL-12Rbeta1 subunit is necessary for the conversion of central memory CD4 T cells into effector memory cells.

Memory and flexibility of cytokine gene expression as separable properties of human T(H)1 and T(H)2 lymphocytes

CD4+ T cell priming under T helper type I (T(H)1) or T(H)2 conditions gives rise to polarized cytokine gene expression. We found that in these conditions human naive T cells acquired stable histone hyperacetylation at either the Ifng or Il4 promoter. Effector memory T cells showed polarized cytokine gene acetylation patterns in vivo, whereas central memory T cells had hypoacetylated cytokine genes but acquired polarized acetylation and expression after appropriate stimulation. However, hypoacetylation of the nonexpressed cytokine gene did not lead to irreversible silencing because most T(H)1 and T(H)2 cells acetylated and expressed the alternative gene when stimulated under opposite T(H) conditions. Such cytokine flexibility was absent in a subset of T(H)2 cells that failed to up-regulate T-bet and to express interferon-gamma when stimulated under T(H)1 conditions. Thus, most human CD4+ T cells retain both memory and flexibility of cytokine gene expression.

IL-12p35-deficient mice are susceptible to experimental autoimmune encephalomyelitis: evidence for redundancy in the IL-12 system in the induction of central nervous system autoimmune demyelination

Experimental autoimmune encephalomyelitis (EAE) serves as a model for multiple sclerosis and is considered a CD4(+), Th1 cell-mediated autoimmune disease. IL-12 is a heterodimeric cytokine, composed of a p40 and a p35 subunit, which is thought to play an important role in the development of Th1 cells and can exacerbate EAE. We induced EAE with myelin oligodendrocyte glycoprotein (MOG) peptide 35-55 (MOG(35-55)) in C57BL/6 mice and found that while IL-12p40-deficient (-/-) mice are resistant to EAE, IL-12p35(-/-) mice are susceptible. Typical spinal cord mononuclear cell infiltration and demyelination were observed in wild-type and IL-12p35(-/-) mice, whereas IL-12p40(-/-) mice had normal spinal cords. A Th1-type response to MOG(35-55) was observed in the draining lymph node and the spleen of wild-type mice. A weaker MOG(35-55)-specific Th1 response was observed in IL-12p35(-/-) mice, with lower production of IFN-gamma. By contrast, a Th2-type response to MOG(35-55) correlated with disease resistance in IL-12p40(-/-) mice. Production of TNF-alpha by microglia, CNS-infiltrating macrophages, and CD4(+) T cells was detected in wild-type and IL-12p35(-/-), but not in IL-12p40(-/-), mice. In addition, NO production was higher in IL-12p35(-/-) and wild-type mice than in IL-12p40(-/-) mice. These data demonstrate a redundancy of the IL-12 system in the induction of EAE and suggest that p40-related heterodimers, such as the recently cloned IL-23 (p40p19), may play an important role in disease pathogenesis.

Activation and apoptosis of macrophages in cat scratch disease

Cat scratch disease is an infectious disease usually caused by Bartonella henselae. Within 1-3 weeks after inoculation, patients typically develop regional self-limited lymphadenopathy. Lymph nodes reveal granulomas consisting of central necrosis, an inner rim of palisading macrophages, and an outer rim of lymphocytes and non-palisading macrophages. In animals, cat-scratch disease leads to an interferon-gamma (IFNgamma)-mediated T-helper 1 immune response, resulting in macrophage recruitment, stimulation, and thereby granuloma formation. The present study has sought to find in situ evidence for macrophage migration, activation, and cell death in human cat scratch disease. By non-radioactive in situ hybridization and immunohistochemistry on serial sections, it was demonstrated that IFNgamma+ T lymphocytes and S100A8+, S100A9+ macrophages embrace granulomas, which consisted of S100A8-, S100A9-, HLA-DR+, CD40+, TNFalpha+ macrophages. Combination of in situ end-labelling and immunofluorescence revealed large numbers of DNA-fragmented CD68+ cells with intact plasma membranes corresponding to apoptotic macrophages. On the basis of these data, it was hypothesized that in human cat scratch disease, S100A8+, S100A9+ macrophages continuously migrate to the granulomas. During this process, they may be activated by IFNgamma T-helper 1 lymphocytes and be differentiated to S100A8-, S100A9-sessile, HLA-DR+, CD40+ antigen-presenting, TNFalpha+ pro-inflammatory macrophages forming granulomas. In parallel, macrophages undergo apoptosis in the centre of granulomata, a phenomenon that may restrict the destructive potential of macrophages and contribute to self-limitation of cat scratch disease.

Type 1 and type 2 responses in regulation of Ig isotype expression in cattle

Regulation of humoral immune responses is multifactorial involving appropriate activation, costimulation and the presence of specific soluble factors. Polarized type 1 or type 2 humoral responses in the laboratory mouse have been linked to expression of specific cytokines and thus can be used to provide insight into the type of response generated by infection. For example, IFN-gamma has been linked to IgG2a and IgG3 production, IL-4 to IgG1 and IgE production and TGF-beta to IgA production. Unlike the laboratory mouse, generally housed under defined conditions, highly skewed isotype expression patterns generally occur in cattle in chronic infections. A few examples of polarized responses have been noted in chronic experimental or naturally occurring infections including F. hepatica, M. paratuberculosis, C. parvum and B. abortus. In vitro studies using purified bovine B cells and various forms of costimulation and cytokines have demonstrated that isotype responses can be polarized under certain experimental conditions in vitro. That is, IgG1 expression is positively regulated by IL-4 and IgG2 expression is positively regulated by IFN-gamma. Other as yet unidentified factors may play pivotal roles in regulating humoral immune responses in large ruminant species in vivo. This possibility is best exemplified by recent studies using DNA vaccines in cattle that have been demonstrated in the mouse to be generally polarizing to a type 1 response. Surprisingly, studies in cattle using plasmid DNA as vaccination material show an almost exclusive IgG1 response. Based on a number of studies using T cell clones and various biological assays, it is clear that the classical roles of many cytokines in the laboratory mouse do not extrapolate entirely or at all to cattle. Thus, the design of adjuvants and immune modulators should be based on studies done in cattle or using bovine cells. Based on studies to date, several "holes" in the cytokine repertoire exist and these roles may be assumed by unique factors or activities of other known cytokines.

Hlx is induced by and genetically interacts with T-bet to promote heritable T(H)1 gene induction

Type 1 helper T (T(H)1) cells are essential for cellular immunity, but their ontogeny, maturation and durability remain poorly understood. By constructing a dominant-negative form of T-bet, we were able to determine the role played by this lineage-inducing trans-activator in the establishment and maintenance of heritable T(H)1 gene expression. Optimal induction of interferon-gamma (IFN-gamma) expression required genetic interaction between T-bet and its target, the homeoprotein Hlx. In fully mature T(H)1 cells, reiteration of IFN-gamma expression and stable chromatin remodeling became relatively independent of T-bet activity and coincided with demethylation of DNA. In contrast, some lineage attributes, such as expression of IL-12R beta 2 (interleukin 12 receptor beta 2), required ongoing T-bet activity in mature T(H)1 cells and their progeny. These findings suggest that heritable states of gene expression might be maintained by continued expression of the inducing factor or by a mechanism that confers a stable imprint of the induced state.

T(H) cell differentiation is accompanied by dynamic changes in histone acetylation of cytokine genes

Naïve T cells differentiate into effector cells upon stimulation with antigen, a process that is accompanied by changes in the chromatin structure of effector cytokine genes. Using histone acetylation to evaluate these changes, we showed that T cell receptor (TCR) stimulation results in early activation of the genes encoding both interleukin 4 and interferon-gamma. We found that continued culture in the presence of polarizing cytokines established a selective pattern of histone acetylation on both cytokine genes; this correlated with restricted access of the transcription factor NFAT1 to these gene regulatory regions as well as mutually exclusive gene expression by the differentiated T cells. Our data point to a biphasic process in which cytokine-driven signaling pathways maintain and reinforce chromatin structural changes initiated by the TCR. This process ensures that cytokine genes remain accessible to the relevant transcription factors and promotes functional cooperation of the inducible transcription factor NFAT with lineage-specific transcription factors such as GATA-3 and T-bet.

T cell memory

Typical immune responses lead to prominent clonal expansion of antigen-specific T and B cells followed by differentiation into effector cells. Most effector cells die at the end of the immune response but some of these cells survive and form long-lived memory cells. The factors controlling the formation and survival of memory T cells are reviewed.

The effect of nitrostyrene on cell proliferation and macrophage immune responses

The use of mood enhancing drugs such as amphetamine and ecstasy are now prevalent in society. These compounds are known to produce serious psychological and physiological problems in users, which can, in some circumstances result in death. While there has been much research into the effects of these drugs on the body, little if any research has investigated the effect of the side products and synthetic reaction by-products which are a consequence of there illegal production. In the study the effects of nitrostyrene, a reaction by-product in one of the routes to synthesis of amphetamine sulphate, on cell viability and macrophage function was determined. Treatment with nitrostyrene at doses >0.75 microg/mL had a significant suppressive effect on the proliferation of stomach cancer lines. Treatment of macrophages with doses as high as 10 microg/mL did not effect cell viability. Nitrostyrene treatment of macrophages, stimulated with IFN gamma and LPS, resulted in a dose dependent differential inhibition in IL12, IL6 and nitrite production, even using doses < 0.5 microg/mL. Thus ranking of the three, on the basis of the suppressive effect obtained, is IL12 > nitrite > IL6. Thus ingestion of nitrostyrene contaminated ecstasy is likely to have a adverse effect on the immune responses of the recreational user.

Th2 lineage commitment and efficient IL-4 production involves extended demethylation of the IL-4 gene

The relation of CpG methylation to gene silencing is well established, but the contribution of DNA demethylation to gene expression during cell differentiation remains unclear. We show that the IL-4 locus undergoes a complex series of methylation and demethylation steps during T helper cell differentiation. The 5' region of the IL-4 locus is hypermethylated in naive T cells and becomes specifically demethylated in Th2 cells, whereas a highly conserved DNase I-hypersensitive region at the 3' end shows the converse behavior, being hypomethylated in naive T cells and becoming methylated during Th1 differentiation. 5' demethylation is not required for chromatin remodeling or primary transcription of the IL-4 gene but is strongly associated with efficient, high-level induction of IL-4 transcripts by differentiated Th2 cells.

Cutting edge: polarized Th cell response induction by transferred antigen-pulsed dendritic cells is dependent on IL-4 or IL-12 production by recipient cells

To assess the influence of dendritic cell (DC) production of polarizing cytokines on Th2 and Th1 development we transferred Ag-pulsed DC generated from wild-type, IL-4(-/-), or IL-12(-/-) mice into wild-type, IL-4(-/-), or IL-12(-/-) recipients. We found that DC IL-4 was not necessary for Th2 induction and that, surprisingly, DC IL-12 was not an absolute requirement for Th1 development. However, DC IL-12 production facilitated optimal Th1 response development. Critically, recipient ability to produce IL-4 or IL-12 was essential for either Th2 or Th1 development. These data help delineate the source and importance of IL-4 and IL-12 in the process of induction of polarized T cell responses by DC.