Regulation of adipogenic differentiation and adipose tissue inflammation by interferon regulatory factor 3

Dysfunction of adipocytes and adipose tissue is a primary defect in obesity and obesity-associated metabolic diseases. Interferon regulatory factor 3 (IRF3) has been implicated in adipogenesis. However, the role of IRF3 in obesity and obesity-associated disorders remains unclear. Here, we show that IRF3 expression in human adipose tissues is positively associated with insulin sensitivity and negatively associated with type 2 diabetes. In mouse pre-adipocytes, deficiency of IRF3 results in increased expression of PPARγ and PPARγ-mediated adipogenic genes, leading to increased adipogenesis and altered adipocyte functionality. The IRF3 knockout (KO) mice develop obesity, insulin resistance, glucose intolerance, and eventually type 2 diabetes with aging, which is associated with the development of white adipose tissue (WAT) inflammation. Increased macrophage accumulation with M1 phenotype which is due to the loss of IFNβ-mediated IL-10 expression is observed in WAT of the KO mice compared to that in wild-type mice. Bone-marrow reconstitution experiments demonstrate that the nonhematopoietic cells are the primary contributors to the development of obesity and both hematopoietic and nonhematopoietic cells contribute to the development of obesity-related complications in IRF3 KO mice. This study demonstrates that IRF3 regulates the biology of multiple cell types including adipocytes and macrophages to prevent the development of obesity and obesity-related complications and hence, could be a potential target for therapeutic interventions for the prevention and treatment of obesity-associated metabolic disorders.

CD40L signaling from CD8+ T cells confers protection against influenza infection

CD40L is a principal mediator of a large range of humoral and cellular responses and CD40L-mediated licensing of dendritic cells is known to be necessary for the generation of robust effector and memory CD8+ T cell responses. Although the effects of CD40L when expressed on CD4+ T cells are well studied, its role when expressed on CD8+ T cells remain unclear. We have previously reported that CD40L signaling mediates the induction of IL-12 p70 production in dendritic cells when expressed by CD8+ T cells. However, the role and importance of this mechanism in CD8+ T cell responses during an infection are not known. To investigate the function of CD40L when expressed on CD8+ T cells in an in vivo mouse model, we crossed OT-I CD8+ T cell receptor transgenic mice with CD40L−/− mice to generate OVA-specific CD8+ T cells that are unable to expressed CD40L. By transferring CD8+ T cells from these mice into CD40L-competent mice and using a strain of influenza that expresses the OVA epitope recognized by OT-I CD8+ T cells, we were able to create an influenza mouse model where CD40L signaling is absent only on the responding CD8+ T cells. Our analysis indicates that CD40L signaling by CD8+ T cells confers protection against influenza infection and that this is likely dependent on the ability of CD8+ T cells to induce IL-12 p70 production in a CD40L-dependent manner.

Gamma interferon regulates contraction of the influenza virus-specific CD8 T cell response and limits the size of the memory population

The factors that regulate the contraction of the CD8 T cell response and the magnitude of the memory cell population against localized mucosal infections such as influenza are important for generation of efficient vaccines but are currently undefined. In this study, we used a mouse model of influenza to demonstrate that the absence of gamma interferon (IFN-γ) or IFN-γ receptor 1 (IFN-γR1) leads to aberrant contraction of antigen-specific CD8 T cell responses. The increased accumulation of the effector CD8 T cell population was independent of viral load. Reduced contraction was associated with an increased fraction of CD8 T cells expressing the interleukin-7 receptor (IL-7R) at the peak of the response, resulting in enhanced numbers of memory/memory precursor cells in IFN-γ(-/-) and IFN-γR(-/-) compared to wild-type (WT) mice. Blockade of IL-7 within the lungs of IFN-γ(-/-) mice restored the contraction of influenza virus-specific CD8 T cells, indicating that IL-7R is important for survival and is not simply a consequence of the lack of IFN-γ signaling. Finally, enhanced CD8 T cell recall responses and accelerated viral clearance were observed in the IFN-γ(-/-) and IFN-γR(-/-) mice after rechallenge with a heterologous strain of influenza virus, confirming that higher frequencies of memory precursors are formed in the absence of IFN-γ signaling. In summary, we have identified IFN-γ as an important regulator of localized viral immunity that promotes the contraction of antigen-specific CD8 T cells and inhibits memory precursor formation, thereby limiting the size of the memory cell population after an influenza virus infection.

Attenuated Bordetella pertussis BPZE1 protects against allergic airway inflammation and contact dermatitis in mouse models

BACKGROUND

We previously reported that prior nasal administration of highly attenuated Bordetella pertussis BPZE1 provides effective and sustained protection against lethal challenge with influenza A viruses. The protective effect was mediated by suppressing the production of major pro-inflammatory mediators. To further explore the anti-inflammatory properties of BPZE1, we investigated the effect of BPZE1 nasal pretreatment on two mouse models of allergic disease, allergic airway inflammation, and contact hypersensitivity (CHS).

METHODS

Allergic reactions were induced in mice nasally pretreated with live attenuated BPZE1 bacteria using the ovalbumin (OVA)-induced allergic airway inflammation and dinitrochlorobenzene (DNCB)-induced CHS models.

RESULTS

Prior BPZE1 nasal treatment suppressed OVA-induced lung inflammation and inflammatory cell recruitment and significantly reduced IgE levels and cytokine production. Similarly, BPZE1 nasal pretreatment markedly inhibited ear swelling, skin inflammation, and production of pro-inflammatory cytokines in the DNCB-induced CHS model. For both models, we showed that BPZE1 pretreatment does not affect the sensitization phase. Upon challenge, BPZE1 pretreatment selectively reduced the level of cytokines whose production is increased and did not affect the basal level of other cytokines. Together, our observations suggest that BPZE1 pretreatment specifically targets those cytokine-producing effector cells that are recruited and involved in the inflammatory reaction.

CONCLUSION

Our study demonstrates the broad anti-inflammatory properties of the attenuated B. pertussis BPZE1 vaccine candidate and supports its development as a promising agent to prevent and/or treat allergic diseases.

NK cells regulate CD8+ T cell priming and dendritic cell migration during influenza A infection by IFN-γ and perforin-dependent mechanisms

An effective immune response against influenza A infection depends on the generation of virus-specific T cells. NK cells are one of the first-line defenses against influenza A infection. We set out to delineate the role of NK cells in T cell immunity using a murine model of influenza A infection with A/PR/8/34. We show that early T cell recruitment mainly occurs in the posterior mediastinal lymph node (pMLN). Depletion of NK cells significantly impaired both dendritic cell (DC) and T cell recruitment into the pMLN. A similar reduction of T cell recruitment was observed when migration was blocked by pertussis toxin, suggesting that migration of pulmonary NK cells and DCs regulates cell recruitment to the pMLN. T cell recruitment was dependent on IFN-γ, and transfer of IFN-γ-competent naive NK cells into IFN-γ-/- mice restored T cell recruitment, whereas IFN-γ-deficient NK cells failed to do so. In addition, NK cell depletion reduced the uptake and transport of influenza A virus by DCs, and significantly impaired the virus-specific T cell response. Both IFN-γ-/- and perforin-/- mice showed reduced viral Ag transport by DCs, suggesting that the ability of NK cells to influence virus transport depends on IFN-γ and perforin. In summary, our data suggest that NK cells play a critical role in the initiation and shaping of the T cell response after influenza A infection.

Soluble molecules are key in maintaining the immunomodulatory activity of murine mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) possess both immuno-privileged and immuno-inhibitory properties that contribute to their therapeutic effects. Ex vivo expansion is required to obtain sufficient cells for therapy, but might also alter their immunological properties. To date there has been no systematic study of MSC immunobiology during extended culture. Here, we demonstrate that both immuno-privilege and immunosuppressive properties of MSCs change with increasing passage. We demonstrate that although MSCs exhibit powerful immunosuppressive effects through secretion of transforming growth factor-β (TGF-β) and induction of interleukin-10, these effects are diminished by a concomitant increase in MSC immunogenicity. Interferon-γ treatment for 3 days induced extendedly cultured MSCs to express significantly higher levels of major histocompatibility complex class I. In vivo, this results in cells that induce significant delayed-type hypersensitivity reactions in allogeneic recipients. Importantly, these effects are alleviated by isolation of the transplanted MSCs using a semi-permeable barrier. Under these conditions, even MSCs cultured through as many as 14 passages still exhibit immuno-inhibitory effects in vivo. Furthermore, the levels of anti-inflammatory molecule TGF-β secreted by MSCs were maintained in the extended culture. These data shed light on the variable results of allogeneic MSCs in transplantation and suggest alternative strategies for prolonging the effect of allogeneic MSCs in cell-based therapy.

Lung CD103+ dendritic cells efficiently transport influenza virus to the lymph node and load viral antigen onto MHC class I for presentation to CD8 T cells

The uptake, transport, and presentation of Ags by lung dendritic cells (DCs) are central to the initiation of CD8 T cell responses against respiratory viruses. Although several studies have demonstrated a critical role of CD11b(low/neg)CD103(+) DCs for the initiation of cytotoxic T cell responses against the influenza virus, the underlying mechanisms for its potent ability to prime CD8 T cells remain poorly understood. Using a novel approach of fluorescent lipophilic dye-labeled influenza virus, we demonstrate that CD11b(low/neg)CD103(+) DCs are the dominant lung DC population transporting influenza virus to the posterior mediastinal lymph node as early as 20 h postinfection. By contrast, CD11b(high)CD103(neg) DCs, although more efficient for taking up the virus within the lung, migrate poorly to the lymph node and remain in the lung to produce proinflammatory cytokines instead. CD11b(low/neg)CD103(+) DCs efficiently load viral peptide onto MHC class I complexes and therefore uniquely possess the capacity to potently induce proliferation of naive CD8 T cells. In addition, the peptide transporters TAP1 and TAP2 are constitutively expressed at higher levels in CD11b(low/neg)CD103(+) DCs, providing, to our knowledge, the first evidence of a distinct regulation of the Ag-processing pathway in these cells. Collectively, these results show that CD11b(low/neg)CD103(+) DCs are functionally specialized for the transport of Ag from the lung to the lymph node and also for efficient processing and presentation of viral Ags to CD8 T cells.

Human CD8⁺ T cells drive Th1 responses through the differentiation of TNF/iNOS-producing dendritic cells

TNF/iNOS-producing dendritic cells (Tip-DCs) have been shown to arise during inflammation and are important mediators of immune defense. However, it is still relatively unclear which cell types contribute to their differentiation. Here we show that CD8(+) T cells, through the interaction with DCs, can induce the rapid development of human monocytes into Tip-DCs that express high levels of TNF-α and iNOS. Tip-DCs exhibited T-cell priming ability, expressed high levels of MHC class II, upregulated co-stimulatory molecules CD40, CD80, CD86, toll-like receptors TLR2, TLR3, TLR4, chemokine receptors CCR1 and CX3CR1 and expressed the classical mature DC marker, CD83. Differentiation of monocytes into Tip-DCs was partially dependent on IFN-γ as blocking the IFN-γ receptor on monocytes resulted in a significant decrease in CD40 and CD83 expression and in TNF-α production. Importantly, these Tip-DCs were capable of further driving Th1 responses by priming naive CD4(+) T cells for proliferation and IFN-γ production and this was partially dependent on Tip-DC production of TNF-α and NO. Our study hence identifies a role for CD8(+) T cells in orchestrating Th1-mediating signals through the differentiation of monocytes into Th1-inducing Tip-DCs.

Importin beta plays an essential role in the regulation of the LysRS-Ap(4)A pathway in immunologically activated mast cells

We recently reported that diadenosine tetraphosphate hydrolase (Ap(4)A hydrolase) plays a critical role in gene expression via regulation of intracellular Ap(4)A levels. This enzyme serves as a component of our newly described lysyl tRNA synthetase (LysRS)-Ap(4)A biochemical pathway that is triggered upon immunological challenge. Here we explored the mechanism of this enzyme's translocation into the nucleus and found its immunologically dependent association with importin beta. Silencing of importin beta prevented Ap(4)A hydrolase nuclear translocation and affected the local concentration of Ap(4)A, which led to an increase in microphthalmia transcription factor (MITF) transcriptional activity. Furthermore, immunological activation of mast cells resulted in dephosphorylation of Ap(4)A hydrolase, which changed the hydrolytic activity of the enzyme.

A novel technique to explore the functions of bronchial mucosal T cells in chronic obstructive pulmonary disease: application to cytotoxicity and cytokine immunoreactivity

Bronchial mucosal CD8(+) cells are implicated in chronic obstructive pulmonary disease (COPD) pathogenesis, but there are few data on their functional properties. We have developed a novel technique to outgrow these cells from COPD patients in sufficient numbers to examine effector functions. Endobronchial biopsies from 15 COPD smokers and 12 ex-smokers, 11 control smokers and 10 non-smokers were cultured with anti-CD3/interleukin (IL)-2 ± IL-15. Outgrown CD3(+) T cells were characterized in terms of phenotype (expression of CD4, 8, 25, 28, 69 and 56), cytotoxicity and expression of COPD-related cytokines. Compared with IL-2 alone, additional IL-15 increased the yield and viability of biopsy-derived CD3(+) T cells (12-16-day culture without restimulation) without alteration of CD4(+) /CD8(+) ratios or expression of accessory/activation molecules. Biopsy-derived T cells, principally CD8(+)/CD56(+) cells, exhibited statistically significantly greater cytotoxic activity in current or ex-smokers with COPD compared with controls (P < 0·01). Elevated percentages of CD8(+) T cells expressed interferon (IFN)-γ, tumour necrosis factor (TNF)-α and IL-13 (P < 0·01) in current COPD smokers compared with all comparison groups. It is possible to perform functional studies on bronchial mucosal T cells in COPD. We demonstrate increased CD8(+)CD56(+) T cell cytotoxic activity and expression of remodelling cytokines in smokers who develop COPD.

A subpopulation of mesenchymal stromal cells with high osteogenic potential

Current bone disease therapy with bone marrow-derived mesenchymal stromal cells (MSC) is hampered by low efficiency. Advanced allogeneic studies on well-established mouse genetic and disease models are hindered by difficulties in isolating murine MSC (mMSC). And mMSC prepared from different laboratories exhibit significant heterogeneity. Hence, this study aimed to identify and isolate a sub-population of mMSC at an early passage number with high osteogenic potential. Enrichment of mMSC was achieved by 1-hr silica incubation and negative selection. Approximately 96% of these cells synthesized osteocalcin after 28 days of osteogenic induction in vitro, and displayed a complete dynamic alteration of alkaline phosphatase (ALP) activity with increasing osteogenic maturation and strong mineralization. Moreover, the cells displayed uniform and stable surface molecular profile, long-term survival, fast proliferation in vitro with maintenance of normal karyotype and distinct immunological properties. CD73 was found to be expressed exclusively in osteogenesis but not in adipogenesis. These cells also retained high osteogenic potential upon allogeneic transplantation in an ectopic site by the detection of bone-specific ALP, osteopontin, osteocalcin and local mineralization as early as 12 days after implantation. Hence, these cells may provide a useful source for improving current strategies in bone regenerative therapy, and for characterizing markers defining the putative MSC population.

Nitric-oxide synthase 2 interacts with CD74 and inhibits its cleavage by caspase during dendritic cell development

Dendritic cells (DC) are professional antigen-presenting cells that possess specific and efficient mechanisms to initiate immune responses. Upon encounter with pathogens, immature DC will go through a maturation process that converts them to highly immunogenic mature DC. Despite the fact that nitric oxide (NO) was produced in large amounts in maturing DC, it is still unclear whether NO is the key molecule that initiates and enhances DC maturation and T cell proliferation, respectively. Here, we report that NO donor and overexpression of either nitric-oxide synthase 2 (NOS2) or nitric-oxide synthase 3 (NOS3) alone can induce surface expression of major histocompatibility complex class II (MHC II) and both the essential co-stimulatory molecules CD80 and CD86 in immature DC. Consistently, NO donor-treated immature DC were capable of enhancing T cell proliferation in vitro in the absence of lipolysaccharide. Interestingly, NOS2 interacts with CD74 (the MHC II-associated invariant chain), and the degradation of CD74 by caspases in immature DC was inhibited upon treatment with NO donor. Because the trafficking of MHC II is CD74-dependent, the increase in cell surface localization of MHC II in maturing DC is in part due to the increase in CD74 protein expression in the presence of NOS2 and NO.

Harnessing the tumour-derived cytokine, CSF-1, to co-stimulate T-cell growth and activation

Aberrant growth factor production is a prevalent mechanism in tumourigenesis. If T-cells responded positively to a cancer-derived cytokine, this might result in selective enhancement of function within the tumour microenvironment. Here, we have chosen colony-stimulating factor-1 (CSF-1) as a candidate to test this concept. CSF-1 is greatly overproduced in many cancers but has no direct effects upon T-lymphocytes, which do not express the c-fms-encoded CSF-1 receptor. To confer CSF-1-responsiveness, we have expressed the human c-fms gene in immortalized and primary T-cells. Addition of soluble CSF-1 resulted in synergistic enhancement of IL-2-driven T-cell proliferation. CSF-1 also co-stimulated the production of interferon (IFN)-gamma by activated T-cells. These effects required Y809 of the CSF-1R and activation of the Ras-MEK-MAP kinase cascade, but were independent of PI3K signalling. T-cells that express c-fms are also responsive to membrane-anchored CSF-1 (mCSF-1) which, unlike its soluble counterpart, could co-stimulate IL-2 production. CSF-1 promoted chemotaxis of c-fms-expressing primary human T-cells and greatly augmented proliferation mediated by a tumour-targeted chimeric antigen receptor, with preservation of tumour cytolytic activity. Taken together, these data establish that T-cells may be genetically modified to acquire responsiveness to CSF-1 and provide proof-of-principle for a novel strategy to enhance the effectiveness of adoptive T-cell immunotherapy.

Inhaled endotoxin in healthy human subjects: A dose-related study on systemic effects and peripheral CD4+ and CD8+ T cells

BACKGROUND

Inhaled endotoxin or lipopolysaccharide (LPS) is implicated in the pathogenesis of pulmonary diseases. We investigated the inhalation effects of two different doses of LPS in healthy human subjects.

METHODS

Eighteen healthy non-atopic human subjects inhaled either 15 microg (n=10) or 50 microg (n=8)Escherichia coli LPS in an open study. As control, each subject had isotonic saline inhalation 1 week before (baseline) and after LPS inhalation. Data collected included those of clinical parameter, induced sputum and peripheral blood CD4+ and CD8+ T cells.

RESULTS

Acute flu-like symptoms and pyrexia were significantly greater in the 50 microg than 15 microg LPS group. Similarly, the increase in sputum and blood total cell and neutrophil counts at 6h following inhaled LPS were greater in the 50 microg group. Myeloperoxidase, human neutrophil elastase and interleukin-8 in sputum sol, but not blood, showed a trend towards greater increase following 50 microg LPS. All these changes were resolved at one week. In the 50 microg dose group alone, there was a reduction in the proportion of peripheral blood interferon (IFN)-gamma-producing CD4+ and CD8+ T cells at 6h followed by an increase at 1 week after inhaled LPS.

CONCLUSIONS

The airway and systemic effects of inhaled LPS are dose-related and predominantly neutrophilic. The changes in the proportions of circulating CD4+ and CD8+ T cells suggests preferential recruitment of IFN-gamma-producing T cells into tissue from inhaled 50 microg LPS, followed by reappearance of these cells in blood 1 week later.

The Immunogenicity and Immunomodulatory Function of Osteogenic Cells Differentiated from Mesenchymal Stem Cells

Multipotent mesenchymal stem cells (MSC) are reported to be immunoprivileged as well as immunosuppressive. Hence, they are ideal candidates for allogeneic transplantation to induce regeneration of diseased tissues and organs. However, it is not known whether MSC would retain their immunoprivileged and immunomodulatory properties after differentiating into the local cell types of the transplantation site. This study sought to investigate this question with a novel New Zealand White rabbit osteogenesis model. Results showed that osteogenic cells differentiated from MSC (DOC) in vitro did not express the MHC class II molecule, were incapable of inducing allogeneic lymphocyte proliferation in mixed lymphocyte culture or generating CTL, were inhibitory in ongoing lymphocyte proliferation, and secreted anti-inflammatory cytokines (IL-10 and TGF-beta). There was a significantly higher secretion of IL-10 by DOC than that by MSC, while there was no significant difference between the TGF-beta secretion of MSC and DOC in vitro. However, after IFN-gamma treatment, TGF-beta secretion by DOC significantly decreased despite the increased production by MSC. Four weeks after local DOC implantation, despite MHC class II expression, second-set allogeneic skin rejection showed similar survival to first-set allogeneic skin rejection and DOC appeared to function as osteoblasts. In conclusion, DOC retained their immunoprivileged and immunomodulatory properties in vitro, but the latter was lost following transplantation.

Murine models of asthma

In vivo animal models can offer valuable information on several aspects of asthma pathogenesis and treatment. The mouse is increasingly used in these models, mainly because this species allows for the application in vivo of a broad range of immunological tools, including gene deletion technology. Mice, therefore, seem particularly useful to further elucidate factors influencing the response to inhaled allergens. Examples include: the role of immunoregulatory mechanisms that protect against T-helper cell type 2 cell development; the trafficking of T-cells; and the contribution of the innate immunity. However, as for other animal species, murine models also have limitations. Mice do not spontaneously develop asthma and no model mimics the entire asthma phenotype. Instead, mice should be used to model specific traits of the human disease. The present task force report draws attention to specific aspects of lung structure and function that need to be borne in mind when developing such models and interpreting the results. In particular, efforts should be made to develop models that mimic the lung function changes characteristic of asthma as closely as possible. A large section of this report is therefore devoted to an overview of airway function and its measurement in mice.

BiP, a putative autoantigen in rheumatoid arthritis, stimulates IL-10-producing CD8-positive T cells from normal individuals

OBJECTIVES

We have reported that synovial fluid T cells from patients with rheumatoid arthritis (RA) proliferate in response to the endoplasmic reticulum molecular chaperone immunoglobulin binding protein (BiP). The aim of the present work was to clone and define T cells responding to this protein.

METHODS

T-cell clones were generated from the peripheral blood of an individual known to respond to BiP by limiting dilution of BiP-stimulated peripheral blood mononuclear cells. T-cell receptor usage of BiP-responsive clones was determined by monoclonal antibody staining followed by flow cytometric analysis. Cytokine production by the BiP-responsive clones was determined by analysis of post-stimulation supernatants by ELISA. Additional phenotyping was performed by flow cytometry.

RESULTS

Of 49 clones isolated, six were shown to proliferate in response to BiP. Proliferation was low but consistent. One clone expressed CD4 and five were CD8-positive. Three clones, all CD8(+), grew strongly and were investigated further. T-cell receptor usage was determined in two clones (Vbeta 7.1 and Vbeta 12); the Vbeta element of the remaining clone was not recognized by the panel of antibodies used. All three clones produced interleukin 10 (IL-10) (80-380 pg/ml) and two of them produced IL-4 (10-80 pg/ml) and IL-5 (>5000 pg/ml). One clone produced both IL-10 and interferon gamma (>5000 pg/ml). Additional phenotyping of these clones showed them to express CD25, CD28, CD80 and 86 but not CD56 or 57. One clone constitutively expressed CTLA-4 cytoplasmically.

CONCLUSIONS

This study demonstrates that a population of CD8(+) T cells with the cytokine profile of Tc2 cells can be stimulated by the chaperone BiP. These cells may perform a regulatory role in the normal response to inflammation. The increase in response to this antigen in the synovial joint in RA may indicate an attempt to regulate the ongoing inflammation.

Activation-induced cell death of human T-cell subsets is mediated by Fas and granzyme B but is independent of TNF-alpha

Human primary effector T cells were analyzed for their susceptibility to anti-CD3-induced activation-induced cell death (AICD). Th1 and Tc1 cells were more susceptible to AICD than their type 2 counterparts. Type 1 and type 2 subsets were also found to be differentially susceptible to CD95-mediated apoptosis, although cell-surface expression of CD95 and CD95L was at similar levels on all subsets. A role for CD95 in AICD was confirmed by the addition of anti-CD95L antibodies that partially abrogated AICD. Residual apoptosis could not be accounted for by TNF-alpha/TNFR interactions because although type 1 cells secreted more TNF-alpha than type 2 cells, the addition of TNFR:Fc fusion protein did not inhibit AICD. Instead, a reduction in AICD was observed in the presence of EGTA or concanamycin A. The inhibition of apoptosis by a granzyme B inhibitor z-AAD-CMK in Tc1 cells further indicated an involvement of the granule exocytosis mechanism in AICD.

Early Th1/Th2 cell polarization in the absence of IL-4 and IL-12: T cell receptor signaling regulates the response to cytokines in CD4 and CD8 T cells

Differentiation of developing T cells into the type 1 (IFN-gamma-producing) or type 2 (IL-4-producing) subsets is a central theme of immune regulation. The balance of IL-4 and IL-12 present during T cell activation has been considered the major influence on type 1 versus type 2 development. Here we show that CD4 T cells can become biased towards type 1 or type 2 phenotypes during their initial activation in the absence of IL-4 or IL-12. This type of regulation is dependent on the balance of MAPkinase, protein kinase C, and calcineurin signaling after TCR engagement. Later maturation of Th1 or Th2 effectors is dependent on IL-12 or IL-4. However Tc1 CD8 effector development is independent of IL-12, and Tc2 cell generation requires both appropriate TCR signals and IL-4 early in effector development. Using an altered peptide ligand to stimulate TCR transgenic T cells, we show that altered signaling regulates the numbers of CD8 cells capable of developing into Tc2 effectors, and also their responsiveness to IL-4. Together, the results support a two-stage model of differentiation in which intermediate cells biased towards the type 1 or type 2 pathways after activation, are subsequently matured in response to IL-12 or IL-4, respectively.

Allergen-specific Th1 cells counteract efferent Th2 cell-dependent bronchial hyperresponsiveness and eosinophilic inflammation partly via IFN-gamma

Th2 T cell immune-driven inflammation plays an important role in allergic asthma. We studied the effect of counterbalancing Th1 T cells in an asthma model in Brown Norway rats that favors Th2 responses. Rats received i.v. transfers of syngeneic allergen-specific Th1 or Th2 cells, 24 h before aerosol exposure to allergen, and were studied 18-24 h later. Adoptive transfer of OVA-specific Th2 cells, but not Th1 cells, and OVA, but not BSA exposure, induced bronchial hyperresponsiveness (BHR) to acetylcholine and eosinophilia in a cell number-dependent manner. Importantly, cotransfer of OVA-specific Th1 cells dose-dependently reversed BHR and bronchoalveolar lavage (BAL) eosinophilia, but not mucosal eosinophilia. OVA-specific Th1 cells transferred alone induced mucosal eosinophilia, but neither BHR nor BAL eosinophilia. Th1 suppression of BHR and BAL eosinophilia was allergen specific, since cotransfer of BSA-specific Th1 cells with the OVA-specific Th2 cells was not inhibitory when OVA aerosol alone was used, but was suppressive with OVA and BSA challenge. Furthermore, recipients of Th1 cells alone had increased gene expression for IFN-gamma in the lungs, while those receiving Th2 cells alone showed increased IL-4 mRNA. Importantly, induction of these Th2 cytokines was inhibited in recipients of combined Th1 and Th2 cells. Anti-IFN-gamma treatment attenuated the down-regulatory effect of Th1 cells. Allergen-specific Th1 cells down-regulate efferent Th2 cytokine-dependent BHR and BAL eosinophilia in an asthma model via mechanisms that depend on IFN-gamma. Therapy designed to control the efferent phase of established asthma by augmenting down-regulatory Th1 counterbalancing mechanisms should be effective.

T cytotoxic 1 and T cytotoxic 2 CD8 T cells both inhibit IgE responses

BACKGROUND

It is well recognized that CD8 T cells inhibit IgE responses. In this study, we investigated the mechanism of CD8 T cell-mediated IgE suppression by comparing the capacity of T cytotoxic 1 (Tc1) and T cytotoxic 2 (Tc2) CD8 T cells to inhibit IgE responses to ovalbumin (OVA).

METHODS

Tc1 and Tc2 CD8 T cells were generated from OVA(257-264)-specific Vbeta5.2 T cell receptor (TcR) transgenic mice by stimulation with anti-CD3 and anti-CD28 under Tc1 and Tc2 polarizing conditions. Tc1 and Tc2 Vbeta5.2 TcR CD8 T cells (10(6)) were adoptively transferred to syngeneic mice, and following immunization with 100 micro of OVA/alum, serum IgE antibodies were measured by passive cutaneous anaphylaxis and expressed as the highest dilution that gave a detectable skin response.

RESULTS

Both Tc1 and Tc2 CD8 T cells from OT-I mice inhibited IgE.

CONCLUSION

Both Tc1 and Tc2 CD8 T cells promote Th1 immunity and inhibit IgE responses. This process appears to be independent of CD8 T cell-derived IFN-gamma, as both Tc2 (IFN-gamma-) and Tc1 (IFN-gamma+) CD8 T cells inhibited IgE.

The effects of pollutants on the allergic immune response

An increase in the prevalence of allergy and allergic diseases has taken place in the industrialised countries. Allergic diseases represent a major health problem, and appear linked to affluence and modern lifestyle. In the 20th century air pollution from industrial sources largely has been replaced by diesel exhaust and other traffic pollution. Further, the indoor environment in which we spend most of our time has changed dramatically. In order to understand the contribution of pollution and other environmental changes to the development of allergy, we need to understand the biologic processes that underlie allergic immune responses. In the present paper, immune regulatory pathways that control the allergic immune response are delineated. Castor bean dust causes widespread allergic sensitisation. The investigations that made clear the importance of CD8 T cells for the regulation of IgE production were triggered by studies of castor bean allergy. A special focus is in this review placed on the regulatory role of CD8 T cells in the development of the allergic immune response.

Antigen-specific and nonspecific determinants of cytokine production during topical sensitization of mice to chemical allergens

BACKGROUND

Topical exposure to chemical allergens such as trimellitic anhydride or 1-chloro-2,4-dinitrochlorobenzene results in the accumulation of dendritic cells (DCs) and subsequent rapid up-regulation of CD4 T-cell proliferation and cytokine secretion within draining lymph nodes.

OBJECTIVE

We investigated the contribution of antigen-specific and CD40 ligand (CD40L)-mediated signals to chemical allergen-induced CD4 T-cell growth and cytokine production.

METHODS

DCs enriched from lymph nodes of allergen-challenged animals by metrizamide centrifugation were used to stimulate cytokine and proliferative responses by magnetic immunobead-sorted CD4 T cells primed in vivo with the same or unrelated allergen. Cultures of DCs and T cells were supplemented with antibodies that block IL-12 and CD40L activity.

RESULTS

Proliferation of CD4 T cells was stimulated by DCs primed with the same but not unrelated antigen, whereas IFN-gamma, IL-12, and IL-10 secretion were provoked equally well by DCs primed with either hapten. Blockade of CD40L engagement abrogated production of IFN-gamma (80%) and IL-12 (95%) under antigen-nonspecific stimulatory conditions. In contrast, IL-10 secretion was enhanced after CD40L blockade under both antigen-specific and nonspecific conditions. Primary CD4 T cells activated by mitogen were also influenced by DCs in the same way.

CONCLUSION

These results show that during the development of chemical sensitization emerging CD4 T-cell growth and cytokine production are regulated by independent mechanisms requiring antigen presentation and CD40 signaling, respectively.

The role of CD23 on allergen-induced IgE levels, pulmonary eosinophilia and bronchial hyperresponsiveness in mice

BACKGROUND

The role of Immunoglobulin (Ig)E in inflammation is the subject of considerable study and a number of studies have shown conflicting evidence for its role in eosinophil recruitment and bronchial hyperresponsiveness in a number of murine models. The low affinity IgE receptor, CD23, is known to act as a negative regulator of IgE production and we have used knockout mice deficient in CD23 to investigate the role of IgE in eosinophil recruitment and bronchial hyperresponsiveness in a murine model of airway inflammation.

OBJECTIVE

To study the role of the low affinity FcepsilonII receptor, CD23 in IgE production, lung inflammation and bronchial hyperresponsiveness.

METHODS

Wild-type and CD23 knockout C57Bl/6 mice (CD23-/-) were immunized by intraperitoneal injection with ovalbumin on days 0 and 14 and challenged with aerosolized antigen on day 21 for a period of up to 1 week. Blood samples, bronchoalveolar lavage and lung tissue samples were obtained to determine serum IgE levels and inflammatory cell numbers, respectively. Furthermore, airway resistance was measured to increasing concentrations of aerosolized 5-hydroxytryptamine in order to evaluate the effect of CD23 deficiency on bronchial hyperresponsiveness to antigen challenge.

RESULTS

Sensitization of wild-type C57Bl/6 mice to ovalbumin resulted in elevated levels of total serum IgE and ovalbumin-specific IgE, which was significantly augmented in CD23 knockout C57Bl/6 mice (CD23-/-). A significant increase in the percentage of eosinophils recovered in bronchoalveolar lavage fluid from wild-type and CD23-/- mice was observed 24 h following 3 or 7 days aerosol exposure with ovalbumin (10 mg/mL). At 3 days, the increase in the percentage of eosinophils was significantly greater in CD23-/- groups. Immunohistochemical analysis of lungs sections revealed the presence of CD3+, CD4+ and CD23+ cells in wild-type mice but a lack of immunofluorescence of CD23+ cells in CD23-/- mice. In wild-type ovalbumin-immunized mice, bronchial hyperresponsiveness to aerosolized 5-hydroxytryptamine was observed following a 3-day antigen challenge, which was significantly greater in CD23-/- ovalbumin-immunized mice.

CONCLUSION

These studies demonstrate that CD23-/- mice have increased capacity to produce IgE consistent with the view of a negative feedback role for membrane-bound CD23 and under such conditions, may account for the greater numbers of eosinophils recruited to the airways and bronchial hyperresponsiveness observed following acute but not chronic antigen challenge.

The balance of protein kinase C and calcium signaling directs T cell subset development

Development of naive T cells into type 1 (Th1, Tc1) or type 2 (Th2, Tc2) effector cells is thought to be under the control of cytokines. In this study, we show that when both IL-12 and IL-4 are present, murine and human T cell differentiation is regulated by the balance of protein kinase C (PKC) and calcium signaling within T cells. Although both biochemical signals were required for T cell activation via the TCR, altering the balance between them redirected type 1 cells to type 2 and vice versa. Stimulation of calcium signaling or inhibition of PKC favored type 1 differentiation, whereas stimulation of PKC or inhibition of calcineurin resulted in type 2 effectors. Altered peptide ligands induced distinct balances of PKC/calcium signaling and altered Tc1/Tc2 development in TCR-transgenic CD8 T cells. The data suggest novel strategies for manipulation of the immune response in vivo.

Human Tc1 and Tc2/Tc0 CD8 T-cell clones display distinct cell surface and functional phenotypes

It has recently become clear that distinct subsets of CD8 T cells, analogous to their CD4 counterparts, exist in rodents and humans. To examine functional differences between human CD8 T-cell subsets, we generated Tc1, Tc2, and Tc0 T-cell clones from the peripheral blood of healthy individuals. The majority of CD8 T-cell clones generated displayed a classic Tc1 phenotype, but 10% to 20% secreted interleukin (IL)-4 in addition to interferon-gamma (Tc0 phenotype). Generation of Tc2 clones was dependent on the use of anti-CD3 and anti-CD28 as the primary stimulus. The cytokine profiles of established clones remained susceptible to modification by the addition of IL-12 and IL-4. In addition, IL-12 enhanced and IL-4 inhibited the growth of Tc1 but not Tc2/0 CD8 T-cell clones. Significant functional differences were observed between the subsets. Tc2/0 clones expressed CD30 and CD40 ligand at a much higher level than Tc1 clones. Both Tc1 and Tc2/0 clones showed comparable cytotoxicity and produced similar levels of perforin and Fas L. However, Tc2 clones were much more resistant to activation-induced cell death and less susceptible to apoptosis by direct Fas ligation. Moreover, Tc1 and Tc2 clones had opposing effects on the development of CD4 effectors, promoting type 1 and type 2 responses, respectively. These data provide evidence for profound differences between human CD8 T-cell subsets that may be important in their functions as cytotoxic or immunoregulatory cells. (Blood. 2000;95:231-240)

Nonatopic wheezy children have reduced interferon-gamma

Viruses cause asthmatic exacerbations in schoolchildren. We tested the hypothesis that children who wheezed with viral respiratory tract infections secrete higher levels of the type 1 cytokine interferon-gamma (IFN-gamma) in the peripheral circulation than children who had never wheezed. Blood was taken from 13 children (eight atopic) with episodic wheeze and 11 controls. CD4 and CD8 cells were separated from peripheral blood mononuclear cells and stimulated with phorbol 12-myrisate 13-acetate (PMA) and ionomycin for 24 h. IFN-gamma, IL-4, and IL-5 were measured in the supernatant by ELISA. IFN-gamma production by CD4 and CD8 cells was lower in children with a history of wheeze (CD4, P = 0.046; CD8, P = 0.037). These children were then analysed according to atopic status. CD4 and CD8 IFN-gamma production in nonatopic wheezy children was reduced (CD4, P=0.009; CD8, P=0.003). IFN-gamma production by atopic wheezy children was lower than by controls, but the differences were not significant (CD4, P = 0.2831; CD8, P = 0.1372). CD8 IL-5 was lower in children who wheezed (P=0.012). Release of IL-4 and IL-5 by CD4 cells did not differ between the three groups. We propose that defective IFN-gamma secretion by CD4 and CD8 cells may contribute to viral-induced wheeze in nonatopic children.

DNase I footprinting of the human interleukin-5 gene promoter

A characteristic feature of allergic asthma is the overexpression of the T helper type 2 (Th2) cytokines interleukin-4 (IL-4), IL-5 and IL-13 by T lymphocytes. Of these cytokines, IL-5 is critical for the growth, survival and recruitment of eosinophils which are thought to be responsible for the tissue damage observed in asthmatic airways. The expression of human IL-5 is primarily regulated at the transcriptional level; however, little is known about the mechanisms that control its transcription. Using nuclear extracts from allergen-specific human T-cell clones we have performed DNase I footprinting of the human IL-5 promoter in order to establish sites occupied by transcription factors. We show footprints covering the conserved lymphokine element 0 ¿(CLE0) -60 to -44 base pairs (bp) and GATA (-73 to -62 bp) elements, which have previously been identified to be important in the regulation of the murine IL-5 promoter. We also describe a footprint covering a considerably extended Octamer binding site (-249 to -217 bp), which encompasses two hitherto unidentified CCAAT/enhancer binding protein consensus binding sites. We have also identified a previously unknown Ets binding site (-274 to -264 bp). These novel data on the regions of the human IL-5 promoter that are bound by transcription factors should allow dissection of the regulatory mechanisms involved in the transcription of IL-5 in the T-helper lymphocytes of asthmatics.

CD8(+) T cell subsets and chronic obstructive pulmonary disease

COPD is a debilitating and progressive condition in which the airways become irreversibly obstructed and the lungs progressively damaged. Unlike asthma, we know little about the cells that initiate and drive this process. Research has shown that CD8(+) T cells are overrepresented in the lungs of patients with COPD and that they are inversely related to lung function. However, not all CD8(+) T cells are alike and subsets that make IFN-gamma but not IL-4 (Tc1), IL-4 but not IFN-gamma (Tc2) as well as those that make both (Tc0) have been described. This article focuses on the characteristics of CD8(+) T cell subsets and considers their potential contribution to chronic obstructive pulmonary disease (COPD). Kemeny DM, Vyas B, Vukmanovic-Stejic M, Thomas M, Noble A, Loh LC, O'Connor BJ. CD8(+) T cell subsets and chronic obstructive pulmonary disease.

Inhibitory effects of endogenous and exogenous interferon-gamma on bronchial hyperresponsiveness, allergic inflammation and T-helper 2 cytokines in Brown-Norway rats

Interferon-gamma (IFN-gamma) is an important cytokine involved in the regulation of allergen-induced immune responses. We examined the role of IFN-gamma in a Brown-Norway rat model of bronchial hyperresponsiveness (BHR) and airway eosinophilia, and its effects on the mRNA expression of T helper type 1 (Th1)/Th2 cytokine. Ovalbumin (OA)-sensitized animals were given either exogenous IFN-gamma (105 U/rat over 3 days, intraperitoneally) or anti-IFN-gamma blocking antibody (DB-1 0.3 mg/rat, intravenously) prior to exposure to OA aerosol and were studied 18-24 hr later. In sensitized animals, OA induced significant BHR, accumulation of eosinophils, T lymphocytes and neutrophils in bronchoalveolar lavage (BAL) fluid, and also increased eosinophils and CD8+ T cells in the airways. Exogenous IFN-gamma attenuated allergen-induced BHR (P<0.02, compared with sham-treated animals) together with a significant reduction in eosinophil and neutrophil numbers in BAL fluid (P<0. 005), and eosinophils and CD8+ T cells in airways (P<0.05). By contrast, anti-IFN-gamma antibody increased airway CD4+ T cells and BHR. Using reverse transcriptase-polymerase chain reaction, significant increases in Th2 [interleukin-4 (IL-4), IL-5 and IL-10], and IFN-gamma cytokine mRNA were found in the lungs of sensitized and OA-exposed animals, while exogenous IFN-gamma significantly suppressed IL-4, IL-5 and IL-10 mRNA expression, and anti-IFN-gamma antibody increased IL-4 and IL-5 mRNA expression. These results indicate that Th1 effects, such as those mediated by IFN-gamma, play a down-regulatory role to suppress the Th2 responses associated with allergen-induced BHR and eosinophilic inflammation.

Effect of CD8+ T-cell depletion on bronchial hyper-responsiveness and inflammation in sensitized and allergen-exposed Brown-Norway rats

We examined the role of CD8+ T cells in a Brown-Norway rat model of asthma, using a monoclonal antibody to deplete CD8+ T cells. Ovalbumin (OA)-sensitized animals were given anti-CD8 antibody (0.5 mg/rat) intravenously 1 week prior to exposure to 1% OA aerosol and were studied 18-24 hr after aerosol exposure. Following administration of anti-CD8 antibody, CD8+ cells were reduced to <1% of total lymphocytes in whole blood and in spleen. In sensitized animals, OA exposure induced bronchial hyper-responsiveness (BHR), accumulation of eosinophils, lymphocytes and neutrophils in bronchoalveolar lavage (BAL) fluid, and also an increase in tissue eosinophils and CD2+, CD4+ and CD8+ T cells in airways. Anti-CD8 antibody caused a further increase in allergen-induced BHR (P<0.03, compared with sham-treated animals), together with a significant increase in eosinophil number in BAL fluid (P<0.05). While CD2+ and CD4+ T cells in airways were not affected by anti-CD8 treatment, the level of CD8+ T cells was significantly reduced in sensitized, saline-exposed animals (P<0.04, compared with sham-treated rats), and sensitized and OA-challenged rats (P<0.002, compared with sham-treated rats). Using reverse transcription-polymerase chain reaction, an increase of T helper (Th)2 cytokine [interleukin (IL)-4 and IL-5], and also of Th1 cytokine [interferon-gamma (IFN-gamma) and IL-2], mRNA in the lung of sensitized and OA-exposed animals was found; after CD8+ T-cell depletion, Th1 cytokine expression was significantly reduced (P<0.02), while Th2 cytokine expression was unchanged. CD8+ T cells have a protective role in allergen-induced BHR and eosinophilic inflammation, probably through activation of the Th1 cytokine response.

IL-4 inhibits human CD8 T cell expression of the common IL-2 receptor gamma chain

Previous studies in both rats and humans have shown that interleukin (IL) 4 can suppress the generation of IL-2-producing CD8 T cells. In an attempt to elucidate the mechanism by which this suppression is brought about, we set out to investigate whether the IL-4 signal interferes with the IL-2 receptor system. It has already been reported that IL-2 can affect the expression of its own receptor and thus provide a means of controlling its own activities. In this study, we demonstrate that the IL-2 Ralpha- and the IL-2 Rgamma-chains are dramatically upregulated following stimulation of CD8 T cells, whereas lower levels of beta-chain are observed. IL-4 did not affect the expression of the alpha- or beta-chains, but was found to inhibit the generation of common gamma-chain-expressing cells. Moreover, CD4 T cells were found to express much lower levels of this subunit and appeared less sensitive to the effects of IL-4. We postulate that the differential expression of the gamma-chain subunit, in the presence and absence of IL-4, may provide a tool for identifying functionally distinct subpopulations of CD8 T cells.

Distribution of alloreactivity amongst the CD45 isoforms of circulating CD4 and CD8 T lymphocytes

The expression of different isoforms of the CD45 surface molecule allows lymphocytes to be divided into two nonoverlapping categories, CD45RA and CD45RO. Previous studies of CD4 T cells have shown that responses to soluble antigens are present predominantly in the RO subset and to mitogens in the RA, alloreactivity being present in both subsets. Responses of CD8 T cells have not been investigated in such detail, nor have responses been compared to CD4 cells. Here we report the alloreactive responses of both CD45RA and RO subsets amongst both CD4 and CD8 T lymphocytes. Following isolation of CD4 and CD8 cells with immunomagnetic beads, CD45 subsets were separated by negative depletion using specific monoclonal antibodies. CD45RA populations were greater than 97% pure and CD45RO cells greater than 91%. One-way primary mixed lymphocyte reactions were established using the purified responder cells with irradiated allogeneic peripheral blood mononuclear cells as stimulators; experiments were all repeated at least three times. In assays of CD4+ RA and RO subsets, reactivity was present in both isoforms, being consistently, but not significantly, greater amongst the RO subset. With CD8+ T cells, reactivity was also present in both isoforms, but was significantly greater in the CD45RA subset, with mean proliferation 2.5-3-fold that of the CD45RO cells (P < 0.05).

Effect of IL-4, IFN-gamma and IL-12 on cytokine production from human CD45RA and CD45RO CD4 T cell precursors

The aim of this study was to compare the effects of IL-4, IL-12 and IFN-gamma on the production of T helper-1 (Th1) and T helper-2 (Th2)-type cytokines from human peripheral blood 'naive' CD45RA and 'memory' CD45RO CD4 T cells. CD45RA or CD45RO CD4 T cells were cultured for 4 days with phorbol myristate acetate (PMA) and ionomycin and either IL-4, IFN-gamma or IL-12 and their ability to proliferate and secrete IFN-gamma and IL-4 determined. Purified CD45RO CD4 T cells stimulated with PMA and ionomycin secreted higher levels of IL-4 and IFN-gamma, as measured by ELISA, than CD45RA CD4 T cells which secreted little IL-4 or IFN-gamma. However, CD45RA and CD45RO CD4 T cells proliferated to the same extent and IL-4, IFN-gamma and IL-12 had no effect on this. IL-12 and IFN-gamma had no effect on the amount of IL-4 secreted by PMA and ionomycin-stimulated CD45RO CD4 T cells, but culture with IL-4 enhanced IL-4 production 7-fold. IL-12 increased the amount of IFN-gamma produced by CD45RO CD4 T cells 2- to 3-fold. Small amounts of IFN-gamma production were induced in CD4 CD45RA T cells by IL-12 and IFN-gamma. These results indicate: (1) that CD45RA cells cannot make significant amounts of IL-4 under the conditions used, (2) that CD45RO cells can produce both Th1 and Th2 cytokines immediately upon restimulation, (3) that IL-12 favours Th1 cytokine production in both CD45RA and CD45RO CD4 T cells, and (4) that IFN-gamma favours IFN-gamma production in CD45RA but not CD45RO cells.

CD8+ T cells in atopic disease

In recent years there has been a tremendous expansion in our understanding about CD8(+) T cells. We now know that, as for CD4(+) T cells, they can be divided into subsets (Tc1 and Tc2) according to the cytokines they secrete. These subsets may differ in their capacity to kill and may even, in some cases, provide help for B cell antibody production or be involved in the induction of inflammatory responses. In addition, there is a host of cross-regulatory networks between different CD4(+) and CD8(+) subsets that control the magnitude and duration of immune responses. The observation that some antigens that are normally presented by MHC class II and seen by CD4(+) T cells can be presented by MHC class I and stimulate CD8(+) T cells increases the possibility for such interactions. During the next few years we can expect that our understanding of the biology of CD8(+) T cells and their role in immunity will increase.

Cytokine production by CD4+ and CD8+ T cells in mice following primary exposure to chemical allergens: evidence for functional differentiation of T lymphocytes in vivo

It has been demonstrated previously that repeated exposure of mice to chemical allergens of different types results in the development of qualitatively divergent immune responses characterized by the production by draining lymph node cells (LNC) of distinct cytokine patterns. Chronic exposure of mice to contact allergens, such as 2,4-dinitrochlorobenzene (DNCB), resulted in the secretion by LNC of low or undetectable levels of interleukins 4 and 10 (IL-4 and IL-10), but comparatively high levels of interferon gamma (IFN-gamma); the latter cytokine being produced by both CD4+ and CD8+ cells. In contrast, chronic exposure of mice to trimellitic anhydride (TMA), a respiratory allergen associated in humans with occupational asthma, induced instead the production by LNC of relatively high concentrations of IL-4 and IL-10, but little IFN-gamma. The low levels of IFN-gamma secretion which were provoked by treatment with TMA were shown to derive from CD8+ cells exclusively. In the present investigations we have sought to determine whether the polarized responses observed following repeated exposure to these chemical allergens are reflected by cytokine secretion patterns provoked by primary exposure. To this end, mice of BALB/c strain were exposed epicutaneously daily for 3 consecutive days to concentrations of DNCB and TMA (1 and 10%, respectively), or to oxazolone, another contact allergen (0.25%), that resulted in substantial proliferative activity in draining lymph nodes. The production by draining LNC of IFN-gamma and of mitogen-inducible IL-4 was measured by enzyme-linked immunosorbent assay and the relative contribution of CD4+ and CD8+ cells to the patterns of cytokine secretion observed was analyzed using both positive and negative selection methods. It was found that primary exposure to DNCB, oxazolone and TMA each resulted in the production by LNC of both IFN-gamma and IL-4. Selective depletion of, or enrichment for, CD4+ and CD8+ cells revealed that only CD4+ cells elaborated mitogen-inducible IL-4. Depletion of neither CD4+ nor CD8+ cells compromised the production by TMA- or DNCB-activated LNC of IFN-gamma, although positively selected CD8+ cells were considerably less able than CD4+ cells to elaborate this cytokine, presumably secondary to a lack of appropriate accessory cells. Taken together the results demonstrate that early during immune responses to DNCB or oxazolone and TMA there is no evidence for the selectivity of cytokine secretion patterns that characterizes responses following more chronic exposure. Moreover, it is clear that exposure to TMA initially induces the production of IFN-gamma by both CD4+ and CD8+ cells, whereas after more chronic treatment the secretion of this cytokine is a function of CD8+ cells exclusively. Collectively, these results indicate that the polarized responses that develop in mice following chronic exposure to different classes of chemical allergen are not reflected by the characteristics of primary immune responses. As such the development of qualitatively divergent immune responses to chemical allergens provides a paradigm for the evolution of differentiated T cell function with time and/or with antigen exposure.

Superior biologic activity of the recombinant bee venom allergen hyaluronidase expressed in baculovirus-infected insect cells as compared with Escherichia coli

BACKGROUND

Hyaluronidase (Hya) is one of several allergens in honeybee venom. Its cDNA sequence was recently described.

OBJECTIVE

We sought to express recombinant Hya in prokaryotic and eukaryotic systems and to compare it with natural (n)Hya for biologic activity.

METHODS

In Escherichia coli Hya was produced as inclusion body 6 x His-fusion protein. In baculovirus-infected insect cells expression was obtained by cotransfection of linearized Bac-N-Blue DNA and pMelBac transfer vector into Spodoptera frugiperda cells.

RESULTS

Enzymatic activity of Hya from the baculovirus system was equal to nHya, and that of the enzyme expressed in E. coli was only 20% to 30% of nHya. In vitro IgE binding was similar in nHya and the enzyme from baculovirus but markedly lower in Hya expressed in E. coli.

CONCLUSIONS

Biologic activity of Hya expressed in baculovirus-infected insect cells was comparable with that of the natural enzyme, indicating a native-like conformation of the recombinant protein. In contrast, the enzyme expressed in E. coli as an inclusion-body protein and reconstituted in vitro reached only 20% to 30% of the activity of nHya.

Ovalbumin-specific, MHC class I-restricted, alpha beta-positive, Tc1 and Tc0 CD8+ T cell clones mediate the in vivo inhibition of rat IgE

In the following study, we demonstrate that medium responder PVG rats immunized i.p. with OVA complexed to the adjuvant aluminum hydroxide exhibit a moderate IgE response (400-1000 ng/ml). In these rats, we demonstrate that underlying the MHC class II-restricted CD4+ T cell response, there is an MHC class I-restricted CD8+ T cell component that plays an important role in restricting the magnitude and duration of the IgE response. We show that in vivo depletion of CD8+ T cells effects a massive increase in IgE (20-fold), and that they are MHC class I-restricted, OVA-specific, cytolytic cells that universally produce IFN-gamma (25-69 ng/ml) and IL-2 (7.6-22 U/ml), and occasionally secrete IL-4 (68-81 U/ml IL-4), and when adoptively transferred into CD8-depleted recipients, can effect a significant reduction in IgE (3- to 50-fold). We also demonstrate that this in vivo inhibition of IgE is dependent on the Ag-specific activation of the CD8+ T cells, and that the activated CD8+ T cells will suppress total/bystander IgE in an Ag-nonspecific manner. These data are consistent with a growing literature demonstrating sensitization of MHC class I-restricted CD8+ T cells by exogenous protein Ags delivered to mucosal sites, and may represent a mechanism whereby a selective pressure can be applied on the functional outcome of an immunoglobulin response to environmental allergens.

Antigen-specific CD8+ T cells inhibit IgE responses and interleukin-4 production by CD4+ T cells

There is a growing body of evidence which suggests that CD8+ T cells play an important part in regulating the IgE response to non-replicating antigens. In this study we have systematically investigated their role in the regulation of IgE and of CD4+ T cell responses to ovalbumin (OVA) by CD8+ T cell depletion in vivo. Following intraperitoneal immunization with alum-precipitated OVA, OVA-specific T cell responses were detected in the spleen and depletion of CD8+ T cells in vitro significantly enhanced the proliferative response to OVA. Depletion of CD8+ T cells in vivo 7 days after immunization failed to enhance IgE production, while depletion of CD8+ T cells on days 12-18 greatly enhanced the IgE response, which rose to 26 micrograms/ml following a second injection of anti-CD8 on day 35 and remained in excess of 1 microgram/ml over 300 days afterwards. Reconstitution on day 21 of rats CD8-depleted on day 12 with purified CD8+ T cells from animals immunized on day 12 completely inhibited the IgE response. This effect was antigen specific; CD8+ T cells from OVA-primed animals had little effect on the IgE response of bovine serum albumin immunized rats. In vivo, CD8+ T cell depletion decreased interferon (IFN)-gamma production but enhanced interleukin (IL)-4 production by OVA-stimulated splenic CD4+ T cells. Furthermore, CD8+ T cell depletion and addition of anti-IFN-gamma antibody enhanced IgE production in vitro in an IL-4-supplemented mixed lymphocyte reaction. These data clearly show that antigen-specific CD8+ T cells inhibit IgE in the immune response to non-replicating antigens. The data indicate two possible mechanisms: first, CD8+ T cells have direct inhibitory effects on switching to IgE in B cells and second, they inhibit OVA-specific IL-4 production but enhance IFN-gamma production by CD4+ T cells.

Regulation of cytokine production by human Th0 cells following stimulation with peptide analogues: differential expression of TGF-beta in activation and anergy

The different biological activities of T-cell-derived cytokines and their level of production influences the qualitative nature of immune responses and, in certain forms of T-cell tolerance, the lack of antigen responsiveness is associated with the production of transforming growth factor-beta (TGF-beta) and interleukin-4 (IL-4). In this study we have investigated the effects of T-cell receptor (TCR) ligation with peptide analogues and the native peptide, in the presence and absence of costimulation, on cytokine production by human T-helper type 0 (Th0) cells reactive with influenza virus haemagglutinin (HA) peptide (HA306-318) and restricted by HLA-DRB1*0101. We observed that resting Th0 cells constitutively produced TGF-beta, but when stimulated with peptide and antigen-presenting cells (APC) under conditions that induce clonal expansion, TGF-beta secretion was abrogated. Furthermore, exposure of the T cells to the wild-type HA peptide under conditions that induce T-cell anergy resulted in the secretion of TGF-beta, and subsequent antigenic rechallenge was unable to override this signal and down-regulate TGF-beta production. Stimulation with altered TCR ligands that failed to induce proliferation also resulted in marked production of TGF-beta, although in many instances the levels were less than those observed in the total absence of antigen, suggesting that partial signalling has occurred. Although in general, there was a direct positive correlation between proliferation and the production of IL-2, IL-4 and interferon-gamma (IFN-gamma) following stimulation with certain analogues, the production of selected cytokines was dissociated.

GM-CSF increases the ability of cultured macrophages to support autologous CD4+ T-cell proliferation in response to Dermatophagoides pteronyssinus and PPD antigen

Previous studies have demonstrated an infiltration of monocytes and increased levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) in the asthmatic lung. To study the possible effects of this cytokine upon the differentiation and function of these newly recruited monocytes, we have developed a model in which monocytes isolated from human peripheral blood were differentiated into macrophages in serum in the presence or absence of GM-CSF. After 7 days, the macrophages increased in size and granularity, had increased phagocytic activity, and expressed various adhesion molecules, CD14 and major histocompatibility complex (MHC) class II. The effects of GM-CSF on antigen presentation by cultured macrophages on the antigen-specific proliferative response of CD4+ T cells to Dermatophagoides pteronyssinus or purified protein derivative of tuberculin and the mitogen phytohaemagglutinin was determined. CD4+ T-cell proliferation was reduced when either antigen was presented by macrophages cultured in serum alone, compared with the values obtained with freshly isolated monocytes. However, CD4+ cell proliferation was comparable to that observed with monocytes when antigen was presented by macrophages which had been pre-cultured with 50 U/ml GM-CSF. CD4+ T-cell proliferation to phytohaemagglutinin was similar when all three populations were used as accessory cells. High numbers of macrophages partially suppressed CD4+ T-cell proliferation in response to antigen presented by monocytes, but there was no significant difference between macrophages cultured in the presence or absence of GM-CSF. This data suggests that GM-CSF directs monocyte differentiation into macrophages with an antigen-presenting, rather than a suppressive, phenotype. Elevated levels of GM-CSF in the asthmatic lung may therefore maintain recently recruited monocytes in an inflammatory and T-cell activating state.

Immune memory in CD4+ CD45RA+ T cells

This study addresses the question of whether human peripheral CD4+ CD45RA+ T cells possess antigen-specific immune memory. CD4+ CD45RA+ T cells were isolated by a combination of positive and negative selection. Putative CD4+ CD45RA+ cells expressed CD45RA (98.9%) and contained < 0.1% CD4+ CD45RO+ and < 0.5% CD4+ CD45RA+ CD45RO+ cells. Putative CD45RO+ cells expressed CD45RO (90%) and contained 9% CD45RA+ CD45RO+ and < 0.1% CD4+ CD45RA+ cells. The responder frequency of Dermatophagoides pteronyssinus-stimulated CD4+ CD45RA+ and CD4+ CD45RO+ T cells was determined in two atopic donors and found to be 1:11,314 and 1:8031 for CD4+ CD45RA+ and 1:1463 and 1:1408 for CD4+ CD45RO+ T cells. The responder frequencies of CD4+ CD45RA+ and CD4+ CD45RO+ T cells from two non-atopic, but exposed, donors were 1:78031 and 1:176,903 for CD4+ CD45RA+ and 1:9136 and 1:13,136 for CD4+ CD45RO+ T cells. T cells specific for D. pteronyssinus were cloned at limiting dilution following 10 days of bulk culture with D. pteronyssinus antigen. Sixty-eight clones were obtained from CD4+ CD45RO+ and 24 from CD4+ CD45RA+ T cells. All clones were CD3+ CD4+ CD45RO+ and proliferated in response to D. pteronyssinus antigens. Of 40 clones tested, none responded to Tubercule bacillus purified protein derivative (PPD). No difference was seen in the pattern of interleukin-4 (IL-4) or interferon-gamma (IFN-gamma) producing clones derived from CD4+ CD45RA+ and CD4+ CD45RO+ precursors, although freshly isolated and polyclonally activated CD4+ CD45RA+ T cells produced 20-30-fold lower levels of IL-4 and IFN-gamma than their CD4+ CD45RO+ counterparts. Sixty per cent of the clones used the same pool of V beta genes. These data support the hypothesis that immune memory resides in CD4+ CD45RA+ as well as CD4+ CD45RO+ T cells during the chronic immune response to inhaled antigen.