Control of immune responses by naturally arising CD4+ regulatory T cells that express toll-like receptors

Altered T-Cell Subsets are Associated with Dysregulated Cytokine Secretion of CD4+ T Cells During HIV Infection

Background

CD4⁺ T cells play a critical role in the regulation of immunopathogenesis in HIV infection. Previous studies have shown contradictory results of the CD4⁺ T-cell responses in people living with HIV (PLHIV).

Methods

A cross-sectional study was performed on 40 healthy controls, 134 ART-naïve PLHIV, and 34 individuals who experienced 3-year ART with low baseline CD4 count from 4 August 2016 to 23 January 2019. We determined the frequencies of CD4⁺ T-cell subsets and described the cytokine secretion pattern of total and subsets of CD4⁺ T cells in these individuals.

Results

We found that CD4⁺ T cells in PLHIV displayed enhanced secretion of pro-inflammation cytokines and polyfunctionality due to HIV disease progression (r = -0.282, P = 0.0035 for IFN-γ; r = -0.412, P = 0.0002 for TNF-α; r = -0.243, P < 0.0001 for GM-CSF; r = -0.252, P = 0.0093 for IFN-γ⁺ TNF-α⁺ cells). However, the altered T-cell subsets, as presented by the loss of naïve cells and expansion of memory/effector population in PLHIV, were associated with discordant results in total and subsets of CD4⁺ T cells. As major cytokine-producing T subsets, effector/memory CD4 subsets showed impaired cytokine production (P < 0.05). We further demonstrated that 3-year ART treatment could improve CD4 counts by increasing the pool of naïve T cells but could not restore cytokine secretion in CD4⁺ T-cell subsets (P < 0.05).

Conclusion

These data identified the impaired capacity of cytokine secretion in CD4⁺ T-cell subsets due to HIV disease progression, and the altered T-cell subsets were associated with pseudo-elevation of cytokine production in total CD4⁺ T cells. This study collectively suggested the importance of therapies that can preserve and/or enhance the function of CD4⁺ T cells in strategies of HIV remission.

Injecting Immunosuppressive M2 Macrophages Alleviates the Symptoms of Periodontitis in Mice

Periodontitis is the second most common oral disease affecting tooth-supporting structures. The tissue damage is mainly initiated by the excessive secretion of proinflammatory cytokines by immune cells. Macrophages are a type of antigen-presenting cells that influence the adaptive immunity function. We used a unique set of cytokines, i.e., a combination of IL-4, IL-13, and IL-10, to stimulate macrophages into a subset of M2 polarization cells that express much higher levels of ARG-1, CD206, and PDL-2 genes. The cells’ anti-inflammatory potential was tested with mixed-lymphocyte reaction assay, which showed that this subset of macrophages could increase IL-2 secretion and suppress IL-17, IL-6, and TNF-α secretion by splenocytes. The gram-negative bacterial species Porphyromonas gingivalis was used to initiate an inflammatory process in murine periodontal tissues. In the meantime, cell injection therapy was used to dampen the excessive immune reaction and suppress osteoclast differentiation during periodontitis. Maxilla was collected and analyzed for osteoclast formation. The results indicated that mice in the cell injection group exhibited less osteoclast activity within the periodontal ligament region than in the periodontitis group. Moreover, the injection of M2 macrophages sustained the regulatory population ratio. Therefore, the M2 macrophages induced under the stimulation of IL-4, IL-13, and IL-10 combined had tremendous immune modulation ability. Injecting these cells into local periodontal tissue could effectively alleviate the symptom of periodontitis.

Cinnamtannin D1 attenuates autoimmune arthritis by regulating the balance of Th17 and treg cells through inhibition of aryl hydrocarbon receptor expression

The suppression of the abnormal systemic immune response constitutes a primary strategy for treatment of rheumatoid arthritis (RA); toward this end, the identification of natural compounds with immunosuppressive activity represents a promising strategy for RA drug discovery. Cinnamtannin D1 (CTD-1), a polyphenolic compound isolated from Cinnamomum tamala, was previously reported to possess good immunosuppressive activity. However, the beneficial effect of CTD-1 on RA is currently unknown. The aim of this study was to evaluate the anti-arthritic effect of CTD-1 in collagen-induced arthritis (CIA) mice and clarify the underlying mechanisms. CTD-1 treatment significantly alleviated the severity of CIA mice, affording reduced clinical scores and paw swelling, along with reduced inflammatory cell infiltration and cartilage damage in the joints; in addition, the serum levels of IL-17, IL-6, and IL-1β were decreased whereas those of TGF-β and IL-10 were increased. CTD-1-treated mice exhibited lower frequency of Th17 cells and higher frequency of Treg cells compared to those in untreated mice, indicating that the balance of Th17/Treg cells may serve as the target for CTD-1. Consistent with this, in ex vivo assays, CTD-1 inhibited Th17 cell differentiation through the downregulation of phospho-STAT3/RORγt, whereas it promoted Treg differentiation by upregulating phospho-STAT5/Foxp3 in response to the stimulation of collagen type II. Moreover, in an in vitro naïve CD4⁺ T cell differentiation assay, CTD-1 directly inhibited Th17 cell differentiation and promoted Treg differentiation, suggesting that CTD-1 regulated the balance of Th17 and Treg cells to inhibit excessive immune response. Furthermore, the regulation effect of CTD-1 on Th17 and Treg cells was dependent on Ahr expression, as this effect was abolished when Ahr was knocked down and was impaired when Ahr was overexpressed. Together, our results indicated that CTD-1 treatment benefits CIA mice by regulating Th17 and Treg differentiation through the inhibition of AHR expression, and suggested a potential application of CTD-1 toward RA treatment.

Pathophysiology of CD4+ T-Cell Depletion in HIV-1 and HIV-2 Infections

The hall mark of human immunodeficiency virus (HIV) infection is a gradual loss of CD4+ T-cells and imbalance in CD4+ T-cell homeostasis, with progressive impairment of immunity that leads ultimately to death. HIV infection in humans is caused by two related yet distinct viruses: HIV-1 and HIV-2. HIV-2 is typically less virulent than HIV-1 and permits the host to mount a more effective and sustained T-cell immunity. Although both infections manifest the same clinical spectrum, the much lower rate of CD4+ T-cell decline and slower progression of disease in HIV-2 infected individuals have grabbed the attention of several researchers. Here, we review the most recent findings on the differential rate of decline of CD4+ T-cell in HIV-1 and HIV-2 infections and provide plausible reasons for the observed differences between the two groups.

Immune modulation by ER stress and inflammation in the tumor microenvironment

It is now increasingly evident that the immune system represents a barrier to tumor emergence, growth, and recurrence. Although this idea was originally proposed almost 50 years ago as the "immune surveillance hypothesis", it is commonly recognized that, with few rare exceptions, tumor cells always prevail. Thus, one of the central unsolved paradoxes of tumor immunology is how a tumor escapes immune control, which is reflected in the lack of effective autochthonous or vaccine-induced anti-tumor T cell responses. In this review, we discuss the role of the endoplasmic reticulum (ER) stress response/unfolded protein response (UPR) in the immunomodulation of myeloid cells and T cells. Specifically, we will discuss how the tumor cell UPR polarizes myeloid cells in a cell-extrinsic manner, and how in turn, thus polarized myeloid cells negatively affect T cell activation and clonal expansion.

Intravenous immunoglobulin attenuates experimental autoimmune arthritis by inducing reciprocal regulation of Th17 and Treg cells in an interleukin-10-dependent manner

OBJECTIVE

Intravenous immunoglobulin (IVIG) is used as a therapeutic agent in various autoimmune diseases. The aims of this study were to investigate the therapeutic effects of IVIG on collagen-induced arthritis (CIA) and identify the mechanism responsible for any therapeutic effects.

METHODS

IVIG was administered to mice with CIA, and the in vivo effects were determined. Th17 and Treg cell frequencies were analyzed by flow cytometry, and cytokine levels in the supernatant were measured by enzyme-linked immunosorbent assay. Subpopulations of T cells and B cells in the spleen were assessed by confocal microscopy.

RESULTS

The arthritis severity score and incidence of arthritis were lower in mice treated with IVIG compared with untreated mice. Histopathologic analysis showed less joint damage in mice treated with IVIG. The expression of proinflammatory cytokines, specific type II collagen antibodies, and osteoclast markers was significantly reduced in mice treated with IVIG. Administration of IVIG induced increased FoxP3 expression and inhibited Th17 cell development. The number of FoxP3+ Treg cells was increased, and the number of Th17 cells was decreased in the spleens of mice treated with IVIG. The number of FoxP3+ follicular helper T cells was increased, and subsequent maturation of germinal center B cells was inhibited by IVIG. In addition, IVIG up-regulated interleukin-10 (IL-10) and Fcγ receptor IIB expression. The treatment effects of IVIG on arthritis were lost in IL-10-knockout mice.

CONCLUSION

These results showed that IVIG has therapeutic effects by modulating CD4+ T cell differentiation. The therapeutic effects of IVIG are dependent on IL-10.

Effects of Bacille Calmette-Guerin after the first demyelinating event in the CNS

OBJECTIVE

To evaluate Bacille Calmette-Guérin (BCG) effects after clinically isolated syndromes (CIS).

METHODS

In a double-blind, placebo-controlled trial, participants were randomly assigned to receive BCG or placebo and monitored monthly with brain MRI (6 scans). Both groups then entered a preplanned phase with IM interferon-β-1a for 12 months. From month 18 onward, the patients took the disease-modifying therapies (DMTs) that their neurologist considered indicated in an open-label extension phase lasting up to 60 months.

RESULTS

Of 82 randomized subjects, 73 completed the study (33 vaccinated and 40 placebo). During the initial 6 months, the number of cumulative lesions was significantly lower in vaccinated people. The relative risks were 0.541 (95% confidence interval [CI] 0.308-0.956; p = 0.03) for gadolinium-enhancing lesions (the primary endpoint), 0.364 (95% CI 0.207-0.639; p = 0.001) for new and enlarging T2-hyperintense lesions, and 0.149 (95% CI 0.046-0.416; p = 0.001) for new T1-hypointense lesions. The number of total T1-hypointense lesions was lower in the BCG group at months 6, 12, and 18: mean changes from baseline were -0.09 ± 0.72 vs 0.75 ± 1.81 (p = 0.01), 0.0 ± 0.83 vs 0.88 ± 2.21 (p = 0.08), and -0.21 ± 1.03 vs 1.00 ± 2.49 (p = 0.02). After 60 months, the cumulative probability of clinically definite multiple sclerosis was lower in the BCG + DMT arm (hazard ratio = 0.52, 95% CI 0.27-0.99; p < 0.05), and more vaccinated people remained DMT-free (odds ratio = 0.20, 95% CI 0.04-0.93; p = 0.04).

CONCLUSIONS

Early BCG may benefit CIS and affect its long-term course.

CLASSIFICATION OF EVIDENCE

BCG, as compared to placebo, was associated with significantly reduced development of gadolinium-enhancing lesions in people with CIS for a 6-month period before starting immunomodulating therapy (Class I evidence).

Human Treg responses allow sustained recombinant adeno-associated virus-mediated transgene expression

Recombinant adeno-associated virus (rAAV) vectors have shown promise for the treatment of several diseases; however, immune-mediated elimination of transduced cells has been suggested to limit and account for a loss of efficacy. To determine whether rAAV vector expression can persist long term, we administered rAAV vectors expressing normal, M-type α-1 antitrypsin (M-AAT) to AAT-deficient subjects at various doses by multiple i.m. injections. M-specific AAT expression was observed in all subjects in a dose-dependent manner and was sustained for more than 1 year in the absence of immune suppression. Muscle biopsies at 1 year had sustained AAT expression and a reduction of inflammatory cells compared with 3 month biopsies. Deep sequencing of the TCR Vβ region from muscle biopsies demonstrated a limited number of T cell clones that emerged at 3 months after vector administration and persisted for 1 year. In situ immunophenotyping revealed a substantial Treg population in muscle biopsy samples containing AAT-expressing myofibers. Approximately 10% of all T cells in muscle were natural Tregs, which were activated in response to AAV capsid. These results suggest that i.m. delivery of rAAV type 1-AAT (rAAV1-AAT) induces a T regulatory response that allows ongoing transgene expression and indicates that immunomodulatory treatments may not be necessary for rAAV-mediated gene therapy.

Avian CD4(+)CD25(+) regulatory T cells: properties and therapeutic applications

Regulatory T cells (Tregs) are a subset of T cells that specialize in immune suppression. CD4(+)CD25(+)FoxP3(+) T cells have been characterized as Tregs and extensively studied in mammals. In the absence of a putative FoxP3 ortholog in avians, CD4(+)CD25(+) cells is characterized as Tregs in avians. Avian CD4(+)CD25(+) cells produce high amounts of IL-10, TGF-β, CTLA-4, and LAG-3 mRNA; lack IL-2 mRNA; and suppress T cell proliferation in vitro through both contact-dependent and -independent pathways. Depleting avian CD4(+)CD25(+) cells increases the proliferation of, IL-2 amount, and IFNγ mRNA amount of CD4(+)CD25(-) cells. Avian CD4(+)CD25(+) cells lose their suppressive properties immediately after inflammation and acquire supersuppressive properties once inflammation subsides. Although Treg activity could be beneficial to the host, Tregs simultaneously inhibit host immunity and cause persistent infections of certain pathogens. Therapy targeted toward alleviating Treg mediated immune suppression can improve host immunity against those persistent pathogens and benefit poultry production.

Regulatory T cells and the immune pathogenesis of prenatal infection

Pregnancy in placental mammals offers exceptional comprehensive benefits of in utero protection, nutrition, and metabolic waste elimination for the developing fetus. However, these benefits also require durable strategies to mitigate maternal rejection of fetal tissues expressing foreign paternal antigens. Since the initial postulate of expanded maternal immune tolerance by Sir Peter Medawar 60 years ago, an amazingly elaborate assortment of molecular and cellular modifications acting both locally at the maternal-placental interface and systemically have been shown to silence potentially detrimental maternal immune responses. In turn, simultaneously maintaining host defense against the infinite array of potential pathogens during pregnancy is equally important. Fortunately, resistance against most infections is preserved seamlessly throughout gestation. On the other hand, recent studies on pathogens with unique predisposition for prenatal infections have uncovered distinctive holes in host defense associated with the reproductive process. Using these infections to probe the response during pregnancy, the immune suppressive regulatory subset of maternal CD4 T cells has been increasingly shown to dictate the inter-workings between prenatal infection susceptibility and pathogenesis of ensuing pregnancy complications. Herein, the recent literature suggesting a necessity for maternal regulatory T cells (Tregs) in pregnancy-induced immunological shifts that sustain fetal tolerance is reviewed. Additional discussion is focused on how expansion of maternal Treg suppression may become exploited by pathogens that cause prenatal infections and the perilous potential of infection-induced immune activation that may mitigate fetal tolerance and inadvertently inject hostility into the protective in utero environment.

Immune regulation and evasion of Mammalian host cell immunity during viral infection

The mammalian host immune system has wide array of defence mechanisms against viral infections. Depending on host immunity and the extent of viral persistence, either the host immune cells might clear/restrict the viral load and disease progression or the virus might evade host immunity by down regulating host immune effector response(s). Viral antigen processing and presentation in the host cells through major histocompatibility complex (MHC) elicit subsequent anti-viral effector T cell response(s). However, modulation of such response(s) might generate one of the important viral immune evasion strategies. Viral peptides are mostly generated by proteolytic cleavage in the cytosol of the infected host cells. CD8(+) T lymphocytes play critical role in the detection of viral infection by recognizing these peptides displayed at the plasma membrane by MHC-I molecules. The present review summarises the current knowledge on the regulation of mammalian host innate and adaptive immune components, which are operative in defence mechanisms against viral infections and the variety of strategies that viruses have evolved to escape host cell immunity. The understanding of viral immune evasion strategies is important for designing anti-viral immunotherapies.

Listeria monocytogenes cytoplasmic entry induces fetal wastage by disrupting maternal Foxp3+ regulatory T cell-sustained fetal tolerance

Although the intracellular bacterium Listeria monocytogenes has an established predilection for disseminated infection during pregnancy that often results in spontaneous abortion or stillbirth, the specific host-pathogen interaction that dictates these disastrous complications remain incompletely defined. Herein, we demonstrate systemic maternal Listeria infection during pregnancy fractures fetal tolerance and triggers fetal wastage in a dose-dependent fashion. Listeria was recovered from the majority of concepti after high-dose infection illustrating the potential for in utero invasion. Interestingly with reduced inocula, fetal wastage occurred without direct placental or fetal invasion, and instead paralleled reductions in maternal Foxp3(+) regulatory T cell suppressive potency with reciprocal expansion and activation of maternal fetal-specific effector T cells. Using mutants lacking virulence determinants required for in utero invasion, we establish Listeria cytoplasmic entry is essential for disrupting fetal tolerance that triggers maternal T cell-mediated fetal resorption. Thus, infection-induced reductions in maternal Foxp3(+) regulatory T cell suppression with ensuing disruptions in fetal tolerance play critical roles in pathogenesis of immune-mediated fetal wastage.

In vitro lipopolysaccharide treatment alters regulatory T cell properties in chickens

The objective of this study was to identify the effect of in vitro lipopolysaccharide (LPS) treatment on regulatory T cells (Tregs) from chickens. Tregs had approximately 30-fold higher TLR 2-type 2 and six-fold higher TLR 4 mRNA content than CD4+CD25- cells. Tregs were treated with either 0 or 1 μg/ml LPS for 0, 2, and 4d. LPS treatment increased the IL-2 mRNA amount in Tregs at 2 and 4d post-LPS treatment. LPS treatment increased the IL-10 mRNA amount in Tregs at 4d post-LPS treatment. The total live cell numbers were approximately two-fold higher at 2d and three-fold higher at 4d in the 1 μg/ml LPS-treated groups than in the 0 μg LPS-treated controls. LPS treatment abrogated suppressive properties of Tregs at 2d post-LPS treatment. At 4d post-LPS treatment, Tregs became supersuppressive. In conclusion, chicken Tregs are differentially activated to facilitate immune response during the early stage of inflammation and to facilitate immune suppression at a later stage of inflammation.

Estradiol-dependent perforin expression by human regulatory T-cells

BACKGROUND

CD4+CD25+FoxP3+ regulatory T-cells (nT(Reg)) have been shown to suppress immune responses to autoantigens and to other diverse antigens, this suppression is mainly mediated by a cell contact-dependent mechanism not yet fully defined. It has been reported that both human natural and induced T(Reg) exert cytotoxic activity against autologous target cells, which suggests that the perforin/granzyme pathway may be a relevant candidate mechanism for the suppressive function of T(Reg). Previous reports have shown that oestradiol (E2) modulates T(Reg) percentages and function.

METHODS

We have evaluated in pregnant and non-pregnant subjects perforin intracellular expression in CD4+CD25+FoxP3+ regulatory T-cells by flow cytometry in whole blood, ex-vivo purified nT(Reg) and ex-vivo purified nT(Reg) after TCR and E2 stimulation. The expression of cellular degranulation markers was also phenotypically determined.

RESULTS

We show that E2 expands T(Reg), enhances in vitro T(Reg) function and induces a T(Reg) phenotype in activated responder (CD4+CD25) T-cells, further increasing the expression of perforin on T(Reg) than in vitro T-cell receptor activation alone. We found surface lysosomal-associated membrane glycoproteins (LAMP)-1 and LAMP-2 expression by T(Reg), which is a sign of cell degranulation and therefore of cytotoxicity exerted by these cells.

CONCLUSION

Our data demonstrates the presence of functional T(Reg) cytotoxic properties in biological systems and support the concept that E2 enhances the number and function of T(Reg) suggesting the potential interaction between E2 and immunoregulatory mechanisms.

Autoimmune Gastritis: Historical Antecedents, Outstanding Discoveries, and Unresolved Problems

The earliest recorded history of autoimmune gastritis can be traced to 1849 in London, when Thomas Addison described "a very remarkable form of anemia" later called pernicious (fatal) anemia (PA). This was followed by the recognition of a gastric mucosal defect suspected to have a nutritional basis, the discovery of the megaloblast that characterized the anemia, the insufficiency of a dietary extrinsic factor characterized as vitamin B12 (cobalamin), and a gastric-secreted intrinsic factor. Treatment with vitamin B12 proved curative. The link between PA and gastritis and atrophy was first confirmed histologically after immediate fixation of the stomach postmortem and later, in the 1940s, by peroral tube biopsy. The causes of gastritis remained enigmatic until the era of autoimmunity, when autoantibodies were detected first to gastric intrinsic factor and then to gastric parietal cells. Hints of a dichotomy in pathogenesis of gastritis were crystallized by the description in 1973 of Type A (Autoimmune) and Type B (later, Bacterial) gastritis. Clarification was enhanced by identification in Type A gastritis of the autoantigen of the parietal cell antibody, by the alpha and beta subunits of gastric H+/K+ ATPase, and by the highly informative experimental murine model of postneonatal thymectomy autoimmune gastritis, and in Type B of the causative role of gastric infection with Helicobacter pylori (H. pylori). A denouement will require a full understanding of (1) the origin and pathogenetic contribution of antibody to intrinsic factor; (2) the connection, if any, between H. pylori infection and Type A autoimmune gastritis; and (3) the genetic contributions to gastritis, whether due to autoimmunity or to H. pylori infection.

Modulation of the TCR stimulation strength can render human activated CD4+ T cells suppressive

In this study, we explored the potential of human naive CD4(+) T cells to acquire regulatory properties upon stimulation. We demonstrated that, in vitro, pre-activated naive CD4(+)CD25(-)CD45RA(+) T cells could become anergic and suppressive CD4(+)CD25(+) T cells upon lower intensity TCR stimulation. These CD4(+)CD25(+) T cells generated in vitro potently suppress the proliferation of allogenic CD4(+)CD25(-) T cells independently of cytokines and in a contact-dependent manner. Our data indicate that expression of Foxp3 is not necessary to induce the suppressive T cell activity. We demonstrate that these CD4(+)CD25(+) T cells are unresponsive upon re-stimulation and that their suppressive activity is transient. However, we showed that the anergy and the suppressive function could be reversed by increasing the stimulus and their level of activation. We concluded from our data that these anergy and suppressive activities are related to a fine tuning of TCR activation threshold.

How the immune system achieves self-nonself discrimination during adaptive immunity

We propose an "Avidity Model of Self-Nonself Discrimination" in which self-nonself discrimination is achieved by both central thymic selection and peripheral immune regulation. The conceptual framework that links these two events is the understanding that both in the thymus and in the periphery the survival or the fate of T cells is determined by the avidity of the interactions between T cell receptors (TCRs) on T cells, specific to any antigens and MHC/antigen peptides presented by antigen-presenting cells (APCs). We envision that the immune system achieves self-nonself discrimination, during adaptive immunity, not by recognizing the structural differences between self versus foreign antigens, but rather by perceiving the avidity of T cell activation. Intrathymic deletion of high avidity T cell clones responding to the majority of self-antigens generates a truncated peripheral self-reactive repertoire composed of mainly intermediate and low but devoid of high avidity T cells compared with the foreign-reactive repertoire. The existence of intermediate avidity self-reactive T cells in the periphery represents a potential danger of pathogenic autoimmunity inherited in each individual because potentially pathogenic self-reactive T cells are included in the pool of intermediate avidity T cells and can often be functionally activated to elicit autoimmune diseases. The distinct composition of peripheral T cell repertoires to self versus to foreign antigens provides a unique opportunity for the immune system to discriminate self from nonself, in the periphery, by selectively downregulating intermediate avidity T cells to both self and foreign antigens. Selective downregulation of the intermediate avidity T cell populations containing the potentially pathogenic self-reactive T cells enables the immune system to specifically control autoimmune diseases without damaging the effective anti-infection immunity, which is, largely, mediated by high avidity T cells specific to the infectious pathogens. In this regard, it has been recently shown that Qa-1-restricted CD8(+) T cells selectively downregulate intermediate avidity T cells, to both self and foreign antigens, and as a consequence, specifically dampen autoimmunity yet optimize the immune response to foreign antigens. Selective downregulation of intermediate avidity T cells is accomplished via specific recognition, by the Qa-1-restricted CD8(+) T cells, of particular Qa-1/self-peptide complexes, such as Qa-1/Hsp60sp, which function as a common surrogate target structure and preferentially expressed on the activated intermediate avidity T cells. This regulatory pathway thus represents one example of the peripheral mechanisms that the immune system evolved to complete self-nonself discrimination that is achieved, imperfectly, by thymic negative selection, in order to maintain self-tolerance. The conceptual framework of the "Avidity Model" differs from, but contains intellectual wisdom of certain conceptual elements of, the "Tunable Activation Thresholds Hypothesis," the "Danger Model," and the "Ergotypic Regulation Phenomenon." It provides a unified and simple paradigm to explain various seemingly unrelated biomedical problems inherent in immunological disorders that cannot be uniformly interpreted by any currently existing paradigms. The potential impact of the conceptual framework of the "Avidity Model" on our understanding of the development and control of commonly seen autoimmune diseases is also discussed.

Host response to colorectal cancer

It has long been established that inflammation and immunity play critical roles in the pathogenesis, control and eventual metastasis of cancers. With the advent of more sophisticated animal models and immunohistochemical techniques a greater understanding of the immune system and its interactions has occurred. Individual immune cells are dynamic structures that have variable behaviour controlled by complex interactions in the tumour microenvironment. In the setting of colorectal cancer it was first observed that peritumoral inflammatory infiltrates were associated with improved prognosis. Immunohistochemistry has shown the individual cells types within these infiltrates. It now appears that an adaptive immune response, differentiated along the T-helper 1 pathway controls tumour invasion and metastasis. Furthermore, the immune system exerts selection pressure leading to the evolution of tumour cell variants that can induce tolerance and disable adaptive immunity. These tumour cells then use the mechanisms of innate immunity to facilitate further growth, angiogenesis, invasion and eventual metastasis. These issues are investigated with particular relevance to colorectal cancer. Using the immune response to defeat CRC has been under intense investigation but has so far been unsuccessful. Nevertheless, researchers remain optimistic that immunotherapy will play an important role in the treatment of this common disease.

The role of regulatory T cells in chronic and acute viral infections

Regulatory T cells, a subset of CD4(+) T lymphocytes, play a pivotal role in the maintenance of the balance between the tissue-damaging and protective effects of the immune response. These cells have immunosuppressive function and have been intensely studied in the context of autoimmunity, cancer, allergies, asthma, and infectious diseases. Their role in chronic and persistent viral infections is well appreciated. In acute viral infections, the function of these cells is still unclear. The host and pathogen factors that control the generation and activity of regulatory T cells and the role of these cells in modulating expansion, contraction, and development of immune memory in acute respiratory virus infection need to be further elucidated.

Toll-like receptor 2 and 4 ligation results in complex altered cytokine profiles early and late after burn injury

BACKGROUND

Toll-like receptors (TLR) 2 and TLR4 expressed on innate immune cells are important mediators of the immune response to pathogens. In this study, we hypothesized that burn injury results in altered cytokine secretion profiles after TLR2 or TLR4 ligation that is associated with altered TLR expression on innate immune cells.

METHODS

Female C56BL/6 mice were subjected to 20% full thickness burn or sham injury. Three or 14 days after injury whole splenocytes or purified splenic macrophages were cultured with TLR2 ligand peptidoglycan or TLR4 ligand lipopolysaccharide. Supernatants were assayed for TNF-alpha, MCP-1, IL-6 and IL-10. Cell death was assessed using flow cytometry. Innate CD11b F4/80 macrophages were sorted 14 days after burn injury and TLR2 and 4 expression was determined by quantitative reverse-transcriptase polymerase chain reaction and flow cytometry.

RESULTS

Burn injury results in a steady accumulation in the periphery of CD11bF4/80 macrophages. Macrophages purified early after burn injury upregulated TLR2 and 4, followed by a decrease of TLR2 and TLR4 expression late after burn injury. TLR2 and TLR4 ligation of an equivalent number of purified macrophages 3 days after burn injury revealed no significant differences in cytokine secretion compared with sham. Stimulation 14 days after burn injury revealed a significant reduction in tumor necrosis factor-alpha secretion by macrophages compared with sham mice. In contrast, interleukin-10 was significantly increased (mean, approximately 1.8-fold) late after burn injury after either TLR2 or TLR4 stimulation. Interleukin-6 and monocyte chemotactic protein-1 secretion was unchanged from sham levels. In contrast, whole splenocyte stimulation resulted in increased cytokine 3 days and 14 days after burn injury. This effect is likely caused by the accumulation of TLR macrophages, which are resistant to TLR-induced cell death.

CONCLUSIONS

Cytokine secretion profiles after TLR2 and TLR4 ligation after burn injury are altered in a manner not clearly reflective of an anti-inflammatory or proinflammatory state and are associated with unique changes in the macrophage population. TLR2 and TLR4 ligation have complex and varied roles in mediating the immune response to burn injury.

Aflatoxin-related immune dysfunction in health and in human immunodeficiency virus disease

Both aflatoxin and the human immunodeficiency virus (HIV) cause immune suppression and millions of HIV-infected people in developing countries are chronically exposed to aflatoxin in their diets. We investigated the possible interaction of aflatoxin and HIV on immune suppression by comparing immune parameters in 116 HIV positive and 80 aged-matched HIV negative Ghanaians with high (> or =0.91 pmol/mg albumin) and low (<0.91 pmol/mg albumin) aflatoxin B1 albumin adduct (AF-ALB) levels. AF-ALB levels and HIV viral load were measured in plasma and the percentages of leukocyte immunophenotypes and cytokine expression were determined using flow cytometry. The cross-sectional comparisons found that (1) among both HIV positive and negative participants, high AF-ALB was associated with lower perforin expression on CD8+ T-cells (P = .012); (2) HIV positive participants with high AF-ALB had significantly lower percentages of CD4+ T regulatory cells (Tregs; P = .009) and naive CD4+ T cells (P = .029) compared to HIV positive participants with low AF-ALB; and (3) HIV positive participants with high AF-ALB had a significantly reduced percentage of B-cells (P = .03) compared to those with low AF-ALB. High AF-ALB appeared to accentuate some HIV associated changes in T-cell phenotypes and in B-cells in HIV positive participants.

Regulatory T cell populations in sepsis and trauma

Sepsis syndrome remains the leading cause of mortality in intensive care units. It is now believed that along with the body's hyperinflammatory response designated to eliminate the underlying pathogen, mechanisms are initiated to control this initial response, which can become deleterious and result in immune dysfunctions and death. A similar state of immune suppression has been described after numerous forms of severe trauma/injury. Although the evidence for immune dysfunctions after sepsis has grown, much remains to be understood about mechanisms underpinning its development and how it acts to increase the morbid state of the critically ill patient. In this context, although the majority of clinical and basic science conducted so far has focused on the roles of myeloid cell populations, the contribution of T lymphocytes and in particular, of regulatory T cells has been somewhat ignored. The studies presented here support the concept that regulatory T lymphocytes (CD4+CD25+ regulatory, gammadelta, and NK T cells) play a role in the control of immune responses and are affected by injury and sepsis. This may be related to their capacity to interact with components of the innate and adaptive immune responses and to their ability to be activated nonspecifically by bacterial products and/or cytokines and to regulate through direct cell-cell and/or soluble mediators. It is our hope that a better understanding of the mechanism through which those rare lymphocyte subsets exert such a profound effect on the immune response may help in improving our ability not only to diagnose but also to treat the critically ill individual.

The perfect mix: recent progress in adjuvant research

Developing efficient and safe adjuvants for use in human vaccines remains both a challenge and a necessity. Past approaches have been largely empirical and generally used a single type of adjuvant, such as aluminium salts or emulsions. However, new vaccine targets often require the induction of well-defined cell-mediated responses in addition to antibodies, and thus new immunostimulants are required. Recent advances in basic immunology have elucidated how early innate immune signals can shape subsequent adaptive responses and this, coupled with improvements in biochemical techniques, has led to the design and development of more specific and focused adjuvants. In this Review, I discuss the research that has made it possible for vaccinologists to now be able to choose between a large panel of adjuvants, which potentially can act synergistically, and combine them in formulations that are specifically adapted to each target and to the relevant correlate(s) of protection.

Infiltration of a mesothelioma by IFN-gamma-producing cells and tumor rejection after depletion of regulatory T cells

Depletion of CD4+CD25+Foxp3+ regulatory T cells (CD25+ T(reg)) with an anti-CD25 Ab results in immune-mediated rejection of tolerogenic solid tumors. In this study, we have examined the immune response to a mesothelioma tumor in mice after depletion of CD25+ cells to elucidate the cellular mechanisms of CD25+ T(reg), a subject over which there is currently much conjecture. Tumor rejection was found to be primarily due to the action of CD8+ T cells, although CD4+ cells appeared to play some role. Depletion of CD25+ cells resulted in an accumulation in tumor tissue of CD4+ and CD8+ T cells and NK cells that were producing the potent antitumor cytokine IFN-gamma. Invasion of tumors by CD8+ T cells was partially dependent on the presence of CD4+ T cells. Although a significant increase in the proliferation and number of tumor-specific CD8+ T cells was observed in lymph nodes draining the tumor of anti-CD25-treated mice, this effect was relatively modest compared with the large increase in IFN-gamma-producing T cells found in tumor tissue, which suggests that the migration of T cells into tumor tissue may also have been altered. Depletion of CD25+ cells did not appear to modulate antitumor CTL activity on a per cell basis. Our data suggests that CD25+ T(reg) limit the accumulation of activated T cells producing IFN-gamma in the tumor tissue and, to a lesser extent, activation and/or rate of mitosis of tumor-specific T cells in lymph nodes.

The regulation of Foxp3 expression in regulatory CD4(+)CD25(+)T cells: multiple pathways on the road

Regulatory T cells (Treg cells) have been well documented to have a crucial physiological role in preventing the development of autoimmune diseases and keeping self-tolerance. Foxp3, a recently identified member of the forkhead transcription factors, serves as a master regulator for the development and function of CD4(+)CD25(+)Treg cells. Though it is well defined that Foxp3 expression is sufficient to program CD4(+)CD25(+)Treg cell development, the physiological factors initiating intracellular Foxp3 expression remain poorly understood so far. In the present manuscript, we try to summarize the recent advances regarding the regulatory roles of T-cell receptor (TCR), co-stimulatory molecules, interleukin-2 (IL-2), transforming growth factor-beta (TGF-beta) and beyond pathways on Foxp3 expression.

The levels of CD4+CD25+ regulatory T cells in paediatric patients with allergic rhinitis and bronchial asthma

Our purpose was to determine whether numbers of CD4(+)CD25(+) T [T regulatory (T(reg))] cells and mRNA expression of functional molecules of T(reg) are related to airway allergy and disease severity in 51 paediatric patients with allergic rhinitis or bronchial asthma and 47 healthy controls. Surface markers were evaluated with flow cytometry, and mRNA was determined with real-time polymerase chain reaction. Children with allergic disease had fewer CD4(+)CD25(+) T cells (8 x 49% +/- 2 x 41% versus 9 x 58% +/- 2 x 43%, P<0 x 05) and CD4(+)CD25(hi) T cells (1 x 32% +/- 0 x 68% versus 1 x 70% +/- 0 x 68%, P<0 x 01) than control subjects. Numbers of CD4(+)CD25(+) and CD4(+)CD25(hi) T lymphocytes were higher in children with persistent allergic rhinitis and/or moderate-severe bronchial asthma than in those with respective milder disease. The number of T(reg) cells was correlated positively with total immunoglobulin E level. The mRNA expression of forkhead box P3 (FoxP3) was increased in moderate-severe versus mild asthma (2 x 93 +/- 0 x 38 versus 1 x 60 +/- 0 x 31, P< 0 x 01). Patients with moderate-severe bronchial asthma also had increased mRNA expression of interleukin (IL)-10 compared with patients with mild asthma (15 x 24 +/- 4 x 07 versus 3 x 77 +/- 2 x 18, P<0 x 01). The suppressive function of T(reg) cells from patients with more severe asthma was competent in vitro. On average, decreased numbers of T(reg) cells in children with allergic airway disease might represent a defect of the T(reg) population. With increased expression of FoxP3 and IL-10 in T(reg) from patients with relatively severe allergic disease, adaptive and functional T(reg) might be generated in response to aggravated atopy and disease severity.

CD4+ T Cells in Lymph Nodes of UVB-Irradiated Mice Suppress Immune Responses to New Antigens Both In Vitro and In Vivo

The mechanisms by which erythemal UVB irradiation modulates systemic immune responses to antigens applied to non-irradiated sites are poorly understood. In this study, regulatory CD4+ T cells were identified in the skin-draining lymph nodes (SDLNs) of UVB-irradiated, but otherwise naive mice. A transgenic mouse strain (DO11.10) was utilized in which the majority of CD4+ T cells expressed the ovalbumin (OVA(323-339)) T-cell receptor. Thus, T-cell responses could be examined following erythemal UVB irradiation without further antigen sensitization. CD4+ T cells from the SDLNs of UVB-irradiated mice had significantly reduced capacity to respond to presentation of the OVA(323-339) peptide in vitro. Transfer of CD4+ T cells from the SDLNs of UVB-irradiated antigen-naive mice significantly reduced both OVA sensitization and contact hypersensitivity responses to an experimental hapten in the recipient mice. Depletion of CD4+CD25+ cells abrogated this UVB-suppressive effect in the in vitro proliferation assay. There was also a significant increase in the proportion of CD4+CD25+Foxp3+ cells in the SDLNs of UVB-irradiated mice. The potential of these regulatory cells poised to regulate responses to incoming antigens at distant non-irradiated sites broadens the biological impact of UVB irradiation of skin on immunity.

TLR4 Hyperresponsiveness via Cell Surface Expression of Heat Shock Protein gp96 Potentiates Suppressive Function of Regulatory T Cells

As one of the main mediators of the endoplasmic reticulum unfolded protein response, heat shock protein gp96 is also an obligate chaperone for multiple TLRs including TLR4. We demonstrated recently that enforced cell surface expression of gp96 in a transgenic (Tg) mouse (96tm-Tg) conferred hyperresponsiveness to LPS and induced TLR4-dependent lupus-like autoimmune diseases. In this study, we investigated the function of CD4(+)CD25(+) Foxp3(+) regulatory T cells (T(reg)) in these mice in light of the important roles of T(reg) in the maintenance of peripheral tolerance against self-Ag as well as the increasing appreciation of TLR signaling on the regulation of T(reg). We found that the development of T(reg) was not impaired in 96tm-Tg mice. Contrary to the prediction of dampened T(reg) activity, we discovered that the suppressive functions of T(reg) were increased in 96tm-Tg mice. Inactivation of T(reg) during the neonatal stage of life exacerbated not only organ-specific diseases but also systemic autoimmune diseases. By crossing 96tm-Tg mice into the TLR4 null background, we demonstrated the critical roles of TLR4 in the amplification of T(reg) suppressive function. These findings illustrate that gp96 plays dual roles in regulating immune responses by augmenting proinflammatory responses and inducing T(reg) function, both of which are dependent on its ability to chaperone TLR4. Our study provides strong support to the notion of compensatory T(reg) activation by TLR ligation to dampen inflammation and autoimmune diseases.

Stimulation of TLR9 with CpG ODN enhances apoptosis of glioma and prolongs the survival of mice with experimental brain tumors

Toll-like receptors (TLRs) recognize a set of conserved molecular structures, so called pathogen-associated molecular patterns, which allow them to sense and initiate innate and adaptive immune responses. In this study, we examined the expression of TLRs in both human and murine glioma. We then analyzed the change in TLR expression after treatment with synthetic phosphorothioate oligodeoxynucleotides (ODNs) containing unmethylated CpG dinucleotides (CpG ODNs), strong activators of both innate and adaptive immunity. In addition, we investigated the in vivo effect of CpG injection into C57BL/6 mice implanted with syngeneic GL261 glioma. Our results indicate that TLR9 is overexpressed in human and murine glioma cell lines and CpG stimulation prolongs the survival of mice with experimental brain tumors. CpGs induce TLR9 down-regulation, followed by apoptosis of GL261 cells in vitro as well as in vivo. Furthermore, the effects of CpG stimulation appear to enhance the antigen presenting capacity of microglia, shift the immune response toward CD8(+) T cells, and decrease the number of CD4(+)CD25(+) regulatory T cells. Taken together, our data support the role of CpG in glioma immunotherapy and provide a rationale for further clinical development of CpG therapy in patients with malignant glioma.

Ex vivo activated OVA specific and non-specific CD4+CD25+ regulatory T cells exhibit comparable suppression to OVA mediated T cell responses

CD4+CD25+ regulatory T cells (Tr) are important in maintaining immune tolerance to self-antigen (Ag) and preventing autoimmunity. Reduced number and inadequate function of Tr are observed in chronic autoimmune diseases. Adoptively transferred Tr effectively suppress ongoing autoimmune disease in multiple animal models. Therefore, strategies to modulate Tr have become an attractive approach to control autoimmunity. Activation of Tr is necessary for their optimal immune regulatory function. However, due to the low ratio of Tr to any given antigen (Ag) and the unknown nature of Ag in many autoimmune diseases, specific activation is not practical for potential therapeutic intervention. It has been shown in animal models that once activated, Tr can exhibit immune suppression in a bystander Ag-non-specific fashion, suggesting the effector phase of Tr is Ag independent. To investigate whether the immune suppression by activated bystander Tr is as potent as that of the Ag specific Tr, Tr cells were isolated from BALB/c or ovalbumin (OVA) specific T cell receptor (TCR) transgenic mice (DO11.10) and their immune suppression of an OVA specific T cell response was compared. We found that once activated ex vivo, Tr from BALB/c and DO11.10 mice exhibited comparable inhibition on OVA specific T cell responses as determined by T cell proliferation and cytokine production. Furthermore, their immune suppression function was compared in a delayed type hypersensitivity (DTH) model induced by OVA specific T cells. Again, OVA specific and non-specific Tr exhibited similar inhibition of the DTH response. Taken together, the results indicate that ex vivo activated Ag-non-specific Tr are as efficient as Ag specific Tr in immune suppression, therefore our study provides additional evidence suggesting the possibility of applying ex vivo activated Tr therapy for the control of autoimmunity.

Increased Toll-like receptor 4 expression on T cells may be a mechanism for enhanced T cell response late after burn injury

BACKGROUND

Burn injury is associated with a dynamic T cell response. We have previously reported an enhanced functional T cell response 14 days after burn injury. Toll-like receptors (TLR), primarily expressed on innate immune cells, have recently been identified on certain T cell subsets, including activated and memory T cells. Our hypothesis is that increased TLR4 expression on memory T cells may be a mechanism for enhanced T cell response 14 days after burn injury.

METHODS

Splenocytes from wild-type C57Bl/6 mice were harvested 14 days after a 20% total body surface area (TBSA) scald burn or sham injury. Splenocytes ex vivo were surface stained either with monoclonal anti-CD3, anti-CD4, anti-CD8, or anti-CD44 antibodies or a two-step biotin-TLR4 monoclonal antibody-streptavidin-FITC surface stain and results analyzed by flow cytometry.

RESULTS

TLR4 expression is successfully detected on CD4 and CD8 T cells. TLR4 expression is significantly (p < 0.05) increased on CD4 T cells and CD8 T cells 14 days after burn injury. There is a significant (p < 0.05) increase in CD44 (memory) CD4 and CD44 (memory) CD8 T cells 14 days after burn injury and this is associated with a significant (p < 0.05) increase of TLR4 expression in both T cell populations.

CONCLUSIONS

This study demonstrates for the first time the potential role of TLR4 expression on memory T cells generated late after burn injury. Although further analysis is required, these data reiterate the importance of adaptive immunity and the complexity of the immune response to burn injury.

The role of virus-induced regulatory T cells in immunopathology

In recent years, regulatory T cells have received increased attention for their role in immune responses to microbial infections. The list of microbial pathogens associated with regulatory T cell responses is growing rapidly and includes bacteria, viruses, parasites, and fungi. As the biology of regulatory T cells is revealed, we are discovering that their induction during infection is a normal aspect of immunity, necessary to limit collateral damage from inflammatory responses and aggressive immunological effectors. Thus, these cells play a critical role in maintaining the delicate balance between preventing immunopathology and allowing the immune response to clear infections. While generally successful, there are notable exceptions where regulatory T cell-mediated suppression appears to be responsible for allowing certain viruses to establish and maintain a persistent state. In this review, we will discuss our current understanding of what virus-induced regulatory T cells are, how they are induced, and what mechanisms they use to suppress immunity. The complex role of Tregs in regulating immunity to viral infections, and the consequences their activity has on disease is illustrated by a review of specific viral infections including hepatitis C virus and human immunodeficiency virus.

CD4+ T Regulatory Cell Induction and Function in Transplant Recipients after CD154 Blockade Is TLR4 Independent

Although the role of CD4(+) T regulatory cells (Treg) in transplantation tolerance has been established, putative mechanisms of Treg induction and function in vivo remain unclear. TLR4 signaling has been implicated in the regulation of CD4(+)CD25(+) Treg functions recently. In this study, we first examined the role of recipient TLR4 in the acquisition of operational CD4(+) Treg following CD154 blockade in a murine cardiac transplant model. Then, we determined whether TLR4 activation in allograft tolerant recipients would reverse alloimmune suppression mediated by CD4(+) Treg. We document that donor-specific immune tolerance was readily induced in TLR4-deficient recipients by a single dose of anti-CD154 mAb, similar to wild-type counterparts. The function and phenotype of CD4(+) Treg in both wild-type and TLR4 knockout long-term hosts was demonstrated by a series of depletion experiments examining their ability to suppress the rejection of secondary donor-type test skin grafts and to inhibit alloreactive CD8(+) T cell activation in vivo. Furthermore, TLR4 activation in tolerant recipients following exogenous LPS infusion in conjunction with donor-type skin graft challenge, failed to break Treg-mediated immune suppression. In conclusion, our data reveals a distinctive property of CD4(+) Treg in tolerant allograft recipients, whose induction and function are independent of TLR4 signaling.

Signatures of human regulatory T cells: an encounter with old friends and new players

BACKGROUND

Naturally occurring CD4+ CD25+ regulatory T cells (TReg) are involved in the control of autoimmune diseases, transplantation tolerance, and anti-tumor immunity. Thus far, genomic studies on TReg cells were restricted to murine systems, and requirements for their development, maintenance, and mode of action in humans are poorly defined.

RESULTS

To improve characterization of human TReg cells, we compiled a unique microarray consisting of 350 TReg cell associated genes (Human TReg Chip) based on whole genome transcription data from human and mouse TReg cells. TReg cell specific gene signatures were created from 11 individual healthy donors. Statistical analysis identified 62 genes differentially expressed in TReg cells, emphasizing some cross-species differences between mice and humans. Among them, several 'old friends' (including FOXP3, CTLA4, and CCR7) that are known to be involved in TReg cell function were recovered. Strikingly, the vast majority of genes identified had not previously been associated with human TReg cells (including LGALS3, TIAF1, and TRAF1). Most of these 'new players' however, have been described in the pathogenesis of autoimmunity. Real-time RT-PCR of selected genes validated our microarray results. Pathway analysis was applied to extract signaling modules underlying human TReg cell function.

CONCLUSION

The comprehensive set of genes reported here provides a defined starting point to unravel the unique characteristics of human TReg cells. The Human TReg Chip constructed and validated here is available to the scientific community and is a useful tool with which to study the molecular mechanisms that orchestrate TReg cells under physiologic and diseased conditions.

Anti-CD25 Antibody Enhancement of Vaccine-Induced Immunogenicity: Increased Durable Cellular Immunity with Reduced Immunodominance

An efficacious vaccine strategy must be capable of inducing strong responses of an appropriate phenotype that are long lasting and sufficiently broad to prevent pathogen escape mechanisms. In the present study, we use anti-CD25 mAb to augment vaccine-induced immunity in mice. We demonstrate that coformulation of Ab and poxviral- or adenoviral-vectored vaccines induces significantly increased T cell responses to a malaria Ag; prior anti-CD25 Ab administration was not required for this effect. Furthermore, this vaccination approach subverts immunodominant epitope hierarchies by enhancing responses to subdominant epitopes induced by recombinant modified vaccinia virus Ankara immunization. Administration of anti-CD25 with a vaccine also induces more durable immunity compared with vaccine alone; significantly higher T cell responses were observed 100 days after the primary immunization. Enhanced immunogenicity is observed for multiple vaccine types with enhanced CD4+ and CD8+ T cell responses induced by bacillus Calmette-Guérin and a recombinant subunit protein vaccine to hepatitis B virus and with multiple Ags of tumor, viral, bacterial, and parasitic origin. Vaccine strategies incorporating anti-CD25 lead to improved protection against pre-erythrocytic malaria challenge. These data underpin new strategies for the design and development of more efficacious vaccines in clinical settings.

Recent advances in dendritic cell biology

Dendritic cells are professional antigen presenting cells that are central to the induction and regulation of immunity. This review discusses recent advances in the understanding of dendritic cell biology.

Concurrent induction of antitumor immunity and autoimmune thyroiditis in CD4+ CD25+ regulatory T cell-depleted mice

When CD4+ CD25+ regulatory T cells are depleted or inactivated for the purpose of enhancing antitumor immunity, the risk of autoimmune disease may be significantly elevated because these regulatory T cells control both antitumor immunity and autoimmunity. To evaluate the relative benefit and risk of modulating CD4+ CD25+ regulatory T cells, we established a new test system to measure simultaneously the immune reactivity to a tumor-associated antigen, neu, and an unrelated self-antigen, thyroglobulin. BALB/c mice were inoculated with TUBO cells expressing an activated rat neu and treated with anti-CD25 monoclonal antibody to deplete CD25+ cells. The tumors grew, then regressed, and neu-specific antibodies and IFN-gamma-secreting T cells were induced. The same mice were also exposed to mouse thyroglobulin by chronic i.v. injections. These mice produced thyroglobulin-specific antibody and IFN-gamma-secreting T cells with inflammatory infiltration in the thyroids of some mice. The immune responses to neu or thyroglobulin were greater in mice undergoing TUBO tumor rejection and thyroglobulin injection than in those experiencing either alone. To the best of our knowledge, this is the first experimental system to assess the concurrent induction and possible synergy of immune reactivity to defined tumor and self-antigens following reduction of regulatory T cells. These results illustrate the importance of monitoring immune reactivity to self-antigens during cancer immunotherapy that involves immunomodulating agents, and the pressing need for novel strategies to induce antitumor immunity while minimizing autoimmunity.

Immunity, Inflammation and Infection in Post-partum Breast and Formula Feeders

PROBLEM

Little is known about immunological recovery in post-partum women and if lactational status affects immunocompetence. Many physiological changes occur, such as uterine involution and recovery of non-pregnant immune status. These changes may also affect susceptibility to disease.

METHOD

The study compared immune and inflammatory activation markers (serum cytokines, Epstein Barr viral antibody titer, neopterin, c-reactive protein (CRP), lymphocyte subset percentages, ex vivo cytokine production, lymphocyte proliferation, salivary Immunoglubulin A (sIgA) in exclusively breastfeeding (EB) and exclusively formula feeding (EF) women at 4-6 weeks post-partum, and control (C) women.

RESULTS

EBs had higher ratios of interferon-gamma (IFN-gamma)/interleukin-10 (IL-10) than EFs, and post-partums were higher than Cs. Both IFN-gamma and IL-10 were significantly higher in post-partums compared to controls. Post-partums also had higher proinflammatory cytokines, CRP and neopterin, salivary IgA and fewer infection symptoms. There were also differences in lymphocyte subsets.

CONCLUSIONS

The post-partum period is oriented towards heightened and activated innate and specific immune defenses, with breastfeeding providing a boost in these phenomena.

Recent advances in dendritic cell biology

Dendritic cells are professional antigen presenting cells that are central to the induction and regulation of immunity. This review discusses recent advances in the understanding of dendritic cell biology.

The regulation and activation of lupus-associated B cells

Anti-double-stranded DNA (anti-dsDNA) B cells are regulated in non-autoimmune mice. While some are deleted or undergo receptor editing, a population of anti-dsDNA (VH3H9/V lambda 1) B cells that emigrate into the periphery has also been identified. These cells have an altered phenotype relative to normal B cells in that they have a reduced lifespan, appear developmentally arrested, and localize primarily to the T/B-cell interface in the spleen. This phenotype may be the consequence of immature B cells encountering antigen in the absence of T-cell help. When provided with T-cell help, the anti-dsDNA B cells differentiate into antibody-forming cells. In the context of the autoimmune-prone lpr/lpr or gld/gld mutations, the VH3H9/V lambda 1 anti-dsDNA B cells populate the B-cell follicle and by 12 weeks of age produce serum autoantibodies. The early event of anti-dsDNA B-cell follicular entry, in the absence of autoantibody production, is dependent upon CD4(+) T cells. We hypothesize that control of autoantibody production in young autoimmune-prone mice may be regulated by the counterbalancing effect of T-regulatory (T(reg)) cells. Consistent with this model, we have demonstrated that T(reg) cells are able to prevent autoantibody production induced by T-cell help. Additional studies are aimed at investigating the mechanisms of this suppression as well as probing the impact of distinct forms of T-cell-dependent and -independent activation on anti-dsDNA B cells.

Peripheral and intestinal regulatory CD4+ CD25(high) T cells in inflammatory bowel disease

BACKGROUND & AIMS

Regulatory CD25+ T cells (T(reg)) are effective in the prevention and down-regulation of inflammatory bowel disease (IBD) in animal models. Functional T(reg) cells are characterized by the expression of the transcription factor FOXP3 and show a CD4+ CD25(high) phenotype in humans. The aim of this study was to determine whether disease activity in IBD correlates with changes in frequency of T(reg) cells and their distribution in the intestinal mucosa.

METHODS

T(reg) cells were analyzed from peripheral blood and from biopsy specimens of IBD patients, inflammatory controls, and healthy volunteers by flow cytometry (CD4+ CD25(high)), immunochemistry (FOXP3), and real-time PCR (FOXP3). Regulatory properties of purified peripheral CD4+ CD25(high) T(reg) cells were determined by their suppressive effect on the proliferation of CD4+ CD25- T cells.

RESULTS

In peripheral blood, CD4+ CD25(high) T cells from IBD patients retain their suppressive activity. CD4+ CD25(high) and FOXP3+ T(reg) cells are increased during remission but decreased during active disease. This contrasts with their strong increase in peripheral blood of patients with acute diverticulitis. Different than peripheral blood, inflamed IBD mucosa contains an increased number of CD4+ CD25(high) T cells, FOXP3+ T cells, and transcripts for FOXP3 compared with noninflamed mucosa. However, the increase of FOXP3+ T cells in IBD lesions is significantly lower compared with inflammatory controls.

CONCLUSIONS

The frequency of CD4+ CD25+ T(reg) cells varies with IBD activity. Active IBD is not associated with a functional defect but with a contraction of the peripheral blood T reg pool and an only moderate expansion in intestinal lesions. Thus, compensatory mechanisms, numerically, are not successfully achieved in these diseases.

CD4+ CD25+ T cells with the phenotypic and functional characteristics of regulatory T cells are enriched in the synovial fluid of patients with rheumatoid arthritis

CD4(+) CD25(+) regulatory T (T(reg)) cells play a critical role in the maintenance of peripheral tolerance and the prevention of autoimmunity. In the present study, we have explored the characteristics of CD4(+) CD25(+) T(reg) cells in patients with rheumatoid arthritis (RA). The frequency and phenotype of CD4(+) CD25(+) T cells in paired samples of synovial fluid (SF) and peripheral blood (PB) from patients with RA and PB from normal controls were analysed. An increased frequency of CD4+ cells T cells expressing CD25 was detected in SF compared to PB from patients with RA. No significant difference was observed in the numbers of CD4(+) CD25(+) T cells in PB from patients and controls. SF CD4(+) CD25(+) T cells expressed high levels of CTLA-4 (both surface and intracellular), GITR and OX40, as well as Foxp3 transcripts. Functionally, SF CD4(+) CD25(+) T cells were impaired in their proliferative responses and could suppress the proliferation of their CD4(+) CD25(-) counterparts. In conclusion, these data demonstrate that CD4(+) CD25(+) T(reg) cells, with the potential to regulate the function of effector T cells and antigen-presenting cells, accumulate in the synovium of patients with RA.

Intrinsic and extrinsic regulation of T lymphocyte quiescence

The outcome of an immune response is dependent on the interplay and complex interactions of positive (stimulatory) and negative (inhibitory) pathways and a major goal of modern immunology is to dissect these physiologic interactions in order to apply these physiologic mechanisms therapeutically. The balance of stimulatory and inhibitory signals is critical for maximizing the ability of the adoptive immune response to defend the host while maintaining immunologic tolerance and preventing autoimmunity. Cellular quiescence is a state characterized by decreased cell size and metabolic activity. The quiescent state of unstimulated T lymphocytes is thought to be due to the lack of activation signals. However, recent studies have shown that quiescence in lymphocytes is not a default state, but an actively maintained gene program. This program regulates intrinsic expression of quiescence factors in T lymphocytes. In addition to intrinsic mechanisms regulating T cell quiescence, CD4 + CD25 + regulatory T cells (Treg) naturally arising in the thymus, engage in the maintenance of immunological self-tolerance by preventing autoimmunity in vivo in a non cell-autonomous manner. Although there is still only a rudimentary knowledge of the molecular mechanisms that govern the activity of the intrinsic quiescence factors and the development of Treg, it is now clear that immune quiescence is regulated by constitutively ongoing active mechanisms.

Depletion of Regulatory T Cells in HIV Infection Is Associated with Immune Activation

Immune activation during chronic HIV infection is a strong clinical predictor of death and may mediate CD4(+) T cell depletion. Regulatory T cells (Tregs) are CD4(+)CD25(bright)CD62L(high) cells that actively down-regulate immune responses. We asked whether loss of Tregs during HIV infection mediates immune activation in a cross-sectional study of 81 HIV-positive Ugandan volunteers. We found that Treg number is strongly correlated with both CD4(+) and CD8(+) T cell activation. In multivariate modeling, this relationship between Treg depletion and CD4(+) T cell activation was stronger than any other clinical factor examined, including viral load and absolute CD4 count. Tregs appear to decline at different rates compared with other CD4(+) T cells, resulting in an increased regulator to helper ratio in many patients with advanced disease. We hypothesize that this skewing may contribute to T cell effector dysfunction. Our findings suggest Tregs are a major contributor to the immune activation observed during chronic HIV infection.

CD4 T cells in tumor immunity

T cell immunity is the key to protective immune responses against tumors. Traditionally, this function has been ascribed to CD8 T lymphocytes with cytotoxic activity, which are restricted by MHC class I molecules. In recent years the realization that CD4 T cells can also play a relevant role in protective anti-tumor responses has received growing attention. Here we will discuss the role of MHC class II-restricted T cells in response to, and in the regulation of, tumor antigens. Emphasis will be placed on four areas: (1) the role of CD4 T cell immunity in tumor protection in animal models and putative mode of action, (2) tumor antigens recognized by human CD4 T cells, (3) the cooperation between two CD4 T cells of different specificity as a new way to jump start the response against sub-immunogenic determinants of tumor antigens in a tolerant environment, and (4) the negative impact of regulatory CD4 T cells on anti-tumor T cell responses. By drawing attention to these four areas, it is our intention to provide the reader with a comprehensive view of issues of contemporary importance for this field, in the expectation that the information will help a better design of therapeutic cancer vaccines.

Regulatory T cell suppression and anergy are differentially regulated by proinflammatory cytokines produced by TLR-activated dendritic cells

CD25(+)CD4(+) regulatory T cells (Tregs) are required for the maintenance of peripheral tolerance to certain self Ags. In this study, the requirements for murine Treg-suppressive activity and proliferation were examined in the context of the maturation of myeloid dendritic cells (DCs). We find that the suppressive function of Tregs is critically dependent on immature DCs and is readily reversed by the maturation of DCs induced by GM-CSF, but does not require TLR activation of either DCs or Tregs. In contrast, reversal of Treg anergy is dependent on TLR activation of DCs, and involves the potentiation of Treg responsiveness to IL-2 by cooperative effects of IL-6 and IL-1, both of which are produced by TLR-activated, mature DCs. Thus, proinflammatory cytokines produced by TLR-activated, mature DCs are required for reversal of Treg anergy, but are not required to overcome Treg suppression.