Immune response to chemically modified flagellin. 3. Enhanced cell-mediated immunity during high and low zone antibody tolerance to flagellin

Severe murine schistosomiasis results from disrupted CD4+ T-cell modulation by immunodominance of a single egg epitope

OBJECTIVE

This study examined the correlation between immunodominance of the major egg antigen Sm-p40234-246, a robust Th1/Th17 anti-egg CD4 T-cell response, and severe liver immunopathology in experimental murine schistosomiasis. It serves as a platform to analyze how varying degrees of immunodominance affect CD4+ T cell modulation and disease outcomes.

METHODS

We used a murine model of schistosomiasis to investigate the effects of immunodominance. Infected mice were divided into two groups: one treated with a combination of epitopes targeting immunodominance of the major egg antigen Sm-p40 and the other with a mock mixture of non-immunogenic epitopes. Liver granuloma area, a hallmark of schistosomiasis pathology, was quantified using histological and morphometric analyses. The average granuloma areas between the treated and untreated groups were compared using one-way ANOVA with Tukey's multiple comparison test. Additionally, we isolated CD4+ T cells from mesenteric lymph nodes, stimulated them with specific egg antigens, and collected purified supernatants to assess their signature cytokine secretion profiles for each treatment group.

RESULTS

Results showed that strong immunodominance of a single egg epitope undermines effective CD4+ T-cell modulation, promoting a strongly polarized Th1/Th17 pathogenic response. Conversely, neutralizing this immunodominance produces the opposite restorative effect.

CONCLUSION

Immunodominance is an important pathogenic component that influences CD4+ T cell modulation in experimental murine schistosomiasis. Moreover, immunodominance can be used to treat these and other important CD4+ T cell-mediated diseases.

Dose-Dependent Prophylactic Efficacy of Filarial Antigens Glutathione-S-Transferase and Abundant Larval Transcript-2 against Brugia malayi Challenge in Mastomys

Objective

To identify the most effective dose of filarial rBmALT-2 and rWbGST alone or in combination against B. malayi infection in vitro and in vivo.

Methods

Mastomys (n = 5-7/group) received intramuscular (i.m.) injection with three different doses (25, 50, and 100 μg) of rBmALT-2 or rWbGST, either alone or in combination with alum as the adjuvant. Protective immunity was studied by in vivo and in vitro cytotoxicity assay. To evaluate the cellular immune response, splenocyte proliferation and cytokine profile were assessed.

Results

Serological results revealed a substantial (p < 0.005) induction of IgG1, IgG2a, and IgG3 responses in vaccinated Mastomys. Mastomys immunized with 50 μg rBmALT-2 + alum induced 79-81% killing against the L3 larvae challenge in vivo and in vitro ADCC assay (p < 0.005); whereas rWbGST + alum alone or in combination with rBmALT-2 + alum induced 63-68% killing (p < 0.005) in vivo and in vitro. Antigen-specific cytokine profiles of Mastomys vaccinated with either BmALT-2, WbGST or a combination showed elevated IL-10, IL-4, and IFN-γ levels, signifying both Th1 and Th2 immune response.

Conclusions

These findings suggest that immunization of Mastomys with a 50 μg/dose of rBmALT-2 + alum four times at a 4-week interval demonstrated considerable protection against B. malayi infection.

What Determines the Class of Immunity an Antigen Induces? A Foundational Question Whose Rational Consideration Has Been Undermined by the Information Overload

Activated CD4 T helper cells are required to activate B cells to produce antibody and CD8 T cells to generate cytotoxic T lymphocytes. In the absence of such help, antigens inactivate B cells and CD8 T cells. Thus, the activation or inactivation of CD4 T cells determines whether immune responses are generated, or potentially ablated. Most consider that the activation of CD4 T cells requires an antigen-dependent signal, signal 1, as well as a critical costimulatory signal, initiated when a pattern recognition receptor (PRR) engages with a danger- or pathogen-associated molecular pattern (DAMP or PAMP). Most also envisage that the nature of the DAMP/PAMP signal determines the Th subset predominantly generated and so the class of immunity predominantly induced. I argue that this framework is implausible as it is incompatible with diverse observations of the variables of immunization affecting the class of immunity induced. An alternative framework, the threshold hypothesis, posits that different levels of antigen mediated CD4 T cell interactions lead to the generation of different Th subsets and so different classes of immunity, that it is compatible with these observations. This alternative supports a rational approach to preventing and treating diverse clinical conditions associated with infectious disease and, more speculatively, with cancer.

Understanding the development of Th2 cell-driven allergic airway disease in early life

Allergic diseases, including atopic dermatitis, allergic rhinitis, asthma, and food allergy, are caused by abnormal responses to relatively harmless foreign proteins called allergens found in pollen, fungal spores, house dust mites (HDM), animal dander, or certain foods. In particular, the activation of allergen-specific helper T cells towards a type 2 (Th2) phenotype during the first encounters with the allergen, also known as the sensitization phase, is the leading cause of the subsequent development of allergic disease. Infants and children are especially prone to developing Th2 cell responses after initial contact with allergens. But in addition, the rates of allergic sensitization and the development of allergic diseases among children are increasing in the industrialized world and have been associated with living in urban settings. Particularly for respiratory allergies, greater susceptibility to developing allergic Th2 cell responses has been shown in children living in urban environments containing low levels of microbial contaminants, principally bacterial endotoxins [lipopolysaccharide (LPS)], in the causative aeroallergens. This review highlights the current understanding of the factors that balance Th2 cell immunity to environmental allergens, with a particular focus on the determinants that program conventional dendritic cells (cDCs) toward or away from a Th2 stimulatory function. In this context, it discusses transcription factor-guided functional specialization of type-2 cDCs (cDC2s) and how the integration of signals derived from the environment drives this process. In addition, it analyzes observational and mechanistic studies supporting an essential role for innate sensing of microbial-derived products contained in aeroallergens in modulating allergic Th2 cell immune responses. Finally, this review examines whether hyporesponsiveness to microbial stimulation, particularly to LPS, is a risk factor for the induction of Th2 cell responses and allergic sensitization during infancy and early childhood and the potential factors that may affect early-age response to LPS and other environmental microbial components.

Immune tolerance against infused FVIII in hemophilia A is mediated by PD-L1+ Tregs

A major complication of hemophilia A therapy is the development of alloantibodies (inhibitors) that neutralize intravenously administered coagulation factor VIII (FVIII). Immune tolerance induction therapy (ITI) by repetitive FVIII injection can eradicate inhibitors, and thereby reduce morbidity and treatment costs. However, ITI success is difficult to predict and the underlying immunological mechanisms are unknown. Here, we demonstrated that immune tolerance against FVIII under nonhemophilic conditions was maintained by programmed death (PD) ligand 1-expressing (PD-L1-expressing) regulatory T cells (Tregs) that ligated PD-1 on FVIII-specific B cells, causing them to undergo apoptosis. FVIII-deficient mice injected with FVIII lacked such Tregs and developed inhibitors. Using an ITI mouse model, we found that repetitive FVIII injection induced FVIII-specific PD-L1+ Tregs and reengaged removal of inhibitor-forming B cells. We also demonstrated the existence of FVIII-specific Tregs in humans and showed that such Tregs upregulated PD-L1 in patients with hemophilia after successful ITI. Simultaneously, FVIII-specific B cells upregulated PD-1 and became killable by Tregs. In summary, we showed that PD-1-mediated B cell tolerance against FVIII operated in healthy individuals and in patients with hemophilia A without inhibitors, and that ITI reengaged this mechanism. These findings may impact monitoring of ITI success and treatment of patients with hemophilia A.

A Comparison of XGBoost, Random Forest, and Nomograph for the Prediction of Disease Severity in Patients With COVID-19 Pneumonia: Implications of Cytokine and Immune Cell Profile

Background and Aims

The aim of this study was to apply machine learning models and a nomogram to differentiate critically ill from non-critically ill COVID-19 pneumonia patients.

Methods

Clinical symptoms and signs, laboratory parameters, cytokine profile, and immune cellular data of 63 COVID-19 pneumonia patients were retrospectively reviewed. Outcomes were followed up until Mar 12, 2020. A logistic regression function (LR model), Random Forest, and XGBoost models were developed. The performance of these models was measured by area under receiver operating characteristic curve (AUC) analysis.

Results

Univariate analysis revealed that there was a difference between critically and non-critically ill patients with respect to levels of interleukin-6, interleukin-10, T cells, CD4+ T, and CD8+ T cells. Interleukin-10 with an AUC of 0.86 was most useful predictor of critically ill patients with COVID-19 pneumonia. Ten variables (respiratory rate, neutrophil counts, aspartate transaminase, albumin, serum procalcitonin, D-dimer and B-type natriuretic peptide, CD4+ T cells, interleukin-6 and interleukin-10) were used as candidate predictors for LR model, Random Forest (RF) and XGBoost model application. The coefficients from LR model were utilized to build a nomogram. RF and XGBoost methods suggested that Interleukin-10 and interleukin-6 were the most important variables for severity of illness prediction. The mean AUC for LR, RF, and XGBoost model were 0.91, 0.89, and 0.93 respectively (in two-fold cross-validation). Individualized prediction by XGBoost model was explained by local interpretable model-agnostic explanations (LIME) plot.

Conclusions

XGBoost exhibited the highest discriminatory performance for prediction of critically ill patients with COVID-19 pneumonia. It is inferred that the nomogram and visualized interpretation with LIME plot could be useful in the clinical setting. Additionally, interleukin-10 could serve as a useful predictor of critically ill patients with COVID-19 pneumonia.

TH Cells and Cytokines in Encephalitogenic Disorders

The invasion of immune cells into the central nervous system (CNS) is a hallmark of the process we call neuroinflammation. Diseases such as encephalitides or multiple sclerosis (MS) are characterised by the dramatic influx of T lymphocytes and monocytes. The communication between inflammatory infiltrates and CNS resident cells is primarily mediated through cytokines. Over the years, numerous cytokine networks have been assessed to better understand the development of immunopathology in neuroinflammation. In MS for instance, many studies have shown that CD4+ T cells infiltrate the CNS and subsequently lead to immunopathology. Inflammatory CD4+ T cells, such as TH1, TH17, GM-CSF-producing helper T cells are big players in chronic neuroinflammation. Conversely, encephalitogenic or meningeal regulatory T cells (TREGs) and TH2 cells have been shown to drive a decrease in inflammatory functions in microglial cells and thus promote a neuroprotective microenvironment. Recent studies report overlapping as well as differential roles of these cells in tissue inflammation. Taken together, this suggests a more complex relationship between effector T cell subsets in neuroinflammation than has hitherto been established. In this overview, we review the interplay between helper T cell subsets infiltrating the CNS and how they actively contribute to neuroinflammation and degeneration. Importantly, in this context, we will especially focus on the current knowledge regarding the contribution of various helper cell subsets to neuroinflammation by referring to their helper T cell profile in the context of their target cell.

An emphasis of T-cell subsets as regulators of periodontal health and disease

BACKGROUND

The pathogenesis of complex diseases like periodontitis is moderated by the balance in immune inflammatory responses. T-lymphocytes are immune cells that descend from the bone marrow. Furthermore, they develop in the thymus playing an indispensable role in adaptive immune responses. The periodontal microenvironment allows differentiation of various groups of T-lymphocytes such as CD4+ (Th1/Th2/Th17/Treg/Tfh/Th9/T22), CD8+ cells, gamma-delta (γd) T cells, or memory cells based on the current regional cytokine milieu to secrete distinct cytokines and other molecules required for resolution of inflammation or result in progression of the disease based on interactions among various cells.

AIM

The dynamism of T-lymphocytes in the immunopathogenesis of periodontal diseases resulting in tissue destruction is established but the mechanisms of immunoregulation that underpins periodontal disease progression are cumbersome. This review aims to understand the distinct types of T cells and their effector functions with their portrayal in periodontal disease.

RELEVANCE FOR PATIENTS

This review gives valuable insights on the possibility of predicting periodontal disease progression, on the management and its prognosis by evaluating specific cytokines of destructive T-cell phenotype, and on the future perspectives of therapeutic modalities including ways of modulating host immune and inflammatory responses to establish periodontal homeostasis and areas of research.

Repositioning TH cell polarization from single cytokines to complex help

When helper T (T_H) cell polarization was initially described three decades ago, the T_H cell universe grew dramatically. New subsets were described based on their expression of few specific cytokines. Beyond T_H1 and T_H2 cells, this led to the coining of various T_H17 and regulatory (T_reg) cell subsets as well as T_H22, T_H25, follicular helper (T_FH), T_H3, T_H5 and T_H9 cells. High-dimensional single-cell analysis revealed that a categorization of T_H cells into a single-cytokine-based nomenclature fails to capture the complexity and diversity of T_H cells. Similar to the simple nomenclature used to describe innate lymphoid cells (ILCs), we propose that T_H cell polarization should be categorized in terms of the help they provide to phagocytes (type 1), to B cells, eosinophils and mast cells (type 2) and to non-immune tissue cells, including the stroma and epithelium (type 3). Studying T_H cells based on their helper function and the cells they help, rather than phenotypic features such as individual analyzed cytokines or transcription factors, better captures T_H cell plasticity and conversion as well as the breadth of immune responses in vivo.

In Vivo CD4+ T Cell Differentiation and Function: Revisiting the Th1/Th2 Paradigm

The discovery of CD4⁺ T cell subset-defining master transcription factors and framing of the Th1/Th2 paradigm ignited the CD4⁺ T cell field. Advances in in vivo experimental systems, however, have revealed that more complex lineage-defining transcriptional networks direct CD4⁺ T cell differentiation in the lymphoid organs and tissues. This review focuses on the layers of fate decisions that inform CD4⁺ T cell differentiation in vivo. Cytokine production by antigen-presenting cells and other innate cells influences the CD4⁺ T cell effector program [e.g., T helper type 1 (Th1), Th2, Th17]. Signals downstream of the T cell receptor influence whether individual clones bearing hallmarks of this effector program become T follicular helper cells, supporting development of B cells expressing specific antibody isotypes, or T effector cells, which activate microbicidal innate cells in tissues. These bifurcated, parallel axes allow CD4⁺ T cells to augment their particular effector program and prevent disease.

Pathogen Dose in Animal Models of Hemorrhagic Fever Virus Infections and the Potential Impact on Studies of the Immune Response

Viral hemorrhagic fever viruses come from a wide range of virus families and are a significant cause of morbidity and mortality worldwide each year. Animal models of infection with a number of these viruses have contributed to our knowledge of their pathogenesis and have been crucial for the development of therapeutics and vaccines that have been approved for human use. Most of these models use artificially high doses of virus, ensuring lethality in pre-clinical drug development studies. However, this can have a significant effect on the immune response generated. Here I discuss how the dose of antigen or pathogen is a critical determinant of immune responses and suggest that the current study of viruses in animal models should take this into account when developing and studying animal models of disease. This can have implications for determination of immune correlates of protection against disease as well as informing relevant vaccination and therapeutic strategies.

Regulation of T Helper Cell Fate by TCR Signal Strength

T cells are critical in orchestrating protective immune responses to cancer and an array of pathogens. The interaction between a peptide MHC (pMHC) complex on antigen presenting cells (APCs) and T cell receptors (TCRs) on T cells initiates T cell activation, division, and clonal expansion in secondary lymphoid organs. T cells must also integrate multiple T cell-intrinsic and extrinsic signals to acquire the effector functions essential for the defense against invading microbes. In the case of T helper cell differentiation, while innate cytokines have been demonstrated to shape effector CD4⁺ T lymphocyte function, the contribution of TCR signaling strength to T helper cell differentiation is less understood. In this review, we summarize the signaling cascades regulated by the strength of TCR stimulation. Various mechanisms in which TCR signal strength controls T helper cell expansion and differentiation are also discussed.

Dedicator of cytokinesis 8-deficient CD4+ T cells are biased to a TH2 effector fate at the expense of TH1 and TH17 cells

BACKGROUND

Dedicator of cytokinesis 8 (DOCK8) deficiency is a combined immunodeficiency caused by autosomal recessive loss-of-function mutations in DOCK8. This disorder is characterized by recurrent cutaneous infections, increased serum IgE levels, and severe atopic disease, including food-induced anaphylaxis. However, the contribution of defects in CD4+ T cells to disease pathogenesis in these patients has not been thoroughly investigated.

OBJECTIVE

We sought to investigate the phenotype and function of DOCK8-deficient CD4+ T cells to determine (1) intrinsic and extrinsic CD4+ T-cell defects and (2) how defects account for the clinical features of DOCK8 deficiency.

METHODS

We performed in-depth analysis of the CD4+ T-cell compartment of DOCK8-deficient patients. We enumerated subsets of CD4+ T helper cells and assessed cytokine production and transcription factor expression. Finally, we determined the levels of IgE specific for staple foods and house dust mite allergens in DOCK8-deficient patients and healthy control subjects.

RESULTS

DOCK8-deficient memory CD4+ T cells were biased toward a TH2 type, and this was at the expense of TH1 and TH17 cells. In vitro polarization of DOCK8-deficient naive CD4+ T cells revealed the TH2 bias and TH17 defect to be T-cell intrinsic. Examination of allergen-specific IgE revealed plasma IgE from DOCK8-deficient patients is directed against staple food antigens but not house dust mites.

CONCLUSION

Investigations into the DOCK8-deficient CD4+ T cells provided an explanation for some of the clinical features of this disorder: the TH2 bias is likely to contribute to atopic disease, whereas defects in TH1 and TH17 cells compromise antiviral and antifungal immunity, respectively, explaining the infectious susceptibility of DOCK8-deficient patients.

Evaluation of mRNA expression of the transcription factors of Th1 and Th2 subsets (T-bet and GATA-3) in periodontal health and disease - A pilot study in south Indian population

Background:

Based on their respective pro- or anti-inflammatory cytokine profiles, the Th1/Th2 paradigm explains pathogenic mechanisms involved in periodontal disease. Establishment of Th1 and Th2 subsets from a naive T-cell precursor depends on transcriptional regulation. The aim of this study was to compare the expression of master transcription factor regulators T-bet and GATA-3, respectively, to indicate the predominance of Th1 and Th2 subsets in the presence and absence of periodontal disease.

Materials and Methods:

A gingival tissue biopsy sample was obtained from each of 10 severe periodontitis patients (>5 mm attachment loss) and 10 periodontally healthy patients (no attachment loss). Biopsies were immediately processed by real-time reverse transcriptase polymerase chain reaction and the difference in mRNA expression of T-bet and GATA-3 was assessed for each group.

Results:

The mRNA expression of T-bet was marginally increased about 1.31-fold in disease, while the GATA-3 levels showed a significant decrease of 4.39-fold in disease.

Conclusion:

The advanced periodontal lesions lack Th2 cells, which produce anti-inflammatory cytokines. The biopsies were therefore dominated by Th1 cells, which activate macrophages and osteoclasts.

Combined Immune Therapy for the Treatment of Visceral Leishmaniasis

Chronic disease caused by infections, cancer or autoimmunity can result in profound immune suppression. Immunoregulatory networks are established to prevent tissue damage caused by inflammation. Although these immune checkpoints preserve tissue function, they allow pathogens and tumors to persist, and even expand. Immune checkpoint blockade has recently been successfully employed to treat cancer. This strategy modulates immunoregulatory mechanisms to allow host immune cells to kill or control tumors. However, the utility of this approach for controlling established infections has not been extensively investigated. Here, we examined the potential of modulating glucocorticoid-induced TNF receptor-related protein (GITR) on T cells to improve anti-parasitic immunity in blood and spleen tissue from visceral leishmaniasis (VL) patients infected with Leishmania donovani. We found little effect on parasite growth or parasite-specific IFNγ production. However, this treatment reversed the improved anti-parasitic immunity achieved by IL-10 signaling blockade. Further investigations using an experimental VL model caused by infection of C57BL/6 mice with L. donovani revealed that this negative effect was prominent in the liver, dependent on parasite burden and associated with an accumulation of Th1 cells expressing high levels of KLRG-1. Nevertheless, combined anti-IL-10 and anti-GITR mAb treatment could improve anti-parasitic immunity when used with sub-optimal doses of anti-parasitic drug. However, additional studies with VL patient samples indicated that targeting GITR had no overall benefit over IL-10 signaling blockade alone at improving anti-parasitic immune responses, even with drug treatment cover. These findings identify several important factors that influence the effectiveness of immune modulation, including parasite burden, target tissue and the use of anti-parasitic drug. Critically, these results also highlight potential negative effects of combining different immune modulation strategies.

Peptide Dose and/or Structure in Vaccines as a Determinant of T Cell Responses

While T cells recognise the complex of peptide and major histocompatibility complex (MHC) at the cell surface, changes in the dose and/or structure of the peptide component can have profound effects on T cell activation and function. In addition, the repertoire of T cells capable of responding to any given peptide is variable, but broader than a single clone. Consequently, peptide parameters that affect the interaction between T cells and peptide/MHC have been shown to select particular T cell clones for expansion and this impacts on clearance of disease. T cells with high functional avidity are selected on low doses of peptide, while low avidity T cells are favoured in high peptide concentrations. Altering the structure of the peptide ligand can also influence the selection and function of peptide-specific T cell clones. In this review, we will explore the evidence that the choice of peptide dose or the structure of the peptide are critical parameters in an effective vaccine designed to activate T cells.

CD4+ T Cells: guardians of the phagosome

CD4(+) T cells are key cells of the adaptive immune system that use T cell antigen receptors to recognize peptides that are generated in endosomes or phagosomes and displayed on the host cell surface bound to major histocompatibility complex molecules. These T cells participate in immune responses that protect hosts from microbes such as Mycobacterium tuberculosis, Cryptococcus neoformans, Leishmania major, and Salmonella enterica, which have evolved to live in the phagosomes of macrophages and dendritic cells. Here, we review studies indicating that CD4(+) T cells control phagosomal infections asymptomatically in most individuals by secreting cytokines that activate the microbicidal activities of infected phagocytes but in a way that inhibits the pathogen but does not eliminate it. Indeed, we make the case that localized, controlled, persistent infection is necessary to maintain large numbers of CD4(+) effector T cells in a state of activation needed to eradicate systemic and more pathogenic forms of the infection. Finally, we posit that current vaccines for phagosomal infections fail because they do not produce this "periodic reminder" form of CD4(+) T cell-mediated immune control.

NDV-3 protects mice from vulvovaginal candidiasis through T- and B-cell immune response

We have previously reported that vaccination with rAls3p-N protein of Candida albicans, formulated with alum adjuvant (also designated as NDV-3) protects immunocompetent mice from, lethal disseminated candidiasis and mucosal oropharyngeal candidiasis. NDV-3 vaccine was recently, tested in a Phase 1 clinical trial and found to be safe, well-tolerated, and induced robust humoral and, cellular immune responses with increased interferon (IFN)-gamma and interleukin (IL)-17 secretion. In preparation for a Phase 2 clinical trial against vulvovaginal candidiasis (VVC), we evaluated NDV-3, efficacy in a murine VVC model. Here, NDV-3 induced a strong immune response characterized by high, anti-rAls3p-N serum IgG and vaginal IgA titers. Furthermore, moderate doses of the vaccine (a range of 1-30μg given subcutaneously [SQ] or 0.3-10μg given intramuscularly [IM]) elicited a 10-1000 fold, decrease in vaginal fungal burden vs. control (mice injected with alum adjuvant alone) in both inbred, and outbred mice infected with different clinical C. albicans isolates. Additionally, NDV-3 required both, T and B lymphocytes for efficacy in reducing C. albicans tissue burden, which is followed by a reduction, in neutrophil influx to the affected site. Finally, anti-rAls3p-N antibodies enhanced the ex vivo killing, of C. albicans by neutrophils primed with IFN-gamma. These data indicate that NDV-3 protects mice, from VVC by a mechanism that involves the concerted priming of both humoral and adaptive immune, responses.

Single naive CD4+ T cells from a diverse repertoire produce different effector cell types during infection

A naive CD4(+) T cell population specific for a microbial peptide:major histocompatibility complex II ligand (p:MHCII) typically consists of about 100 cells, each with a different T cell receptor (TCR). Following infection, this population produces a consistent ratio of effector cells that activate microbicidal functions of macrophages or help B cells make antibodies. We studied the mechanism that underlies this division of labor by tracking the progeny of single naive T cells. Different naive cells produced distinct ratios of macrophage and B cell helpers but yielded the characteristic ratio when averaged together. The effector cell pattern produced by a given naive cell correlated with the TCR-p:MHCII dwell time or the amount of p:MHCII. Thus, the consistent production of effector cell subsets by a polyclonal population of naive cells results from averaging the diverse behaviors of individual clones, which are instructed in part by the strength of TCR signaling.

Microbial-induced Th17: superhero or supervillain?

Th17 cells are an effector lineage of CD4 T cells that can contribute to protection against microbial pathogens and to the development of harmful autoimmune and inflammatory conditions. An increasing number of studies suggests that Th17 cells play an important protective role in mobilizing host immunity to extracellular and intracellular microbial pathogens, such as Candida and Salmonella. Furthermore, the generation of Th17 cells is heavily influenced by the normal microbial flora, highlighting the complex interplay among harmless microbes, pathogens, and host immunity in the regulation of pathogen-specific Th17 responses. In this article, we review the current understanding of microbe-induced Th17 cells in the context of infectious and inflammatory disease.

Cytokines of the γ(c) family control CD4+ T cell differentiation and function

Naive CD4(+) T cells undergo massive proliferation and differentiation into at least four distinct helper T cell subsets after recognition of foreign antigen-derived peptides presented by dendritic cells. Each helper T cell subset expresses a distinct set of genes that encode unique transcription factor(s), as well as hallmark cytokines. The cytokine environment created by activated CD4(+) T cells, dendritic cells and/or other cell types during the course of differentiation is a major determinant for the helper T cell fate. This Review focuses on the role of cytokines of the common γ-chain (γ(c)) family in the determination of the effector helper T cell phenotype that naive CD4(+) T cells adopt after being activated and in the function of these helper T cells.

T-helper cells in the etiopathogenesis of periodontal disease: A mini review

Our traditional understanding of the T-helper (Th)1/Th2 paradigm in periodontal disease has undergone considerable changes in recent years. This review focuses on the Th subsets, including the recently identified cells of the CD4 lineage, their activation pathways and effector function in periodontal disease. The roles of Th17 and regulatory T (Treg) cells in disease pathogenesis have been explored. Newer Th subsets such as Th9 and Th22 cells and their potential role in periodontal disease have also been outlined.

Th2 polarization enhanced by oral administration of higher doses of antigen

Although oral administration of a soluble proteinantigen can induce various immune responses, theeffect of the dosage of oral antigen on thepredominance of Th2-type cytokine and antibodyresponses has not been well clarified yet. In thepresent study, we fed T cell receptor (TCR) transgenic(tg) mice various amounts of chicken ovalbumin (0.1,5, and 250 mg) and examined the resulting immuneresponses to this antigen. In these TCR tg mice, theresponses of antigen-specific T cells were greatlyamplified concomitantly with significantantigen-specific cytokine secretion. We found that ahigh dose (250 mg) of antigen significantlyupregulated the serum antigen-specific IgG1 and IgAantibody responses in mice later intraperitoneallyinjected with antigen plus adjuvant. The miceadministered the same oral dose but not immunizedshowed upregulation of Th2-type IL-4 and IL-5secretion and downregulation of Th1-type IL-2 andIFN-gamma. This enhancement of Th2-type cytokineand antibody responses was more marked when largerdoses of antigen orally administered. These resultsdemonstrated that antigen feeding induces thedevelopment of T cells secreting Th2-type cytokines ina dose-dependent manner and that these T cells have ahelper function for the production of antibodies ofthe Th2-type isotypes. This experimental system shouldbe useful to screen foods and other substances thatcan modulate Th2-type responses relating to allergy.

Th9: a new player in asthma pathogenesis?

CD4(+) T helper (Th) cells act as important regulators of the mammalian adaptive immune response. CD4(+) Th cells were originally characterized as either Th1 or Th2 types, based on the cytokines they produce. Over the past two decades, however, we have attained a much more detailed understanding of CD4(+) T-cell differentiation, functions, and gene expression profiles, which led to the identification of additional types, such as the Th17 and induced regulatory T cells. Recently, researchers have characterized yet another novel and distinct population that exists among these immune-modulatory cells. The 'Th9' cells were first identified as a Th2 subpopulation that produced exceptionally large quantities of the Th2-specific cytokine interleukin 9. However, experimental analysis revealed that Th9 cells had divergent regulatory capabilities and were critically involved in different immune processes. In particular, we now know that Th9 acts as a major contributor to the onset and progression of allergies, especially asthma. Here, we will review the heterogeneity and biology of CD4(+) Th cells and summarize the characteristics known to date of interleukin 9 and Th9 cells to build a framework for better understanding of their roles in disease processes, especially in allergy-induced asthma.

T helper cell differentiation more than just cytokines

CD4(+) T helper (T(H)) cells play a critical role in orchestrating a pleiotropy of immune activities against a large variety of pathogens. It is generally thought that this is achieved through the acquisition of highly specialized functions after activation followed by the differentiation into various functional subsets. The differentiation process of naive precursor T(H) cells into defined effector subsets is controlled by cells of the innate immune system and their complex array of effector molecules such as secreted cytokines and membrane bound costimulatory molecules. These provide a unique quantitative or qualitative signal initiating T(H) development, which is subsequently reinforced via T cell-mediated feedback signals and selective survival and proliferative cues, ultimately resulting in the predominance of a particular T cell subset. In recent years, the number of defined T(H)cell subsets has expanded and the once rigid division of labor among them has been blurred with reports of plasticity among the subsets. In this chapter, we summarize and speculate on the current knowledge of the differentiation requirements of T(H) cell lineages, with particular focus on the T(H)17 subset.

Heterogeneity of human effector CD4+ T cells

For many years the heterogeneity of CD4⁺ T-helper (Th) cells has been limited to Th1 and Th2 cells, which have been considered not only to be responsible for different types of protective responses, but also for the pathogenesis of many disorders. Th1 cells are indeed protective against intracellular microbes and they are thought to play a pathogenic role in organ-specific autoimmune and other chronic inflammatory disorders. Th2 cells provide protection against helminths, but are also responsible for the pathogenesis of allergic diseases. The identification and cloning of new cytokines has allowed one to enlarge the series of functional subsets of CD4⁺ Th effector cells. In particular, CD4⁺ Th cells producing IL-17 and IL-22, named Th17, have been initially implicated in the pathogenesis of many chronic inflammatory disorders instead of Th1 cells. However, the more recent studies in both humans and mice suggest that Th17 cells exhibit a high plasticity toward Th1 cells and that both Th17 and Th1 cells may be pathogenic. More recently, another two subsets of effector CD4⁺ Th cells, named Th9 and Th22 cells, have been described, even if their pathophysiological meaning is still unclear. Despite the heterogeneity of CD4⁺ effector Th cells being higher than previously thought and some of their subsets exhibiting high plasticity, the Th1/Th2 paradigm still maintains a strong validity.

IL-4 from Th2-type cells suppresses induction of delayed-type hypersensitivity elicited shortly after immunization

The pure delayed-type hypersensitivity reaction obtained in 4-day ovalbumin-sensitized mice after antigen challenge in the footpad was abrogated by transfer of in vitro expanded, antigen-specific lymphoblasts derived from ovalbumin-hyperimmunized donors (high antibody producers), 12 h before immunization. This effect was specific inasmuch as Trypanosoma cruzi-specific blasts derived from Tc-Ag-hyperimmunized mice did not inhibit delayed-type hypersensitivity in ovalbumin-immunized recipients. The ovalbumin-specific blasts displayed a Th2 cytokine profile, secreting IL-4 and IL-10 upon restimulation in vitro with ovalbumin, but not IFN-gamma or IL-2. In addition, recipients of such cells produced much more IgG1 and IgE antibodies. When the frequency of T-cell blasts was enriched among these cells, transfer of four million cells was enough to prevent the induction of delayed-type hypersensitivity. Neutralization of IL-4 alone just before cell transfer not only restored the delayed-type hyper-sensitivity reaction, but also maintained it in a plateau for at least 72 h after challenge. Recipients treated in this way also showed a shift back towards a Th1 phenotype, indicated by the increase in IL-2, IFN-gamma and IL-12 synthesis. No synergistic action was observed when IL-4 and IL-10 were concomitantly neutralized. These results indicate that activation of Ag-specific Th2 cells early in the course of the immune response to a protein antigen provides an immunological environment rich in IL-4, thus leading to the inhibition of cell-mediated immunity.

Induction and regulation of CD4+ T cell subsets

It is now generally accepted that CD4+ T cells can be divided into at least two distinct subsets: Th1 and Th2. Th1 cells characteristically secrete interleukin 1 (IL-2) and gamma-interferon (IFN-gamma) whereas Th2 cells produce mainly IL-4, IL-5 and IL-10. Studies from many laboratories have demonstrated that the balance between these two subsets of T cells frequently determines the outcome of infectious and autoimmune diseases. Several factors influence the preferential induction and regulation of Th1 or Th2 cells in vitro and in vivo. Mice were infected with the protozoan parasite Leishmania to show that the gene encoding a major surface glycoprotein of the parasite, delivered orally in a plasmid carried by an auxotrophic Salmonella typhimurium vaccine strain (BRD509), preferentially induced Th1 cells and protective immunity against a challenge infection. The protective effect of the vaccine was augmented by administration of BRD509 carrying the genes encoding IL-2, IFN-gamma or tumour necrosis factor alpha. Cloned mouse Th1 cells specific for malarial antigens have been used to show that nitric oxide (NO) can inhibit the production of IFN-gamma by Th1 cells. Oral delivery of antigen and selective cytokines may preferentially induce CD4+ T cell subsets. Modulation of NO synthesis may further influence this induction and sustain such selective responses leading to effective therapy.

Differentiation and tolerance of CD4+ T lymphocytes

The development of effector and memory populations of T lymphocytes is determined by antigen-induced growth and differentiation of naive T cells, and it is regulated by antigen-induced functional tolerance and cell death. CD4+ helper T lymphocytes that vary in their profiles of cytokine production and in effector functions also show distinct responses to antigens and co-stimulatory signals, and they differ in their sensitivity to tolerance induction. Thus, stimuli that trigger T cell growth and differentiation, as well as mechanisms that inhibit T cell expansion, determine both the magnitude and the nature of T cell-dependent immune responses to protein antigens.

Influence of Slc11a1 on the outcome of Salmonella enterica serovar Enteritidis infection in mice is associated with Th polarization

Genetic analyses identified Ses1 as a significant quantitative trait locus influencing the carrier state of 129S6 mice following a sublethal challenge with Salmonella enterica serovar Enteritidis. Previous studies have determined that Slc11a1 was an excellent candidate gene for Ses1. Kinetics of infection in 129S6 mice and Slc11a1-deficient (129S6-Slc11a1(tm1Mcg)) mice demonstrated that the wild-type allele of Slc11a1 contributed to the S. enterica serovar Enteritidis carrier state as early as 7 days postinfection. Gene expression profiling demonstrated that 129S6 mice had a significant up-regulation of proinflammatory genes associated with macrophage activation at day 10 postinfection, followed by a gradual increase in immunoglobulin transcripts, whereas 129S6-Slc11a1(tm1Mcg) mice had higher levels of immunoglobulins earlier in the infection. Quantitative reverse transcription-PCR revealed an increase in Th1 cytokine (Ifng and Il12) and Th1-specific transcription factor Tbx21 expression during infection in both the 129S6 and 129S6-Slc11a1(tm1Mcg) strains. However, the expression of Gata3, a transcription factor involved in Th2 polarization, Cd28, and Il4 was markedly increased in Slc11a1-deficient mice during infection, suggesting a predominant Th2 phenotype in 129S6-Slc11a1(tm1Mcg) animals following S. enterica serovar Enteritidis infection. A strong immunoglobulin G2a response, reflecting Th1 activity, was observed only in 129S6 mice. All together, these results are consistent with an impact of Slc11a1 on Th cell differentiation during chronic S. enterica serovar Enteritidis infection. The presence of a Th2 bias in Slc11a1-deficient mice is associated with improved bacterial clearance.

Salmonella flagellin, a microbial target of the innate and adaptive immune system

Bacterial flagellins are important components of the motility apparatus used by many microbial pathogens. These proteins are also targets of the innate and adaptive immune response of the host during infection and autoimmune disease. Flagellin interacts with TLR-5 and leads to the generation of a pro-inflammatory response and activation of host dendritic cells in vivo. Furthermore, flagellin is recognized by antibody and CD4 T cells responses during Salmonella infection. Here, we review recent developments in the understanding of flagellin interactions with the host immune system.

Germ-free mice produce high levels of interferon-gamma in response to infection with Leishmania major but fail to heal lesions

In order to investigate the importance of the host microbiota on differentiation of T cell subsets in response to infection, Swiss/NIH germ-free mice and conventional (microbiota-bearing) mice were infected with Leishmania major, and lesion development, parasite loads, and cytokine production were assessed. Germ-free mice failed to heal lesions and presented a higher number of parasites at the site of infection than their conventional counterparts. In addition, histopathological analysis indicated a higher density of parasitized macrophages in lesions from germ-free mice than in conventional mice. The initial production of interleukin (IL)-12 and interferon-gamma (IFN-gamma) in germ-free mice was comparable to the conventional controls. Also, germ-free mice produced elevated levels of IFN-gamma and lower levels of IL-4 throughout the course of infection, suggesting the development of a Th1 response. Macrophages from germ-free mice exposed to IFN-gamma and infected with amastigotes in vitro were not as efficient at killing parasites as macrophages from conventional animals. These observations indicate that the microbiota is not essential for the development of Th1 immune responses, but seems to be important for macrophage activation.

Vaccination with recombinant N-terminal domain of Als1p improves survival during murine disseminated candidiasis by enhancing cell-mediated, not humoral, immunity

Candida spp. are opportunistic fungal pathogens that are among the most common causes of nosocomial bloodstream infections. The mortality attributable to disseminated candidiasis is 40 to 50% despite antifungal therapy. Clearly, new strategies are needed to prevent this life-threatening infection. Because risk factors for disseminated candidiasis are well defined and frequently of limited duration, vaccination is an appealing prophylactic strategy. We have identified a cell surface protein, Als1p, that mediates adherence of Candida albicans to a variety of human substrates and plastic. Here we report that immunizing BALB/c mice with the recombinant N-terminal domain of Als1p (rAls1p-N) improved survival during a subsequent challenge with a lethal inoculum of C. albicans. The protective 20-mug dose of rAls1p-N significantly increased Candida stimulation of Th1 splenocytes and increased in vivo delayed-type hypersensitivity. In contrast, antibody titers did not correlate with protection. Finally, the vaccine was not protective in T-cell-deficient mice but was protective in B-cell-deficient mice. These data indicate that the mechanism of action of the rAls1p-N vaccine is stimulation of cell-mediated, rather than humoral, immunity against C. albicans. The majority of efforts to date have focused on the development of passive immunization strategies to prevent or treat disseminated candidiasis. In contrast, our results provide proof of principle for vaccination with an adhesin of C. albicans and emphasize the potential for cell-mediated immune modulation as a prophylactic or therapeutic strategy against disseminated candidiasis.

In vivo generated Th1 cells can migrate to B cell follicles to support B cell responses

The description of Th1 and Th2 T cell subsets rationalized the inverse correlation between humoral and cell-mediated immunity. Although Th1 cells were described to support cell-mediated immune responses, their role in supporting certain B cell responses was firmly established. However, there is now a prevailing preconception that provision of B cell help is entirely the domain of Th2 cells and that Th1 cells lack this capacity. Previous studies demonstrated that immunization using aluminum hydroxide adjuvants induces Ag-specific Th2 responses, whereas incorporation of IL-12 with aluminum hydroxide produces a Th1 inducing adjuvant. By immunizing TCR transgenic recipient mice in this fashion, we have generated Ag-specific, traceable Th1 and Th2 cells in vivo and assessed their follicular migration and ability to support B cell responses. In this study we have shown that in vivo polarized Th1 and Th2 cells clonally expand to similar levels and migrate into B cell follicles in which they support B cell responses to a similar degree. Critically, we present direct evidence that in vivo polarized, IFN-gamma secreting Th1 cells migrate into B cell follicles where they can interact with Ag-specific B cells.

'Educated' dendritic cells act as messengers from memory to naive T helper cells

Ingested antigens lead to the generation of effector T cells that secrete interleukin 4 (IL-4) rather than interferon-gamma (IFN-gamma) and are capable of influencing naive T cells in their immediate environment to do the same. Using chimeric mice generated by aggregation of two genotypically different embryos, we found that the conversion of a naive T cell occurs only if it can interact with the same antigen-presenting cell, although not necessarily the same antigen, as the effector T cell. Using a two-step culture system in vitro, we found that antigen-presenting dendritic cells can act as 'temporal bridges' to relay information from orally immunized memory CD4 T cells to naive CD4 T cells. The orally immunized T cells use IL-4 and IL-10 (but not CD40 ligand) to 'educate' dendritic cells, which in turn induce naive T cells to produce the same cytokines as those produced by the orally immunized memory T cells.

The relationship between distress and the development of a primary immune response to a novel antigen

Forty-five medical students were recruited to examine the effects of distress on the development of an immune response to the novel antigen, keyhole limpet hemocyanin (KLH). The subjects' level of distress was manipulated by immunizing them either at the time of an important viva voce examination (n=22) or during examination-free term time (n=23). This manipulation increased variance amongst the subjects, but the emphasis in this research was on individual distress as a predictor of immune function. In the group as a whole, the likelihood of developing DTH skin responses to KLH was reduced in the more distressed subjects (r=-.45; p=.002), independently of a number of behavioral (e.g., sleep disturbance) and demographic (e.g., sex) variables. Proliferation of T cells against KLH in vitro and the development of anti-KLH IgG antibodies were not related to levels of distress. Thus, cellular, rather than humoral, immune responses in vivo appear susceptible to the influence of distress. This immunization model provides the opportunity to further dissect the basis of these stress-immune pathways.

Generating neutralizing antibodies, Th1 response and MHC non restricted immunogenicity of HIV-I env and gag peptides in liposomes and ISCOMs with in-built adjuvanticity

For enhancing immunogenicity and develop vaccine strategies using peptide based constructs against HIV-1, a chimeric peptide containing V3 loop and transmembrane sequence of gp41 with two glycine motifs as spacer was constructed. The V3-gp41, gp41 peptide and p17 and p24 peptides separately or in a cocktail were entrapped with or without MA729 as an immunoadjuvant in liposomes or ISCOMs. The immunogenicity, antigen induced T-cell proliferation and cytokine profiles of various formulations were studied in four different inbred strains of mice of H-2^d, H-2^b, H-2^k and H-2^q haplotypes, keeping alum as a control adjuvant. Both liposomes and ISCOM preparations elicited high titer and long lasting antibody response (60 days and above). When compared to the alum formulation, the liposomes co-entrapped with MA729 produced high antibody levels, comparable with that induced by ISCOMs. Peptide in alum, liposomes and ISCOMs enhanced both antigen specific IgG2a and IgG2b isotypes and high T-cell stimulation index. Peptide formulations also induced antibodies with high affinity and in vitro neutralizated the formation of HIV-1 syncytia. T-cell supernatants contained high levels of IFN-γ and IL-2. Thus formulation in these adjuvants induced a predominant Th1 like response with MA729 as a versatile novel delivery vehicle for stimulating the appropriate arm of the immune response that can selectively modulate MHC class I or MHC class II response. The above peptide can be of wide vaccination interest as a means to improve immune responses to several other HIV-1 antigens and may serve as candidates for vaccine development.

A Murine Locus on Chromosome 18 Controls NKT Cell Homeostasis and Th Cell Differentiation

Th cell differentiation is a critical event in the adaptive immune response. C57BL strains develop predominant Th1 responses while BALB/c develops a predominant Th2 response. To identify quantitative trait loci controlling this variation, we performed Th1/Th2 differentiation assays of F(1) x BALB/c progeny. A single strong quantitative trait locus was identified on chromosome 18, with weaker effects detectable on chromosomes 5, 12, and 14. By preparing a congenic BALB.B10.D2c18 strain, we were able to demonstrate that this single locus was sufficient to "repolarize" spleen cell cultures. This difference was not due to intrinsic differences in CD4(+) T cells. Rather, introgression of the chromosome 18 locus into BALB/c disrupted Va14Ja18 NKT cell homeostasis resulting in the almost complete absence of this T cell subset. Taken together, these data indicate that genes within chromosome 18 control strain-dependent development of Va14Ja18 NKT cells.

Shared modes of protection against poxvirus infection by attenuated and conventional smallpox vaccine viruses

The concern about bioterrorism with smallpox has raised the possibility of widespread vaccination, but the greater prevalence of immunocompromised individuals today requires a safer vaccine, and the mechanisms of protection are not well understood. Here we show that, at sufficient doses, the protection provided by both modified vaccinia Ankara and NYVAC replication-deficient vaccinia viruses, safe in immunocompromised animals, was equivalent to that of the licensed Wyeth vaccine strain against a pathogenic vaccinia virus intranasal challenge of mice. A similar variety and pattern of immune responses were involved in protection induced by modified vaccinia Ankara and Wyeth viruses. For both, antibody was essential to protect against disease, whereas neither effector CD4+ nor CD8+ T cells were necessary or sufficient. However, in the absence of antibody, T cells were necessary and sufficient for survival and recovery. Also, T cells played a greater role in control of sublethal infection in unimmunized animals. These properties, shared with the existing smallpox vaccine, provide a basis for further evaluation of these replication-deficient vaccinia viruses as safer vaccines against smallpox or against complications from vaccinia virus.