A natural immunological adjuvant enhances T cell clonal expansion through a CD28-dependent, interleukin (IL)-2-independent mechanism

Increased vesicular dynamics and nanoscale clustering of IL-2 after T cell activation

T cells coordinate intercellular communication through the meticulous regulation of cytokine secretion. Direct visualization of vesicular transport and intracellular distribution of cytokines provides valuable insights into the temporal and spatial mechanisms involved in regulation. Employing Jurkat E6-1 T cells and interleukin-2 (IL-2) as a model system, we investigated vesicular dynamics using single-particle tracking and the nanoscale distribution of intracellular IL-2 in fixed T cells using superresolution microscopy. Live-cell imaging revealed that in vitro activation resulted in increased vesicular dynamics. Direct stochastic optical reconstruction microscopy and 3D structured illumination microscopy revealed nanoscale clustering of IL-2. In vitro activation correlated with spatial accumulation of IL-2 nanoclusters into more pronounced and elongated clusters. These observations provide visual evidence that accelerated vesicular transport and spatial concatenation of IL-2 clusters at the nanoscale may constitute a potential mechanism for modulating cytokine release by Jurkat T cells.

The Impact of Nigella sativa Essential Oil on T Cells in Women with Hashimoto's Thyroiditis

BACKGROUND

Hashimoto's thyroiditis (HT) is an autoimmune disease mediated by T cells. It is characterized by the presence of thyroid autoantibodies in the serum, such as anti-thyroid peroxidase antibodies (TPO-Ab) and anti-thyroglobulin antibodies (TG-Ab). The essential oil extracted from Nigella sativa seeds is rich in bioactive substances, such as thymoquinone and cymene.

METHODS

Therefore, we examined the effect of essential oil from Nigella sativa (NSEO) on T cells from HT patients, especially their proliferation capacity, ability to produce cytokines, and susceptibility to apoptosis.

RESULTS

The lowest ethanol (EtOH) dilution (1:10) of NSEO significantly inhibited the proliferation of CD4⁺ and CD8⁺ T cells from HT patients and healthy women by affecting the percentage of dividing cells and the number of cell divisions. In addition, 1:10 and 1:50 NSEO dilutions induced cell death. Different dilutions of NSEO also reduced the concentration of IL-17A and IL-10. In healthy women, the level of IL-4 and IL-2 significantly increased in the presence of 1:10 and 1:50 NSEO dilutions. NSEO did not influence the concentration of IL-6 and IFN-γ.

CONCLUSIONS

Our study demonstrates that NSEO has a strong immunomodulatory effect on the lymphocytes of HT patients.

Distinct spatial and temporal roles for Th1, Th2, and Th17 cells in asthma

Immune response in the asthmatic respiratory tract is mainly driven by CD4⁺ T helper (Th) cells, represented by Th1, Th2, and Th17 cells, especially Th2 cells. Asthma is a heterogeneous and progressive disease, reflected by distinct phenotypes orchestrated by τh2 or non-Th2 (Th1 and Th17) immune responses at different stages of the disease course. Heterogeneous cytokine expression within the same Th effector state in response to changing conditions in vivo and interlineage relationship among CD4⁺ T cells shape the complex immune networks of the inflammatory airway, making it difficult to find one panacea for all asthmatics. Here, we review the role of three T helper subsets in the pathogenesis of asthma from different stages, highlighting timing is everything in the immune system. We also discuss the dynamic topography of Th subsets and pathogenetic memory Th cells in asthma.

VAV1 Gene Polymorphism is Associated With Kidney Allograft Rejection

BACKGROUND

VAV1 is an intracellular signal transduction protein that plays a significant role in signal transduction in T cells. Several studies suggest that VAV1 signaling plays significant roles in allograft rejection. The aim of this study was to examine the association between VAV1 gene polymorphisms and renal allograft function.

METHODS

The study included 270 patients after allograft renal transplantation. We examined the associations between VAV1 gene polymorphisms and complications after transplantation, such as delayed graft function, acute rejection, and chronic allograft dysfunction.

RESULTS

There were no statistically significant associations between VAV1 genotypes and delayed graft function and chronic allograft dysfunction. Among patients with acute allograft rejection, we observed decreased frequencies of VAV1 rs2546133 TT and CT genotypes (P = .03) and T allele (P = .02), as well as VAV1 rs2617822 GG and AG genotypes (P = .05) and G allele (P = 0.04). In the multivariate regression analysis, the higher number of VAV1 rs2546133 T alleles showed a protective effect against the acute rejection in kidney allograft recipients.

CONCLUSIONS

The results of our study suggest that polymorphisms in the VAV1 gene are associated with kidney allograft rejection.

IgE-activated mast cells enhance TLR4-mediated antigen-specific CD4+ T cell responses

Mast cells are potent mediators of allergy and asthma, yet their role in regulating adaptive immunity remains ambiguous. On the surface of mast cells, the crosslinking of IgE bound to FcεRI by a specific antigen recognized by that IgE triggers the release of immune mediators such as histamine and cytokines capable of activating other immune cells; however, little is known about the mast cell contribution to the induction of endogenous, antigen-specific CD4⁺ T cells. Here we examined the effects of specific mast cell activation in vivo on the initiation of an antigen-specific CD4⁺ T cell response. While CD4⁺ T cells were not enhanced by FcεRI stimulation alone, their activation was synergistically enhanced when FcεRI activation was combined with TLR4 stimulation. This enhanced activation was dependent on global TLR4 stimulation but appeared to be less dependent on mast cell expressed TLR4. This study provides important new evidence to support the role of mast cells as mediators of the antigen-specific adaptive immune response.

TRB sequences targeting ORF1a/b are associated with disease severity in hospitalized COVID-19 patients

The potential protective or pathogenic role of the adaptive immune response to SARS‐CoV‐2 infection has been vigorously debated. While COVID‐19 patients consistently generate a T lymphocyte response to SARS‐CoV‐2 antigens, evidence of significant immune dysregulation in these patients continues to accumulate. In this study, next generation sequencing of the T cell receptor beta chain (TRB) repertoire was conducted in hospitalized COVID‐19 patients to determine if immunogenetic differences of the TRB repertoire contribute to disease course severity. Clustering of highly similar TRB CDR3 amino acid sequences across COVID‐19 patients yielded 781 shared TRB sequences. The TRB sequences were then filtered for known associations with common diseases such as EBV and CMV. The remaining sequences were cross‐referenced to a publicly accessible dataset that mapped COVID‐19 specific TCRs to the SARS‐CoV‐2 genome. We identified 158 SARS‐CoV‐2 specific TRB sequences belonging to 134 clusters in our COVID‐19 patients. Next, we investigated 113 SARS‐CoV‐2 specific clusters binding only one peptide target in relation to disease course. Distinct skewing of SARS‐CoV‐2 specific TRB sequences toward the nonstructural proteins (NSPs) encoded within ORF1a/b of the SARS‐CoV‐2 genome was observed in clusters associated with critical disease course when compared to COVID‐19 clusters associated with a severe disease course. These data imply that T‐lymphocyte reactivity towards peptides from NSPs of SARS‐CoV‐2 may not constitute an effective adaptive immune response and thus may negatively affect disease severity.

Two sequential activation modules control the differentiation of protective T helper-1 (Th1) cells

Interferon-γ (IFN-γ)-producing CD4+ T helper-1 (Th1) cells are critical for protection from microbes that infect the phagosomes of myeloid cells. Current understanding of Th1 cell differentiation is based largely on reductionist cell culture experiments. We assessed Th1 cell generation in vivo by studying antigen-specific CD4+ T cells during infection with the phagosomal pathogen Salmonella enterica (Se), or influenza A virus (IAV), for which CD4+ T cells are less important. Both microbes induced T follicular helper (Tfh) and interleukin-12 (IL-12)-independent Th1 cells. During Se infection, however, the Th1 cells subsequently outgrew the Tfh cells via an IL-12-dependent process and formed subsets with increased IFN-γ production, ZEB2-transcription factor-dependent cytotoxicity, and capacity to control Se infection. Our results indicate that many infections induce a module that generates Tfh and poorly differentiated Th1 cells, which is followed in phagosomal infections by an IL-12-dependent Th1 cell amplification module that is critical for pathogen control.

VAV1 Gene Polymorphisms in Patients with Rheumatoid Arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is an important public health problem because this disease often causes disability. RA is a chronic, destructive autoimmune disease that leads to joint destruction and the development of extraarticular manifestations. VAV1 is an intracellular signal transduction protein that plays a significant role in signal transduction in T cells and affects T cell development, proliferation and activation. The VAV1 gene contains 27 exons and is located on chromosome 19. In this study, we examined the association between VAV1 rs2546133 and rs2617822 polymorphisms and RA.

METHODS

We examined 422 patients with RA and 338 healthy subjects as the control group.

RESULTS

Among RA patients, there was a statistically significant increase in the frequency of VAV1 rs2546133 polymorphism in T allele carriers (TT + CT versus CC, odds ratio: 1.69, 95% confidence interval 1.05-2.73, p = 0.035). There was no statistically significant difference in the distribution of the rs2617822 genotypes and alleles between RA patients and the control group. Additionally, patients who carried the VAV1 rs2546133 T and rs2617822 G allele presented an increased frequency of extraarticular manifestations: vasculitis, amyloidosis and Sjogren syndrome.

CONCLUSIONS

The results suggest an association between VAV1 gene rs2617822 polymorphism and RA.

Inhibitory effect of berberine on interleukin-2 secretion from PHA-treated lymphocytic Jurkat cells

Berberine is an isoquinoline alkaloid isolated from herb plants, such as Cortex phellodendri (Huangbai) and Rhizoma coptidis (Huanglian). Huanglian and Huangbai have been used as "heat-removing" agents. In addition, berberine has been reported to exert anti-inflammatory effect both in vivo and in vitro, where mitogen-activated protein kinase (MAPK) and cyclooxygenase-2 (COX-2) expressions are critically implicated. We herein tested the hypothesis that berberine exerts an anti-inflammatory effect through MAPK and COX-2 signaling pathway in T-cell acute lymphoblastic leukemia (T-ALL). In Jurkat cells, we found that PHA exposure caused elevation on interleukin-2 (IL-2) production in a time-dependent manner. PHA-stimulated reactions were steeply suppressed by berberine, such as IL-2 mRNA expression and protein secretion. However, berberine did not exert any cytotoxic effect at doses of 40 μg/ml. In addition, the possible molecular mechanism of anti-inflammation effect of berberine could be the inhibition of PHA-evoked phosphorylation of p38, since c-Jun N-terminal kinases (JNK) and extracellular signal-regulated kinase (ERK) expressions did not alter. Consistent with above results, berberine inhibition on PHA-induced IL-2 secretion could be reversed by treatment of SB203580, a specific inhibitor of p38-MAPK. Interestingly, upregulation of PHA-induced COX-2 expression was also observed following berberine treatment of Jurkat cells. Furthermore, flow cytometry analysis showed berberine-induced cell cycle arrest at G1 phase after PHA stimulation and decreased percentage of G2/M phase. In conclusion, our study demonstrated that the anti-inflammatory effect of berberine largely potentially results from its ability to attenuate p38 MAPK expression, and does not exclude a positive action of berberine on cell cycle arrest. These results provide an innovative medicine strategy to against or treat T-ALL patients.

Gut immunity: its development and reasons and opportunities for modulation in monogastric production animals

The intestine performs the critical roles of nutrient acquisition, tolerance of innocuous and beneficial microorganisms, while retaining the ability to respond appropriately to undesirable microbes or microbial products and preventing their translocation to more sterile body compartments. Various components contribute to antimicrobial defenses in the intestine. The mucus layer(s), antimicrobial peptides and IgA provide the first line of defense, and seek to trap and facilitate the removal of invading microbes. If breached, invading microbes next encounter a single layer of epithelial cells and, below this, the lamina propria with its associated immune cells. The gut immune system has developmental stages, and studies from different species demonstrate that innate capability develops earlier than acquired. In addition, various factors may influence the developmental process; for example, the composition and activity of the gut microbiota, antimicrobials, maternally derived antibodies, host genetics, and various stressors (e.g. feed deprivation). Therefore, it is clear that particularly younger (meat-producing) animals are reliant on innate immune responses (as well as passive immunity) for a considerable period of their productive life, and thus focusing on modulating appropriate innate responses should be an intervention priority. The gut microbiota is probably the most influential factor for immune development and capability. Interventions (e.g. probiotics, prebiotics, antibodies, etc.) that appropriately modulate the composition or activity of the intestinal microbiota can play an important role in shaping the desired functionality of the innate (and acquired) response. In addition, innate immune mediators, such as toll-like receptor agonists, cytokines, etc., may provide more specific ways to suitably modulate the response. A better understanding of mucosal immunology, signaling pathways, and processes, etc., will provide even more precise methods in the future to boost innate immune capability and minimize any associated (e.g. nutrient) costs. This will provide the livestock industry with more effective options to promote robust and efficient productivity.

Rapid G0/1 transition and cell cycle progression in CD8+ T cells compared to CD4+ T cells following in vitro stimulation

T-cell population consists of two major subsets, CD4⁺ T cells and CD8⁺ T cells, which can be distinguished by the expression of CD4 or CD8 molecules, respectively. Although they play quite different roles in the immune system, many of their basic cellular processes such as proliferation following stimulation are presumably common. In this study, we have carefully analyzed time-course of G0/1 transition as well as cell cycle progression in the two subsets of quiescent T-cell population following in vitro growth stimulation. We found that CD8⁺ T cells promote G0/1 transition more rapidly and drive their cell cycle progression faster compared to CD4⁺ T cells. In addition, expression of CD25 and effects of its blockade revealed that IL-2 is implicated in the rapid progression, but not the earlier G0/1 transition, of CD8⁺ T cells.

BATF Modulates the Th2 Locus Control Region and Regulates CD4+ T Cell Fate during Antihelminth Immunity

The AP-1 factor basic leucine zipper transcription factor, ATF-like (BATF) is important for CD4⁺ Th17, Th9, and follicular Th cell development. However, its precise role in Th2 differentiation and function remains unclear, and the requirement for BATF in nonallergic settings of type-2 immunity has not been explored. In this article, we show that, in response to parasitic helminths, Batf^-/- mice are unable to generate follicular Th and Th2 cells. As a consequence, they fail to establish productive type-2 immunity during primary and secondary infection. Batf^-/- CD4⁺ T cells do not achieve type-2 cytokine competency, which implies that BATF plays a key role in the regulation of IL-4 and IL-13. In contrast to Th17 and Th9 cell subsets in which BATF binds directly to promoter and enhancer regions to regulate cytokine expression, our results show that BATF is significantly enriched at Rad50 hypersensitivity site (RHS)6 and RHS7 of the locus control region relative to AP-1 sites surrounding type-2 cytokine loci in Th2 cells. Indeed, Batf^-/- CD4⁺ T cells do not obtain permissive epigenetic modifications within the Th2 locus, which were linked to RHS6 and RHS7 function. In sum, these findings reveal BATF as a central modulator of peripheral and humoral hallmarks of type-2 immunity and begin to elucidate a novel mechanism by which it regulates type-2 cytokine production through its modification of the Th2 locus control region.

IL-15 enhances the antitumor effect of human antigen-specific CD8+ T cells by cellular senescence delay

Optimal expansion protocols for adoptive human T-cell therapy often include interleukin (IL)-15; however, the mechanism by which IL-15 improves the in vivo antitumor effect of T cells remains to be elucidated. Using human T cells generated from HLA-A2+ donors against novel T-cell epitopes derived from the human U266 myeloma cell line Ig light chain V-region (idiotype) as a model, we found that T cells cultured with IL-15 provided superior resistance to tumor growth in vivo, compared with IL-2, after adoptive transfer into immunodeficient hosts. This effect of IL-15 was associated with delayed/reversed senescence in tumor antigen-specific memory CD8⁺ T cells mediated through downregulation of P21^WAF1, P16^INK4a, and P53 expression. Compared to IL-2, IL-15 stimulation dramatically activated JAK3-STAT5 signaling and inhibited the expression of DNA damage genes. Thus, our study elucidates a new mechanism for IL-15 in the regulation of STAT signaling pathways and CD8⁺ T-cell senescence.

NADPH Oxidase-Derived Superoxide Provides a Third Signal for CD4 T Cell Effector Responses

Originally recognized for their direct induced toxicity as a component of the innate immune response, reactive oxygen species (ROS) can profoundly modulate T cell adaptive immune responses. Efficient T cell activation requires: signal 1, consisting of an antigenic peptide-MHC complex binding with the TCR; signal 2, the interaction of costimulatory molecules on T cells and APCs; and signal 3, the generation of innate immune-derived ROS and proinflammatory cytokines. This third signal, in particular, has proven essential in generating productive and long-lasting immune responses. Our laboratory previously demonstrated profound Ag-specific hyporesponsiveness in the absence of NADPH oxidase-derived superoxide. To further examine the consequences of ROS deficiency on Ag-specific T cell responses, our laboratory generated the OT-II.Ncf1(m1J) mouse, possessing superoxide-deficient T cells recognizing the nominal Ag OVA323-339 In this study, we demonstrate that OT-II.Ncf1(m1J) CD4 T cells displayed a severe reduction in Th1 T cell responses, in addition to blunted IL-12R expression and severely attenuated proinflammatory chemokine ligands. Conversely, IFN-γ synthesis and IL-12R synthesis were rescued by the addition of exogenous superoxide via the paramagnetic superoxide donor potassium dioxide or superoxide-sufficient dendritic cells. Ultimately, these data highlight the importance of NADPH oxidase-derived ROS in providing a third signal for adaptive immune maturation by modulating the IL-12/IL-12R pathway and the novelty of the OT-II.Ncf1(m1J) mouse model to determine the role of redox-dependent signaling on effector responses. Thus, targeting ROS represents a promising therapeutic strategy in dampening Ag-specific T cell responses and T cell-mediated autoimmune diseases, such as type 1 diabetes.

Interleukin-2-Dependent Allergen-Specific Tissue-Resident Memory Cells Drive Asthma

Exposure to inhaled allergens generates T helper 2 (Th2) CD4(+) T cells that contribute to episodes of inflammation associated with asthma. Little is known about allergen-specific Th2 memory cells and their contribution to airway inflammation. We generated reagents to understand how endogenous CD4(+) T cells specific for a house dust mite (HDM) allergen form and function. After allergen exposure, HDM-specific memory cells persisted as central memory cells in the lymphoid organs and tissue-resident memory cells in the lung. Experimental blockade of lymphocyte migration demonstrated that lung-resident cells were sufficient to induce airway hyper-responsiveness, which depended upon CD4(+) T cells. Investigation into the differentiation of pathogenic Trm cells revealed that interleukin-2 (IL-2) signaling was required for residency and directed a program of tissue homing migrational cues. These studies thus identify IL-2-dependent resident Th2 memory cells as drivers of lung allergic responses.

Generation of Th17 cells in response to intranasal infection requires TGF-β1 from dendritic cells and IL-6 from CD301b+ dendritic cells

Intranasal (i.n.) infections preferentially generate Th17 cells. We explored the basis for this anatomic preference by tracking polyclonal CD4(+) T cells specific for an MHC class II-bound peptide from the mucosal pathogen Streptococcus pyogenes. S. pyogenes MHC class II-bound peptide-specific CD4(+) T cells were first activated in the cervical lymph nodes following i.n. inoculation and then differentiated into Th17 cells. S. pyogenes-induced Th17 formation depended on TGF-β1 from dendritic cells and IL-6 from a CD301b(+) dendritic cell subset located in the cervical lymph nodes but not the spleen. Thus, the tendency of i.n. infection to induce Th17 cells is related to cytokine production by specialized dendritic cells that drain this site.

A novel model for IFN-γ-mediated autoinflammatory syndromes

Autoinflammatory disease and hyperinflammatory syndromes represent a growing number of diseases associated with inappropriately controlled inflammation in multiple organs. Systemic inflammation commonly results from dysregulated activation of innate immune cells, and therapeutic targeting of the IL-1β pathway has been used to ameliorate some of these diseases. Some hyperinflammatory syndromes, however, such as hemophagocytic lymphohistiocytosis and the newly classified proteasome disability syndromes, are refractory to such treatments, suggesting that other factors or environmental stressors may be contributing. In comparing two cytokine reporter mouse strains, we identify IFN-γ as a mediator of systemic autoinflammatory disease. Chronically elevated levels of IFN-γ resulted in progressive multiorgan inflammation and two copies of the mutant allele resulted in increased mortality accompanied by myeloproliferative disease. Disease was alleviated by genetic deletion of T-bet. These studies raise the possibility that therapeutics targeting the IFN-γ pathway might be effective in hyperinflammatory conditions refractory to IL-1β-targeted therapies.

Advances in swine immunology help move vaccine technology forward

In veterinary animal species, vaccines are the primary tool for disease prevention, a key tool for treatment of infection, and essential for helping maintain animal welfare and productivity. Traditional vaccine development by trial-and-error has achieved many successes. However, effective vaccines that provide solid cross-protective immunity with excellent safety are still needed for many diseases. The path to development of vaccines against difficult pathogens requires recognition of uniquely evolved immunological interactions of individual animal hosts and their specific pathogens. Here, general principles that currently guide veterinary immunology and vaccinology research are reviewed, with an emphasis on examples from swine. Advances in genomics and proteomics now provide the community with powerful tools for elucidation of regulatory and effector mechanisms of protective immunity that provide new opportunities for successful translation of immunological discoveries into safe and effective vaccines.

Ndfip1 mediates peripheral tolerance to self and exogenous antigen by inducing cell cycle exit in responding CD4+ T cells

The NDFIP1 (neural precursor cell expressed, developmentally down-regulated protein 4 family-interacting protein 1) adapter for the ubiquitin ligase ITCH is genetically linked to human allergic and autoimmune disease, but the cellular mechanism by which these proteins enable foreign and self-antigens to be tolerated is unresolved. Here, we use two unique mouse strains--an Ndfip1-YFP reporter and an Ndfip1-deficient strain--to show that Ndfip1 is progressively induced during T-cell differentiation and activation in vivo and that its deficiency causes a cell-autonomous, Forkhead box P3-independent failure of peripheral CD4(+) T-cell tolerance to self and exogenous antigen. In small cohorts of antigen-specific CD4(+) cells responding in vivo, Ndfip1 was necessary for tolerogen-reactive T cells to exit cell cycle after one to five divisions and to abort Th2 effector differentiation, defining a step in peripheral tolerance that provides insights into the phenomenon of T-cell anergy in vivo and is distinct from the better understood process of Bcl2-interacting mediator of cell death-mediated apoptosis. Ndfip1 deficiency precipitated autoimmune pancreatic destruction and diabetes; however, this depended on a further accumulation of nontolerant anti-self T cells from strong stimulation by exogenous tolerogen. These findings illuminate a peripheral tolerance checkpoint that aborts T-cell clonal expansion against allergens and autoantigens and demonstrate how hypersensitive responses to environmental antigens may trigger autoimmunity.

Concanavalin A-mediated T cell proliferation is regulated by herpes virus entry mediator costimulatory molecule

T cell activation is regulated by two distinct signals, signals one and two. Concanavalin A (ConA) is an antigen-independent mitogen and functions as signal one inducer, leading T cells to polyclonal proliferation. CD28 is known to be one of major costimulatory receptors and to provide signal two in the ConA-induced T cell proliferation. Here, we have studied the implication of other costimulatory pathways in the ConA-mediated T cell proliferation by using soluble recombinant proteins consisting of an extracellular domain of costimulatory receptors and Fc portion of human IgG. We found that T cell proliferation induced by ConA, but not PMA plus ionomycin or anti-CD3 mAb, is significantly inhibited by herpes virus entry mediator (HVEM)-Ig, even in the presence of CD28 signaling. Moreover, the high concentration of HVEM-Ig molecules almost completely suppressed ConA-mediated T cell proliferation. These results suggest that HVEM might play more important roles than CD28 in ConA-mediated T cell proliferation.

miR-155: an ancient regulator of the immune system

MicroRNAs (miRNAs) are a newly recognized class of regulatory genes which repress the expression of protein-coding genes. Numerous studies have uncovered a complex role for miRNAs regulating many aspects of a variety of cellular processes including cell growth, differentiation, and lineage commitment. In the immune system, miR-155 is unique in its ability to shape the transcriptome of activated myeloid and lymphoid cells controlling diverse biological functions ranging from inflammation to immunological memory. Not surprisingly, a tight control of miR-155 expression is required to avoid malignant transformation, as evidenced by miR-155 overexpression in many cancers of B-cell origin. In this review, we discuss the potential of miR-155 as a molecular target for therapeutic intervention and discuss the function of miR-155 in the context of protective immunity. We first look back into the emergence of miR-155 in evolution, which is coincidental with the emergence of the ancestors of the antigen receptors. We then summarize what we have learned about the role of miR-155 in the regulation of lymphoid subsets at the cellular and molecular level in the context of recent progress in this field.

Increased numbers of monocyte-derived dendritic cells during successful tumor immunotherapy with immune-activating agents

Local treatment with selected TLR ligands or bacteria such as bacillus Calmette-Guérin increases antitumor immune responses and delays tumor growth. It is thought that these treatments may act by activating tumor-associated dendritic cells (DCs), thereby supporting the induction of antitumor immune responses. However, common parameters of successful immune activation have not been identified. We used mouse models to compare treatments with different immune-activating agents for the ability to delay tumor growth, improve priming of tumor-specific T cells, and induce early cytokine production and DC activation. Treatment with polyinosinic-polycytidylic acid or a combination of monosodium urate crystals and Mycobacterium smegmatis was effective at delaying the growth of s.c. B16 melanomas, orthotopic 4T1 mammary carcinomas, and reducing 4T1 lung metastases. In contrast, LPS, monosodium urate crystals, or M. smegmatis alone had no activity. Effective treatments required both NK1.1(+) and CD8(+) cells, and resulted in increased T cell priming and the infiltration of NK cells and CD8(+) T cells in tumors. Unexpectedly, both effective and ineffective treatments increased DC numbers and the expression of costimulatory molecules in the tumor-draining lymph node. However, only effective treatments induced the rapid appearance of a population of monocyte-derived DCs in the draining lymph node, early release of IL-12p70 and IFN-γ, and low IL-10 in the serum. These results suggest that the activation of existing DC subsets is not sufficient for the induction of antitumor immune responses, whereas early induction of Th1 cytokines and monocyte-derived DCs are features of successful activation of antitumor immunity.

Adjuvant activity of naturally occurring monophosphoryl lipopolysaccharide preparations from mucosa-associated bacteria

Natural heterogeneity in the structure of the lipid A portion of lipopolysaccharide (LPS) produces differential effects on the innate immune response. Gram-negative bacterial species produce LPS structures that differ from the classic endotoxic LPS structures. These differences include hypoacylation and hypophosphorylation of the diglucosamine backbone, both differences known to decrease LPS toxicity. The effect of decreased toxicity on the adjuvant properties of many of these LPS structures has not been fully explored. Here we demonstrate that two naturally produced forms of monophosphorylated LPS, from the mucosa-associated bacteria Bacteroides thetaiotaomicron and Prevotella intermedia, function as immunological adjuvants for antigen-specific immune responses. Each form of mucosal LPS increased vaccination-initiated antigen-specific antibody titers in both quantity and quality when given simultaneously with vaccine antigen preparations. Interestingly, adjuvant effects on initial T cell clonal expansion were selective for CD4 T cells. No significant increase in CD8 T cell expansion was detected. MyD88/Toll-like receptor 4 (TLR4) and TRIF/TLR4 signaling pathways showed equally decreased signaling with the LPS forms studied here as with endotoxic LPS or detoxified monophosphorylated lipid A (MPLA). Natural monophosphorylated LPS from mucosa-associated bacteria functions as a weak but effective adjuvant for specific immune responses, with preferential effects on antibody and CD4 T cell responses over CD8 T cell responses.

Construction and evaluation of a novel recombinant T cell epitope-based vaccine against Coccidioidomycosis

Clinical and animal studies of coccidioidomycosis have demonstrated that activated CD4(+) T lymphocytes are essential for protection against this fungal respiratory disease. We previously reported a vaccine against Coccidioides infection which contained three recombinant CD4(+) T cell-reactive proteins and induced a robust, protective immune response in mice. Due to the anticipated high cost of production and clinical assessment of this multivalent vaccine, we generated a single protein which contained immunodominant T cell epitopes of the three polypeptides. Epitopes were initially identified by computational prediction of their ability to bind promiscuously to human major histocompatibility complex class II (MHC II) molecules. Cellular immunoassays confirmed the immunogenicity of the synthesized epitope peptides, while in vitro binding assays revealed a range of peptide affinity for MHC II. A DNA construct was synthesized for bacterial expression of a recombinant protein vaccine which contained five epitopes with the highest affinity for human MHC II, each fused with leader and spacer peptides proposed to optimize epitope processing and presentation to T cell receptors. Recall assays of immune T lymphocytes obtained from human MHC II-expressing HLA-DR4 transgenic mice confirmed that 4 of the 5 epitope peptides were processed. Mice immunized with the epitope-based vaccine admixed with a synthetic oligodeoxynucleotide adjuvant or loaded into yeast glucan particles and then challenged intranasally with Coccidioides showed early lung infiltration of activated T helper-1 (Th1), Th2, and Th17 cells, elevated gamma interferon (IFN-γ) and interleukin (IL)-17 production, significant reduction of fungal burden, and prolongation of survival compared to nonvaccinated mice. This is the first report of an epitope-based vaccine against coccidioidomycosis.

CD28 promotes CD4+ T cell clonal expansion during infection independently of its YMNM and PYAP motifs

CD28 is required for maximal proliferation of CD4+ T cells stimulated through their TCRs. Two sites within the cytoplasmic tail of CD28, a YMNM sequence that recruits PI3K and activates NF-κB and a PYAP sequence that recruits Lck, are candidates as transducers of the signals responsible for these biological effects. We tested this proposition by tracking polyclonal peptide:MHCII-specific CD4+ T cells in vivo in mice with mutations in these sites. Mice lacking CD28 or its cytoplasmic tail had the same number of naive T cells specific for a peptide:MHCII ligand as wild-type mice. However, the mutant cells produced one tenth as many effector and memory cells as wild-type T cells after infection with bacteria expressing the antigenic peptide. Remarkably, T cells with a mutated PI3K binding site, a mutated PYAP site, or both mutations proliferated to the same extent as wild-type T cells. The only observed defect was that T cells with a mutated PYAP or Y170F site proliferated even more weakly in response to peptide without adjuvant than wild-type T cells. These results show that CD28 enhances T cell proliferation during bacterial infection by signals emanating from undiscovered sites in the cytoplasmic tail.

Intratumoral TLR-4 Agonist Injection Is Critical for Modulation of Tumor Microenvironment and Tumor Rejection

The tumor microenvironment shelters a complex network of mechanisms that enables local Immunosuppression to support tumor growth. In this study we found that, B16F10 melanoma growth is inversely correlated with peritumoral infiltrate cell number and with cell numbers in draining lymph nodes. Tumor growth ensued even when a foreign antigen was expressed by B16F10 cells in the presence of naïve specific CD8+ T cells. Treatment with TLR agonists has shown to sometimes result in tumor regression, however, not always with long-lasting effects. We compared the relevance of different injection regimens of lipopolysaccharide (LPS). Tumor growth was arrested only by intratumoral LPS injection after the tumor was already established. This result was accompanied by a dramatic change in DC activation inside the tumor. Intratumoral LPS also enhanced antigen presentation and tumor-specific CD4+ T cell production of IFN-γ. Injection of LPS before tumor challenge or codelivery of tumor cells and LPS did not have any effect on tumor progression. Our results suggest that an efficient antitumor immune response leading to tumor regression can be achieved with proper TLR4 activation inside the tumor tissue, impacting the tumor microenvironment. These findings are relevant for the design of treatment for patients with malignant melanomas.

Anti-IL-2 treatment impairs the expansion of T(reg) cell population during acute malaria and enhances the Th1 cell response at the chronic disease

Plasmodium chabaudi infection induces a rapid and intense splenic CD4(+) T cell response that contributes to both disease pathogenesis and the control of acute parasitemia. The subsequent development of clinical immunity to disease occurs concomitantly with the persistence of low levels of chronic parasitemia. The suppressive activity of regulatory T (T(reg)) cells has been implicated in both development of clinical immunity and parasite persistence. To evaluate whether IL-2 is required to induce and to sustain the suppressive activity of T(reg) cells in malaria, we examined in detail the effects of anti-IL-2 treatment with JES6-1 monoclonal antibody (mAb) on the splenic CD4(+) T cell response during acute and chronic P. chabaudi AS infection in C57BL/6 mice. JES6-1 treatment on days 0, 2 and 4 of infection partially inhibits the expansion of the CD4(+)CD25(+)Foxp3(+) cell population during acute malaria. Despite the concomitant secretion of IL-2 and expression of high affinity IL-2 receptor by large CD4(+) T cells, JES6-1 treatment does not impair effector CD4(+) T cell activation and IFN-γ production. However, at the chronic phase of the disease, an enhancement of cellular and humoral responses occurs in JES6-1-treated mice, with increased production of TNF-α and parasite-specific IgG2a antibodies. Furthermore, JES6-1 mAb completely blocked the in vitro proliferation of CD4(+) T cells from non-treated chronic mice, while it further increased the response of CD4(+) T cells from JES6-1-treated chronic mice. We conclude that JES6-1 treatment impairs the expansion of T(reg) cell population during early P. chabaudi malaria and enhances the Th1 cell response in the late phase of the disease.

Opposing signals from the Bcl6 transcription factor and the interleukin-2 receptor generate T helper 1 central and effector memory cells

Listeria monocytogenes infection generates T helper 1 (Th1) effector memory cells and CC chemokine receptor 7 (CCR7)(+) cells resembling central memory cells. We tracked endogenous L. monocytogenes-specific CD4(+) T cells to determine how these memory cells are formed. Two effector cell populations were already present several days after infection. One highly expressed the T-bet transcription factor and produced Th1 memory cells in an interleukin-2 (IL-2) receptor-dependent fashion. The other resided in the T cell areas, expressed CCR7 and CXC chemokine receptor 5 (CXCR5), and like follicular helper cells depended on the Bcl6 transcription factor and inducible costimulator ligand on B cells. The CCR7(+)CXCR5(+) effector cells produced similar memory cells that generated diverse effector cell populations in a secondary response. Thus, Th1 effector memory and follicular helper-like central memory cells are produced from early effector cell populations that diverge in response to signals from the IL-2 receptor, Bcl6, and B cells.

Apoptosis of purified CD4+ T cell subsets is dominated by cytokine deprivation and absence of other cells in new onset diabetic NOD mice

BACKGROUND

Regulatory T cells (Treg) play a significant role in immune homeostasis and self-tolerance. Excessive sensitivity of isolated Treg to apoptosis has been demonstrated in NOD mice and humans suffering of type 1 diabetes, suggesting a possible role in the immune dysfunction that underlies autoimmune insulitis. In this study the sensitivity to apoptosis was measured in T cells from new onset diabetic NOD females, comparing purified subsets to mixed cultures.

PRINCIPAL FINDINGS

Apoptotic cells are short lived in vivo and death occurs primarily during isolation, manipulation and culture. Excessive susceptibility of CD25(+) T cells to spontaneous apoptosis is characteristic of isolated subsets, however disappears when death is measured in mixed splenocyte cultures. In variance, CD25(-) T cells display balanced sensitivity to apoptosis under both conditions. The isolation procedure removes soluble factors, IL-2 playing a significant role in sustaining Treg viability. In addition, pro- and anti-apoptotic signals are transduced by cell-to-cell interactions: CD3 and CD28 protect CD25(+) T cells from apoptosis, and in parallel sensitize naïve effector cells to apoptosis. Treg viability is modulated both by other T cells and other subsets within mixed splenocyte cultures. Variations in sensitivity to apoptosis are often hindered by fast proliferation of viable cells, therefore cycling rates are mandatory to adequate interpretation of cell death assays.

CONCLUSIONS

The sensitivity of purified Treg to apoptosis is dominated by cytokine deprivation and absence of cell-to-cell interactions, and deviate significantly from measurements in mixed populations. Balanced sensitivity of naïve/effector and regulatory T cells to apoptosis in NOD mice argues against the concept that differential susceptibility affects disease evolution and progression.

Abrogating Cbl-b in effector CD8(+) T cells improves the efficacy of adoptive therapy of leukemia in mice

The clinical use of adoptive immunotherapy with tumor-reactive T cells to treat established cancers is limited in part by the poor in vivo survival and function of the transferred T cells. Although administration of exogenous cytokines such as IL-2 can promote T cell survival, such strategies have many nonspecific activities and are often associated with toxicity. We show here that abrogating expression of Casitas B-lineage lymphoma b (Cbl-b), a negative regulator of lymphocyte activation, in tumor-reactive CD8(+) T cells expanded ex vivo increased the efficacy of adoptive immunotherapy of disseminated leukemia in mice. Mechanistically, Cbl-b abrogation bypassed the requirement for exogenous IL-2 administration for tumor eradication in vivo. In addition, CD8(+) T cells lacking Cbl-b demonstrated a lower threshold for activation, better survival following target recognition and stimulation, and enhanced proliferative responses as a result of both IL-2-dependent and -independent pathways. Importantly, siRNA knockdown of Cbl-b in human CD8(+)CD28- effector T cell clones similarly restored IL-2 production and proliferation following target recognition independent of exogenous IL-2, enhanced IFN-γ production, and increased target avidity. Thus, abrogating Cbl-b expression in effector T cells may improve the efficacy of adoptive therapy of some human malignancies.

Primed antigen-specific CD4+ T cells are required for NK cell activation in vivo upon Leishmania major infection

The ability of NK cells to rapidly produce IFN-gamma is an important innate mechanism of resistance to many pathogens including Leishmania major. Molecular and cellular components involved in NK cell activation in vivo are still poorly defined, although a central role for dendritic cells has been described. In this study, we demonstrate that Ag-specific CD4(+) T cells are required to initiate NK cell activation early on in draining lymph nodes of L. major-infected mice. We show that early IFN-gamma secretion by NK cells is controlled by IL-2 and IL-12 and is dependent on CD40/CD40L interaction. These findings suggest that newly primed Ag-specific CD4(+) T cells could directly activate NK cells through the secretion of IL-2 but also indirectly through the regulation of IL-12 secretion by dendritic cells. Our results reveal an unappreciated role for Ag-specific CD4(+) T cells in the initiation of NK cell activation in vivo upon L. major infection and demonstrate bidirectional regulations between innate and adaptive immunity.

CD28 co-signaling in the adaptive immune response

T-cell proliferation and function depends on signals from the antigen-receptor complex (TCR/CD3) and by various co-receptors such as CD28 and CTLA-4. The balance of positive and negative signals determines the outcome of the T-cell response to foreign and self-antigen. CD28 is a prominent co-receptor in naïve and memory T-cell responses. Its blockade has been exploited clinically to dampen T-cell responses to self-antigen. Current evidence shows that CD28 both potentiates TCR signaling and engages a unique array of mediators (PI3K, Grb2, FLNa) in the regulation of aspects of T-cell signaling including the transcription factor NFkB. In this mini-review, we provide an up-to-date overview of our understanding of the signaling mechanisms that underlie CD28 function and its potential application to the modulation of reactivity to autoimmunity.

Defining the heterogeneity of skeletal muscle-derived side and main population cells isolated immediately ex vivo

Myoblast transfer therapy for Duchenne muscular dystrophy (DMD) largely fails due to cell death and inability of transplanted cells to engraft in diseased muscles. One method attempting to enrich for cell subpopulations is the Hoechst 33342 dye exclusion assay, yielding a side population (SP) thought to be progenitor enriched and a main population (MP). However, in vitro and transplant studies yielded inconsistent results relative to downstream progeny. Cell surface markers expressed by skeletal muscle-derived MP and SP cells have not been fully characterized directly ex vivo. Using flow cytometry, MP and SP cells were characterized based on their expression of several well-accepted progenitor cell antigens. Both the MP and SP populations are heterogeneous and overlapping in the cells they contain. The percentages of cells in each population vary with species and specific muscle examined. MP and SP populations contain both satellite and multipotent progenitor cells, based on expression of CD34, Sca-1, Pax7, and M-cadherin. Thus, isolation using this procedure cannot be used to predict downstream differentiation outcomes, and explains the conflicting literature on these cells. Hoechst dye also results in significant mortality of sorted cells. As defined subpopulations are easily obtained using flow cytometry, sorting immediately ex vivo based on accepted myogenic precursor cell markers will yield superior results in terms of cell homogeneity for transplantation therapy.

T cells demonstrate a Th1-biased response to native beta2-glycoprotein I in a murine model of anti-phospholipid antibody induction

Anti-phospholipid syndrome (APS) is an autoimmune disorder characterized by the presence of autoantibody (AAb) to phospholipid (PL)-binding proteins, such as beta2-glycoprotein I (beta2GPI), and clinical manifestations including thrombosis and/or recurrent pregnancy loss. beta2GPI-reactive T cells are clearly implicated in the generation of these AAb, but the mechanism responsible for their activation remains unclear. We hypothesized that immunization of mice with human beta2GPI, in the context of a potent innate immune activator lipopolysaccharide (LPS), would generate not only high titers of anti-PL AAb, but also a strong beta2GPI-specific T cell response. Healthy, nonautoimmune C57BL/6 mice were immunized repeatedly with human beta2GPI in the presence of LPS. High titers of anti-PL to beta2GPI appeared after the second immunization, with T cell reactivity to beta2GPI detectable only after the fourth immunization. Splenic T cells from these mice proliferated in response to native beta2GPI, alone or bound to anionic PL. These T cells produced IL-2 and IFN-gamma, but not IL-4 or IL-10, indicating a Th1 bias of the beta2GPI-specific response. These findings suggest that T cells responsive to beta2GPI may become activated in APS patients by exposure to their cognate Ag in the context of innate immune activation and a pro-inflammatory environment.

Different routes of bacterial infection induce long-lived TH1 memory cells and short-lived TH17 cells

A sensitive peptide-major histocompatibility complex II (pMHCII) tetramer-based method was used to determine whether CD4⁺ memory T cells resemble the T_H1 and T_H-17 subsets described in vitro. Intravenous or intranasal Listeria monocytogenes infection induced pMHCII-specific CD4⁺ naïve T cells to proliferate and produce effector cells, about 10% of which resembled T_H1 or T_H-17 cells, respectively. T_H1 cells were also present among the memory cells that survived three months post-infection whereas T_H-17 cells disappeared. The short lifespan of T_H-17 cells was associated with low amounts of Bcl-2, interleukin 15 receptor, CD27 and little homeostatic proliferation. These results suggest that T_H1 cells induced by intravenous infection are more efficient at entering the memory pool than T_H-17 cells induced by intranasal infection.

Ligation of the OX40 co-stimulatory receptor reverses self-Ag and tumor-induced CD8 T-cell anergy in vivo

Tumor-specific CD8 T-cell peripheral tolerance occurs through clonal deletion, suppression, and the induction of anergy and can limit the generation of anti-tumor immunity. Several groups have demonstrated that prostate cancer can render tumor-specific CD8 T cells anergic, suggesting reversing tumor-induced anergy may greatly augment anti-tumor immunity. Recent work has demonstrated that signaling through the OX40 (CD134) co-stimulatory receptor, a member of the TNFR super-family, can augment CD4 and CD8 T-cell expansion, differentiation, and the generation of memory cells. However, whether OX40 ligation can reverse CD8 T-cell anergy, and more specifically, tumor-induced CD8 T-cell anergy, remains unclear. In the current study, we demonstrate that OX40 ligation can reverse CD8 T-cell anergy to a prostate-specific self-Ag in non-tumor-bearing hosts. Furthermore, OX40 engagement reversed tumor-specific CD8 T-cell anergy and restored the proliferative capacity of tumor-reactive CD8 T cells, which attenuated tumor growth and enhanced the survival of tumor-bearing hosts. These data demonstrate that OX40 ligation can rescue the function of anergic self- or tumor-reactive CD8 T cells in vivo and suggests that OX40-mediated therapy may provide a novel means of boosting anti-tumor immunity by restoring the responsiveness of previously anergic tumor-specific CD8 T cells.

Cell cycle progression following naive T cell activation is independent of Jak3/common gamma-chain cytokine signals

T cell proliferation following activation is an essential aspect of the adaptive immune response. Multiple factors, such as TCR signaling, costimulation, and signals from cytokines, each contribute to determine the magnitude of T cell expansion. In this report, we examine in detail the role of Jak3/common gamma-chain-dependent cytokines in promoting cell cycle progression and proliferation of naive T cells. Using naive CD4+ T cells from Jak3-deficient mice and wild-type CD4+ T cells treated with a small molecule inhibitor of Jak3, we find that these cytokine signals are not required for proliferation; instead, they are important for the survival of activated T cells. In addition, we show that the percentage of cells entering the cell cycle and the percentage of cells in each round of cell division are comparable between Jak3-deficent and wild-type T cells. Furthermore, cell cycle progression and the regulated expression of key cell cycle proteins are independent of Jak3/common gamma-chain cytokine signals. These findings hold true over a wide range of TCR signal strengths. However, when CD28 costimulatory signals, but not TCR signals, are limiting, Jak3-dependent cytokine signals become necessary for the proliferation of naive T cells. Because CD28 signaling has been found to be dispensable for autoreactive T cell responses, these data suggest the potential for interfering with autoimmune T cell responses by inhibition of Jak3 signaling.

The initial phase of an immune response functions to activate regulatory T cells

An early reaction of CD4(+) T lymphocytes to Ag is the production of cytokines, notably IL-2. To detect cytokine-dependent responses, naive Ag-specific T cells were stimulated in vivo and the presence of phosphorylated STAT5 molecules was used to identify the cell populations responding to IL-2. Within hours of T cell priming, IL-2-dependent STAT5 phosphorylation occurred primarily in Foxp3(+) regulatory T cells. In contrast, the Ag-specific T cells received STAT5 signals only after repeated Ag exposure or memory differentiation. Regulatory T cells receiving IL-2 signals proliferated and developed enhanced suppressive activity. These results indicate that one of the earliest events in a T cell response is the activation of endogenous regulatory cells, potentially to prevent autoimmunity.

Lipopolysaccharide potentiates effector T cell accumulation into nonlymphoid tissues through TRIF

LPS is a natural adjuvant that potentiates Ag-specific T cell survival and Th1 differentiation by stimulating MyD88 and Toll/IL-1R domain-containing adaptor-inducing IFN-beta (TRIF) signaling pathways. In this study, we reveal the TRIF pathway is critical for amplifying murine effector T cell accumulation into nonlymphoid tissues following immunization with Ag plus LPS. Although LPS increased the accumulation of splenic T cells in TRIF-deficient mice, markedly fewer T cells were recovered from liver and lung in comparison to wild type. Most of the T cells primed in TRIF-deficient mice failed to up-regulate CXCR3 and had an overall reduced capacity to produce IFN-gamma, demonstrating effector T cell differentiation was linked to their migration. To investigate the role of TRIF-dependent cytokines, neutralization studies were performed in wild type mice. Although TNF neutralization reduced T cell numbers, its coneutralization with IL-10 unexpectedly restored the T cells, suggesting the balance between pro- and anti-inflammatory cytokines influences T cell survival rather than their magnitude. To investigate a role for costimulatory molecules, we tested whether the T cell defect in TRIF-deficient mice could be corrected with enforced costimulation. Boosting with a CD40 agonist in addition to LPS restored the effector CD8 T cell response in livers of TRIF-deficient mice while only partially restoring CD4 T cells, suggesting that LPS primes CD8 and CD4 T cell immunity through different mechanisms. Overall, our data support targeting TRIF for vaccines aimed to direct immune responses to nonlymphoid tissues.

Interleukin-2 in the development and control of inflammatory disease

Interleukin-2 (IL-2) has multiple, sometimes opposing, functions during an inflammatory response. It is a potent inducer of T-cell proliferation and T-helper 1 (Th1) and Th2 effector T-cell differentiation and provides T cells with a long-lasting competitive advantage resulting in the optimal survival and function of memory cells. In a regulatory role, IL-2 is important for the development, survival, and function of regulatory T cells, it enhances Fas-mediated activation-induced cell death, and it inhibits the development of inflammatory Th17 cells. Thus, in its dual and contrasting functions, IL-2 contributes to both the induction and the termination of inflammatory immune responses.

Understanding how lipopolysaccharide impacts CD4 T-cell immunity

Lipopolysaccharide (LPS) is a natural adjuvant synthesized by gram-negative bacteria that has profound effects on CD4 T-cell responses. LPS stimulates cells through the Toll-like receptor 4 (TLR4), causing the release of inflammatory cytokines and upregulation of costimulatory molecules on antigen-presenting cells (APCs). The combination of signals from antigens, costimulation, and cytokines allows CD4 T cells to overcome suppressive barriers and accumulate in large numbers. T cells that are primed in an LPS-stimulated environment are programmed for long-term survival following clonal expansion. LPS is well-known for generating Th1 responses. However, under appropriate conditions it can also support differentiation into other T-helper lineages, demonstrating its pleiotropic nature. Although molecular analyses have provided insights into how immune responses are controlled by LPS in vivo, its powerful adjuvant activity is also associated with toxicity. Research on partial TLR4 agonists such as monophosphoryl lipid A have demonstrated that toxicity and immunogenicity are not always linked, making them useful candidates for human vaccines. In this sense, many years of LPS research have ultimately contributed to vaccine design, and the next generation may involve studying how the balance between different CD4 T-cell subsets is controlled.

Dendritic cell antigen presentation drives simultaneous cytokine production by effector and regulatory T cells in inflamed skin

Effector (Teff) and regulatory (Treg) T cells produce cytokines that balance immunity and immunopathology at sites of infection. It is not known how this balance is achieved. Here, we show that Treg and Teff cells specific for the same foreign peptide:major histocompatibility complex II (pMHCII) ligand accumulated preferentially in a subcutaneous site injected with the relevant antigen plus an adjuvant. Some of the Treg cells in this site were producing IL-10 12 days after injection, whereas a similar fraction of the Teff cells were producing IFN-gamma. Acute ablation of Treg cells increased the fraction of IFN-gamma-producing Teff cells, indicating that Teff function was limited by the Treg cells. Production of cytokines by both populations was driven by pMHCII presentation by local CD11b(hi) dermal dendritic cells. Therefore, balanced production of microbicidal and suppressive cytokines in inflamed skin is achieved by simultaneous dendritic cell antigen presentation to Teff and Treg cells.

Casitas B-lineage lymphoma b inhibits antigen recognition and slows cell cycle progression at late times during CD4+ T cell clonal expansion

Optimal clonal expansion of CD4(+) T cells during the primary response to Ag requires prolonged TCR recognition of peptide Ag/MHC complexes. In this study, we investigated the capacity of Casitas B-lineage lymphoma b (Cbl-b) to counter-regulate late TCR signals necessary for continued cell division in vivo. During the first 24 h of a primary response to Ag, Cblb(-/-) 5C.C7 CD4(+) T cells demonstrated no alteration in CD69, CD25, and CD71 up-regulation or cell growth as compared with wild-type cells. Nevertheless, beyond 24 h, both the expression of CD71 and the rate of cell division were increased in the genetic absence of Cbl-b, leading to an augmented clonal expansion. This deregulation of late T cell proliferation in the absence of Cbl-b resulted in part from an inability of Cblb(-/-) T cells to desensitize Akt, PLCgamma-1, and ERK phosphorylation events downstream of the TCR/CD3 complex, in addition to their failure to undergo a growth arrest in the absence of Ag. These observations now suggest a novel role for Cbl-b in triggering the exit from cell cycle at the end of a CD4(+) T cell clonal expansion.

The immunity-related GTPase Irgm1 promotes the expansion of activated CD4+ T cell populations by preventing interferon-gamma-induced cell death

Mice deficient in the interferon-gamma (IFN-gamma)-inducible, immunity-related GTPase Irgm1 have defective host resistance to a variety of intracellular pathogens. This greater susceptibility to infection is associated with impaired IFN-gamma-dependent macrophage microbicidal activity in vitro. Here we show that Irgm1 also regulated the survival of mature effector CD4(+) T lymphocytes by protecting them from IFN-gamma-induced autophagic cell death. Mice deficient in both IFN-gamma and Irgm1 were 'rescued' from the lymphocyte depletion and greater mortality that occurs in mice singly deficient in Irgm1 after mycobacterial infection. Our studies identify a feedback mechanism in the T helper type 1 response that limits the detrimental effects of IFN-gamma on effector T lymphocyte survival while promoting the antimicrobial functions of IFN-gamma.