Control Of Adaptive Immune Responses Research Articles

Circadian rhythms in adaptive immunity and vaccination.

Adaptive immunity allows an organism to respond in a specific manner to pathogens and other non-self-agents. Also, cells of the adaptive immune system, such as T and B lymphocytes, can mediate a memory of an encounter with a pathogen, allowing a more efficient response to a future infection. As for other aspects of physiology and of the immune system, the adaptive immune system is regulated by circadian clocks. Consequently, the development, differentiation, and trafficking between tissues of adaptive immune cells have been shown to display daily rhythms. Also, the response of T cells to stimuli (e.g., antigen presentation to T cells by dendritic cells) varies according to a circadian rhythm, due to T cell-intrinsic mechanisms as well as cues from other tissues. The circadian control of adaptive immune response has implications for our understanding of the fight against pathogens as well as auto-immune diseases, but also for vaccination, a preventive measure based on the development of immune memory.

Complement as a Therapeutic Target in Systemic Autoimmune Diseases.

The complement system (CS) includes more than 50 proteins and its main function is to recognize and protect against foreign or damaged molecular components. Other homeostatic functions of CS are the elimination of apoptotic debris, neurological development, and the control of adaptive immune responses. Pathological activation plays prominent roles in the pathogenesis of most autoimmune diseases such as systemic lupus erythematosus, antiphospholipid syndrome, rheumatoid arthritis, dermatomyositis, and ANCA-associated vasculitis. In this review, we will review the main rheumatologic autoimmune processes in which complement plays a pathogenic role and its potential relevance as a therapeutic target.

Control of adaptive immune responses by adrenergic nerves

Control of adaptive immune responses by adrenergic nerves

Assessment of Lymph Node Stromal Cells as an Underlying Factor in Age-Related Immune Impairment.

Aging negatively impacts immunity, resulting in inefficient responses to vaccinations and infections. Fibroblastic reticular cells (FRCs) are the major stromal cell subset in lymph nodes (LNs) and play an intricate role in the orchestration and control of adaptive immune responses. Although stromal cells have a major impact on immune responses, the impact of aging on LN stromal cells remains unclear. Quantitative analysis of LN stromal cells by flow cytometry revealed that there are no significant differences in the number of stromal cells in young and aged LN at steady state but after influenza infection aged FRCs have delayed expansion as a result of reduced proliferation. Aged LNs also produce reduced levels of homeostatic chemokines, which correlates with reduced homing of naive T cells. Image analysis reveals that young and aged T-cell zone FRCs have similar morphology at steady state and after infection. Furthermore, aged FRCs did not appear to be a contributing factor in the reduced proliferation of young T cells transferred into aged LNs after influenza infection. These results demonstrate that aging alters LN stromal cell response to challenge and these age-related changes may be an underlying contributor to impaired immune responses in the elderly people.

PKCδ-Mediated Nox2 Activation Promotes Fluid-Phase Pinocytosis of Antigens by Immature Dendritic Cells.

Macropinocytosis is a major endocytic pathway by which dendritic cells (DCs) internalize antigens in the periphery. Despite the importance of DCs in the initiation and control of adaptive immune responses, the signaling mechanisms mediating DC macropinocytosis of antigens remain largely unknown. The goal of the present study was to investigate whether protein kinase C (PKC) is involved in stimulation of DC macropinocytosis and, if so, to identify the specific PKC isoform(s) and downstream signaling mechanisms involved. Various cellular, molecular and immunological techniques, pharmacological approaches and genetic knockout mice were utilized to investigate the signaling mechanisms mediating DC macropinocytosis. Confocal laser scanning microscopy confirmed that DCs internalize fluorescent antigens (ovalbumin) using macropinocytosis. Pharmacological blockade of classical and novel PKC isoforms using calphostin C abolished both phorbol ester- and hepatocyte growth factor-induced antigen macropinocytosis in DCs. The qRT-PCR experiments identified PKCδ as the dominant PKC isoform in DCs. Genetic studies demonstrated the functional role of PKCδ in DC macropinocytosis of antigens, their subsequent maturation, and secretion of various T-cell stimulatory cytokines, including IL-1α, TNF-α and IFN-β. Additional mechanistic studies identified NADPH oxidase 2 (Nox2) and intracellular superoxide anion as important players in DC macropinocytosis of antigens downstream of PKCδ activation. The findings of the present study demonstrate a novel mechanism by which PKCδ activation via stimulation of Nox2 activity and downstream redox signaling promotes DC macropinocytosis of antigens. PKCδ/Nox2-mediated antigen macropinocytosis stimulates maturation of DCs and secretion of T-cell stimulatory cytokines. These findings may contribute to a better understanding of the regulatory mechanisms in DC macropinocytosis and downstream regulation of T-cell-mediated responses.

Assessment of lymph node stromal cells as an underlying factor in age related immune impairment to influenza infection

Abstract It is well established that aging negatively impacts immunity, resulting in inefficient responses to vaccinations and infections, like influenza. Fibroblastic reticular cells (FRCs) are the major stromal cell subset in lymph nodes and play an intricate role in the orchestration and control of adaptive immune responses. Although stromal cells have a major impact on immune responses, the impact of aging on LN stromal cells has yet to be determined. We sought to determine how aging impacts FRC number, phenotype and morphology at steady state and after influenza infection. An enzymatic and mechanical digestion was used to make single cell suspensions of lymph node stromal cells for analysis. Flow cytometry was performed to quantify the number and frequency of stromal cells in lymph nodes from young (13 weeks) and aged (19 months) C57BL/6 mice. To analyze stromal cell morphology, lymph nodes from young and aged mice were cryopreserved, and then sectioned for confocal microscopy. Quantitative analysis of lymph node stromal cells by flow cytometry revealed that there are no significant differences in the number stromal cells in young and aged lymph nodes at steady state, but after influenza infection aged FRCs fail to expand in number. Reduced proliferation and activation of aged FRCs, but not increased death leads to the decreased expansion. Microscopic analysis revealed that young and aged LN T cell zone FRCs have similar morphology at steady state and after infection. These results are the first evidence that aging alters lymph node stromal cells ability to respond to challenge. These changes in aged FRCs may be an underlying cause behind the impaired immune response to influenza infection found in the elderly.

Regulatory role of neutrophils in the inflammatory responses to paramyxovirus infection in mice

Abstract Neutrophils are the most abundant leukocytes (50% to 70%) in humans and are the first immune cell population recruited to the sites of infection. They are known to act in the first line of innate immune defense against invading pathogens, and more recently, to playing a crucial role in orchestrating adaptive immune responses. However, the role of neutrophils in the control of adaptive immune response during respiratory viral infections is still largely unknown. In order to elucidate the role of neutrophils in respiratory antiviral defense, we employed an experimental mouse model of human metapneumovirus (hMPV) infection. HMPV is a member of the Paramyxoviridae family, and a leading respiratory pathogen causing severe symptoms such as bronchiolitis and pneumonia in the young, elderly and immunocompromised patients. Our findings demonstrate that neutrophils are rapidly recruited in high numbers to the lungs of infected mice (>80%) during the acute phase of infection. Specific depletion of neutrophil in vivo using a monoclonal antibody and simultaneous infection with hMPV exhibited significantly higher levels of inflammatory cytokines, pulmonary inflammation and severe clinical disease (as indicated by an enhanced body weight loss and clinical illness) compared to hMPV-infected competent mice. Interestingly, the lack of neutrophils altered the T cell responses in the lung, particularly the γδ-T-cell subset. Finally, we also observed that the recruitment of neutrophils to the lung was controlled by the expression of the hMPV attachment protein. These novel findings demonstrate that neutrophils regulate T cell responses and are critically important for the control of the hMPV-induced inflammatory responses in the respiratory tract.

Antigen Receptor-Intrinsic Non-Self: The Key to Understanding Regulatory Lymphocyte-Mediated Idiotypic Control of Adaptive Immune Responses.

The clone-specific or idiotypic characters of B as well as T cell antigen receptors (BCRs/TCRs) are associated with (1) the third-complementarity-determining regions (CDR3s) that are created during V(D)J recombination (they scarcely occur in antibody light chains) and (2) BCR idiotopes created by somatic hypermutations (SHMs) during immune responses. Therefore, BCR/TCR idiotypic sites are antigen receptor-intrinsic Non-Self (AgR-iNS) portions that fulfill two tasks: serving as a crucial component of the epitope-binding paratope and serving as target sites for anti-idiotypic BCR/TCR paratopes of other anti-Non-Self clones that are contained in both normal repertoires. The antigen-induced immune response is thus directed not only toward the environmental stimulus but also against the AgR-iNS portions of the directly and further activated clones that form a subsiding idiotypic cascade. These idiotypic chain reactions form a completely integrated idiotypic control circuit among B and T cells which contains all regulatory T and B cells. However, this circuit cannot be viewed as a network of fixed interacting nodes but rather uses the genetic Self as reference. Hence, AgR-iNS offers a mechanistic understanding of regulatory lymphocyte-mediated idiotypic control of adaptive immune responses and reconciles clonal selection and idiotypic network theories hitherto believed to be incompatible.

Regulatory and Effector Helper T-Cell Profile after Nerve Xenografting in the Toll-Like Receptor-Deficient Mice.

Introduction: The balance between regulatory T cells (Tregs) and effector T help cells (Th cells) is critical for the control of adaptive immune response during nerve transplantation. However, whether the homeostasis of immune regulation between Tregs and Th cells requires toll-like receptor (TLR) signaling is unclear. The aim of this study is to profile the distribution of spleen Tregs and Th cells in a mouse model of nerve xenografting in the TLR2 and NF-κB gene knockout mice.Methods: The sciatic nerve was taken from a SD rat or an allogeneic mouse and transplanted to a right back leg of recipient C57BL/6, TLR2-/-, or NF-κB-/- mice by subcutaneous transplantation. After 7 days, the T lymphocytes were then isolated from spleen, stained with phenotyping kits, and analyzed by flow cytometry.Results: The results showed that Tregs were decreased after nerve xenografting in the recipient C57BL/6 mouse. In addition, nerve xenografting also increased the Th1 and Th17 but not the Th2 cell populations. In contrast, amelioration of the Tregs elimination was found in TLR2-/- and NF-κB-/- mice after transplantation of the nerve xenograft. Moreover, the mice lacking TLR2 or NF-κB showed attenuation of the increase in Th1 and Th17 cells after nerve xenografting.Conclusions: TLR signaling is involved in T cell population regulation during tissue transplantation. Knock-out of TLR2 and NF-κB prevented Tregs elimination and inhibited Th1- and Th17-driven immune response after nerve xenografting. This study highlighted the potential of inhibiting TLR signaling to modulate T cell-mediated immune regulation to facilitate tolerance to nerve transplantation.

25-Hydroxycholesterol Activates the Integrated Stress Response to Reprogram Transcription and Translation in Macrophages

25-Hydroxycholesterol (25OHC) is an enzymatically derived oxidation product of cholesterol that modulates lipid metabolism and immunity. 25OHC is synthesized in response to interferons and exerts broad antiviral activity by as yet poorly characterized mechanisms. To gain further insights into the basis for antiviral activity, we evaluated time-dependent responses of the macrophage lipidome and transcriptome to 25OHC treatment. In addition to altering specific aspects of cholesterol and sphingolipid metabolism, we found that 25OHC activates integrated stress response (ISR) genes and reprograms protein translation. Effects of 25OHC on ISR gene expression were independent of liver X receptors and sterol-response element-binding proteins and instead primarily resulted from activation of the GCN2/eIF2α/ATF4 branch of the ISR pathway. These studies reveal that 25OHC activates the integrated stress response, which may contribute to its antiviral activity.

Control of Adaptive Immune Responses by Staphylococcus aureus through IL-10, PD-L1 and TLR2

Microbes induce innate immune responses in hosts. It is critical to know how different microbes control adaptive responses through innate pathways. The impact of gram-positive bacteria on the innate and adaptive responses is unclear. Herein we report that Staphylococcus aureus induces IL-10, Th17-inducing cytokines IL-6 and IL-23, chemokines, and regulates dendritic cell markers. S. aureus inhibits T-cell IL-2 responses through modulation of HLA-DR, CD86 and PD-L1. IFN-gamma, Src kinase inhibitors, or TLR2 antibodies prevented the down-modulation of HLA-DR by S. aureus. Our data demonstrate that innate TLR signaling induces multi-dimensional inhibition of adaptive immune responses, which may contribute to the lack of protective immunity to bacteria or microbe tolerance. IL-10 and PD-L1 antagonists may boost immunity to vaccines for S. aureus and other microbes.

Regulatory dendritic cells program B cells to differentiate into CD19hiFcγIIbhi regulatory B cells through IFN-β and CD40L

AbstractRegulatory dendritic cells (DCs) play important roles in the induction of peripheral tolerance and control of adaptive immune response. Our previous studies demonstrate that splenic stroma can drive mature DCs to proliferate and further differentiate into a unique subset of CD11bhiIalow regulatory DCs, which could inhibit T-cell response, program generation of immunosuppressive memory CD4 T cells. However, the effect of regulatory DCs on B-cell function remains unclear. Here, we report that regulatory DCs can induce splenic B cells to differentiate into a distinct subtype of IL-10–producing regulatory B cells with unique phenotype CD19hiFcγIIbhi. CD19hiFcγIIbhi B cells inhibit CD4 T-cell response via IL-10. CD19hiFcγIIbhi B cells have enhanced phagocytic capacity compared with conventional CD19+ B cells, and FcγRIIb mediates the uptake of immune complex by CD19hiFcγIIbhi B cells. We found that regulatory DC-derived IFN-β and CD40 ligand are responsible for the differentiation of CD19hiFcγIIbhi B cells. Furthermore, an in vivo counterpart of CD19hiFcγIIbhi B cells in the spleen and lymph nodes with similar phenotype and regulatory function has been identified. Our results demonstrate a new manner for regulatory DCs to down-regulate immune response by, at least partially, programming B cells into regulatory B cells.

Human leukocyte antigen genotypes in the genetic control of adaptive immune responses to smallpox vaccine.

The role of human leukocyte antigen (HLA) genes in mediating adaptive immune responses to smallpox vaccine remains unknown. We determined genotypes for a group of individuals (n = 1071) who received a single dose of smallpox vaccine (Dryvax, Wyeth Laboratories) and examined associations between HLA alleles and 15 immune outcomes to smallpox vaccine on a per-locus and a per-allele level. We found significant associations between the HLA-B and HLA - DQB1 loci and vaccinia-induced antibodies (P = .04 for each locus), with the HLA-B*1302 (P = .036), B*3802 (P = .011), DQB1*0302 (P = .015), and DQB1*0604 (P = .017) alleles being associated with higher levels. Significant global associations were identified between vaccinia-specific interferon (IFN)-γ and DQA1 (P = .003), interleukin (IL)-1β and HLA-B (P = .004), tumor necrosis factor (TNF)-α and HLA-B (P = .006), and IL-6 and HLA-B locus (P = .016) for secreted cytokines, as well as between CD8α(+) IFN-γ Elispot responses and DQB1 (P = .027). Subjects carrying B*3906 (P = .006) and B*5701 (P < .001) secreted higher levels of IL-1β than did subjects who did not carry these alleles. Subjects carrying the B*5301 (P = .047) and B*5601 (P = .008) alleles secreted less IL-1β, compared with subjects who did not carry these alleles. The B*3502 (P = .009), B*5601 (P = .004), and B*5701 (P < .001) alleles were significantly associated with variations in TNF-α secretion. These data suggest that variations in antibody and cellular IFN-γ, IL-1β, TNF-α, and IL-6 immune responses after receipt of smallpox vaccine are genetically controlled by HLA genes or genes in close linkage disequilibrium to these alleles.

Here today – not gone tomorrow: Roles for activating receptors in sustaining NK cells during viral infections

The conclusive evidence supporting a role for NK cells in defense against viruses has been obtained under conditions of NK cell deficiencies prior to infections. NK cell proliferation can be induced during infections, but the advantages of resulting expansion have been unclear because NK cell basal frequency is already high. However, NK cell decreases are also observed during certain conditions of viral infection. Given the range of potent antiviral and immunoregulatory functions of NK cells, such "disappearance" dramatically changes the resources available to the host. New studies demonstrate that proliferation dependent on activating receptors for virus-induced ligands is key for NK cell maintenance, and allows their continued availability for control of adaptive immune responses and immunopathology. This pathway for sustaining NK cells may represent a system used generally to select subsets for rescue during homeostatic purging. In the case of NK cells, though, nonselection limits continued access to the many beneficial functions of NK cells. The observations resolve the long-standing conundrum of reported NK cell increases and decreases during viral infections. Moreover, they demonstrate a previously unappreciated role for activating receptors, i.e. to keep NK cells here today and also tomorrow.

The role of complement and Toll-like receptors in organ transplantation

The innate immune system not only participates in host defence but also contributes to the control of adaptive immune responses. Complement and Toll-like receptors (TLR) are key components of innate immunity. Emerging evidence suggests their activation is involved in all major aspects of transplantation. This paper reviews the current understanding of how the complement and TLR on impact transplant injury.

Role of MHC class II expressing CD4+ T cells in proteolipid protein91–110‐induced EAE in HLA‐DR3 transgenic mice

MHC class II molecules play a central role in the control of adaptive immune responses through selection of the CD4(+) T cell repertoire in the thymus and antigen presentation in the periphery. Inherited susceptibility to autoimmune disorders such as multiple sclerosis, rheumatoid arthritis and IDDM are associated with particular MHC class II alleles. Advent of HLA transgenic mice has helped us in deciphering the role of particular HLA DR and DQ class II molecules in human autoimmune diseases. In mice, the expression of class II is restricted to professional antigen-presenting cells (APC). However, in humans, class II is also expressed on T cells, unlike murine T cells. We have developed new humanized HLA class II transgenic mice expressing class II molecules not only on APC but also on a subset of CD4(+) T cells. The expression of class II on CD4(+) T cells is inducible, and class II(+) CD4(+) T cells can present antigen in the absence of APC. Further, using EAE, a well-established animal model of MS, we tested the functional significance of these class II(+) CD4(+) T cells. DR3.AEo transgenic mice were susceptible to proteolipid protein(91-110)-induced EAE and showed CNS pathology accompanied by widespread inflammation and demyelination seen in human MS patients, suggesting a role for class II(+) CD4(+) T cells in the pathogenesis.

An association study of asthma and related phenotypes with polymorphisms in negative regulator molecules of the TLR signaling pathway

Although associations between endotoxin exposure or respiratory infection and asthma have been recognized, the genetic effects in these conditions are unclear. Toll-like receptors (TLRs) play an essential role in innate host defense and in the control of adaptive immune responses. IL-1R-associated kinase-M (IRAK-M) and single immunoglobulin IL-1R-related molecule (SIGIRR) negatively regulate TLR-signaling pathways. To investigate whether polymorphisms in these genes were associated with asthma or asthma-related phenotypes, we screened these genes for polymorphisms by direct sequencing of 24 asthmatics and identified 19 variants in IRAK-M and 12 variants in SIGIRR. We next conducted linkage disequilibrium mapping of the genes, and examined the association of polymorphisms and haplotypes using 391 child patients with asthma, 462 adult patients with asthma, and 639 controls. None of the alleles or haplotypes of IRAK-M and SIGIRR were associated with asthma susceptibility or asthma-related phenotype. Our results indicate that polymorphisms in IRAK-M and SIGIRR are not likely to be associated with the development of asthma in the Japanese population.

Regulation of Regulatory T Cells: Role of Dendritic Cells and Toll-Like Receptors

Regulatory T cells (Treg) are characterized by high-level surface CD25 and intracellular FoxP3 expression. Treg are instrumental in the maintenance of peripheral immune tolerance and the control of adaptive immune responses. Naturally occuring Treg suppress T-cell responses by cell contact-dependent mechanisms, whereas induced regulatory cells, including Tr1 cells, secrete inhibitory cytokines such as transforming growth factor (TGF)-beta and interleukin-10. The interplay between Treg and antigen-responsive T cells is modulated by dendritic cells (DC). Whereas immature myeloid precursors of DC suppress T-cell activation per se and immature DC support Treg development, mature DC can override Treg-mediated suppression in vitro and in vivo. Mature DC activated through Toll-like receptor (TLR) pattern recognition receptors produce proinflammatory cytokines, including interleukin-6, which render responder T cells refractory to the suppressive effect of Treg. In addition, Treg also express certain TLR, and the activation and/or suppressor function of Treg is modulated directly by the respective ligands. In this review, we discuss current models of how signals delivered through innate immune receptors in response to pathogen-associated molecular patterns affect adaptive immune responses via modulation of Treg function.

2B4 co-stimulation: NK cells and their control of adaptive immune responses

NK cells have primarily been defined by their ability to kill infected cells, tumor cells and some normal cells expressing low levels of MHC class I molecules. NK cells have also been shown to affect adaptive immune responses by their production of both pro- and anti-inflammatory cytokines. Recently it has been shown that adaptive immune responses can be enhanced or maintained also through direct lymphocyte–lymphocyte interactions. One of these interactions was identified to occur between 2B4 and CD48, where 2B4 acted as a co-stimulatory ligand for both NK cells and T cells. In the current article, we discuss the role of 2B4 in the development of adaptive immune responses and the role of NK-T cell interactions in these responses.

Inactivation of class II transactivator by DNA methylation and histone deacetylation associated with absence of HLA-DR induction by interferon-gamma in haematopoietic tumour cells.

By presenting immunogenic peptides at the cell surface, major histocompatibility complex (MHC) class II molecules play a key role in the control of adaptive immune responses. Whether expressed constitutively or induced by interferon-γ, expression of MHC class II molecules is regulated via coactivator class II transactivator (CIITA); moreover, suppression of their expression is one mechanism by which cancer cells escape host immunity. In this study, we surveyed the relationship between the expression of one MHC class II antigen, HLA–DR, and its coactivators in a group of haematopoietic cell lines, and explored the role of the aberrant DNA methylation in silencing HLA-DR expression. Among 26 cell lines studied, HLA-DR expression was lost from eight T-cell and two myeloid leukaemia cell lines, and this loss was closely associated with suppression of CIITA-PIV expression. Notably, nine of the 10 cell lines that lost CIITA-PIV expression showed methylation of the gene's 5′ CpG island. Thus, DNA methylation is believed to inhibit the expression of MHC class II molecules in haematopoietic tumour cells by silencing its coactivator, CIITA-PIV. Furthermore, methylation of CIITA-PIV was detected in seven of 32 primary acute myeloid leukaemia specimens, indicating that epigenetic alteration is not a cell line-specific phenomenon. Collectively, these data suggest that, by suppressing expression of MHC class II molecules, epigenetic inactivation of CIITA provides a survival advantage to a subset of haematopoietic tumours.