Mathematical Model of the Roles of T Cells in Inflammatory Bowel Disease

Gut mucosal homeostasis depends on complex interactions among the microbiota, the intestinal epithelium, and the gut associated immune system. A breakdown in some of these interactions may precipitate inflammation. Inflammatory bowel diseases, Crohn’s disease, and ulcerative colitis are chronic inflammatory disorders of the gastrointestinal tract. The initial stages of disease are marked by an abnormally high level of pro-inflammatory helper T cells, Th1. In later stages, Th2 helper cells may dominate while the Th1 response may dampen. The interaction among the T cells includes the regulatory T cells (Treg). The present paper develops a mathematical model by a system of differential equations with terms nonlocal in the space spanned by the concentrations of cytokines that represents the interaction among T cells through a cytokine signaling network. The model demonstrates how the abnormal levels of T cells observed in inflammatory bowel diseases can arise from abnormal regulation of Th1 and Th2 cells by Treg cells.     

Mathematical model of the primary CD8 T cell immune response: stability analysis of a nonlinear age-structured system

The primary CD8 T cell immune response, due to a first encounter with a pathogen, happens in two phases: an expansion phase, with a fast increase of T cell count, followed by a contraction phase. This contraction phase is followed by the generation of memory cells. These latter are specific of the antigen and will allow a faster and stronger response when encountering the antigen for the second time. We propose a nonlinear mathematical model describing the T CD8 immune response to a primary infection, based on three nonlinear ordinary differential equations and one nonlinear age-structured partial differential equation, describing the evolution of CD8 T cell count and pathogen amount. We discuss in particular the roles and relevance of feedback controls that regulate the response. First we reduce our system to a system with a nonlinear differential equation with a distributed delay. We study the existence of two steady states, and we analyze the asymptotic stability of these steady states. Second we study the system with a discrete delay, and analyze global asymptotic stability of steady states. Finally, we show some simulations that we can obtain from the model and confront them to experimental data.     

Peripheral CD8+ T cell proliferation is prognostic for patients with advanced thoracic malignancies

There is a complex interplay between the immune system and a developing tumor that is manifest in the way that the balance of T cell subsets in the local tumor environment reflects clinical outcome. Tumor infiltration by CD8⁺ T cells and regulatory T cells (Treg) is associated with improved and reduced survival, respectively, in many cancer types. However, little is known of the prognostic value of immunological parameters measured in peripheral blood. In this study, peripheral CD8⁺ T cells and Treg from 43 patients with malignant mesothelioma or advanced non-small-cell lung cancer scheduled to commence palliative chemotherapy were assessed by flow cytometry and evaluated for association with patient survival. Patients had a higher proportion of peripheral Treg, proliferating CD8⁺ T cells and CD8⁺ T cells with an activated effector phenotype compared with age-matched healthy controls. Higher proportions of Treg and proliferating CD8⁺ T cells were both associated with poor survival in univariate analyses (hazard ratio [HR] 3.81, 95 % CI 1.69–8.57; p < 0.01 and HR 2.86, 95 % CI 1.26–6.50; p < 0.05, respectively). CD8⁺ T cell proliferation was independently predictive of reduced survival in multivariate analysis (HR 2.58, 95 % CI 1.01–6.61; p < 0.05). These findings suggest that peripheral CD8⁺ T cell proliferation can be a useful prognostic marker in patients with thoracic malignancies planned for palliative chemotherapy.     

Pulse HIV Vaccination: Feasibility for Virus Eradication and Optimal Vaccination Schedule

We modify the classical virus dynamics model by incorporating an immune response with fixed or fluctuating vaccination frequencies and dosages to obtain a system of impulsive differential equations for the virus dynamics of both the wild-type and mutant strains. This model framework permits us to obtain precise conditions for the virus elimination, which are much more feasible compared with existing results, which require frequent vaccine administration with large dosage. We also consider the corresponding impulsive optimal control problem to describe when and how much of the vaccine should be administered in order to maximize levels of healthy CD4⁺ T cells and immune response cells. A gradient-based optimization method is applied to obtain the optimal schedule numerically. For a case study when the CTL vaccine is administered in a period of one year, our numerical studies support the optimal vaccination schedule consisting of vaccine administration three times, with the first dosage strong (to boost the immune system), followed by a second dosage shortly after (to strengthen the immune response) and then the third and final dosage long after (to ensure the immune system can handle viruses rebound).     

Regulatory T cells dynamically control the primary immune response to foreign antigen

The population dynamics that enable a small number of regulatory T (T(R)) cells to control the immune responses to foreign Ags by the much larger conventional T cell subset were investigated. During the primary immune response, the expansion and contraction of conventional and T(R) cells occurred in synchrony. Importantly, the relative accumulation of T(R) cells at peak response significantly exceeded that of conventional T cells, reflecting extensive cell division within the T(R) cell pool. Transfer of a polyclonal T(R) cell population before immunization antagonized both polyclonal and TCR transgenic responses, whereas blocking T(R) cell function enhanced those responses. These results define an inverse quantitative relationship between T(R) and conventional T cells that controls the magnitude of the primary immune response. The high frequency of dividing T(R) cells suggests degenerate TCR specificity enabling activation by a broad spectrum of Ags.     

Single-Molecule Light-Sheet Imaging of Suspended T Cells

Adaptive immune responses are initiated by triggering of the T cell receptor. Single-molecule imaging based on total internal reflection fluorescence microscopy at coverslip/basal cell interfaces is commonly used to study this process. These experiments have suggested, unexpectedly, that the diffusional behavior and organization of signaling proteins and receptors may be constrained before activation. However, it is unclear to what extent the molecular behavior and cell state is affected by the imaging conditions, i.e., by the presence of a supporting surface. In this study, we implemented single-molecule light-sheet microscopy, which enables single receptors to be directly visualized at any plane in a cell to study protein dynamics and organization in live, resting T cells. The light sheet enabled the acquisition of high-quality single-molecule fluorescence images that were comparable to those of total internal reflection fluorescence microscopy. By comparing the apical and basal surfaces of surface-contacting T cells using single-molecule light-sheet microscopy, we found that most coated-glass surfaces and supported lipid bilayers profoundly affected the diffusion of membrane proteins (T cell receptor and CD45) and that all the surfaces induced calcium influx to various degrees. Our results suggest that, when studying resting T cells, surfaces are best avoided, which we achieve here by suspending cells in agarose.     

microRNA在实体肿瘤免疫反应中的调节作用

免疫反应的作用逐渐成为调节各种复杂癌症的关键因素。免疫治疗也逐渐成为癌症肿瘤的有效干预方式。肿瘤微环境包含不同类型的免疫细胞,这有助于调节抗肿瘤信号中先天性和适应性免疫系统之间的细微平衡。在这种环境下,肿瘤细胞与免疫细胞之间相互关联的机制有待广泛阐明,但目前已被证明,多种microRNA在实体肿瘤相关免疫细胞的发育和功能中起调控作用,其通过肿瘤及免疫细胞介导免疫抑制或免疫刺激因子分泌增强或抑制免疫应答,靶向调控肿瘤发生的相关免疫途径,从而在癌症起始、转移进展的所有阶段中起关键作用,近而在肿瘤免疫治疗中寻找新的治疗靶点。本文针对microRNA在肿瘤免疫反应中的相关调节进行综述。     

Dynamic regulation of T cell immunity by CD43

During a viral response, Ag-specific effector T cells show dramatically increased binding by the mAb 1B11 and the lectin peanut agglutinin (PNA). We investigated the contribution of CD43 expression to 1B11 and PNA binding as well as its role in generation and maintenance of a CD8 T cell response. Analysis of CD43(-/-) mice revealed no increased 1B11 binding and reduced PNA binding on virus-specific CD8 T cells from -/- mice compared with +/+ mice. Furthermore, we examined the role of CD43 in the kinetics of an immune response. We show that CD43 expression modestly effects generation of a primary virus-specific CD8 T cell response in vivo but plays a more significant role in trafficking of CD8 T cells to tissues such as the brain. More interestingly, CD43 plays a role in the contraction of the immune response, with CD43(-/-) mice showing increased numbers of Ag-specific CD8 T cells following initial expansion. Following the peak of expansion, Ag-specific CD8 T cells from -/- mice show similar proliferation but demonstrate increased Bcl-2 levels and decreased apoptosis of Ag-specific effector CD8 T cells in vitro. Consistent with a delay in the down-modulation of the immune response, following chronic viral infection CD43(-/-) mice show increased morbidity. These data suggest a dynamic role of CD43 during an immune response: a positive regulatory role in costimulation and trafficking of T cells to the CNS and a negative regulatory role in the down-modulation of an immune response.     

Therapeutic induction of regulatory, cytotoxic CD8+ T cells in multiple sclerosis

In the setting of autoimmunity, one of the goals of successful therapeutic immune modulation is the induction of peripheral tolerance, a large part of which is mediated by regulatory/suppressor T cells. In this report, we demonstrate a novel immunomodulatory mechanism by an FDA-approved, exogenous peptide-based therapy that incites an HLA class I-restricted, cytotoxic suppressor CD8+ T cell response. We have shown previously that treatment of multiple sclerosis (MS) with glatiramer acetate (GA; Copaxone) induces differential up-regulation of GA-reactive CD8+ T cell responses. We now show that these GA-induced CD8+ T cells are regulatory/suppressor in nature. Untreated patients show overall deficit in CD8+ T cell-mediated suppression, compared with healthy subjects. GA therapy significantly enhances this suppressive ability, which is mediated by cell contact-dependent mechanisms. CD8+ T cells from GA-treated patients and healthy subjects, but not those from untreated patients with MS, exhibit potent, HLA class I-restricted, GA-specific cytotoxicity. We further show that these GA-induced cytotoxic CD8+ T cells can directly kill CD4+ T cells in a GA-specific manner. Killing is enhanced by preactivation of target CD4+ T cells and may depend on presentation of GA through HLA-E. Thus, we demonstrate that GA therapy induces a suppressor/cytotoxic CD8+ T cell response, which is capable of modulating in vivo immune responses during ongoing therapy. These studies not only explain several prior observations relating to the mechanism of this drug but also provide important insights into the natural immune interplay underlying this human immune-mediated disease.     

Quantitating effector and regulatory T lymphocytes in immune responses by limiting dilution analysis modeling

Although there is currently no doubt that regulatory lymphocytes represent a master player in the immune system, a major unresolved problem is the accurate quantitation of these cells among unfractionated cell populations. This difficulty mainly arises because there are no specific immunophenotypic markers that can reliably discriminate between effector and regulatory lymphocytes. To face this problem, we have developed computational models of limiting dilution analyses addressing the question of the accurate estimation of the frequencies of effector and regulatory cells functionally engaged in an immune response. A set of generic equations were provided to form a framework for modeling limiting dilution data, enabling discrimination between qualitatively different models of suppression. These models include either one or two subpopulations of regulatory cells, featured by either low or potent regulatory activity. The potential of this modeling approach was illustrated by the accurate determination of the frequencies of effector and regulatory T lymphocytes in one real limiting dilution experiment of CD4+ CD25+ T lymphocytes performed in the context of an allogeneic response in the human system. The crucial advantage of the limiting dilution method over the "static, phenotype-based" method is the dynamic evaluation of effector and regulatory T cell biology through their actual functional activity.     

Adaptation for Protein Synthesis Efficiency in a Naturally Occurring Self-Regulating Operon

The korAB operon in RK2 plasmids is a beautiful natural example of a negatively and cooperatively self-regulating operon. It has been particularly well characterized both experimentally and with mathematical models. We have carried out a detailed investigation of the role of the regulatory mechanism using a biologically grounded mechanistic multi-scale stochastic model that includes plasmid gene regulation and replication in the context of host growth and cell division. We use the model to compare four hypotheses for the action of the regulatory mechanism: increased robustness to extrinsic factors, decreased protein fluctuations, faster response-time of the operon and reduced host burden through improved efficiency of protein production. We find that the strongest impact of all elements of the regulatory architecture is on improving the efficiency of protein synthesis by reduction in the number of mRNA molecules needed to be produced, leading to a greater than ten-fold reduction in host energy required to express these plasmid proteins. A smaller but still significant role is seen for speeding response times, but this is not materially improved by the cooperativity. The self-regulating mechanisms have the least impact on protein fluctuations and robustness. While reduction of host burden is evident in a plasmid context, negative self-regulation is a widely seen motif for chromosomal genes. We propose that an important evolutionary driver for negatively self-regulated genes is to improve the efficiency of protein synthesis.     

T cell state transition produces an emergent change detector

We model the stages of a T cell response from initial activation to T cell expansion and contraction using a system of ordinary differential equations. Results of this modeling suggest that state transitions enable the T cell population to detect change and respond effectively to changes in antigen stimulation levels, rather than simply the presence or absence of antigen. A key component of the system that gives rise to this emergent change detector is initial activation of naïve T cells. The activation step creates a barrier that separates the long-term, slow dynamics of naïve T cells from the short-term, fast dynamics of effector T cells. This separation allows the T cell population to compare current, up-to-date changes in antigen levels to long-term, steady state levels. As a result, the T cell population responds very effectively to sudden shifts in antigen levels, even if the antigen were already present prior to the change. This feature provides a mechanism for T cells to react to rapidly expanding sources of antigen stimulation, such as viruses, while maintaining tolerance to constant or slowly fluctuating sources of stimulation, such as healthy tissue during growth.In addition to modeling T cell activation, we also formulate a model of the proliferation of effector T cells in response to the consumption of positive growth signal, secreted throughout the T cell response. We discuss how the interaction between T cells and growth signal generates an emergent threshold detector that responds preferentially to large changes in antigen stimulation while ignoring small ones. As a final step, we discuss how the de novo generation of adaptive regulatory T cells during the latter phase of the T cell response creates a negative feedback loop that controls the duration and magnitude of the T cell response. Hence, the immune network continually adjusts to a shifting baseline of (self and non-self) antigens, and responds primarily to abrupt changes in these antigens rather than merely their presence or absence.     

Oral CD3-specific antibody suppresses autoimmune encephalomyelitis by inducing CD4+ CD25- LAP+ T cells

A major goal of immunotherapy for autoimmune diseases and transplantation is induction of regulatory T cells that mediate immunologic tolerance. The mucosal immune system is unique, as tolerance is preferentially induced after exposure to antigen, and induction of regulatory T cells is a primary mechanism of oral tolerance. Parenteral administration of CD3-specific monoclonal antibody is an approved therapy for transplantation in humans and is effective in autoimmune diabetes. We found that orally administered CD3-specific antibody is biologically active in the gut and suppresses autoimmune encephalomyelitis both before induction of disease and at the height of disease. Orally administered CD3-specific antibody induces CD4+ CD25- LAP+ regulatory T cells that contain latency-associated peptide (LAP) on their surface and that function in vitro and in vivo through a TGF-beta-dependent mechanism. These findings identify a new immunologic approach that is widely applicable for the treatment of human autoimmune conditions.     

B lymphocyte regulation of the immune system. I. In vivo biologic activity of the novel lymphokine, B cell-derived enhancing factor (BEF)

B cell-derived enhancing factor (BEF) is a lymphokine of B cell origin which was originally identified and characterized by its ability to enhance in vitro antibody responses, an effect shown to be due to the ability of BEF to reduce the activation of suppressor T cells. The present study was undertaken to determine whether BEF could also be active in modulating antibody responses in vivo. The data presented here demonstrate that BEF is biologically active in vivo, as manifested by significantly enhanced primary IgM and IgG antibody responses in mice that were either injected with BEF prepared exogenously or implanted with growing BEF-secreting cells of a B cell line. Moreover, BEF was shown to enhance subsequent development of immunologic memory in mice pretreated with BEF at the time of primary immunization; these mice then displayed enhanced secondary responses when challenged with the same antigen some weeks later. The mechanism by which BEF exerts biologic activities to positively modulate in vivo antibody responses and immunologic memory reflects the ability of BEF to modulate one or more T cell functions, as evidenced by the following findings. 1) Transient in vitro exposure to BEF of T cells, but not of B cells, endowed such cells with the capacity to adoptively transfer enhanced primary antibody responses to irradiated recipients. 2) Utilizing adoptive in vivo antibody responses, in which fractionated B cell or T cell populations were obtained from BEF-pretreated mice, revealed that one effect of BEF which results in enhanced immunologic memory is related to its activity on T cells during the priming phase of the immune response. Finally, the existence of this B cell-derived lymphokine and the demonstration of its in vivo regulatory effects on the immune system provide yet another example of the emerging biologic importance of B lymphocytes in the overall regulation of the immune system.     

Dynamic demethylation of the IL2RA promoter during in vitro CD4+ T cell activation in association with IL2RA expression

IL2RA, a subunit of the high affinity receptor for interleukin-2 (IL2), plays a crucial role in immune homeostasis. Notably, IL2RA expression is induced in CD4+ T cells in response to various stimuli and is constitutive in regulatory T cells (Tregs). We selected for our study 18 CpGs located within cognate regulatory regions of the IL2RA locus and characterized their methylation in naive, regulatory, and memory CD4+ T cells. We found that 5/18 CpGs (notably CpG + 3502) show dynamic, active demethylation during the in vitro activation of naive CD4+ T cells. Demethylation of these CpGs correlates with appearance of IL2RA protein at the cell surface. We found no influence of cis located SNP alleles upon CpG methylation. Treg cells show constitutive demethylation at all studied CpGs. Methylation of 9/18 CpGs, including CpG +3502, decreases with age. Our data thus identify CpG +3502 and a few other CpGs at the IL2RA locus as coordinated epigenetic regulators of IL2RA expression in CD4+ T cells. This may contribute to unravel how the IL2RA locus can be involved in immune physiology and pathology.     

Oncogenes, anti-oncogenes and the immune response to cancer: a mathematical model.

We develop a mathematical model for the initial growth of a tumour after a mutation in which either an oncogene is expressed or an anti-oncogene (i.e. tumour suppressor gene) is lost. Our model incorporates mitotic control by several biochemicals, with quite different regulatory characteristics, and we consider mutations affecting the cellular response to these control mechanisms. Our mathematical representation of these mutations reflects the current understanding of the roles of oncogenes and anti-oncogenes in controlling cell proliferation. Numerical solutions of our model, for biologically relevant parameter values, show that the different types of mutations have quite different effects. Mutations affecting the cell response to chemical regulators, or resulting in autonomy from such regulators, cause an advancing wave of tumour cells and a receding wave of normal cells. By contrast, mutations affecting the production of a mitotic regulator cause a slow localized increase in the numbers of both normal and mutant cells. We extend our model to investigate the possible effects of an immune response to cancer by including a first order removal of mutant cells. When this removal rate exceeds a critical value, the immune system can suppress tumour growth; we derive an expression for this critical value as a function of the parameters characterizing the mutation. Our results suggest that the effectiveness of the immune response after an oncogenic mutation depends crucially on the way in which the mutation affects the biochemical control of cell division.     

Immune opsonins modulate BLyS/BAFF release in a receptor-specific fashion

TNF ligand superfamily member 13B (B lymphocyte stimulator (BLyS), B cell activating factor (BAFF)) promotes primary B cell proliferation and Ig production. While the soluble form of BLyS/BAFF is thought to be the primary biologically active form, little is known about the regulation of its cleavage and processing. We provide evidence that Fcgamma receptor cross-linking triggers a rapid release of soluble, biologically active BLyS/BAFF from myeloid cells. Surprisingly, this function is primarily mediated by FcgammaRI, but not FcgammaRIIa as defined by specific mAb, and can be initiated by both IgG and C reactive protein as ligands. The generation of a B cell proliferation and survival factor by both innate and adaptive immune opsonins through engagement of an Fcgamma receptor, which can also enhance Ag uptake and presentation, provides a unique opportunity to facilitate Ab production. These results provide a mechanism by which Fcgamma receptors can elevate circulating BLyS levels and promote autoantibody production in immune complex-mediated autoimmune diseases.     

Modeling regulation mechanisms in the immune system

We develop a mathematical framework for modeling regulatory mechanisms in the immune system. The model describes dynamics of key components of the immune network within two compartments: lymph node and tissue. We demonstrate using numerical simulations that our system can eliminate virus-infected cells, which are characterized by a tendency to increase without control (in absence of an immune response), while tolerating normal cells, which are characterized by a tendency to approach a stable equilibrium population. We experiment with different combinations of T cell reactivities that lead to effective systems and conclude that slightly self-reactive T cells can exist within the immune system and are controlled by regulatory cells. We observe that CD8+ T cell dynamics has two phases. In the first phase, CD8+ cells remain sequestered within the lymph node during a period of proliferation. In the second phase, the CD8+ population emigrates to the tissue and destroys its target population. We also conclude that a self-tolerant system must have a mechanism of central tolerance to ensure that self-reactive T cells are not too self-reactive. Furthermore, the effectiveness of a system depends on a balance between the reactivities of the effector and regulatory T cell populations, where the effectors are slightly more reactive than the regulatory cells.