Th1/Th2 balance in infection

Cytokines produced by T helper (Th) cells are of critical importance for the outcome of many infectious diseases. Producing the “right” set of Cyokines in response to an infectious agent can be a matter of life or death. The Th1/Th2 dichotomy, although an oversimplification has proven useful in the analysis of immune responses to infections. In some infectious diseases, most notably leishmaniasis or infections with gastrointestinal helminths, one Th subset is indispensable for clearing the infection, whereas the opposite Th subset is detrimental. More frequently, both Th1 and Th2 responses are required at different time points to effectively eradicate an infectious agent. The granuloma responses to eitherMycobacterium tuberculosis orSchistosoma mansoni provide illustrative examples and are discussed in this review. There is accumulating evidence for frequent coexpression of Th1 and Th2 Cyokines during the in vivo immune response to infections. The mechanisms by which infectious agents modulate Th1/Th2 phenotype development are summarized here. Finally, we review here the current evidence for cytokine imbalances induced by infections as pathogenic or protective factors in autoimmunity and allergy.     

The Th1/Th2 balance in autoimmunity

The study of autoimmune disease in the context of T-helper type 1 (Th1) and T-helper type 2 (Th2) CD4⁺ T-cell responses demonstrates that the relative contribution of either T-cell type to the development of a particular autoimmune response can influence whether or not this response leads to clinical disease. Moreover, this influence can be quite different depending on whether the particular disease process is cell mediated or antibody mediated. Recent studies have demonstrated that the development of Th1 and Th2 responses may be significantly influenced by the costimulatory molecules recognized by responding CD4 T cells, and by other undefined factors in the genetic background. It has also been demonstrated that autoreactive Th2 CD4⁺ cells can regulate the activity of disease-causing Th1 CD4⁺ T cells in vivo. Control of autoimmune disease may thus be achieved by procedures that regulate the relative contribution of Th1/Th2 CD4 T cells to an autoimmune response.     

Cryptococcal infection and Th1-Th2 cytokine balance

Cytokines have been recognized as key factors in determining host resistance to infectious pathogens. In particular, Th1-Th2 cytokine balance in hosts is profoundly associated with the outcome of infection caused by intracellular microbes. In a murine model of pulmonary and disseminated infection with Cryptococcus neoformans, an opportunistic fungal pathogen that frequently leads to fatal meningoencephalitis in severely immunocompromised hosts, expression of cytokine mRNA in the lungs from infected animals revealed Th2-dominant profiles, while administration of IL-12, which rescued mice from fatal infection, converted such balance toward Th1-dominant states in a drastic fashion. Thus, commitment of Th phenotypes critically determines host sensitivity to cryptococcal infection. In this review, we described how Th1-Th2 cytokine balance influences host protective responses to C. neoformans, and we identify the host and pathogen factors that regulate such balance.     

Modulating the Th1/Th2 balance in inflammatory arthritis

The balance between Th1 and Th2 cells regulates the choice between inflammatory and antibody-mediated immune responses. To an increasing extent this balance is thought to involve the participation of antigen-presenting cells, rather than the entirely autonomous activity of T cells and their cytokines. Here we survey current opinion concerning the working of this balance, and its condition in rheumatoid arthritis and the other inflammatory arthritides. The contrast between Lyme arthritis and reactive arthritis is particularly illuminating, since one is triggered by extracellular and the other by intracellular infection. We describe current approaches to the modulation of this balance. Guided by the principles that genetic polymorphism is likely to identify relevant genes, that any cytokine gene picked up by a virus must matter and that natural immunosuppressive activity at mucosal surfaces should be worth exploiting, we identify as particularly worthy of attention: (i) IL-10, (ii) inhibitors of IL-12 production, (iii) inhibitors of CD40 ligand expression and (iv) oral and nasal tolerance. Other protective T cell subsets are touched on, and the impact of oligonucleotide arrays mentioned.     

Critical role of dendritic cells in determining the Th1/Th2 balance upon Leishmania major infection

The onset of T_h1 immunity is in part regulated by genetic background.To elucidate the cell type carrying critical factors determiningthe T_h1 response, we employed Rag-2^–/– mice on Leishmaniamajor-susceptible BALB/c and -resistant B10.D2 backgrounds.By using bone marrow (BM) chimeras generated by the transplantationof B10.D2 BM cells into BALB/c-Rag-2^–/– mice, andvice versa, it was shown that hematopoietic cells carry factorsdetermining the disease outcome and T_h1 response against L.major infection. B10.D2-Rag-2^–/– mice reconstitutedwith BALB/c CD4⁺ T cells exhibited a T_h1 response and controlledL. major infection. Wild-type BALB/c mice inoculated with L.major-parasitized B10.D2-Rag-2^–/– splenocytes alsoexhibited a T_h1 response and a mild disease outcome, whereassuch a T_h1 response was not induced when CD11c⁺ dendritic cells(DCs) were depleted from parasitized B10.D2-Rag-2^–/–splenocytes. T_h1 response was reconstituted by the additionof L. major-parasitized B10.D2 DCs but not L. major-parasitizedBALB/c DCs to DC-depleted parasitized B10.D2-Rag-2^–/–splenocytes. These results indicate that DCs determine the outcomeof the disease upon L. major infection.     

Th1/Th2 lymphocyte balance in patients with aplastic anemia

Activated T cell plays an important role in the pathogenesis of aplastic anemia (AA). CD4+ T cells are divided into Th1 cells producing hematopoietic inhibitory cytokines like interferon-gamma and Th2 cells producing interleukin-4. We investigated the Th1/Th2 cell ratio in the peripheral blood of AA patients treated with immunosuppressive therapy (IST). There were 10 patients who responded well to IST (responders) and 3 patients who were refractory to IST (non-responders). Th1 cells were lower in responders than in non-responders (16.2+/-2.4% vs. 28.8+/-5.5%, respectively, p<0.05), whereas Th2 cells did not differ. The Th1/Th2 ratio was also significantly lower in responders than in non-responders, being 13.2+/-1.5 and 40.4+/-5.1 (p<0.001), respectively. In three responders, the Th1/Th2 ratio was declined according to the hematological recovery (from 10.6 to 8.3, 16.3 to 10.9 and 11.8 to 9.5). Our results suggest that Th1 lymphocytes are more predominant in AA, and it may be very useful to monitor the Th1/Th2 ratio during IST.     

Natural and induced regulation of Th1/Th2 balance

Summary Because Th1/Th2 balance is perturbed during immunological disease, the design of strategies aiming at its rectification has become a priority. The alteration of the balance in pregnancy so as to promote survival of the fetal allograft lends credibility to this aim. Attenuation of the activation signal delivered through the T cell receptor (TCR) represents a promising approach. It is supported by the high level of polymorphism in the MHC class II promoter, which regulates the natural TCR signal and thus modulates Th1/Th2 differentiation. Further support comes from the Th2 shift that occurs in JNK knockout mice, and with kinase inhibitors and anti-CD4 monoclonal antibodies applied in vitro. The approach has implications for nasal tolerance and inhibition of IL-12 production. The further range of options for Th1/Th2 modulation, which are presented throughout this issue of the journal, are here summarised and evaluated.     

Manipulation of the Th1/Th2 balance in autoimmune disease

Many autoimmune diseases are caused by autopathogenic Th1 cells. Because in vitro Th1 and Th2 cells cross-regulate each other, it is likely that the induction of self-antigen-specific Th2 cells can prevent autoimmune disease. In the past year, investigators have further defined the role of Th1 and Th2 cytokines in the induction and regulation of autoimmunity. Furthermore, the role of MHC—antigen—T-cell avidity (strength of signal) in inducing such protective immune responses has been elucidated.     

Th1/Th2 balance of SLE patients with lupus nephritis

Systemic lupus erythematosus (SLE) is a prototypic systemic autoimmune disease that is characterized by the production of multiple autoantibodies and immune complex formation. Lupus nephritis, which has various histological patterns and variable clinical outcomes, is one of the most important complications of SLE. Although this pathogenetic mechanism in each histologically different type of nephritis remains unclear, recent findings in murine lupus elucidate an essential role for the Th1 cytokine in the development of diffuse lupus nephritis (DLN), and Th2 cytokine in that of membranous lupus nephritis (MLN). These data support the hypothesis that individual Th1/Th2 balance is one of the critical determinants for histopathology of lupus nephritis. Therefore the value of Th1/Th2 ratio of the peripheral CD4+ T cells in SLE patients could be a useful index to predict histopathology of lupus nephritis.     

Dietary nucleic acids promote a shift in Th1/Th2 balance toward Th1-dominant immunity

BACKGROUND: Dietary sources of nucleic acids and their relative components are known to affect host immune function; however, it has not yet been clarified whether such dietary nucleic acids influence the pathogenesis of allergic reaction. OBJECTIVE: The purpose of this study is to elucidate the effect of dietary nucleic acids on Th1/Th2 balance. METHODS: Both human flora-associated and specific pathogen-free BALB/c mice were maintained on either nucleic acid-free, or -supplemented diets. The effects of nucleic acids on both in vivo antibody levels and in vitro splenocyte cytokine production were compared using these mice. RESULTS: Supplementation of nucleic acids caused a reduction in the serum antibody levels of total IgM, IgG, IgG1, and IgE in the human flora-associated mice without affecting the composition of intestinal flora. In contrast, there was no significant difference of the serum IgG2a levels between nucleic acid-free and -supplemented mice. Such a phenomenon as that, the supplementation of dietary nucleic acids reduces the serum IgE or IgG1 levels, but not the IgG2a level, was also seen in the specific pathogen free mice. Moreover, when the mice were systematically challenged with ovalbumin, the supplementation of nucleic acids also suppressed the serum ovalbumin-specific IgE and IgG1 antibody levels as well as in vitro IL-4 and IL-10 secretion, while enhancing both the serum ovalbumin-specific IgG2a antibody levels and in vitro IFN gamma secretion. CONCLUSION: These results suggested that dietary nucleic acids may play an important role in promoting a shift in Th1/Th2 balance toward Th1-dominant immunity.     

乳杆菌对原代淋巴细胞中Th1/Th2细胞平衡的影响

目的:分析7种乳杆菌对原代淋巴细胞增殖和细胞因子(CK)分泌的作用,进而探讨其对Th1/Th2细胞平衡的影响。方法:用不同种属、不同浓度的活的/热致死的乳杆菌体外作用于小鼠脾淋巴细胞培养60 h后,采用MTT比色法检测淋巴细胞的增殖效果。用ELISA法检测Th1型细胞因子(IL-12、IFN-γ)、Th2型细胞因子(IL-4、IL-10)和调节型细胞因子(TGF-β)的分泌量。结果:活的/热致死的乳杆菌单独作用,就能促进淋巴细胞体外增殖并表现出剂量依赖关系(P<0.05)。当菌的浓度为107集落形成单位(CFU)/mL(即细菌与细胞的比例为10∶1)时,热致死的发酵乳杆菌和嗜酸乳杆菌的免疫活性近似于活菌。而且,这两株热致死菌还可适当提高淋巴细胞分泌IL-12和IFN-γ,抑制IL-4、IL-10和TGF-β的分泌,使其IFN-γ/IL-4的比值(代表Th1/Th2细胞平衡)均显著高于刀豆蛋白A(ConA)对照组(P<0.05)。结论:乳杆菌可通过提高淋巴细胞的IFN-γ/IL-4分泌率来促进Th1优势状态的Th1/Th2细胞平衡,并具有菌株特异性。     

Th1/Th2、Tc1/Tc2亚群在乙肝肝硬化患者中的作用

目的 :探讨乙肝肝硬化患者外周血 (PBMC)中CD4 和CD8 T细胞内Th1和Th2类细胞的平衡状态 ,探明Th1、Th2类细胞在乙肝肝硬化中的作用。方法 :乙肝肝硬化患者CD4 T细胞和CD8 T细胞中IFN γ 和IL 4 细胞的百分率 ,观察乙肝肝硬化患者Th1 Th2、Tc1 Tc2比例的变化。结果 :乙肝肝硬化患者PBMC中CD4 ,CD8细胞 ,CD4 CD8比值与健康对照者相比无统计学差异 (P >0 0 5 ) ,Th1细胞及Tc1细胞百分率为 8 8% ,9 0 % ,较健康对照者 7 5 % ,7 7%升高 (P <0 0 5 )。结论 :乙肝肝硬化患者外周血T细胞亚群发生Th1类偏移 ,在乙肝肝硬化的发生和发展中可能起重要作用     

细粒棘球蚴感染对哮喘大鼠血清白介素-17水平及Th1/Th2平衡的影响

目的建立细粒棘球蚴感染并发过敏性哮喘实验动物模型及探讨细粒棘球蚴感染对过敏性哮喘的作用。方法 24只健康Wistar大鼠,随机分为3组,A组为正常对照组,B组为单纯哮喘组,C组为细粒棘球蚴感染并发哮喘组。C组大鼠经腹腔注射感染细粒棘球蚴,70 d后,以卵白蛋白(OVA)分别对B组、C组大鼠进行致敏及激发,建立过敏性哮喘模型。取大鼠肺组织作病理切片,观察大鼠肺组织的炎症变化,采用酶联免疫吸附试验(ELISA)检测大鼠血清白介素-17(IL-17)、白介素-4(IL-4)及干扰素-γ(IFN-γ)的水平。结果与B组比较,C组大鼠血清IL-17和IL-4的水平明显下降(P<0.05),而血清IFN-γ的水平明显上升(P<0.05)。各组大鼠血清IL-4与IFN-γ水平呈密切负相关(r=-0.915),IL-4和IFN-γ水平与IL-17呈负相关关系(r=-0.406,-0.603),P<0.05。结论细粒棘球蚴感染对过敏性哮喘的发生有抑制作用。     

自身免疫病的Th1/Th2细胞因子平衡治疗

在很多自身免疫性疾病中存在着细胞因子不平衡的现象，导致机体细胞免疫或体液免疫的失调。Ｔｈ１／Ｔｈ２分别介导细胞免疫和体液免疫，可以代表机体复杂的细胞因子网络，从整个评估机体免疫功能。