Stability of Th1 and Th2 populations

Using an in vitro model for the development of IFN-y-producIng(Th1) and IL-4-produclng (Th1) cells from CD4 T lymphocytesexpressing a transgenlc TCR, we show that IL-12 and IL-4 arethe most potent stimuli for the differentiation of naive T cellsto effector populations. When combinations of cytokines arepresent during T cell priming, the effect of IL-4 Is dominant.Furthermore, differentiated Th1 cells can be converted intoIL-4 producers by exposure to IL-4, but the Th2 phenotype Isnot reversible. The stability of Th2 populations may limit theability to regulate Th2-domlnant responses In pathologic situations.     

The Th1/Th2 paradigm

The Th1/Th2 paradigm provides a useful model for understanding the pathogenesis of several diseases, as well as for developing novel immunotherapeutic strategies. Here, Sergio Romagnani examines Th1/Th2 polarization in the context of associated pathophysiological conditions.     

Th1 and Th1-inducing cytokines in Salmonella infection

Thl and Thl-inducing cytokines and T cell responses were investigated in human salmonellosis. Serum IFN-gamma, IL-12 and IL-18 levels were increased significantly in patients with salmonellosis. The increase in serum IL-15 and IL-18 levels was more significant and prolonged in patients with the systemic form of salmonellosis than in those with the gastroenteric form. The serum IFN-gamma level was correlated significantly with IL-12 and IL18 levels, and the IL-15 level was correlated significantly with IL-18. Upon stimulation with Salmonella in vitro, mononuclear cells from salmonellosis patients produced significantly higher amounts of IFN-gamma and IL-12 compared with those from healthy controls. Anti-IL-12 moAb or anti-IL18 MoAb significantly inhibited Salmonella-induced IFN-gamma production in vitro. gamma delta T cells expressed significantly higher levels of IFN-gamma mRNA in salmonellosis patients than in healthy controls. The results suggest that Th1-inducing cytokines appear to be involved in the in vivo response against Salmonella infection, promoting IFN-gamma production by alpha beta and gamma delta T cells which plays a protective role against Salmonella.     

Development of Neonatal Th1/Th2 Function

Newborn animals generally mount poor T cell-mediated immune responses in vivo. As a result, neonates fall prey to infectious agents and diseases which have little impact on immunocompetent adult animals. For some time, it was believed that this phenomenon was due to an intrinsic inability of newborns to mount developmentally mature Th1 responses. Recent studies in mice have challenged that view; under certain conditions, adult-level Th1 function has been achieved in newborns. More often, however, neonates develop Th2-dominant responses. A major challenge in the field of developmental immunology is to understand why the ‘default’ response for neonates is Th2 function. Cell intrinsic as well as environmental influences may contribute to Th2 skewing in neonates.     

The paradigm of Th1 and Th2 cytokines

In the past few years, considerable evidence has accumulated to suggest the existence of functionally polarized responses by the CD4⁺ T helper (Th)—and the CD8⁺ T cytotoxic (Tc)—cell subsets that depend on the cytokines they produce. The Th1 and Th2 cellular immune response provide a useful model for explaining not only the different types of protection, but also the pathogenic mechanisms of several immunopathological disorders. The factors responsible for the polarization of specific immune response into a predominant Th1 or Th2 profile have been extensively investigated in mice and humans. Evidence has accumulated from animal models to suggest that Th1type lymphokines are involved in the genesis of organ-specific autoimmune diseases, such as experimental autoimmune uveitis, experimental allergic encephalomyelitis, or insulin-dependent diabetes mellitus. Accordingly, data so far available in human diseases favor a prevalent Th1 lymphokine profile in target organs of patients with organ-specific autoimmunity. By contrast, Th2-cell predominance was found in the skin of patients with chronic graft-versus host disease, progressive systemic sclerosis, systemic lupus erythematosus, and allergic diseases. The Th1/Th2 concept suggests that modulation of relative contribution of Th1 or Th2-type cytokines regulate the balance between protection and immunopathology, as well as the development and/or the severity of some immunologie disorders. In this review, we have discussed the paradigm of Th1 and Th2 cytokines in relation to autoimmunity and allergy.     

Development of neonatal Th1/Th2 function

Newborn animals generally mount poor T cell-mediated immune responses in vivo. As a result, neonates fall prey to infectious agents and diseases which have little impact on immunocompetent adult animals. For some time, it was believed that this phenomenon was due to an intrinsic inability of newborns to mount developmentally mature Th1 responses. Recent studies in mice have challenged that view; under certain conditions, adult-level Th1 function has been achieved in newborns. More often, however, neonates develop Th2-dominant responses. A major challenge in the field of developmental immunology is to understand why the 'default' response for neonates is Th2 function. Cell intrinsic as well as environmental influences may contribute to Th2 skewing in neonates.     

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.     

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.     

Revisiting the Th1/Th2 Paradigm

The identification of subsets of CD4⁺ helper cells producing distinct pattern of cytokines has provided a valuable framework for understanding how different effector populations of immune cells can be recruited in vivo during infection. In the view of most investigators, Th1 and Th2 cells produce factors that serve as their own autocrine factors and cytokines exerting suppressive activities on each other's development and activity. This concept intuitively explains the natural tendency of immune responses to become progressively polarized. However, several experimental observations appear difficult to rationalize with a simple, 'symmetrical' Th1/Th2 paradigm including those that Th1 cells do not produce their own growth factor; that both Th1 and Th2 cells can promote inflammatory responses; that interleukin-10 (IL-10) inhibits inflammatory responses in a Th1/Th2-independent fashion; that IL-10 promotes the development of Th1-type effector cells; and that IL-12 can amplify pre-established Th2 responses. The purpose of the present analysis is to provide a revised model for better understanding how cytokines regulate immune responses in vivo .     

Distribution of Th1, Th2, and Th0 and the Th1/Th2 cell ratios in human peripheral and endometrial T cells

PROBLEM: To examine whether normal pregnancy involves type 2 T-helper (Th2) immune condition or not. METHOD OF STUDY: We measured the percentage of Th0, Th1, and Th2 and the Th1/Th2 cell ratios of human peripheral blood and endometrial T cells using flow cytometry, which can analyze both the surface marker CD3, and intracellular cytokines, interleukin 4 (IL-4) and interferon gamma (IFNgamma). RESULTS: No significant differences were found in the percentages of Th1, Th2, and Th0 and the Th1/Th2 cell ratios in the peripheral blood T cells of nonpregnant women and women in early pregnancy. On the other hand, the percentage of Th1 cells was highest during the proliferative phase of the endometrium, followed by the secretory phase and early pregnancy decidua. The percentage of Th2 cells was highest in early pregnancy decidua and lowest during the proliferative phase of the endometrium. The Th1/Th2 ratio was 147.48+/-96.68 during the proliferative phase of the endometrium, 37.74+/-21.33 during the secretory phase, and 1.31+/-0.48 in the early pregnancy decidua. CONCLUSIONS: These data indicate that Th1 cells predominate in the nonpregnant endometrium, especially during the proliferative phase, while Th2 cells predominate in early pregnancy decidua.     

Toll样受体与Th1和Th2型免疫应答

Toll样受体是广泛表达在哺乳动物细胞表面的跨膜信号传导受体,其通过识别多种类型的病原体相关分子模式及一些内源性配体,激活天然免疫系统,同时通过诱导树突状细胞分化成熟,调控获得性免疫反应的建立。大多数TLRs的配体可诱导机体产生Th1型免疫应答,然而在某些条件下也可导致Th2型免疫应答的发生。弄清TLRs参与调节Th0分化的机制,可为今后在感染免疫、自身免疫、超敏反应等方面进行深入研究及相关疾病的治疗提供新的切入点。     

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.     

Th1 and Th2 lymphocytes in autoimmune disease

This review reconsiders how the Th1/Th2 paradigm can be applied to Th1-mediated autoimmune disease. Although there is evidence that autoimmune diseases such as multiple sclerosis, type 1 insulin-dependent diabetes mellitus, and posterior uveitis are Th1 mediated and that in some cases reduction of the Th1 response or a Th2 type shift may alleviate disease, many apparent exceptions are now well documented. These exceptions center around the contradictory actions of the Th1 cytokine IFN-gamma and the evidence that Th2 lymphocytes can also cause disease. Recent information on the regulation of Th1 and Th2 lymphocytes in terms of the innate immune response and by other T cells helps to clarify the reasons for some of these discrepancies and enables the Th1/Th2 concept to be accepted as an integral part of the complex interactions occurring as autoimmune disease develops.     

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.     

Quantitative analysis of peripheral blood Th0, Th1, Th2 and the Th1:Th2 cell ratio during normal human pregnancy and preeclampsia.

We calculated the percentage of Th1, Th2, Th0 cells and the Th1:Th2 cell ratio of peripheral blood from normal pregnant subjects and preeclampsia patients using flow cytometry which can analyse both the surface marker, CD4, and intracellular cytokines, interleukin (IL)-4 and interferon (IFN)-gamma. In normal pregnancy, the percentage of Th1 cells was significantly lower in the third trimester, and the ratios of Th1:Th2 were significantly lower in the second and third trimester than in nonpregnant subjects. In contrast, the percentage of Th1 cells and the ratios of Th1:Th2 in preeclampsia were significantly higher than in normal third trimester pregnant subjects. The percentage of Th2 cells in preeclampsia was significantly lower than in third trimester of normal pregnancy. Additionally, peripheral blood mononuclear cells from these subjects and patients were cultured with phytohemagglutinin stimulation, and IL-4 and IFN-gamma concentrations were determined in the supernatant by enzymed linked immunosorbent assays. The percentage of Th1 and Th2, and the ratios of Th1:Th2 were correlated with cytokine (IFN-gamma and IL-4) secretion level. These results demonstrated that Th2 cells were predominant in the second and third trimesters of normal pregnancy, but Th1 cells predominated in preeclamptic patients.