of IL-4: From Studies in Mice to Therapy of Autoimmune Diseases in Humans
T.Biedermann, M.RoÈcken
13.1 IL-4: A Pro- or Anti-Inflammatory Cytokine? . . . . 235 13.2 Differential Role of IL-4 During the Initiation Versus
Established Immune Response . . . . 236 13.3 IL-4 in the Treatment of the Th1-Dominated Disease Psoriasis 238 13.4 Role of IL-4 in Dendritic Cell Maturation . . . . 238 13.5 Conclusion . . . . 240 References . . . . 240
13.1 IL-4: A Pro- or Anti-InflammatoryCytokine?
Interleukin (IL)-4 is largely known for its anti-inflammatory effects due to its capacity to suppress Th1 responses and protective immu- nity against intracellular pathogens. This was first demonstrated in 1990 in infections of mice with Leishmania major (Sadick et al.
1990). This report showed that early and complete neutralization of IL-4 for 6weeks with anti-IL-4 mAb redirects Th2 into Th1 immu- nity and provides protective immunity against L. major. This con- flicts with a 1989 study, where IL-4 transfection of tumor cells in- duced potent anti-tumor immunity (Tepper et al. 1989). Based on this first report with cytokine-transfected tumor cells, several clinical trials with IL-4 in humans were conducted in tumor patients but failed. The understanding of IL-4 was further complicated by data
showing that IL-4-producing Th2 cells directly mediate tissue de- struction and lead to autoimmune diseases if transferred to immuno- deficient hosts (Pakala et al. 1997; Lafaille et al. 1997). These data indicated that the anti-inflammatory role of IL-4 depends on several co-factors that influence the outcome of immune responses but re- mained to be identified.
13.2 Differential Role of IL-4 During the Initiation Versus Established Immune Response
In leishmaniasis, Th1 cells mediate delayed-type hypersensitivity re- actions (DTHRs), which provide protective immunity. In contrast, Th2 responses to L. major fail to establish protective DTHRs and consequently, Th2-dominated immune reactions to L. major provide only insufficient protection. In the case of leishmaniasis, Th2 cells lead to fatal disease courses. DTHRs are important for the integrity of the host organism in case of infection with intracellular patho- gens, but Th1 cells can also mediate harmful DTHRs that cause in- flammatory autoimmune diseases. In cases of such harmful DTHRs, antigen-specific deviation of Th1 immunity into Th2 immunity may be a new approach possibly devoid of the side effects associated with the current immunosuppressive treatment regimens. Whether it is possible to induce anti-inflammatory Th2 cells in order to protect against Th1-mediated, harmful autoimmune and inflammatory dis- eases was first tested in experimental allergic encephalomyelitis (EAE), an animal model for multiple sclerosis. The results showed that antigen-specific Th2 cells did not induce EAE and that a Th2- inducing regimen prevented the development of EAE (Racke et al.
1994; Nicholson et al. 1995; Falcone et al. 1998). These studies showed that deviation of a Th1 immune response by IL-4 into an IL-4-producing Th2 phenotype can attenuate DTHRs. Based on these and other studies in mice, Th-cell differentiation in patients suffering from organ-specific autoimmune diseases such as multiple sclerosis, inflammatory bowel diseases, rheumatoid arthritis, and psoriasis were analyzed. The data showed that all these diseases were associated with Th1 responses. For human diseases, treatment of ongoing inflammatory processes as opposed to prevention is
needed. Therefore, studies were designed to investigate the therapeu- tic potential of anti-inflammatory Th2 cells in established DTHRs.
Among the various model diseases for inflammatory autoimmune diseases, contact hypersensitivity responses of the skin (CHS) to exog- enous haptens in sensitized animals are of special interest. CHS and skin inflammation can be more rapidly and easily elicited, moni- tored, and correlated with functional ex vivo immune assays than or- gan-specific autoimmune diseases. Studies with such a CHS model al- lowed us to show that therapeutic interventions with IL-4 can even be effective in the therapy of established CHS (Biedermann et al. 2001a).
IL-4 therapy during ongoing CHS-reaction inhibited skin inflamma- tion and significantly reduced the ratio of IFN-c to IL-4 during sub- sequent CHS challenges. This therapeutic effect lasted for at least 8 weeks. Over the past 10 years, inhibition of Th1 cell-mediated de- velopment and DTHRs by IL-4 or Th2 cells was demonstrated in a variety of disease models. Thus, IL-4 and IL-4-producing Th2 cells are generally considered to be important antagonists of Th1-induced inflammatory immune responses (Racke et al. 1994; Ræcken et al.
1996; Liblau et al. 1995). Importantly, adoptive transfer of antigen- specific Th2 cells together with the respective antigen can also inhibit CHS. Yet this inhibition occurs not directly, but only after repeated antigen application (Biedermann et al. 2001a). This delayed therapeu- tic effect of IL-4-producing Th2 cells indicated that Th2 cells may in- terfere with Th1-mediated DTHRs not directly but indirectly by de- viating newly primed naÒve Th cells or even Th1 cells towards a Th2 phenotype. Whether and how Th2 cells can deviate the develop- ment of naÒve Th cells prone to become a Th1 phenotype toward a Th2 phenotype was investigated with T cells from transgenic mice, each expressing a different TCR. One TCR-transgenic Th cell was a Th2 cell line and the other TCR-transgenic Th cell was a naÒve Th cell population. Both were activated with a Th1-driving adjuvant (FA) and the respective peptides, in vivo. With the use of clonotypic antibodies, we were able to show that Th2 cells can co-localize with naÒve Th cells in one lymph node area. If, and only if, the Th2 cells were activated simultaneously and in the same lymph node as the naÒve Th cells, the Th2 cells determined the differentiation of the naÒve Th cells and deviated from a Th1 toward a Th2 phenotype, even in the pres- ence of the Th1-inducing adjuvant CFA (Schipf et al. 2003).
13.3 IL-4 in the Treatment of the Th1-Dominated Disease Psoriasis
Thus, data from animal models demonstrated that in vivo deviation of immune responses by IL-4 or IL-4-producing Th2 cells could be an effective and promising approach to treat inflammatory autoim- mune diseases in humans. To address this question, a dose-escalation study was set up to investigate the therapeutic effects of IL-4 in psoriasis, a Th1-associated inflammatory autoimmune disease of the skin and joints (Ghoreschi et al. 2003). Patients were trained for continuous IL-4 application 5 days a week over a 6-week period.
This regimen strongly reduced the clinical disease score in psoriasis patients at concentrations known to induce Th2-cell development in vitro. Analysis of skin biopsies revealed that this regimen reduced pro-inflammatory Th1-related cytokines such as IFN-c, IL-8, and IL- 19, a cytokine that is thought to promote keratinocyte proliferation.
This was not only due to Th lymphocyte deletion, as Th lympho- cytes were still detectable in psoriatic skin. These Th cells no longer expressed the Th1-marker chemokine receptor CCR5, and IL-4 be- came detectable in skin samples. Thus, IL-4 was capable of induc- ing IL-4 in humans, to inhibit the expression of prototypic pro-in- flammatory Th1 cytokines and to improve human inflammatory autoimmune disease.
13.4 Role of IL-4 in Dendritic Cell Maturation
Besides its capacity to induce in Th cells a Th2 phenotype and in B cells the IgE switch, other effects of IL-4 have been discovered in early experiments. The early report that IL-4 transfection of tumor cells established protective immunity lead to phase I and II trials testing IL-4 in cancer immunotherapy (Tepper et al. 1989). These trials failed. Yet experiments with either IL-4-transgenic or IL-4-de- ficient mice or neutralizing IL-4 antibodies suggested that, under certain conditions, IL-4 may paradoxically promote Th1 differentia- tion and DTHRs (Salerno et al. 1995; Erb et al. 1997; Noben-Trauth et al. 1996; Mencacci et al. 1998; Schuler et al. 1999; Bagley et al.
2000). For instance, genetically IL-4-deficient mice have defects in
developing severe EAE or Th1 responses when infected with certain strains of L. major or Candida albicans (C. albicans) (Noben-Trauth et al. 1996; Mencacci et al. 1998). Similarly, a critical role for IL-4 was demonstrated in the development of efficient Th1 responses against haptens (Salerno et al. 1995; Traidl et al. 1999), and auto-, allo- and even tumor-antigens (Tepper et al. 1989; Schuler et al.
1999; Bagley et al. 2000; Radu et al. 2000; Golumbek et al. 1991).
This phenomenon remained unexplained until recent research led to a better understanding of dendritic cell (DC) maturation. The de- scription of distinct DC phenotypes that induce either Th1 or Th2 cells led to the search for factors that were involved in the develop- ment of the Th1-inducing DC1 or the Th2-inducing DC2. A first hint came from in vitro studies showing that IL-4 influences DC dif- ferentiation into a DC1 phenotype that produces IL-12 (Hochrein et al. 2000; Kalinski et al. 2000; Ebner et al. 2001).
Based on these findings, the apparent paradox that IL-4 may on the one side induce DC1 and on the other side deviate Th-cell differ- entiation towards a Th2 phenotype could be analyzed in vivo. This was first done in the model of L. major infection, which represents the best-established model to study Th2 differentiation in vivo. Prior data had shown that the presence of IL-4 during the period of T-cell activation leads to Th2 differentiation and disease progression (Lau- nois et al. 2002; Himmelrich et al. 2000).
In order to investigate the role of IL-4 in DC1 development in vivo, IL-4 was given to Balb/c mice during the first 6h of infection, the period when DC became activated by Leishmania promastigotes (Biedermann et al. 2001b). This regimen of IL-4 application in- duced DC1 within 12 h, Th1 development, and established protec- tive immunity against L. major. Importantly, if IL-4 application was extended to the period of Th-cell activation, IL-4 again induced a Th2 phenotype and abrogated protective immunity against L. major.
This confirmed that IL-4 early during DC activation is effective in inducing a DC1 phenotype in the activated DC and induces protec- tive Th1 responses, whereas some cytokines drive Th cells towards a Th2 phenotype and abrogate protective immunity against L. major when given during T-cell activation.
13.5 Conclusion
Together the detailed analyses of the actions of IL-4 in various dis- ease and immunization protocols indicated that one single cytokine may exert opposing effects on the development of immune re- sponses. The biological effect of IL-4 depends on the primary target cell of this cytokine during an immune reaction, and factors such as the time of cytokine application and concentration during various phases of immune responses ultimately determine whether this cyto- kine has pro- or anti-inflammatory effects. Similar findings have been reported for other ªparadoxicalº cytokines, including IFN-c, IL-10, and IL-12. Therefore the biological significance of cytokines and especially their use in clinical trials requires a critical review of the underlying animal experiments, including factors such as time, dose, and frequency of application.
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