Schistosoma mansoni in IL-4-deficient mice

The Schistosoma mansoni egg-derived r38 peptide-induced Th1 response affects the synchronous pulmonary but not the asynchronous hepatic granuloma growth

The p38 peptide derived from Schistosoma mansoni egg-antigens (SEA) is a preferential inducer of the Th1 response. In the present study, we investigated whether induction of a p38-specific Th1 or Th2 response can influence granuloma development in infected or sensitized mice. Mice sensitized with SEA/IL-12 3 weeks after infection but before worm oviposition commenced developed Th1 cytokine responses and had significantly reduced hepatic granuloma size. Similar immunization with p38/IL-12 induced a strong peptide-specific Th1, mixed SEA-specific Th1/Th2 responses without effect on hepatic granuloma development. Presentation of p38 with alum or alum/IL-12 mixture enhanced Th2 cytokine responses and hepatic granuloma sizes. In the synchronized pulmonary model, sensitization of naïve mice with p38/IL-12 induced a strong Th1 cytokine production to p38 and SEA, led to a moderate increase in granuloma growth at days 4 and 8 following egg injection and actually promoted the resolution of the lesion by day 16. Sensitization with p38 in alum induced Th2 cytokine production and generated the largest granulomas whereas the p38/alum/IL-12 sensitized group showed intermediate results in cytokine production and granuloma growth. Thus, in infected mice, the p38 induced strong Th1 response was insufficient to cross-regulate the evolving Th2 environment that generated large granulomas.

Mechanisms of resistance to S. mansoni infection: the rat model

Human schistosomiasis is associated with IgE and eosinophilia, feature of a type 2 response. In experimental investigations, murine model has been widely used in order to dissect the immune responses involved in the expression of protective immunity or disease in Schistosoma mansoni infection. Collectively, observations made in this model and in humans demonstrated a strong contrast since a Th2 response in infected mice is involved in the expression of pathology, however, in infected humans the same type of response is rather beneficial for the host. This review will consider the relevance of extrapolating studies of immune responses from experimentally infected rats a semi-permissive host, to studies on S. mansoni infected humans.

Immunopathology of intestinal helminth infection

The relationship between intestinal pathology and immune expulsion of gastrointestinal nematodes remains controversial. Parasite expulsion is associated with intestinal pathology in several model systems and both of these phenomena are T cell dependent. However, while immune expulsion of gastrointestinal helminth parasites is usually associated with Th2 responses, the effector mechanisms directly responsible for parasite loss have not been elucidated. In contrast, the intestinal pathology observed in many other disease models closely resembles that seen in helminth infections, but has been attributed to Th1 cytokines. We have used infection with the nematode Trichinella spiralis in mice defective for cytokines to demonstrate that although parasite expulsion is indeed IL-4 dependent, contrary to expectations, the enteropathy is also regulated by IL-4. Furthermore, abrogation of severe pathology in iNOS deficient and TNF receptor defective animals does not prevent parasite expulsion. TNF and iNOS are therefore involved in intestinal pathology in nematode infections, apparently under regulation by IL-4 and Th2 mediated responses. Therefore, it appears that the IL-4-dependent protective response against the parasite operates by a mechanism other than merely the gross degradation of the parasite's environment brought about by the immune enteropathy. However, it remains important to elucidate the protective mechanisms involved in parasite expulsion, which are still unclear.

Regulation of T helper type 2 cell immunity by interleukin-4 and interleukin-13

Type 2 cytokine responses are typical of immune reactions to parasitic helminth infections, allergies, and asthma, and are characterised by the production of the cytokines interleukin (IL)-4, IL-5, IL-9, and IL-13 by subsets of T helper type 2 (Th2) cells. These cytokines form a complex network of molecular and cellular interactions that mediate protective immunity to worm infection, but also induce inappropriate inflammatory responses to allergic challenge. Although considerable attention has been given to the roles played by IL-4 in Th2 responses, the identification of the related cytokine IL-13 has led to a re-evaluation of how these two molecules combine in the generation of Th2 immunity. Recent reports have highlighted that in certain challenges, IL-4 and IL-13 act in combination to ensure the rapid onset of a Th2-like response. However, these studies have also identified specific responses that are attributable to the individual cytokines. For example, IL-13 appears to play a more dominant role than IL-4 in the expulsion of certain gastrointestinal parasites. In contrast, following schistosome infection, IL-13 induces a detrimental hepatic fibrosis, while IL-4 protects against endotoxemia. These results emphasise the complexity of the cytokine network, and highlight the care that needs to be taken when designing therapeutic intervention.

Interleukin-4 (IL-4) and IL-13 signaling pathways do not regulate Borrelia burgdorferi-induced arthritis in mice: IgG1 is not required for host control of tissue spirochetes

Previous studies have suggested that interleukin-4 (IL-4) has a protective effect in host defense to Borrelia burgdorferi infection, both in limiting the severity of arthritis and in controlling spirochete numbers in tissues, and a mapping study revealed suggestive linkage to a cluster of genes on mouse chromosome 11, including the genes for IL-4 and IL-13. In contrast, other studies have questioned the importance of IL-4. In this study the involvement of IL-4 in murine Lyme disease was examined in C57BL/6J and BALB/cJ mice with targeted disruptions in the IL-4 gene, the IL-4Ralpha chain gene, or both. A spectrum of arthritis severity was seen in BALB/cJ mice, and ablation of IL-4, IL-4Ralpha, or both had no effect on the overall severity of arthritis as determined by joint swelling and histopathology. Wild-type C57BL/6J mice exhibited mild to moderate arthritis, and ablation of IL-4 again had no effect on arthritis severity. IL-4- and IL-4Ralpha-deficient mice produced extremely low levels of immunoglobulin G1 (IgG1) and showed increased production of IgG2b. This shift in immunoglobulin isotype had no effect on the host's ability to control spirochete growth in either strain of mouse, as determined by PCR detection of B. burgdorferi DNA from heart and ankle tissues. In summary, the IL-4-IL-4Ralpha pathway, including IL-13 signaling, neither limits arthritis severity nor is required for control of spirochete growth during B. burgdorferi infection of mice. Furthermore, the IgG1 isotype is not required to control B. burgdorferi cell numbers in tissues. These findings suggest the host defense against B. burgdorferi infection is not dependent on the Th1-Th2 paradigm of T-cell responses.

The role of interleukin-13 in infectious diseases and allergy

Cytokines, also referred to as interleukins, are the major orchestrators of host defence processes, and, as such, are involved in insults, repair and restoration of tissue homeostasis. This review summarises recent findings on and emerging models of the biological roles of the double-edged sword interleukin-13 (IL-13), which have been principally obtained from studies in mice that are deficient for IL-13, or its components. IL-13-mediated functions not only contribute to the susceptible phenotype in Leishmania major infection but also seem to play a protective role in chronic leishmaniasis. Moreover, IL-13 plays a key protective role in the expulsion of helminths from the gut while also actively contributing to the pathology in schistosomiasis. In allergic asthma, IL-13 has also been found to be a key factor. Therapeutic administration of an IL-13 inhibitor in mice successfully prevents both the allergic disease phenotype and schistosoma egg-induced lung pathology. If this scenario holds true in humans, we soon may have an efficient drug for treatment of IL-13-mediated diseases.

IL-10 and the dangers of immune polarization: excessive type 1 and type 2 cytokine responses induce distinct forms of lethal immunopathology in murine schistosomiasis

To dissect the controversial roles of type 1 and type 2 cytokines to the pathogenesis of schistosomiasis, we generated IL-10/IL-4- and IL-10/IL-12-deficient mice that develop highly polarized type 1 and type 2 cytokine responses, respectively. Interestingly, the Th1-polarized IL-10/IL-4-deficient mice rapidly lost weight at the onset of egg-laying and displayed 100% mortality by wk 9 postinfection. This acute mortality was linked to overexpression of the proinflammatory mediators IFN-gamma, TNF-alpha, and inducible NO and the formation of nonfibrotic granulomas. Elevated serum aspartate transaminase levels confirmed that mortality was in part attributable to acute hepatotoxicity. In contrast, the Th2-polarized IL-10/IL-12-deficient mice developed a progressive wasting disease that correlated with increased hepatic fibrosis, formation of large eosinophil-rich granulomas, a 10-fold increase in IL-4 and IL-13, and significant mortality during the chronic stages of infection. Surprisingly, IL-10-deficient mice displayed pathological features that were characteristic of both extremes, while wild-type mice developed relatively successful long term chronic infections. These data demonstrate that IL-10 significantly suppresses type 1 and type 2 cytokine development in IL-4- and IL-12-deficient mice, respectively, thereby impeding the development of severe egg-induced pathology in the single cytokine-deficient animals. Together, these findings reveal the central regulatory role of IL-10 in the pathogenesis of schistosomiasis and illustrate that excessive type 1 and type 2 cytokine responses trigger distinct, but equally detrimental, forms of pathology following infection.

Interleukin 4 and 13 participation in mycobacterial (type-1) and schistosomal (type-2) antigen-elicited pulmonary granuloma formation: multiparameter analysis of cellular recruitment, chemokine expression and cytokine networks

The contribution of IL-4 and IL-13 to inflammation and cytokine responses was compared in mice with types-1 or -2 pulmonary granulomas (GR) elicited by beads bound to antigens of Mycobacteria bovis (PPD) or Schistosoma mansoni eggs (SEA). Type-2 SEA-GR produced the most IL-4 and IL-13. Type-1 PPD-GR produced detectable IL-13, but not IL-4. Mice were treated with anti-IL4 or anti-IL-13 Abs, then lesion size/composition, cytokine/chemokine mRNA and lymph node cytokines were measured. Type-1 GRs resisted individual Abs, but combined Abs augmented lesions by 20%. In contrast, anti-IL-4 abrogated type-2 GR by 30-40% and eosinophil recruitment by 60%. Anti-IL-13 abrogated type-2 GR by 20-30% with no effect on eosinophils. Combined depletion reduced lesion area by 60% and eosinophils by more than 80%. In type-1 GR lungs, anti-IL-4 and anti-IL-13 augmented IFNgamma and TNFalpha mRNA. In type 2 lungs, anti-IL-13 did likewise, but anti-IL-4 decreased TNFalpha without affecting IFNgamma mRNA. In both responses, IL-4 promoted MCP-1 and MCP-5 mRNA, but IL-13 inhibited chemokines in type-1 GR. In lymph nodes, anti-IL-4, but not anti-IL-13, abrogated type-2 cytokines. In fact, IL-13 down-regulated itself and other type-2 cytokines. In summary, IL-4 and IL-13 have common and disparate regulatory functions in types 1 and 2 responses.

Single cell analysis reveals that IL-4 receptor/Stat6 signaling is not required for the in vivo or in vitro development of CD4+ lymphocytes with a Th2 cytokine profile

The concept that IL-4 is the primary signal for Th2 lymphocyte differentiation has recently been put in doubt by studies in which the production of Th2-associated cytokines was detected in mice deficient in IL-4 synthesis or IL-4R triggering. In this study, we formally demonstrate by single cell analysis that CD4+ lymphocytes with a classical Th2 phenotype (IL-4+, IL-5+, IFN-gamma-, IL-2-) develop in significant numbers in helminth-infected mice deficient in either IL-4R alpha-chain or Stat6. While an expanded population of Th1 (IL-4-, IL-5-, IFN-gamma+, IL-2+) lymphocytes was observed in the same animals, surprisingly, cells with a mixed Th0 cytokine pattern were rare. The cytokine production phenotypes of the Th1 and Th2 subpopulations generated in infected Stat6-deficient mice were unaffected by in vitro neutralization of endogenous IL-4 or IFN-gamma. Nevertheless, while addition of exogenous rIL-12 resulted in transitory IFN-gamma production by Th2 lymphocytes from both wild-type and Stat6-deficient mice, IL-4 synthesis was preserved in the former, but temporarily ablated in the latter cells. Importantly, IL-4+ IFN-gamma- and IL-4- IFN-gamma+ populations similar to those arising in helminth-infected Stat6-deficient mice could also be generated in vitro by repetitive polyclonal stimulation of CD4+CD62Lhigh lymphocytes from uninfected mice of the same strain. Together, the results of these single cell analysis experiments demonstrate that IL-4R/Stat6 signaling, while influencing the final frequency of Th2 lymphocytes, is not essential for Th2 cell development, and suggest that this pathway has a previously unrecognized function in stabilizing Th2 populations once they have emerged.

Schistosome infection of transgenic mice defines distinct and contrasting pathogenic roles for IL-4 and IL-13: IL-13 is a profibrotic agent

Experimental Schistosoma mansoni infections of mice lead to a dynamic type 2 cytokine-mediated pathological process. We have used IL-4-deficient, IL-13-deficient, and IL-4/13-deficient mice to dissect the role of these cytokines in the development of immune response and pathology following S. mansoni infection. We demonstrate that while both of these cytokines are necessary to develop a robust Th2 cell-driven, eosinophil-rich granuloma response, they also perform disparate functions that identify novel sites for therapeutic intervention. IL-13-deficient mice demonstrated significantly enhanced survival following infection, which correlated with reduced hepatic fibrosis. In contrast, increased mortality was manifest in IL-4-deficient and IL-4/13-deficient mice, and this correlated with hepatocyte damage and intestinal pathology. Therefore, we demonstrate that during a dynamic type 2 cytokine disease process IL-13 is detrimental to survival following infection, whereas IL-4 is beneficial.

IFN-gamma is necessary but not sufficient for anti-CD40 antibody-mediated inhibition of the Th2 response to Schistosoma mansoni eggs

The injection of Schistosoma mansoni eggs into the footpads of mice results in a localized Th2 cytokine response and tissue eosinophilia. We examined whether treatment with CD40-activating Abs would block the development of Th2 cytokine responses and eosinophilic tissue pathology in this model. Seven days after C57BL/6 mice were injected with eggs and the FGK45 anti-CD40 Ab, Ag-specific synthesis of IL-4, IL-5, and IL-13 in lymph node culture was reduced (>10-fold) relative to control mice treated with eggs and rat IgG. In contrast, IFN-gamma and IL-12 were increased in both culture supernatants and in the serum. Similar changes in lymph node cytokine mRNA were observed in vivo, and tissue eosinophilia was reduced nearly 20-fold. Th2 cytokine responses in anti-CD40-treated IFN-gamma-/- and IL-12 p40-/- C57BL/6 mice were unaffected, although anti-CD40 induced high levels of systemic and local IFN-gamma production in both wild-type and IL-12 p40-/- mice. We conclude that CD40-activating treatments strongly reverse the immune phenotype generated in response to a classic, Th2-biasing stimulus and stimulate IFN-gamma through a novel IL-12-independent pathway. This model for Th1-deviating immune therapy may have relevance to the treatment of Th2-dependent diseases in general.

Aluminium Hydroxide Adjuvant Initiates Strong Antigen-Specific Th2 Responses in the Absence of IL-4- or IL-13-Mediated Signaling

Previous studies demonstrate that aluminium hydroxide adjuvant (alum) produces increased Th1 responses in IL-4-deficient mice compared with wild-type animals, although the continued production of IL-5 by spleen cells from these mice also indicates that Th2 responses are induced. In the present study, we demonstrate that alum can induce Th2-associated IL-4 and IL-5 production in the absence of IL-4 signaling in mice deficient in either IL-4Rα or Stat6. The Th2 responses observed could not be due to IL-13 as IL-13 responses are also impaired in IL-4Rα- and Stat6-deficient mice. We also detected higher levels of IL-4 in IL-4Rα gene-deficient, though not Stat6-deficient, mice compared with their wild-type counterparts. The increased levels of IL-4 could be explained by the IL-4R being unavailable to neutralize this cytokine in IL-4Rα-deficient mice. While levels of IL-5 production in IL-4Rα- or Stat6-deficient mice were similar to IL-4-deficient and wild-type mice, other type 2-associated responses, which are largely or wholly IL-4 dependent, such as the production of IgG1 or IgE Abs, were either reduced or absent. We conclude that alum adjuvants can induce IL-4 production and Th2 responses independently of IL-4 or IL-13, negating the requirement for an early source of IL-4 in the Th2 response induced by this adjuvant.

Interleukin-4 receptor in moderate atopic asthma. A phase I/II randomized, placebo-controlled trial

Interleukin-4 mediates important proinflammatory functions in asthma, including induction of the IgE isotype switch, expression of VCAM-1 on endothelium, mucin production, 15-lipoxygenase activity, and Th2 lymphocyte stimulation leading to the secondary synthesis of IL-4, IL-5, and IL-13. Soluble recombinant human IL-4 receptor (IL-4R; Nuvance; altrakincept) inactivates naturally occurring IL-4 without mediating cellular activation. Nebulized IL-4R has a serum half-life of approximately 1 wk. In this double-blind, placebo-controlled trial, 25 patients with moderate asthma requiring inhaled corticosteroids were randomly assigned to receive a single nebulized dose of IL-4R 1,500 microg, IL-4R 500 microg, or placebo after stopping inhaled corticosteroids. No drug-related toxicity was observed. Treatment with IL-4R produced significant improvement in FEV(1) on Day 4 (1,500 microg versus placebo; p < 0.05) and in FEF(25-75) on Days 2 and 4 (1,500 microg versus placebo; p < 0.05). Asthma symptom scores stabilized among patients treated with IL-4R 1, 500 microg, despite abrupt withdrawal of corticosteroids, but not in the IL-4R 500 microg group or the placebo group (p < 0.05). Patients in the IL-4R 1,500 microg group also required significantly less beta(2)-agonist rescue use (p < 0.05). Anti-inflammatory effects were further demonstrated by significantly reduced exhaled nitric oxide (p < 0.05).

CONCLUSIONS

A single dose of IL-4R appears safe and effective in moderate asthma. The 1,500 microg dose appears as safe but significantly more effective than the 500 microg dose.

Interleukin-12 modulates T-cell responses to microfilariae but fails to abrogate interleukin-5-dependent immunity in a mouse model of onchocerciasis

Infection of mice with microfilariae of Onchocerca lienalis induces high levels of protective immunity to reinfection, which is dependent on interleukin (IL)-5 but not IL-4. Here, we have investigated the effect of exogenous IL-12 administration during either the priming or effector phases of the immune response. When administered during priming, IL-12 induced down-regulation of parasite-specific serum immunoglobulin (Ig)E and up-regulation of IgG2a. Antigen-specific IL-4 responses were strongly suppressed, whilst blood eosinophil levels were partially reduced. When administered during a challenge infection, IL-12 did not significantly influence the balance of antibody isotypes, but partially reduced eosinophil production. Antigen-specific IL-4 responses were again completely ablated. Unusually, interferon-gamma (IFN-gamma) responses were not significantly affected following IL-12 administration, either during priming or after challenge infections. Moreover, despite a fall in antigen-specific IL-5 production, the expression of IL-5-dependent immunity, as determined by reduction in worm recoveries, was fully maintained. These data demonstrate that parasite-induced IL-4 can be abrogated without affecting protective immunity to Onchocerca microfilariae in mice. In view of the established role of IL-4 in pathogenesis, this may have important implications for the development of immunoprophylaxis aimed at microfilariae and the alleviation of pathology in onchocerciasis.

An IL-13 inhibitor blocks the development of hepatic fibrosis during a T-helper type 2-dominated inflammatory response

In schistosomiasis, chronic parasite egg-induced granuloma formation can lead to tissue destruction and fibrosis, which causes much of the morbidity and mortality associated with this disease. Here we show the importance of IL-13 in the pathogenesis of schistosomiasis, and demonstrate, perhaps for the first time, the therapeutic efficacy of an IL-13 inhibitor, sIL-13Ralpha2-Fc, in the control of hepatic fibrosis. T-helper type 2 (Th2) cytokines dominate the immune response in mice infected with Schistosoma mansoni, yet the specific contributions of IL-13 and IL-4 to the development of fibrosis were not previously investigated. Our studies demonstrate that both cytokines play redundant roles in granuloma formation, which explains the ability of IL-4-deficient mice to form granulomas around eggs. More importantly, however, these studies demonstrate that IL-13 is the dominant Th2-type cytokine regulating fibrosis. IL-13 stimulated collagen production in fibroblasts, and procollagen I and procollagen III mRNA expression was decreased in sIL-13Ralpha2-Fc-treated mice. Moreover, the reduction in fibrosis observed in IL-4-deficient mice was much less pronounced than that in sIL-13Ralpha2-Fc-treated animals. Fibrosis is a major pathological manifestation of a number of allergic, autoimmune, and infectious diseases. Thus, our findings provide evidence that IL-13 inhibitors may be of general therapeutic benefit in preventing damaging tissue fibrosis resulting from Th2-dominated inflammatory responses.

Polarization of the immune response to the single immunodominant epitope of p38, a major Schistosoma mansoni egg antigen, generates Th1- or Th2-type cytokines and granulomas

In schistosomiasis mansoni, helminth eggs secrete soluble egg antigens (SEA) that induce T-cell-mediated granulomatous tissue responses. The cloned 38-kDa peptide (p38) of SEA was shown to induce and elicit Th1-type responsiveness in H-2(k) mice. Subsequently, the immunodominant T-cell epitope (P4) of p38 was shown to elicit pulmonary granuloma formation and Th1-type cytokine production in sensitized or infected mice. Here, we report that the immune response to p38 or P4 can be polarized to a Th1 or Th2 profile when the peptides are presented intraperitoneally in soluble recombinant interleukin-12 (IL-12) or alum adjuvant, respectively. The Th1 or Th2 profile was verified by cytokine secretion, enzyme-linked spot assay, and antibody isotype characterization. Importantly, the polarized immune response generated two types of pulmonary granulomas around injected P4-coated beads. The type 1 granulomas were smaller and contained mononuclear cells and occasional thin strands of deposited collagen. In contrast, the type 2 lesions were larger and contained mononuclear cells, large numbers of eosinophils, and several thick bands of deposited collagen. By reverse transcription-PCR cytokine, message in the type 1 granuloma-bearing lungs was found for gamma interferon, tumor necrosis factor alpha, and inducible nitric oxide synthase but not for IL-4 or IL-5. Conversely, lungs with type 2 granulomas had message only for IL-4 and IL-5. These results show that in the proper cytokine environment, the response to a strong Th1 inducer peptide can be deviated to a Th2 profile.

A Model for CD8+ CTL Tumor Immunosurveillance and Regulation of Tumor Escape by CD4 T Cells Through an Effect on Quality of CTL

Understanding immune mechanisms influencing cancer regression, recurrence, and metastasis may be critical to developing effective immunotherapy. Using a tumor expressing HIV gp160 as a model viral tumor Ag, we found a growth-regression-recurrence pattern, and used this to investigate mechanisms of immunosurveillance. Regression was dependent on CD8 T cells, and recurrent tumors were resistant to CTL, had substantially reduced expression of epitope mRNA, but retained the gp160 gene, MHC, and processing apparatus. Increasing CTL numbers by advance priming with vaccinia virus expressing gp160 prevented only the initial tumor growth but not the later appearance of escape variants. Unexpectedly, CD4 cell depletion protected mice from tumor recurrence, whereas IL-4 knockout mice, deficient in Th2 cells, did not show this protection, and IFN-γ knockout mice were more susceptible. Purified CD8 T cells from CD4-depleted mice following tumor regression had more IFN-γ mRNA and lysed tumor cells without stimulation ex vivo, in contrast to CD4-intact mice. Thus, the quality as well as quantity of CD8+ CTL determines the completeness of immunosurveillance and is controlled by CD4 T cells but not solely Th2 cytokines. This model of immunosurveillance may indicate ways to enhance the efficacy of surveillance and improve immunotherapy.

Schistosome-Infected IL-4 Receptor Knockout (KO) Mice, in Contrast to IL-4 KO Mice, Fail to Develop Granulomatous Pathology While Maintaining the Same Lymphokine Expression Profile

Th2 lymphocytes have been postulated to play a major role in the immunopathology induced by Schistosoma mansoni infection. Nevertheless, infected IL-4 knockout (KO) and wild-type (wt) mice develop egg granulomas comparable in size. To further investigate the function of the Th2 response in egg pathology we studied IL-4Rα-deficient mice, which are nonresponsive to both IL-4 and IL-13. In striking contrast to IL-4 KO animals, infected IL-4Rα KO mice developed only minimal hepatic granulomas and fibrosis despite the presence of CD3+ T cells in the residual egg lesions. Moreover, liver lymphokine mRNA levels in these animals and IL-4 KO mice were equivalent. In addition, infected IL-4Rα-deficient, IL-4-deficient, and wt animals developed similar egg Ag-specific IgG Ab titers, arguing that CD4-dependent Th activity is intact in KO mice. As expected, IFN-γ secretion was strongly up-regulated in mesenteric lymph node cultures from both groups of deficient animals, a change reflected in increased serum IgG2a and IgG2b Ab levels. Surprisingly, Th2 cytokine production in infected IL-4Rα KO mice was not abolished but was only reduced and resembled that previously documented in IL-4 KO animals. This residual Th2 response is likely to explain the ability of IL-4 KO mice to generate egg granulomas, which cannot be formed in IL-4Rα-deficient animals because of their lack of responsiveness to the same cytokine ligands. Taken together, these findings argue that tissue pathology in schistosomiasis requires, in addition to egg-specific CD4+ lymphocytes, a previously unrecognized IL-4Rα+ non-T cell effector population.

Simultaneous disruption of interleukin (IL)-4 and IL-13 defines individual roles in T helper cell type 2-mediated responses

Using a single vector targeting strategy, we have generated mice with a combined deficiency of interleukin (IL)-4 and IL-13 to clarify their roles in T helper type 2 (Th2) cell responses. Using immunological challenges normally characterized by a Th2-like response, we have compared the responses of the double-deficient mice with those generated by wild-type, IL-4-deficient, and IL-13-deficient mice. Using a pulmonary granuloma model, induced with Schistosoma mansoni eggs, we demonstrate that although eosinophil infiltration, immunoglobulin E, and IL-5 production are reduced in the IL-4-deficient mice and IL-13-deficient mice, they are abolished only in the combined absence of both cytokines. Furthermore, IL-4/13-deficient animals are severely impaired in their ability to expel the gastrointestinal nematode Nippostrongylus brasiliensis. Unexpectedly, N. brasiliensis-infected IL-4/13-deficient mice developed elevated IL-5 and eosinophilia, indicating that compensatory mechanisms exist for the expression of IL-5, although serum IgE remained undetectable. IL-4/13-deficient mice default to a Th1-like phenotype characterized by the expression of interferon gamma and the production of IgG2a and IgG2b. We conclude that IL-4 and IL-13 cooperate to initiate rapid Th2 cell-driven responses, and that although their functions overlap, they perform additive roles.

IL-4- and IL-4 Receptor-Deficient BALB/c Mice Reveal Differences in Susceptibility to Leishmania major Parasite Substrains

Using genetically pure BALB/c mice deficient in IL-4 (IL-4−/−) or IL-4 receptor α-chain (IL-4Rα−/−), we have observed different disease outcomes to Leishmania major infection depending on the parasite substrain. Infection with L. major LV39 caused progressive, nonhealing ulcers and uncontrolled parasite growth in both IL-4−/− and IL-4Rα−/− mice. In contrast, infection with L. major IR173 was partially controlled in IL-4−/− mice but efficiently controlled in IL-4Rα−/− mice. Both IL-4−/− and IL-4Rα−/− mice infected with either substrain displayed reduced Th2 responses. Surprisingly, IFN-γ secretion was not up-regulated in the mutant mice, even in the IL-4Rα−/− mice, which were resistant to L. major IR173. The lack of increased IFN-γ production suggests that cytokine cross-regulation may not be operating in this model and that the effective ratios of Th1/Th2 cytokines become more indicative of disease outcome. The partial vs complete resistance to IR173 in IL-4−/− or IL-4Rα−/− mice implies that, in addition to IL-4, IL-13 may be involved in disease progression during L. major infection. The results with LV39 infection indicate that yet another unidentified factor is capable of causing susceptibility to L. major in the absence of IL-4 or IL-4 signaling.

Tolerization of Mice to Schistosoma mansoni Egg Antigens Causes Elevated Type 1 and Diminished Type 2 Cytokine Responses and Increased Mortality in Acute Infection

The granuloma that surrounds the Schistosoma mansoni egg is the cause of pathology in murine schistosomiasis, and its formation is driven by egg Ag-stimulated type 1 and type 2 cytokines. To determine the role of egg-driven immune responses during schistosome infection we rendered CBA/Ca mice unresponsive to schistosome eggs by combined cyclophosphamide treatment and thymectomy. In the early acute stages of schistosome infection, egg-tolerized mice suffered high mortalities. Granuloma size and deposition of collagen in the liver were significantly reduced in egg-tolerized mice. Similarly, limited granuloma responses were detected in the intestines of these mice, and this was associated with a &gt;90% reduction in egg excretion. Histologically, egg-tolerized mice had exacerbated hepatocyte damage, with extensive microvesicular steatosis. Elevated plasma transaminase levels confirmed the damage to hepatocytes. Infected egg-tolerized mice had impaired proliferation responses to egg Ag but intact responses to worm Ag. Tolerized mice had diminished Ab responses to egg Ag and had a type 1 cytokine isotype pattern to worm Ag, with elevated IgG2a and diminished IgG1 and IgE. Egg-tolerized mice failed to down-regulate type 1 cytokines that are normally elicited during early schistosome infection. Hepatic granuloma cells from egg-tolerized mice were also type 1 cytokine dominated, with elevated frequencies of Tc1/Th1 and reduced Tc2/Th2 cells. This study demonstrates that mice tolerized to schistosome eggs have elevated type 1 cytokine responses with diminished type 2 responses and reduced anti-egg Ab during schistosome infection, and these effects are detrimental to the host.

Role of cytokines in the formation and downregulation of hepatic circumoval granulomas and hepatic fibrosis in Schistosoma mansoni-infected mice

Schistosoma mansoni infections are associated with a strong Th2 cytokine response. Treatment of mice with IL-12 or anti-IL-2 or anti-IL-4 before i.v. injection of eggs increased IFN-gamma production and downregulated Th2 responses and pulmonary granuloma size. Conversely, anti-IFN-gamma antibody treatment increased Th2 responses and granuloma size. Similar manipulation produced less dramatic results in infected mice. However, sensitization of mice with eggs + IL-12 before infection augmented the Th1 response and decreased Th2 cytokines, granuloma size and fibrosis. Antisera to IFN-gamma, TNF-alpha or IL-12 during IL-12-egg immunization partly restored granuloma size and fibrosis following infection. Variations in the size of granulomas in acute (8 week) infections may be influenced primarily by the number and state of activation of T cells. In chronic (12-16 week) infections immunologic downmodulation proceeded normally in mice without functional CD8+ cells and in IFN-gamma KO mice but not in B cell KO (microMT) mice or in mice deficient in FcR expression in spite of the fact that these mice downregulated their T cell and cytokine responses. It is evident that the participation of cytokines in granuloma formation and regulation is complicated and that the mechanisms controlling both these phenomena are likely to involve both T cells and antibody/FcR interactions.

IL-13 Is a Key Regulatory Cytokine for Th2 Cell-Mediated Pulmonary Granuloma Formation and IgE Responses Induced by Schistosoma mansoni Eggs

Schistosoma mansoni egg-induced pulmonary granuloma formation is a cell-mediated inflammatory response associated with dominant Th2-type cytokine expression, tissue eosinophilia, and high levels of serum IgE. In the present study, we show that in vivo blockade of the Th2 cytokine IL-13, using soluble IL-13R α2-Fc fusion protein, significantly reduced the size of pulmonary granulomas in unsensitized as well as egg-sensitized mice. Blocking IL-13 also significantly reduced total serum IgE levels. Interestingly, however, IL-13 blockade did not affect the evolving egg-induced Th2-type cytokine response. IL-4, IL-5, as well as IL-13 responses were indistinguishable in control-Fc- and soluble IL-13R α2-Fc fusion protein-treated animals. The smaller granulomas were also phenotypically like the control Fc-treated mice, displaying a similar eosinophil content. Additional studies in IL-4-deficient mice demonstrated that IL-13 was produced, but at much lower levels than in wild-type mice, while IL-4 expression was completely independent of IL-13. Moreover, while granuloma formation was partially reduced in IL-4-deficient mice, blocking IL-13 in these animals almost completely abrogated granuloma development and the pulmonary eosinophilia, while it simultaneously increased IFN-γ production. Together, these data demonstrate that IL-13 serves as an important mediator of Th2-mediated inflammation and plays a role in eliciting IgE responses triggered by schistosome eggs.

IFN-γ, IL-12, and TNF-α Are Required to Maintain Reduced Liver Pathology in Mice Vaccinated with Schistosoma mansoni Eggs and IL-12

The development of hepatic fibrosis and portal hypertension is the principal cause of morbidity and mortality in schistosomiasis mansoni. Nevertheless, relatively little is known about the mechanisms that lead to excessive collagen deposition during infection with Schistosoma mansoni. In the murine model, infection leads to significant egg-induced granuloma formation, tissue eosinophilia, and hepatic fibrosis. The pathology has been linked to dominant type 2 cytokine expression, and our recent studies showed that sensitizing animals to egg Ags in combination with IL-12, before infection, led to a highly significant reduction in egg-induced immunopathology. In this study, we demonstrate that in contrast with egg/IL-12-sensitized animals that showed marked decreases in pathology, mice similarly sensitized but depleted of IFN-γ, IL-12, or TNF-α at the time of egg laying developed granulomas that were similar to the non-IL-12-treated control group. Although all three anti-cytokine-treated groups exhibited a dominant type 1 response in lymph node cells restimulated ex vivo, the expression of type 2 cytokine mRNA was markedly restored at the site of granuloma formation, which suggests that all three cytokines are required to maintain the suppressed type 2 pattern. Moreover, egg/IL-12-sensitized mice depleted of IFN-γ or IL-12 displayed a partial reduction in IFN-γ production, suggesting that multiple type 1 cytokines were required to maintain polarized type 1 responses to chronic type 2-inducing stimuli. Together, these data reveal key roles for IFN-γ, IL-12, and TNF-α in the protective effects mediated by this IL-12-based vaccine to prevent pathology.

Cytokine Interaction and Immune Responses during Schistosoma mansoni Infection

Of the estimated 200 million people infected with Schistosoma, a subset develop severe life-threatening disease. Adult Schistosoma mansoni are refractory to the immune response and are long-lived, causing chronic exposure to parasite antigen. Although the adult worms themselves are not antigenically inert, it is the parasite eggs that, by accumulating in the liver and traversing the intestinal wall, place a complex series of often-conflicting demands on the host's immune system. In this article, Laura Rosa Brunet, David Dunne and Edward Pearce discuss data from experimental studies in the mouse and field studies in endemic areas that combine to suggest that it is a failure to juggle this immunological conflict that results in severe disease.

IL-4-regulated enteropathy in an intestinal nematode infection

The relationship between intestinal pathology and immune expulsion of gastrointestinal nematodes remains controversial. Parasite expulsion is associated with intestinal pathology in several model systems and both of these phenomena are T cell dependent. Immune expulsion of gastrointestinal helminth parasites is usually associated with Th2 responses, but the effector mechanisms directly responsible for parasite loss have not been elucidated. In contrast, the intestinal pathology observed in many other disease models closely resembles that seen in helminth infections, but has been attributed to Th1 cytokines. We have used infection with the nematode Trichinella spiralis in mice defective for cytokines or their receptors to investigate cytokine regulation of both immunopathology and parasite rejection. Consistent with previous findings, we found that parasite expulsion is IL-4 dependent. Contrary to expectations, however, the enteropathy is not regulated by IFN-gamma but by IL-4. Moreover, abrogation of severe pathology in TNF receptor-defective animals does not prevent parasite expulsion. TNF is therefore involved in intestinal pathology in nematode infections, apparently under regulation by IL-4- and Th2-mediated responses. This work therefore not only reveals a novel interplay between IL-4 and TNF, but also that the IL-4-dependent protective response against the parasite operates by a mechanism other than merely the gross degradation of the parasite's environment brought about by the immune enteropathy.

Mice deficient for 5-lipoxygenase, but not leukocyte-type 12-lipoxygenase, display altered immune responses during infection with Schistosoma mansoni

Periovular granuloma formation during Schistosoma mansoni infection is a complex, multifaceted immunologic response. Products of arachidonic acid metabolism have been shown to contribute to this response through studies in which general inhibitors of lipoxygenase function reduce granulomatous inflammation. To determine which lipoxygenases are important for granuloma development in schistosomiasis, wild type mice or mice deficient for 5-lipoxygenase (5-LO) or "leukocyte-type" 12-lipoxygenase (12-LO) were infected with S. mansoni and studied for responses to schistosome eggs and egg antigens. At the acute stage of infection, when granuloma formation is usually maximal, 5-LO deficient mice developed smaller granulomas around liver-deposited schistosome eggs compared with wild type or 12-LO deficient mice. 5-LO mice also displayed less antibody-mediated (5 h) and cell-mediated, delayed-type (24 h) hypersensitivity to schistosome egg antigens than did the other two infection groups. In an attempt to determine possible mechanisms for the reduced inflammatory responses, we also measured hepatic mRNA levels of cytokines that have been shown to influence granuloma size (IL-4, IL-10, and IFN-gamma). The mRNA levels for IL-10 were significantly lower in 5-LO-deficient mice, but SEA-stimulated spleen cells did not demonstrate a significant difference in IL-10 production between wild type and 5-LO mice. These data suggest that 5-LO plays a role in host responses to schistosomiasis via a mechanism that cannot be explained solely by changes in expression of these cytokines.

IL-5-Dependent Immunity to Microfilariae Is Independent of IL-4 in a Mouse Model of Onchocerciasis

Th2 lymphocyte responses under the control of IL-4 and IL-5 are frequently associated with protective responses to parasitic helminths. Studies on the role of these cytokines in acquired resistance to parasitic nematodes indicate that, in the case of gastrointestinal nematodes, immunity is mediated by IL-4, while immunity to tissue-dwelling nematodes is dependent on IL-5. Here we investigate the role of IL-5 and eosinophils in protective immunity to Onchocerca microfilariae in IL-4-deficient mice. In the absence of IL-4, and despite the up-regulation of Th1-type responses, immunity remains dependent on IL-5 and eosinophils. Protection was unaffected by the absence of Ab in B cell-deficient mice, confirming that IL-5 is not acting via either B cell differentiation, Ag presentation, or isotype switching mechanisms. These data demonstrate the dissociation of IL-4 and IL-5 in a functional model of protective immunity to a tissue dwelling nematode and cast doubt on the role of IL-4 in the generation of CD4+ T cell-mediated, IL-5-dependent immunity to Onchocerca microfilariae. Importantly, they also segregate T cell-mediated mechanisms of protective immunity from those characterized in ocular pathologic responses in onchocerciasis, which are dependent on IL-4.

Differences between IL-4R alpha-deficient and IL-4-deficient mice reveal a role for IL-13 in the regulation of Th2 responses

Allergens and infections with parasitic helminths preferentially induced Th2 immune responses associated with elevated levels of serum immunoglobulin E (IgE) and expansion of eosinophils and mast cells. Interleukin-4 (IL-4) is a key cytokine in the differentiation of naive CD4+ T cells into Th2 cells, which produce a panel of cytokines including IL-4, IL-5, IL-6, IL-9, IL-10, and IL-13 [1] and have been shown to trigger recovery from gastrointestinal nematodes [2]. Nonetheless, mice deficient for IL-4 have been shown to develop residual Th2 responses [3-5] and can expel the nematode Nippostrongylus brasiliensis [6], suggesting that there is a functional equivalent of IL-4 in these processes. IL-13 is a cytokine that shares some, but not all, biological activities with IL-4 [7,8]. There is now compelling evidence that IL-4 and IL-13 share receptor components, including IL-4R alpha and IL-13R alpha 1 [9]. In order to dissect the roles of IL-4 and IL-13 in the regulation of Th2 cells and in the response to nematode infections, we looked for differences between mice deficient for either the IL-4 gene or the IL-4R alpha gene. Unlike IL-4, IL-4R alpha was required for control of N. brasiliensis, and Th2 development during infection--as characterized by cytokine production, GATA-3 and surface CD30 expression--was more severely affected in IL-4R alpha-/- mice than in IL-4-/- mice. Injection of recombinant IL-13 induced worm expulsion in otherwise incompetent RAG2-/- mice. Our results suggest that IL-13 regulates Th2 responses to nematode infection and requires IL-4R alpha.

IL-10 Regulates Liver Pathology in Acute Murine Schistosomiasis mansoni But Is Not Required for Immune Down-Modulation of Chronic Disease

We have used IL-10 gene knockout mice (IL-10T) to examine the role of endogenous IL-10 in the down-modulation of hepatic granuloma formation and lymphocyte responses that occurs in chronic infection with the helminth parasite Schistosoma mansoni. Although IL-10-deficient animals showed 20 to 30% mortality between 8 and 14 wk postinfection, they displayed no alterations in their susceptibility to infection and produced similar numbers of eggs as their wild-type littermates. The IL-10T mice displayed a significant increase in hepatic granuloma size at the acute stage of infection, which was associated with increased IFN-γ, IL-2, IL-1β, and TNF-α mRNA expression in liver and elevated Th1-type cytokine production by lymphoid cells. Despite developing an enhanced Th1-type cytokine response, the IL-10T mice showed no consistent decrease in their Th2-type cytokine profile. Surprisingly, although granulomatous inflammation was enhanced at the acute stage of infection, the livers of IL-10T mice displayed no significant increase in fibrosis and underwent normal immune down-modulation at the chronic stage of infection. Moreover, the down-modulated state could be induced in IL-10T mice by sensitizing the animals to schistosome eggs before infection, further demonstrating that the major down-regulatory mechanism is not dependent upon IL-10. We conclude that while IL-10 plays an important role in controlling acute granulomatous inflammation, it plays no essential role in the process of immune down-modulation in chronic schistosome infection.

Th2 Cells Are Required for the Schistosoma mansoni Egg-Induced Granulomatous Response

The development of Schistosoma mansoni ova-induced granulomas is regulated by cytokines secreted by distinct Th cell subsets. To determine the importance of Th1 and Th2 cells in granuloma formation, we have studied the immune response to S. mansoni ova in Stat4- and Stat6-deficient mice, which lack Th1 and Th2 cells, respectively. Lymphocytes from both naive and infected Stat6-deficient mice produced minimal levels of Th2 cell cytokines and Ag-specific IgG1 and IgE, but showed enhanced production of IFN-γ and Ag-specific IgG2a and IgG2b following schistosome egg injection. This shift away from a Th2 cell-mediated immune response was coupled with the development of pulmonary and hepatic granulomas that were greatly decreased in size compared with those in control littermates. Hepatic granulomas in Stat6-deficient mice were composed of predominantly mononuclear cells with very sparse appearance of eosinophils, and their diminished size was accompanied by decreased amounts of liver hydroxyproline content as a measure of collagen deposition. In contrast, lymphocytes from infected Stat4-deficient mice produced Th2 cell cytokines in amounts comparable to those produced by control littermates, but low levels of IFN-γ. While infected Stat4-deficient mice developed pulmonary granulomas following schistosome egg injection that were modestly impaired in size, the granuloma size and amount of collagen deposition in the liver were equivalent to those seen in control littermates. These studies demonstrate that Th2 cells are required for the full development of the granulomas and tissue-destructive fibrotic pathology associated with the immune response to S. mansoni ova.

Endogenous interleukin 4 is required for development of protective CD4+ T helper type 1 cell responses to Candida albicans

Interleukin (IL)-4-deficient mice were used to assess susceptibility to systemic or gastrointestinal Candida albicans infections, as well as parameters of innate and elicited T helper immunity. In the early stage of systemic infection with virulent C. albicans, an unopposed interferon (IFN)-gamma response renders IL-4-deficient mice more resistant than wild-type mice to infection. Yet, IL-4-deficient mice failed to efficiently control infection in the late stage and succumbed to it. Defective IFN-gamma and IL-12 production, but not IL-12 responsiveness, was observed in IL-4-deficient mice that failed to mount protective T helper type 1 cell (Th1)-mediated acquired immunity in response to a live vaccine strain of the yeast or upon mucosal immunization in vivo. In vitro, IL-4 primed neutrophils for cytokine release, including IL-12. However, late treatment with exogenous IL-4, while improving the outcome of infection, potentiated CD4(+) Th1 responses even in the absence of neutrophils. These findings indicate that endogenous IL-4 is required for the induction of CD4(+) Th1 protective antifungal responses, possibly through the combined activity on cells of the innate and adaptive immune systems.

Induction of Granulomatous Experimental Autoimmune Thyroiditis in IL-4 Gene-Disrupted Mice

To study the role of IL-4 in development of granulomatous experimental autoimmune thyroiditis (EAT), IL-4 gene-disrupted mice expressing the EAT-susceptible H-2k haplotype were generated and used for EAT induction. Spleen cells from mouse thyroglobulin (MTg) and LPS-primed IL-4+/+ and IL-4−/− donors could induce severe granulomatous EAT when spleen cells were activated with MTg and anti-IL-2R mAb in the presence of IL-12. Thyroid lesions had extensive follicular cell proliferation, large numbers of histiocytes, polymorphonuclear leukocytes, and multinucleated giant cells, in addition to lymphocytes and other mononuclear cells. Expression of IFN-γ gene mRNA and production of IFN-γ by effector spleen cells stimulated with MTg and IL-12 were similar for both IL-4+/+ and IL-4−/− mice. Although IL-4 was undetectable in IL-4−/− mice, expression of mRNA for IL-5, IL-10, and IL-13 and production of IL-5 by both MTg-activated spleen cells and anti-CD3-activated CD4+ T cells were comparable for cells from IL-4+/+ and IL-4−/− mice, indicating that the absence of IL-4 did not prevent production of other Th2 cytokines. Production of MTg-specific IgG1 was very low or undetectable in IL-4−/− mice. IL-4 gene mRNA and MTg-specific IgG1 could be detected in IL-4+/+ or IL-4−/− recipients only when they received effector cells from IL-4+/+ donor mice, indicating that IL-4- and IgG1-secreting cells are of donor origin. These results demonstrate that IL-4 is not essential for development of granulomatous EAT.

Interleukin-7 activates human naive CD4+ cells and primes for interleukin-4 production

Interleukin (IL)-4 is considered to be essential for T helper (Th)2 cell development, yet in areas of primary T cell activation, CD4+ cells are its only source. This implies that other signals must drive the initial expression of IL-4 production. The role of CD28 co-stimulation in Th2 subset development has been described. However, in mice deficient for CD28, Th2 responses are diminished, but not abrogated. Cytokines produced within the lymphoid tissue, e.g. IL-7, may be important in the primary activation of naive CD4+ cells. We have found that human naive CD4+ cells purified from umbilical cord blood express the IL-7 receptor and respond vigorously to IL-7 during primary stimulation. Naive CD4+ cells grown in IL-4, in the presence or absence of IL-2, fail to produce Th2 cytokines upon restimulation. In contrast, IL-7 induces development of a population of T cells that produce large amounts of IL-4. Growth in IL-7 also increases IL-2-induced production of interferon (IFN)-gamma and IL-10 production. IL-7-induced IL-4 production is not inhibited by neutralizing antibodies to IL-4 on its receptor. This implies that IL-7 acts directly to induce Th2 subset development and not by up-regulating either production of IL-4 during culture or expression of the IL-4 receptor. Moreover, IL-7 potentiates the effects of CD28 co-stimulation on both naive CD4+ cell proliferation and subsequent IL-4 production. Following primary stimulation, CD4+ cells lose expression of the IL-7 receptor, resulting in IL-7 unresponsiveness. This work reveals a novel role for IL-7 in the primary activation of CD4+ cells. We propose that in conjunction with CD28 co-stimulation, IL-7 induces the initial expression of IL-4 production and that IL-4 acts subsequently to expand Th2 cytokine-producing cells at the appropriate anatomical site.

CD28-deficient mice generate an impaired Th2 response to Schistosoma mansoni infection

Engagement of CD28 on T cells provides a co-stimulatory signal necessary for T cell activation and differentiation. Recent findings suggest that priming of T helper (Th)2 cells is more dependent on CD28 activation that Th1 cells. The present study examines whether mice that lack expression of CD28 as a result of gene targeting are capable of generating a Th2 response characteristic during infection with the intravascular trematode parasite Schistosoma mansoni. Mutant and control mice were either inoculated in the footpad with S. mansoni eggs (a potent inducer of a Th2 response) or infected percutaneously with the parasite. Draining lymph nodes (after footpad injection) or spleen cells (after natural infection) were harvested at 12 days and 8 weeks, respectively, and examined for cytokine responses to egg antigens. CD28-deficient mice (-/-) generated diminished egg antigen-driven interleukin (IL)-4 and IL-5 production (by 5- to 17-fold, respectively) compared to CD28-expressing (+/+) littermates. In contrast, lymphocyte proliferation and interferon (IFN)-gamma production to egg antigens were equivalent for mutant and control mice. Infected CD28-/- mice also had reduced immunoglobulin secretion. Serum levels of parasite antigen-specific IgG1 and polyclonal IgE were significantly diminished in CD28-/- compared to CD28+/+ mice. Lack of CD28 expression had no effect on granuloma formation around eggs trapped in the liver, but increased susceptibility of mice to primary schistosomiasis infection. These studies indicate that CD28 activation contributes to T cell priming required for generation of a Th2 response to an intravascular dwelling helminth parasite.