Nippostrongylus brasiliensis infection leads to impaired reference memory and myeloid cell interference.

Hookworm infection is endemic in developing countries, leading to poor cognitive function-among other disruptions. In this study, the effects of Nippostrongylus brasiliensis infection (a murine model of Necator Americanus) on cognitive function were investigated. Though impaired cognition has been extensively reported, the exact domain of cognition affected is still unknown, hence requiring investigation. The objective of this study was to identify possible cognitive changes during Nippostrongylus brasiliensis infection in mice, using the Morris water maze. Here, we show for the first time that mice infected with Nippostrongylus brasiliensis were able to learn the Morris water maze task, but demonstrated impaired reference memory. Anxiety measured by thigmotaxis in the maze, did not play a role for the observed cognitive impairment. Of further interest, an increase in the number of hippocampal macrophages and microglia with training and/or infection suggested a significant role of these cell types during spatial learning. Together, these experimental mouse studies suggest that helminth infections do have an impact on cognition. Further experimental animal studies on cognition and infection might open new approaches for a better understanding and impact of pathogen infections.

Protein kinase C-delta (PKCδ), a marker of inflammation and tuberculosis disease progression in humans, is important for optimal macrophage killing effector functions and survival in mice.

We previously demonstrated that protein kinase C-δ (PKCδ) is critical for immunity against Listeria monocytogenes, Leishmania major, and Candida albicans infection in mice. However, the functional relevance of PKCδ during Mycobacterium tuberculosis (Mtb) infection is unknown. PKCδ was significantly upregulated in whole blood of patients with active tuberculosis (TB) disease. Lung proteomics further revealed that PKCδ was highly abundant in the necrotic and cavitory regions of TB granulomas in multidrug-resistant human participants. In murine Mtb infection studies, PKCδ-/- mice were highly susceptible to tuberculosis with increased mortality, weight loss, exacerbated lung pathology, uncontrolled proinflammatory cytokine responses, and increased mycobacterial burdens. Moreover, these mice displayed a significant reduction in alveolar macrophages, dendritic cells, and decreased accumulation of lipid bodies (lungs and macrophages) and serum fatty acids. Furthermore, a peptide inhibitor of PKCδ in wild-type mice mirrored lung inflammation identical to infected PKCδ-/- mice. Mechanistically, increased bacterial growth in macrophages from PKCδ-/- mice was associated with a decline in killing effector functions independent of phagosome maturation and autophagy. Taken together, these data suggest that PKCδ is a marker of inflammation during active TB disease in humans and required for optimal macrophage killing effector functions and host protection during Mtb infection in mice.

The IL-33 receptor (ST2) regulates early IL-13 production in fungus-induced allergic airway inflammation.

Allergic airway inflammation (AAI) in response to environmental antigens is an increasing medical problem, especially in the Western world. Type 2 interleukins (IL) are central in the pathological response but their importance and cellular source(s) often rely on the particular allergen. Here, we highlight the cellular sources and regulation of the prototypic type 2 cytokine, IL-13, during the establishment of AAI in a fungal infection model using Cryptococcus neoformans. IL-13 reporter mice revealed a rapid onset of IL-13 competence within innate lymphoid cells type 2 (ILC2) and IL-33R(+) T helper (Th) cells. ILC2 showed IL-33-dependent proliferation upon infection and significant IL-13 production. Th cells essentially required IL-33 to become either GATA3(+) or GATA3(+)/Foxp3(+) hybrids. GATA3(+) Th cells almost exclusively contributed to IL-13 production but hybrid GATA3(+)/Foxp3(+) Th cells did not. In addition, alveolar macrophages upregulated the IL-33R and subsequently acquired a phenotype of alternative activation (Ym1(+), FIZZ1(+), and arginase-1(+)) linked to type 2 immunity. Absence of adaptive immunity in rag2(-/-) mice resulted in attenuated AAI, revealing the need for Th2 cells for full AAI development. Taken together, in pulmonary cryptococcosis ILC2 and GATA3(+) Th2 cells produce early IL-13 largely IL-33R-dependent, thereby promoting goblet cell metaplasia, pulmonary eosinophilia, and alternative activation of alveolar macrophages.

Lack of IL-4 receptor expression on T helper cells reduces T helper 2 cell polyfunctionality and confers resistance in allergic bronchopulmonary mycosis.

T helper (Th)1 and Th2 cells play decisive roles in the regulation of resistance vs. susceptibility to pulmonary cryptococcosis. To study the function of interleukin (IL)-4 receptor (IL-4R) on Th cells in pulmonary cryptococcosis, we infected mice specifically lacking IL-4Rα on CD4(+) T cells (Lck(Cre)IL-4Rα(-/lox) mice) and IL-4Rα(-/lox) controls. Lck(Cre)IL-4Rα(-/lox) mice developed enhanced resistance accompanied by reduced pulmonary allergic inflammation and diminished production of the Th2 cytokines IL-4, IL-5, and IL-13 as compared with IL-4Rα(-/lox) mice. Polyfunctional antigen-specific Th2 cells producing simultaneously two or three Th2 cytokines were reduced in infected Lck(Cre)IL-4Rα(-/lox) mice, pointing to a critical role of polyfunctional Th2 cells for disease progression. Reduced Th2 polyfunctionality was associated with fewer pulmonary alternatively activated macrophages. This work is the first direct evidence for a critical contribution of the IL-4R on Th cells to Th2-dependent susceptibility during allergic bronchopulmonary mycosis. Moreover, the data demonstrate that the quality of the Th2 response has an impact on type 2 inflammation. The analysis of polyfunctional Th2 cells may be useful for monitoring the course of the disease.

IL-4Rα-responsive smooth muscle cells contribute to initiation of TH2 immunity and pulmonary pathology in Nippostrongylus brasiliensis infections.

Nippostrongylus brasiliensis infections generate pulmonary pathologies that can be associated with strong T(H)2 polarization of the host's immune response. We present data demonstrating N. brasiliensis-driven airway mucus production to be dependent on smooth muscle cell interleukin 4 receptor-α (IL-4Rα) responsiveness. At days 7 and 10 post infection (PI), significant airway mucus production was found in IL-4Rα(-/lox) control mice, whereas global knockout (IL-4Rα(-/-)) and smooth muscle-specific IL-4Rα-deficient mice (SM-MHC(Cre) IL-4Rα(-/lox)) showed reduced airway mucus responses. Furthermore, interleukin (IL)-13 and IL-5 cytokine production in SM-MHC(Cre) IL-4Rα(-/lox) mice was impaired along with a transient reduction in T-cell numbers in the lung. In vitro treatment of smooth muscle cells with secreted N. brasiliensis excretory-secretory antigen (NES) induced IL-6 production. Decreased protein kinase C (PKC)-dependent smooth muscle cell proliferation associated with cell cycle arrest was found in cells stimulated with NES. Together, these data demonstrate that both IL-4Rα and NES-driven responses by smooth muscle cells make important contributions in initiating T(H)2 responses against N. brasiliensis infections.

Intestinal pathology during acute toxoplasmosis is IL-4 dependent and unrelated to parasite burden.

The role of interleukin-4 (IL-4) during the course of Toxoplasma gondii infection was studied using IL-4-/- mice and their wild-type (WT) counterparts on a C57BL/6 background. Following oral infection with T. gondii tissue cysts an exacerbative role for IL-4 was demonstrated and IL-4-/- mice were found to be more resistant to infection than WT mice as measured by significantly reduced mortality. Furthermore pathology in the small intestine was less severe in IL-4-/- mice although conversely liver pathology was greater than in wild-type mice. Significantly, plasma IL-12 and IFN-gamma levels, which peaked at days 6 and 8, respectively, were higher in IL-4-/- mice. The exacerbatory role of IL-4 in the intestine was found by competitive RT-PCR not to be associated with increased parasite burdens but was related to comparative expression of IL-10.

A protective and agonistic function of IL-12p40 in mycobacterial infection.

IL-12p35(-/-)p40(-/-) mice are highly susceptible to Mycobacterium bovis bacillus Calmette-Guérin (BCG) or Mycobacterium tuberculosis infection. In this study IL-12p35(-/-) mice, which are able to produce endogenous IL-12p40, cleared M. bovis BCG and showed reduced susceptibility to pulmonary M. tuberculosis infection, which was in striking contrast to the outcome of mycobacterial infection in IL-12p35(-/-)p40(-/-) mice. Resistance in wild-type and IL-12p35(-/-) mice was accompanied by protective granuloma formation and Ag-specific delayed-type hypersensitivity responses, which were impaired in susceptible IL-12p35(-/- )p40(-/-) mice. Furthermore, IL-12p35(-/-) mice, but not IL-12p35(-/-)p40(-/-) mice, mounted Ag-specific Th1 and cytotoxic T cell responses. In vivo therapy with rIL-12p40 homodimer restored the impaired delayed-type hypersensitivity responses in M. bovis BCG-infected IL-12p35(-/-)p40(-/-) mice and reverted them to a more resistant phenotype. Together, these results show evidence for a protective and agonistic role of endogenous and exogenous IL-12p40 in mycobacterial infection, which is independent of IL-12p70.

Dual role of the IL-12/IFN-gamma axis in the development of autoimmune myocarditis: induction by IL-12 and protection by IFN-gamma.

IL-12 and IFN-gamma positively regulate each other and type 1 inflammatory responses, which are believed to cause tissue damage in autoimmune diseases. We investigated the role of the IL-12/IFN-gamma (Th1) axis in the development of autoimmune myocarditis. IL-12p40-deficient mice on a susceptible background resisted myocarditis. In the absence of IL-12, autospecific CD4(+) T cells proliferated poorly and showed increased Th2 cytokine responses. However, IFN-gamma-deficient mice developed fatal autoimmune disease, and blockade of IL-4R signaling did not confer susceptibility to myocarditis in IL-12p40-deficient mice, demonstrating that IL-12 triggers autoimmunity by a mechanism independent of the effector cytokines IFN-gamma and IL-4. In conclusion, our results suggest that the IL-12/IFN-gamma axis is a double-edged sword for the development of autoimmune myocarditis. Although IL-12 mediates disease by induction/expansion of Th1-type cells, IFN-gamma production from these cells limits disease progression.

Upon prolonged allergen exposure IL-4 and IL-4Ralpha knockout mice produce specific IgE leading to anaphylaxis.

BACKGROUND: IL-4 and IL-13 are key regulators in atopic disorders and both signal through the receptor chain IL-4Ralpha. IL-4 and IL-13 are also the only cytokines known to induce class switching to IgE. We sought to compare allergen-specific IgE responses and allergic reactivity of wild-type (wt) mice with IL-4-/- and IL-4Ralpha-/- mice, which lack both IL-4 and IL-13 functions. METHODS: BALB/c wt, IL-4-/- and IL-4Ralpha-/- mice were immunized with ovalbumin intranasally or intraperitoneally and specific antibody titers were measured by ELISA. Bronchoalveolar lavage fluids and lung tissue were analyzed cytologically and histologically. Allergic reactivity was determined by active cutaneous anaphylaxis and anaphylactic shock. RESULTS: wt mice immunized intranasally or intraperitoneally showed high titers of specific IgE 3 and 6 weeks after primary sensitization, resulting in cutaneous anaphylaxis and anaphylactic shock upon challenge. Intranasal sensitization resulted in airway eosinophilia and goblet cell metaplasia. In contrast, IL-4-/- and IL-4Ralpha-/- mice showed no specific IgE after 3 weeks, but produced high titers after 6 weeks. At this time cutaneous anaphylaxis and anaphylactic shock could be induced as in wt mice, but lung pathology was absent. CONCLUSIONS: We conclude that upon long-term allergen exposure, alternative switch mechanisms independent of IL-4 and IL-4Ralpha may induce IgE but not asthma-like lung pathology. This may be relevant for the development of allergic disease, since long-term allergen exposure is a frequent condition during allergic sensitization.

IL-12-independent IFN-gamma production by T cells in experimental Chagas' disease is mediated by IL-18.

IL-12p35-deficient (IL-12p35(-/-)) mice were highly susceptible to Trypanosoma cruzi infection and succumbed during acute infection, demonstrating the crucial importance of endogenous IL-12 in resistance to experimental Chagas' disease. Delayed immune responses were observed in mutant mice, although comparable IFN-gamma and TNF-alpha blood levels as in wild-type mice were detected 2 wk postinfection. In vivo and in vitro analysis demonstrated that T cells, but not NK cells, were recruited to infected organs. Analysis of mice double deficient in the recombinase-activating gene 2 (RAG2) and IL-12p35, as well as studies involving T cell depletion, identified CD4(+) T cells as the cellular source for IL-12-independent IFN-gamma production. IL-18 was induced in IL-12p35(-/-) mice and was responsible for IFN-gamma production, as demonstrated by in vivo IL-18 neutralization studies. In conclusion, evidence is presented for an IL-12-independent IFN-gamma production in experimental Chagas' disease that is T cell and IL-18 dependent.

Reversal of established delayed type hypersensitivity reactions following therapy with IL-4 or antigen-specific Th2 cells.

Delayed-type hypersensitivity reactions (DTHR) are mediated by IFN-gamma-producing CD4+ (Th1) or CD8+ T cells (Tc1) and can be prevented by steering T cells toward an IL-4-producing Th2 or Tc2 phenotype. It is currently accepted that T cells can be directed toward a Th2 or Tc2 phenotype only during the initiation of an immune response. Once established, the cytokine pattern of immune reactions is believed to be stable. Therefore, inhibition of DTHR by the induction of Th2/Tc2 responses, termed immune deviation, is considered only as a prevention but not as a therapy of harmful DTHR. Here we demonstrate that therapeutic immune deviation can reverse established contact hypersensitivity (CHS), a Th1/Tc1-mediated DTHR. One or two weeks after induction of CHS, mice received either a single cycle of IL-4 therapy or adoptive transfer of antigen-specific Th2 cells. This treatment generated a novel state of immunity that provided long-lasting protection against tissue destruction and neutrophil recruitment during subsequent antigen exposures. Therapeutic immune deviation of established CHS was dependent on CD4+ T cells and the induction of endogenous IL-4 synthesis. Thus, a population of immunoregulatory Th2 cells persists during advanced inflammatory responses that can be used for therapeutic deviation of established DTHR.

Counter-protective role for interleukin-5 during acute Toxoplasma gondii infection.

The role of interleukin-5 (IL-5) during Toxoplasma gondii infection was investigated by comparing disease progression in IL-5 gene deficient (IL-5-/-) mice and their wild-type (WT) counterparts on a C57BL/6 background. IL-5-/- mice infected orally with T. gondii were less susceptible to infection than WT mice as demonstrated by reduced mortality rates. Consistent with this data, orally infected IL-5-/- mice had less severe pathological changes in their small intestines than WT mice at 8 days postinfection. At this time, splenocytes and mesenteric lymph node cells derived from IL-5-/- mice produced levels of IL-12, interferon-gamma (IFN-gamma), IL-4, IL-10, and nitric oxide (measured as nitrite) similar to those derived from WT mice when stimulated with Toxoplasma lysate antigen. However, peak serum IL-12 and IFN-gamma levels (at days 6 and 8, respectively) were significantly higher in IL-5-/- mice than in WT mice. In addition, WT mice but not IL-5-/- mice had raised levels of eosinophils in their peripheral blood between days 5 and 8 following infection. Oral administration of N omega-nitro-L-arginine methyl (from day 4 postinfection) increased mortality rates in both IL-5-/- and WT mice, indicating a protective role for nitric oxide during the early stages of oral T. gondii infection. In comparison with oral infection, no difference in mortality was observed between IL-5-/- and WT mice following intraperitoneal infection with T. gondii, with all mice surviving until 35 days postinfection. Similarly, no significant differences were observed in the severity of the meningitis, perivascular cuffing, or number of microglial nodules or parasites in the brains of intraperitoneally infected mice. Together, these results demonstrate a detrimental role for IL-5 during the early stage of oral infection with T. gondii which is associated with increased small-intestine pathology, eosinophilia, and reduced plasma IL-12 and IFN-gamma levels.

IL-4 exacerbates disease in a Th1 cell transfer model of colitis.

IL-4 is associated with Th2-type immune responses and can either inhibit or, in some cases, promote Th1-type responses. We tested the effect of IL-4 treatment on the development of inflammation in the CD4(+)CD45RB(high) T cell transfer model of colitis, which has been characterized as a Th1-dependent disease. IL-4 treatment significantly accelerated the development of colitis in immunodeficient recipients (recombinase-activating gene-2 (Rag2)(-/-)) of CD4(+)CD45RB(high) T cells. Quantitative analysis of mRNA expression in the colons of IL-4-treated mice showed an up-regulation of both Th1- and Th2-associated molecules, including IFN-gamma, IP-10, MIG, CXCR3, chemokine receptor-8, and IL-4. However, cotreatment with either IL-10 or anti-IL-12 mAb effectively blocked the development of colitis in the presence of exogenous IL-4. These data indicate that IL-4 treatment exacerbates a Th1-mediated disease rather than induces Th2-mediated inflammation. As other cell types besides T cells express the receptor for IL-4, the proinflammatory effects of IL-4 on host cells in Rag2(-/-) recipients were assessed. IL-4 treatment was able to moderately exacerbate colitis in Rag2(-/-) mice that were reconstituted with IL-4Ralpha-deficient (IL-4Ralpha(-/-)) CD4(+)CD45RB(high) T cells, suggesting that the IL-4 has proinflammatory effects on both non-T and T cells in this model. IL-4 did not cause colitis in Rag2(-/-) mice in the absence of T cells, but did induce an increase in MHC class II expression in the lamina propria of the colon, which was blocked by cotreatment with IL-10. Together these results indicate that IL-4 can indirectly promote Th1-type inflammation in the CD4(+)CD45RB(high) T cell transfer model of colitis.

Signaling via interleukin-4 receptor alpha chain is required for successful vaccination against schistosomiasis in BALB/c mice.

Although protective immunity in C57BL/6 mice induced by a single dose of the radiation-attenuated schistosome vaccine is believed to be mediated by Th1-type immune responses, we here report that in BALB/c mice protection can also depend upon signaling via the interleukin-4 (IL-4) receptor which conventionally governs the development of Th2-type immune responses. We show that in BALB/c mice deficient for the IL-4 receptor alpha chain (IL-4Ralpha(-/-)), which are unresponsive to IL-4 and IL-13, vaccine-induced protection is abrogated compared with that in wild-type (WT) mice. In vaccinated IL-4Ralpha(-/-) mice, IL-12p40 production by cells from the skin exposure site was elevated, although gamma interferon (IFN-gamma) production in draining lymphoid tissues was similar in WT and IL-4Ralpha(-/-) mice. Nevertheless, the effector response in IL-4Ralpha(-/-) mice was Th1 biased with elevated IFN-gamma in the lungs and higher immunoglobulin G2a (IgG2a) and IgG2b titers but negligible quantities of Th2-associated IgG1 and IgE. Interestingly, levels of IL-4 were equivalent in WT and IL-4Ralpha(-/-) mice, indicating that Th2 responses were not dependent upon signaling by IL-4 or IL-13. No differences in the phenotype and composition of the pulmonary effector mechanism that might explain the failure to induce protection in IL-4Ralpha(-/-) mice were detected. However, passive transfer of partial protection to naive IL-4Ralpha(-/-) mice, using serum from vaccinated WT mice, indicates that Th2-associated antibodies such as IgG1 have a role in parasite elimination in BALB/c strain mice and that signaling via IL-4R can be an important factor in the generation of protection.

Tumor necrosis factor alpha-mediated toxic shock in Trypanosoma cruzi-infected interleukin 10-deficient mice.

Using interleukin-10 (IL-10)-deficient (IL-10(-/-)) mice, previous studies revealed a pathological immune response after infection with Trypanosoma cruzi that is associated with CD4(+) T cells and overproduction of proinflammatory cytokines. In this study we further investigate the pathology and potential mediators for the mortality in infected animals. T. cruzi-infected IL-10(-/-) mice showed reduced parasitemia accompanied by increased systemic release of gamma interferon (IFN-gamma), IL-12, and reactive nitrogen intermediates and overproduction of tumor necrosis factor alpha (TNF-alpha). Despite this early resistance, IL-10(-/-) mice died within the third week of infection, whereas all control mice survived acute infection. The clinical manifestation with weight loss, hypothermia, hypoglycemia, hyperkalemia, and increased liver-derived enzymes in the blood together with hepatic necrosis and intravascular coagulation in moribund mice indicated a toxic shock-like syndrome, possibly mediated by the systemic TNF-alpha overproduction. Indeed, high production of systemic TNF-alpha significantly correlated with mortality, and moribund mice died with critically high TNF-alpha concentrations in the blood. Consequent treatment with anti-TNF-alpha antiserum attenuated pathological changes in T. cruzi-infected IL-10(-/-) mice and significantly prolonged survival; the mice died during the fourth week postinfection, again with a striking correlation between regaining high systemic TNF-alpha concentrations and the time of death. Since elevated serum IL-12 and IFN-gamma concentrations were not affected by the administration of antiserum, these studies suggest that TNF-alpha is the direct mediator of this toxic shock syndrome. In conclusion, induction of endogenous IL-10 during experimentally induced Chagas' disease seems to be crucial for counterregulating an overshooting proinflammatory cytokine response resulting in TNF-alpha-mediated toxic shock.

IL-12 is dispensable for innate and adaptive immunity against low doses of Listeria monocytogenes.

We have studied IL-12p35-deficient (IL-12p35(-/-)) mice to evaluate the role of IL-12 in resistance against Listeria monocytogenes. In the absence of bioactive IL-12p75, mutant mice acquired higher bacterial organ burden than wild-type mice and died during the first week following infection with normally sublethal doses of Listeria. Moreover, blood IFN-gamma levels were strikingly reduced in mutant mice at day 2 post-infection. These results suggest that in IL-12p35-deficient mice impaired production of IFN-gamma which is crucial for activation of listericidal effector functions of macrophages leads to defective innate immunity against Listeria. In contrast to mice deficient for IFN-gamma or IFN-gamma receptor which are unable to resist very low infection doses of Listeria, IL-12p35(-/-) mice resisted up to 1000 c.f.u. and were able to eliminate Listeria. Spleen cells from mutant mice re-stimulated with heat-killed Listeria produced considerable amounts of IFN-gamma, suggesting that at low dose infection sufficient IFN-gamma is produced independently of IL-12. Subsequent challenge of these immunized mice with high doses of L. monocytogenes resulted in sterile elimination demonstrating efficient memory responses. These results demonstrate for the first time that at low doses of Listeria IL-12 is neither critical for innate immunity nor for the development of protective T cell-dependent acquired immunity.

The PACAP-type I receptor agonist maxadilan from sand fly saliva protects mice against lethal endotoxemia by a mechanism partially dependent on IL-10.

Sand fly saliva contains maxadilan, a peptide that causes vasodilation and modifies the secretion of pro-inflammatory cytokines by macrophages. We show that 1 to 10 microg maxadilan protected BALB/c mice against a lethal dose of LPS. Maxadilan reduced serum levels of TNF-alpha by approximately tenfold, while it caused a threefold increase in IL-6 and IL-10. The protective effect of maxadilan is partially dependent on its ability to induce IL-10 production since maxadilan did not prevent death from endotoxic shock in IL-10(-/-) mice. Finally, maxadilan is a selective agonist of the pituitary adenylate cyclase-activating peptide (PACAP) type I receptor, and we found that the natural ligand of this receptor (PACAP 38) also protected mice against lethal endotoxemia. These results indicate that activation of the PACAP type I receptor may contribute to the control of systemic inflammation by a mechanism that is partially dependent on IL-10.

IgD can largely substitute for loss of IgM function in B cells.

The mu and delta heavy chains of IgM and IgD, the first antibody isotypes expressed during bone-marrow B-cell development, are encoded by a common transcription unit. Expression of the mu chain on the surface of late pre-B cells allows their further development to immature B cells. Coexpression of the delta chain and emigration of the immature B cells to the periphery eventually leads to the development of naive mature IgM/IgD double-positive cells. Although IgM is important in driving B-cell development, the contribution of IgD is not clear. Here we investigate the function of IgD. We generated mice deficient in IgM (IgM-/- mice) by deleting the mu region in embryonic stem cells. IgM-/- mice showed normal B-cell development and maturation, with IgD replacing membrane-bound and secretory IgM. Moreover, specific B-cell responses and isotype class switches occurred during immunization or infection. In contrast to mice deficient in B cells, IgM-/- mice survived infection with vesicular stomatitis virus by developing neutralizing immunoglobulins, but they were more susceptible than wild-type controls with delayed specific immunoglobulin responses. These data lead us to conclude that IgD is largely able to substitute for IgM functions.

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.

The role of IL-4 in adult acquired and congenital toxoplasmosis.

The course of Toxoplasma gondii infection was studied in IL-4-deficient mice from three genetic backgrounds and their wild-type counterparts following peroral inoculation of tissue cysts. Survival rates were significantly reduced in disease-susceptible C57 BL/6 mice and F1 (C57BL/6 x 129Sv) mice deficient in IL-4 compared with wild-type controls. In contrast, this difference was not observed in T. gondii-resistant BALB/c mice. However, brain tissue cyst burdens in IL-4-deficient mice were either equivalent to (C57BL/6 and BALB/c mice) or significantly less (B6/129 mice) than similarly infected wild-type mice. Thus strain-specific differences in the course of T. gondii were demonstrated in the absence of IL-4. The course of T. gondii infection was also compared between B6/129 IL-4-deficient mice and their wild-type counterparts following peroral challenge with 20 tissue cysts on day 12 of pregnancy. Age-matched non-pregnant IL-4-/- and IL-4+/+ mice were also infected to assess the role of IL-4 on T. gondii infection during pregnancy. Disease phenotypes, as measured by mortality, were reversed if infections were initiated during pregnancy compared with non-pregnant infection. Thus significant mortality occurred immediately post partum in IL-4+/+ mothers, while all IL-4-/- mothers survived. Cyst burdens 28 days p.i. were significantly lower in IL-4-/- mothers than IL-4+/+ mothers and both IL-4-/- and IL-4+/+ non-pregnant mice. Congenital disease transmission as measured by foetal death or vertical disease transmission was independent of the presence or absence of IL-4. These studies demonstrate a role for IL-4 in pregnancy-induced immunosuppression and the associated increased susceptibility to T. gondii infection.