Th2 cytokines,IgE and mast cells play a crucial role in the induction of para-phenylenediamine-induced contact hypersensitivity in mice

We previously reported the establishment of a mouse model system of contact hypersensitivity (CHS) to paraphenylemediamine (PPD). In order to analyse the functional contribution of Th2 cytokines, IL-4 and IL-5, in PPD induced CHS, STAT6 deficient (STAT6-/-) and wild-type control (WT) mice (C57BL/6) were immunized by the topical application of a PPD solution, and then the subsequent skin reactions were examined. Ear swelling was significantly reduced with a delayed peak response in STAT6-/- mice as compared with that of WT mice. A histological analysis showed the infiltration of both eosinophils and neutrophils in the skin of STAT6-/- mice challenged 24 h previously to significantly decrease in comparison with that in the WT mice. The expression of Th2 cytokines (IL-4, IL-5) by ELISA in the PPD-challenged skin tissue specimens as well as the IgE and IgG1 response after challenge were also profoundly reduced in the STAT6-/- mice. The adoptive transfer of the serum obtained from sensitized WT mice for the putative IgE transfer induced a peak response at 3 h and 24 h after challenge. To further investigate the role of mast cells in the induction of PPD-CHS, mast cell deficient W/Wv mice were sensitized with PPD and then were challenged. Maximal ear swelling was detected from 12 to 24 h and another small peak response was observed at 1 h in+/+mice, whereas only a small peak response at 24 h was detected in W/Wv mice. These data indicate that not only Th2 cytokines and IgE but also mast cells play an essential role in the induction of PPD-CHS.     

A role for DRAK2 in the germinal center reaction and the antibody response

DAP-related apoptotic kinase-2 (DRAK2), a death-associated protein kinase family member, is highly expressed in B and T lymphocytes in the human and the mouse. To determine whether DRAK2 plays a role in B-cell activation and differentiation, we analyzed germinal centers (GCs) and the specific antibody response to NP in drak2-/- mice immunized with the thymus-dependent (TD) conjugated hapten NP16-CGG. In drak2-/- mice, spleen GCs were normal in size and morphology, but their number was reduced by as much as 5-fold, as compared to their wild-type littermates. This was not due to a defect in B-cell proliferation, as the BrdU uptake was comparable in DRAK2-deficient and wild-type B cells. Rather, the proportion of apoptotic GC B and T cells in drak2-/- mice was significantly higher than that in wild-type control mice, as shown by 7-AAD and terminal deoxynucleotide transferase dUTP nick end labeling (TUNEL) staining. In drak2-/- mice, the generation high affinity IgG antibodies was impaired in spite of the seemingly normal somatic hypermutation and class switch DNA recombination machineries in drak2-/- B cells. In NP16-CGG-immunized drak2-/- mice, T-cell-intrinsic Bcl-xL transgene expression increased the number of GCs and rescued the high affinity IgG response to NP. These findings suggest a novel role for DRAK2 in regulating the GC reaction and the response to TD antigens, perhaps through increased survival of T cells and enhanced B-cell positive selection. They also suggest that DRAK2-deficiency is not involved in regulating intrinsic B-cell apoptosis.     

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.     

Endogenous Interleukin-12 Is Not Required for Resolution of Chlamydophila abortus (Chlamydia psittaci Serotype 1) Infection in Mice

A Th1 immune response involving gamma interferon (IFN-gamma) production is required to eliminate Chlamydophila abortus infections. In this study, the role of interleukin-12 (IL-12) in protecting against C. abortus infection was investigated using IL-12(-/-) and wild-type (WT) C57BL/6 mice to determine the role of this Th1-promoting cytokine. IL-12(-/-) mice were able to eliminate the C. abortus infection in a primary infection. However, there was a delay in the clearance of bacteria when IL-12(-/-) mice were infected with a sublethal dose of C. abortus, the delay being associated with a lower production of IFN-gamma. The low level of IFN-gamma was essential for survival of IL-12(-/-) infected mice. Both WT and IL-12(-/-) mice developed a Th1 immune response against C. abortus infection, since they both produced IFN-gamma and immunoglobulin G2a antibody isotype. In addition, when mice were given a secondary infectious challenge with C. abortus, a protective host response which resolved the secondary infection was developed by both WT and IL-12(-/-) mice. The lack of IL-12 resulted in few infiltrating CD4(+) T cells in the liver relative to the number in WT mice, although the number of CD8(+) T cells was slightly higher. The more intense Th1 response presented by WT mice may have a pathogenic effect, as the animals showed higher morbidity after the infection. In conclusion, these results suggest that although IL-12 expedites the clearance of C. abortus infection, this cytokine is not essential for the establishment of a protective host response against the infection.     

Stat 4 but not Stat 6 mediated immune mechanisms are essential in protection against plague

The Caf1 and LcrV sub-unit vaccine for plague has been shown to be highly protective against challenge with virulent Yersinia pestis in a mouse model. Production of large amounts of IgG1 in response to the vaccine correlates with protection against aerosol and parenteral infection. In this study the effect of genetic mutation in the immune system on protection was addressed. Stat 6(-/-) mice which are unable to utilise the type 2 cytokines IL-4 and IL-13 and so should have reduced IgG1 responses were utilised in order to determine whether an immune system biased towards the type 1 axis could mount an effective response to the vaccine. Conversely in the Stat 4(-/-) mouse model, IL-12 and interferon-gamma-mediated immune mechanisms are inactive and the immune response should be biased towards the type 2 axis. Serum antibody responses to vaccination in both the knockout strains and their wild type controls revealed little difference in levels of IgG and isotype profiles. Elispot analysis of cytokine production at the single cell level did however reveal a functional defect in the Stat 4(-/-) mice which had low levels of IFN-gamma producing cells. Following virulent challenge, the Stat 6(-/-) mice showed high levels of protection, while the Stat 4(-/-) mice were poorly protected, indicating a fundamental defect in their immune systems which could not be overcome even by the passive transfer of CD4(+) cells from immunised BALB/c donors. It appears therefore that type 1 immune mechanisms, activated following Stat 4 phosphorylation, are essential in protection against plague.     

Essential roles of SIRPα in homeostatic regulation of skin dendritic cells

Signal regulatory protein α (SIRPα) is an immunoglobulin superfamily protein that is predominantly expressed in dendritic cells (DCs). Its cytoplasmic region binds SHP-1 or SHP-2 protein tyrosine phosphatases, while its extracellular region interacts with CD47, another immunoglobulin superfamily protein, constituting cell-cell signaling. SIRPα was previously shown to be important for development of contact hypersensitivity, likely as a result of its positive regulation of the priming by DCs of CD4(+) T cells. However, the mechanism by which SIRPα regulates DC functions remains unknown. Here we found that the number of I-A(+) cells, which represent migratory DCs such as Langerhans cells (LCs) or dermal DCs from the skin, in the peripheral lymph nodes (LNs) was markedly decreased in mice expressing a mutant form of SIRPα that lacks the cytoplasmic region compared with that of wild-type (WT) mice. In addition, an increase of fluorescein isothiocyanate (FITC)-bearing I-A(+) cells in the draining lymph nodes (LNs) after skin-painting with FITC was markedly blunted in SIRPα mutant mice. However, migratory ability, as well as expression of CCR7, of bone marrow-derived DCs prepared from SIRPα mutant mice were not impaired. By contrast, the number of I-A(+) LCs in the epidermis of SIRPα mutant mice was markedly decreased compared with that of WT mice. In addition, the mRNA expression of transforming growth factor-β receptor II in LCs of SIRPα mutant mice was markedly decreased compared with that of WT mice. These results suggest that SIRPα is important for homeostasis of LCs in the skin, as well as of migratory DCs in the LNs, but unlikely for migration of these cells from the skin to draining LNs.     

IL-23 dampens the allergic response to Cryptococcus neoformans through IL-17-independent and -dependent mechanisms

The cytokines IL-23 and IL-17 have been implicated in resistance to cryptococcal disease, but it is not clear whether IL-23-mediated production of IL-17 promotes fungal containment following pulmonary challenge with Cryptococcus neoformans. We used mice lacking IL-23 (IL-23p19(-/-)) or IL-17RA (IL-17RA(-/-)), and wild type (WT) C57BL/6 mice to examine the IL-23/IL-17 axis after intranasal infection with the C. neoformans strain 52D. The absence of IL-23 or IL-17RA had no effect on pulmonary or brain fungal burden at 1 or 6 weeks after infection. However, survival of IL-23p19(-/-) mice was reduced compared to IL-17RA(-/-) mice. IL-I7 production by CD4 T cells and natural killer T (NKT) cells was impaired in IL-23p19(-/-) lungs, but was not completely abolished. Both IL-23p19(-/-) and IL-17RA(-/-) mice exhibited impaired neutrophil recruitment, increased serum levels of IgE and IgG2b, and increased deposition of YM1/YM2 crystals in the lung, but only IL-23p19(-/-) mice developed persistent lung eosinophilia. Although survival of IL-17RA(-/-) and WT mice was similar after 17 weeks of infection, only surviving IL-17RA(-/-) mice exhibited cryptococcal dissemination to the blood. These data demonstrate that IL-23 dampens the allergic response to cryptococcal infection through IL-17-independent suppression of eosinophil recruitment and IL-17-dependent regulation of antibody production and crystal deposition. Furthermore, IL-23, and to a lesser extent IL-17, contribute to disease resistance.     

Mouse germinal center B cells with the xid mutation retain responsiveness to antimouse CD40 antibodies but diminish IL-5 responsiveness

The germinal center (GC) develops in secondary lymphoid tissues in response to thymus-dependent (TD) antigens. To investigate the molecular mechanism of B cell differentiation in GC, we enriched GC B cells from spleen of TD antigen-immunized wild-type and X-linked immunodeficient (XID) mice, and examined the differentiation of GC B cells into antigen-specific IgG1 antibody-forming cells (AFC) in response to anti-CD40 mAb and cytokines. A significant proportion of freshly purified GC B cells expressed receptors for IL-4 and IL-5. Anti- CD40 mAb sustained the viability of GC B cells and IL-4 co-operated with anti-CD40 mAb for further enhancement of the cell viability. Anti- CD40 mAb and IL-4 were essential for inducing differentiation of GC B cells into antigen-specific IgG1-AFC and IL-5 efficiently enhanced their differentiation. GC B cells with the xid mutation responded for proliferation to CD40 ligation to a lesser extent and for the IgG1-AFC response to anti-CD40 mAb together with IL-4, but they showed impaired responsiveness to IL-5, regardless of enhanced expression of IL-5R in response to anti-CD40 mAb and IL-4. These results suggest that anti- CD40 mAb, IL-4 and IL-5 play a critical role in the differentiation of mouse GC B cells. The GC B cells from XID mice show a functional defect with respect to IL-5-mediated differentiation.      

Central role of endogenous gamma interferon in protective immunity against blood-stage Plasmodium chabaudi AS infection

The role of endogenous gamma interferon (IFN-gamma) in protective immunity against blood-stage Plasmodium chabaudi AS malaria was studied using IFN-gamma gene knockout (GKO) and wild-type (WT) C57BL/6 mice. Following infection with 10(6) parasitized erythrocytes, GKO mice developed significantly higher parasitemia during acute infection than WT mice and had severe mortality. In infected GKO mice, production of interleukin 12 (IL-12) p70 and tumor necrosis factor alpha in vivo and IL-12 p70 in vitro by splenic macrophages was significantly reduced compared to that in WT mice and the enhanced nitric oxide (NO) production observed in infected WT mice was completely absent. WT and GKO mice had comparable numbers of total nucleated spleen cells and B220(+) and Mac-1(+) spleen cells both before and after infection. Infected WT mice, however, had significantly more F4/80(+), NK1.1(+), and F4/80(+)Ia(+) spleen cells than infected GKO mice; male WT had more CD3(+) cells than male GKO mice. In comparison with those from WT mice, splenocytes from infected GKO mice had significantly higher proliferation in vitro in response to parasite antigen or concanavalin A stimulation and produced significantly higher levels of IL-10 in response to parasite antigen. Infected WT mice produced more parasite-specific immunoglobulin M (IgM), IgG2a, and IgG3 and less IgG1 than GKO mice. Significant gender differences in both GKO and WT mice in peak parasitemia levels, mortality, phenotypes of spleen cells, and proliferation of and cytokine production by splenocytes in vitro were apparent during infection. These results thus provide unequivocal evidence for the central role of endogenous IFN-gamma in the development of protective immunity against blood-stage P. chabaudi AS.     

IL-17 regulates DC migration to the peribronchial LNs and allergen presentation in experimental allergic asthma

IL-17 is associated with different phenotypes of asthma, however, it is not fully elucidated how it influences induction and maintenance of asthma and allergy. In order to determine the role of IL-17 in development of allergic asthma, we used IL-17A/F double KO (IL-17A/F KO) and WT mice with or without neutralization of IL-17 in an experimental allergic asthma model and analyzed airway hyperresponsiveness, lung inflammation, T helper cell polarization, and DCs influx and activation. We report that the absence of IL-17 reduced influx of DCs into lungs and lung draining LNs. Compared to WT mice, IL-17A/F KO mice or WT mice after neutralization of IL-17A showed reduced airway hyperresponsiveness, eosinophilia, mucus hypersecretion, and IgE levels. DCs from draining LNs of allergen-challenged IL-17A/F KO mice showed a reduction in expression of migratory and costimulatory molecules CCR7, CCR2, MHC-II, and CD40 compared to WT DCs. Moreover, in vivo stimulation of adoptively transferred antigen-specific cells was attenuated in lung-draining LNs in the absence of IL-17. Thus, we report that IL-17 enhances airway DC activation, migration, and function. Consequently, lack of IL-17 leads to reduced antigen-specific T cell priming and impaired development of experimental allergic asthma.     

Polarized TH1 responses by liposome-entrapped allergen and its potential in immunotherapy of allergic disorders

BACKGROUND: The conventional immunotherapy used for treating allergic individuals may at times lead to varying degrees of anaphylactic reaction. Liposomes have been proposed as a vehicle for safe and effective allergen-specific immunotherapy as multiple injections of liposome-entrapped allergen (LEA) have been shown to reduce specific IgE response and induce specific IgG response in BALB/c mice. OBJECTIVE AND METHODS: To elucidate the effect of LEA on polarization of T-cell responses, its effect on the relative production of TH1/TH2 type cytokines (namely IL-2, IL-4 and IFN-gamma by commercially available ELISA kits and immunoglobulin profile as measured by ELISA) were studied. Histamine release on challenge of immunized mice was measured to examine the efficacy of LEA in preventing anaphylactic reactions. RESULTS: Measurement of cytokine levels in serum and spleen cell culture supernatants of BALB/c mice injected repeatedly with either free allergen (FA) or LEA (three mice per group) indicate that LEA preferentially induces a TH1-type of response dominated by IFN-gamma and IL-2 production. Further, it was also shown that immunization of mice with FA or LEA and subsequent challenge with a large dose of the sensitizing allergen leads to fatal systemic reactions in 50-65% of the animals treated with FA, whereas no mortality was observed in mice injected with LEA. Analysis of IgG subclasses in sera of mice immunized with LEA revealed a sixfold higher production of IgG1 antibodies than mice immunized with FA. Serum IgG2a, IgG2b, IgG3 and IgM responses were also enhanced in the group of mice immunized with LEA in comparison with mice injected with FA. CONCLUSION: The results indicate that LEA confers protection against anaphylaxis to mice due to their ability to induce a high IFN-gamma:IL-4 ratio which may lead to decreased synthesis of IgE and reduced histamine release on challenge with FA.     

Urokinase-deficient mice fail to generate a type 2 immune response following schistosomal antigen challenge

Activated lymphocytes express urokinase-type plasminogen activator (uPA). Previous work suggests that uPA modulates T-lymphocyte responses. Mice deficient in uPA (uPA(-/-)) fail to generate type 1 (T1) immune responses during infection with Cryptococcus neoformans. Failure to generate either a T1 or a T2 immune response is not predictive of defects in the alternative response. Conversely, down-regulation of one type of immune response may result in inappropriate overactivation of the other. It is not known whether the immune defect in uPA(-/-) mice affects only T1 responses or whether T2 responses are also impaired. Impairment of both T1 and T2 responses would suggest a global T-cell defect in the absence of uPA. To determine the role of uPA in T2 immune responses, wild-type (WT) and uPA(-/-) mice were primed and challenged with schistosomal egg antigen (SEA). This elicits strong polarization to T2 immune responses in immunocompetent mice. The challenged WT mice developed delayed-type hypersensitivity (DTH) to SEA; high levels of serum immunoglobulin E (IgE); a strong T2 cytokine phenotype with markedly elevated levels of interleukin-4 (IL-4), IL-5, and IL-13; and eosinophil-rich pulmonary granulomas. uPA(-/-) mice failed to develop DTH to SEA; did not polarize Ig production to IgE; did not produce high levels of IL-4, IL-5, or IL-13; and had markedly reduced numbers of granuloma-associated eosinophils. uPA(-/-) mice fail to generate polarized T2 immune responses to a T2-inducing pathogen. These findings, in conjunction with our previous work, demonstrate that mice deficient in uPA have profoundly impaired immunity involving both T1 and T2 polarization and are largely immunologically unresponsive.     

C57BL/6 mice are more susceptible to antigen-induced pulmonary eosinophilia than BALB/c mice, irrespective of systemic T helper 1/T helper 2 responses

Inflammatory response differences between C57BL/6 and BALB/c mice following ovalbumin (OVA) sensitization and a single challenge were investigated. Serum immunoglobulin (Ig)E and IgG1 levels were higher in C57BL/6 mice than in BALB/c mice. In contrast, IgG2a levels in C57BL/6 mice were lower than in BALB/c mice. Furthermore, the number of eosinophils infiltrating into lungs in C57BL/6 mice was significantly higher than in BALB/c mice after OVA challenge. The levels of the T helper 2 (Th2)-type cytokines interleukin (IL)-4 and IL-5, generated in challenged C57BL/6 lung tissue, were also higher than in BALB/c lung tissue. The participation of IL-4 and IL-5 in the induction of eosinophil infiltration into the lungs was confirmed in both strains of mice by injection of anti-IL-4 and anti-IL-5 monoclonal antibodies (mAbs). However, following OVA stimulation, in vitro IL-4 and IL-5 production in splenocyte cultures from C57BL/6 mice was lower than in splenocyte cultures from BALB/c mice. These results indicate that C57BL/6 mice induce Th2-type responses in the lungs, while BALB/c mice induce T helper 1 (Th1)-type responses in the lungs, despite considerable production of IL-4 and IL-5 from splenocytes. Therefore, local immune responses are more important in the induction of allergic inflammation in the lungs and are different from systemic immune responses, which are thought to depend on genetic background.     

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.     

Impaired germinal centre formation and humoral immune response in the absence of CD28 and interleukin-4

The generation of an optimal humoral immune response requires fully activated T-cells. For complete activation at least two signals are needed. The first one is an antigen dependent one via the T cell receptor, the second one is a costimulatory signal which can be delivered by the CD28 molecule after binding to CD80 (B7.1) or CD86 (B7.2). Fully activated T helper cells are competent to deliver help to B-cells by secreting cytokines (e.g. interleukin (IL)-4) or up-regulating CD40 ligand for proliferation and differentiation of B cells. These interactions mainly take place in germinal centres (GC) that arise after antigen stimulation in B cell-follicles of peripheral lymphatic tissues and are the sites of massive B-cell proliferation, affinity maturation and class switch. The roles of CD28 and IL-4 were investigated in GC formation and antibody production. A markedly diminished humoral immune response was observed in IL-4(-/-) xCD28(-/-) mice whereas in CD28(-/-) and IL-4(-/-) mice the defect was less severe. Especially the formation of germinal centres was significantly reduced in CD28(-/-) or IL-4(-/-) mice and almost undetectable in IL-4(-/-) xCD28(-/-) mice. Taken together these data indicate that CD28 and IL-4 are synergistically involved in GC formation and immunoglobulin production.     

Persistence of bronchopulmonary hyper-reactivity and eosinophilic lung inflammation after anti-IL-5 or -IL-13 treatment in allergic BALB/c and IL-4Rα knockout mice

BACKGROUND: Antigen-induced bronchopulmonary hyper-reactivity (BHR) is generally associated with eosinophilia. It involves cytokines produced by Th2 lymphocytes, including IL-4, IL-5 and IL-13, which are implicated in IgE production, eosinophil differentiation and attraction, and related events relevant to allergic inflammation, whose mechanisms remain unclear. OBJECTIVE: To investigate the mechanisms by which Th2 cytokines mediate eosinophilia and subsequent BHR using ovalbumin (OVA)-immunized and OVA-challenged IL-4Ralpha-/- and IL-4-/- mice, which fail to transduce and/or to produce IL-4 and IgE as compared with wild type (WT) mice, and specific neutralizing antibodies. METHODS: On days 0 and 7, mice were immunized subcutaneously (s.c.) with OVA. At day 14, anti-IL-5 or anti-IL-13 antibodies were administered intranasally and/or intravenously before allergenic challenge. Different functional and cellular parameters were studied in vivo and cytokine production was followed with a newly described ex vivo procedure using lung explants. RESULTS: IL-4Ralpha-/- and IL-4-/- mice developed BHR and pulmonary eosinophilia, even though eosinophil recruitment to the bronchoalveolar liquid lavage (BALF) was reduced. In vivo, IL-4-/- and IL-4Ralpha-/- mice produced, respectively, no or reduced amounts of IL-5 in the BALF/serum as compared with WT mice, whereas no IL-13 in the BALF was detected. By contrast, ex vivo, surviving lung explants from WT and IL-4-/- or IL-4Ralpha-/- mice produced IL-13 and large amounts of IL-5. The neutralization of IL-5 in vivo (BALF and serum) and ex vivo (from lung explant) in IL-4Ralpha-/- and WT mice failed to suppress BHR and lung eosinophilia, and to modify IL-13 production ex vivo. In addition, neutralization of IL-13 in vivo from lung explant also failed to abrogate BHR and lung eosinophilia, whereas IL-5 was unchanged. CONCLUSION: Antigen-induced BHR can develop independently from IL-4, IL-5 or IL-13 and from the IL-4alpha receptor chain, suggesting a possible novel IL-4, IL-5 and IL-13-independent pathway for the development of BHR in allergic BALB/c mice. The failure of IL-5 or IL-13 antibodies to prevent BHR in IL-4Ralpha-/- mice suggests that neither is indispensable for BHR but does not exclude a role for lung tissue eosinophilia.     

Interleukin 17-producing T helper cells and interleukin 17 orchestrate autoreactive germinal center development in autoimmune BXD2 mice

Interleukin 17 (IL-17) is a cytokine associated with inflammation, autoimmunity and defense against some bacteria. Here we show that IL-17 can promote autoimmune disease through a mechanism distinct from its proinflammatory effects. As compared with wild-type mice, autoimmune BXD2 mice express more IL-17 and show spontaneous development of germinal centers (GCs) before they increase production of pathogenic autoantibodies. We show that blocking IL-17 signaling disrupts CD4+ T cell and B cell interactions required for the formation of GCs and that mice lacking the IL-17 receptor have reduced GC B cell development and humoral responses. Production of IL-17 correlates with upregulated expression of the genes Rgs13 and Rgs16, which encode regulators of G-protein signaling, and results in suppression of the B cell chemotactic response to the chemokine CXCL12. These findings suggest a mechanism by which IL-17 drives autoimmune responses by promoting the formation of spontaneous GCs.     

Host genetic background determines whether IL-18 deficiency results in increased susceptibility or resistance to murine Leishmania major infection

Interleukin-18 (IL-18) plays an important role in innate and acquired immunity. IL-18 gene deficient (IL-18-/-) mice of the 129 x CD1 strain were reported to be more susceptible to Leishmania major infection than the wild-type mice. In contrast IL-18-/- mice of the C57BL/6 background were found to be as resistant as the wild-type (WT) mice. To resolve this discrepancy, IL-18 gene deficiency was introduced by backcrossing on to the highly susceptible BALB/c, or the moderately resistant DBA/1 backgrounds. Here we have demonstrated that BALB/c IL-18-/- mice were more resistant to L. major infection than WT BALB/c mice, whereas DBA/1 IL-18-/- mice were markedly more susceptible than their WT littermates. BALB/c IL-18-/- mice produced less IFNgamma and IL-4, whereas DBA/1 IL-18ko mice produced more IFNgamma and IL-4 than their respective WT controls. These result clearly demonstrate that the role of IL-18 in resistance or susceptibility to L. major is determined by host genetic background.