Th1 and Th2 cytokines regulate proteoglycan-specific autoantibody isotypes and arthritis

BALB/c mice immunized with human cartilage proteoglycan (PG) develop arthritis accompanied by the production of autoantibodies to mouse cartilage PG. To determine whether the autoantibody isotype contributes to the onset and severity of arthritis, PG-specific serum IgG1 (Th2, IL-4-cytokine-supporting) and IgG2a (Th1, IFN-gamma-controlling) concentrations were monitored during immunization with PG in IL-4-deficient and IFN-gamma-deficient mice. Paradoxically, despite elevated IFN-gamma, the PG-specific IgG1 isotype was significantly higher than the PG-specific IgG2a response, and the PG-specific IgG1 isotype was independent of IL-4. In contrast, the serum concentration of PG-specific IgG2a isotype was six times higher in IL-4-deficient mice than in wild-type controls. Moreover, the high concentration of PG-specific IgG2a isotype in IL-4-deficient mice corresponded to an increased severity of arthritis. The concentration of PG-specific IgG2a isotype was lower in IFN-gamma-deficient mice than in wild-type mice, and the incidence and severity of arthritis also were significantly lower. Concentrations of PG-specific IgG2a isotype autoantibody correlated with the onset and severity of arthritis, suggesting a pathological role of this isotype, probably locally in the joint.     

Respiratory synctial virus infection in BALB/c mice previously immunized with formalin-inactivated virus induces enhanced pulmonary inflammatory response with a predominant Th2-like cytokine pattern.

Vaccination with formalin-inactivated respiratory syncytial virus (FI-RSV) caused excessive disease in infants upon subsequent natural infection with RSV. Recent studies with BALB/c mice have suggested that T cells are important contributors to lung immunopathology during RSV infection. In this study, we investigated vaccine-induced enhanced disease by immunizing BALB/c mice with live RSV intranasally or with FI-RSV intramuscularly. The mice were challenged with RSV 6 weeks later, and the pulmonary inflammatory response was studied by analyzing cells obtained by bronchoalveolar lavage 4 and 8 days after challenge. FI-RSV-immunized mice had an increased number of total cells, granulocytes, eosinophils, and CD4+ cells but a decreased number of CD8+ cells. The immunized mice also had a marked increase in the expression of mRNA for the Th2-type cytokines interleukin-5 (IL-5) and IL-13 as well as some increase in the expression of IL-10 (a Th2-type cytokine) mRNA and some decrease in the expression of IL-12 (a Th1-type cytokine) mRNA. The clear difference in the pulmonary inflammatory response to RSV between FI-RSV- and live-RSV-immunized mice suggests that this model can be used to evaluate the disease-enhancing potential of candidate RSV vaccines and better understand enhanced disease.     

Reduced expression of STAT4 and IFN-gamma in macrophages from BALB/c mice

BALB/c mice have been shown to easily induce Th2 type responses in several infection models. In this study, to examine the mechanisms of Th2 dominant responses in BALB/c mice, we assessed several macrophage functions using C3H/HeN, C57BL/6, and BALB/c mouse strains. Peritoneal macrophages from three strains of mice equally produced IL-12 by stimulation with LPS plus IFN-gamma. However, IFN-gamma production in response to IL-12 or IL-12 plus IL-18 was much lower in macrophages from BALB/c mice than other strains. IFN-gamma produced by activated macrophages induced IL-12R mRNA expression in T cells and macrophages themselves depending on their amount of IFN-gamma; namely, macrophages from BALB/c mice induced lower expression of IL-12R. Intracellular levels of STAT4 were much lower in macrophages from BALB/c mice. However, other STATs, such as STAT1 or STAT6, were expressed similarly in the three mouse strains. STAT4 and IFN-gamma production by other cell types such as T cells and B cells were equal in C3H/HeN and BALB/c mice. These results indicate that macrophages from Th2-dominant BALB/c mice have different functional characters compared with other mouse strains; that is, STAT4 expression and IFN-gamma production are reduced, which is one of the causes to shift to Th2-type responses.     

Th1 and Th2 cytokines regulate proteoglycan-specific autoantibody isotypes and arthritis

BALB/c mice immunized with human cartilage proteoglycan (PG) develop arthritis accompanied by the production of autoantibodies to mouse cartilage PG. To determine whether the autoantibody isotype contributes to the onset and severity of arthritis, PG-specific serum IgG1 (Th2, IL-4-cytokine-supporting) and IgG2a (Th1, IFN-γ-controlling) concentrations were monitored during immunization with PG in IL-4-deficient and IFN-γ-deficient mice. Paradoxically, despite elevated IFN-γ, the PG-specific IgG1 isotype was significantly higher than the PG-specific IgG2a response, and the PG-specific IgG1 isotype was independent of IL-4. In contrast, the serum concentration of PG-specific IgG2a isotype was six times higher in IL-4-deficient mice than in wild-type controls. Moreover, the high concentration of PG-specific IgG2a isotype in IL-4-deficient mice corresponded to an increased severity of arthritis. The concentration of PG-specific IgG2a isotype was lower in IFN-γ-deficient mice than in wild-type mice, and the incidence and severity of arthritis also were significantly lower. Concentrations of PG-specific IgG2a isotype autoantibody correlated with the onset and severity of arthritis, suggesting a pathological role of this isotype, probably locally in the joint.     

Cytokine expression in murine cytomegalovirus-induced myocarditis: modulation with interferon-alpha therapy

Cytomegalovirus-induced myocarditis is largely immune-mediated. BALB/c mice produced higher levels of IL-4 in the heart indicative of a Th2-like response. Although IL-6, IL-10, IL-18, and TNF-alpha were produced in the heart during acute infection, BALB/c mice lacked a substantial IL-2 and IFN-gamma response. Conversely, C57BL/6 mice produced significant levels of IFN-gamma in the heart with no significant levels of IL-4 or IL-6, suggestive of a dominant Th1-like response to virus infection. IFN-alpha/beta immunotherapy is known to suppress the development of MCMV-myocarditis. Cytokine secretion in IFN-stimulated MCMV-infected BALB/c myocytes was found to be IFN subtype-dependent with elevation of IL-6 and IL-18 levels. During the chronic phase of disease, IFNA6 DNA treatment in vivo increased IL-18 production in the heart. These results suggest that IFN subtype therapy may have immunomodulating effects in reducing disease severity in BALB/c mice via regulation of cytokine production in the heart.     

Schistosoma mansoni and alpha-galactosylceramide: prophylactic effect of Th1 Immune suppression in a mouse model of Graves' hyperthyroidism

Graves' hyperthyroidism, an organ-specific autoimmune disease mediated by stimulatory thyrotropin receptor (TSHR) autoantibodies, has been considered a Th2-dominant disease. However, recent data with mouse Graves' models are conflicting. For example, we recently demonstrated that injection of BALB/c mice with adenovirus coding the TSHR induced Graves' hyperthyroidism characterized by mixed Th1 and Th2 immune responses against the TSHR, and that transient coexpression of the Th2 cytokine IL-4 by adenovirus skewed Ag-specific immune response toward Th2 and suppressed disease induction. To gain further insight into the relationship between immune polarization and Graves' disease, we evaluated the effect of Th2 immune polarization by helminth Schistosoma mansoni infection and alpha-galactosylceramide (alpha-GalCer), both known to bias the systemic immune response to Th2, on Graves' disease. S. mansoni infection first induced mixed Th1 and Th2 immune responses to soluble worm Ags, followed by a Th2 response to soluble egg Ags. Prior infection with S. mansoni suppressed the Th1-type anti-TSHR immune response, as demonstrated by impaired Ag-specific IFN-gamma secretion of splenocytes and decreased titers of IgG2a subclass anti-TSHR Abs, and also prevented disease development. Similarly, alpha-GalCer suppressed Ag-specific splenocyte secretion of IFN-gamma and prevented disease induction. However, once the anti-TSHR immune response was fully induced, S. mansoni or alpha-GalCer was ineffective in curing disease. These data support the Th1 theory in Graves' disease and indicate that suppression of the Th1-type immune response at the time of Ag priming may be crucial for inhibiting the pathogenic anti-TSHR immune response.     

Absence of IL-4, and not suppression of the Th2 response,prevents development of experimental autoimmune Graves' disease

In autoimmune Graves' disease (GD), autoantibodies bind to the thyrotropin receptor (TSHR) and cause hyperthyroidism. We studied the effects of fms-like tyrosine kinase receptor 3 ligand (Flt3-L) or GM-CSF treatment on the development of experimental autoimmune GD (EAGD) in mice, a slowly progressing Ab-mediated organ-specific autoimmune disease of the thyroid induced by immunization with syngeneic cells expressing TSHR. Flt3-L and GM-CSF treatment resulted in up-regulation of CD8a(+) and CD8a(-) dendritic cells, and skewing of cytokine and immune responses to TSHR in favor of Th1 and Th2, respectively. However, this skewing did not persist until the later stages, and thus failed to affect the course or severity of the disease. To determine whether the total absence of either IL-4 or IFN-gamma could affect the development of EAGD, we immunized wild-type, IFN-gamma(-/-) and IL-4(-/-) BALB/c mice with TSHR. Nearly 100% of the wild-type and IFN-gamma(-/-) mice developed EAGD with optimal TSHR-specific immune responses, while IL-4(-/-) mice completely resisted disease and showed delayed and suboptimal pathogenic Ab response. These data demonstrated that skewing immune responses to TSHR, using either Flt3-L or GM-CSF, in favor of Th1 or Th2, respectively, may not be sufficient to alter the course of the disease, while the complete absence of IL-4, but not IFN-gamma, can prevent the development of EAGD.     

IL-4 induces a Th2 response in Leishmania major-infected mice.

The infection of mice with Leishmania major can cause either a fatal disseminated disease or a localized healing disease, depending on the genetic background of the mice. A strong correlation has been shown between disease outcome and the nature of the T cell response, with healer strains developing a Th1-like response and nonhealer strains a Th2-like response. The treatment of nonhealer BALB/c mice with a single dose of an anti-IL-4 antibody, given at the time of infection with L. major, allowed these mice to develop healing Th1-like responses, suggesting that IL-4 is required in BALB/c mice for the differentiation of Th cells into Th2 cells. Anti-IL-4 had to be present during the first 2 wk of infection to have this effect. Anti-IL-4 caused a marked shift from a Th2 to a Th1 pattern of cytokine expression within 4 days, in vivo, and injections of IL-4 had the opposite effect on the early response in healer C3H/HeN mice. These findings demonstrate that IL-4 can induce the development of Th2 response to L. major infection in vivo.     

KM(+), a lectin from Artocarpus integrifolia, induces IL-12 p40 production by macrophages and switches from type 2 to type 1 cell-mediated immunity against Leishmania major antigens, resulting in BALB/c mice resistance to infection.

The outcome and severity of some diseases correlate with the dominance of either the T helper 1 (Th1) or Th2 immune response, which is stimulated by IL-12 or IL-4, respectively. In the present study we demonstrate that gamma interferon (IFN-gamma) secretion by murine spleen cells stimulated with KM(+), a mannose-binding lectin from Artocarpus integrifolia, is due to IL-12 induction, because (1) macrophages from several sources (including cell lines) produced IL-12 p40 in response to KM(+), and (2) lectin-free supernatants from J774 cell line cultures stimulated with KM(+) induced the secretion of IFN-gamma by spleen cell cultures, an effect blocked by the supernatant pretreatment with anti-IL-12 antibody. The known pattern of susceptibility of BALB/c mice to infection with Leishmania major, attributed to high levels of IL-4 production leading to a Th2 nonprotective immune response, was modified by administration of KM(+). Draining lymph node cells from these immunized BALB/c mice (in contrast to cells from animals immunized only with soluble leishmanial antigen [SLA]) secreted high levels of IFN-gamma and low levels of IL-4, which characterized a Th1 rather than a Th2 response pattern. The footpad thickness of BALB/c mice immunized with SLA plus KM(+) and challenged with L. major was similar to that of uninfected mice. This beneficial effect against leishmanial infection was blocked by pretreatment of these mice with anti-IL-12 antibody. These observations indicate that KM(+) induces IL-12 p40 in vivo and has a protective effect against L. major infection.     

IFN-gamma modulates the early development of Th1 and Th2 responses in a murine model of cutaneous leishmaniasis.

Resistance to Leishmania major in mice is associated with the generation of distinct CD4+ Th subsets, termed TH1 and TH2. To define the factors contributing to the genesis of these Th cells, we first investigated when these subsets developed following L. major infection. Lymph node (LN) cells collected 3 days after infection of BALB/c mice secreted IL-4 and IL-5 in vitro, but little IFN-gamma, whereas LN cells from a resistant strain, C3H/HeN, secreted IFN-gamma and no IL-4 or IL-5. Cytokine production was eliminated in both cases by in vivo or in vitro depletion of CD4+ cells, but not after depletion of CD8+ cells. Similar responses were observed after inoculation of killed promastigotes or a soluble leishmanial Ag preparation. These data indicate that the development of Th1- and Th2-like responses can precede lesion formation and does not require a live infection. We next investigated whether IFN-gamma was important in the differentiation of Th1 and Th2 cells. C3H/HeN mice have previously been shown to be susceptible to leishmanial infection after treatment with anti-IFN-gamma. We confirmed this observation and found that the abrogation of resistance was associated with enhanced production of IL-4 and IL-5, and decreased production of IFN-gamma by cells taken from these mice. Conversely, LN cells from BALB/c mice inoculated with parasites plus IFN-gamma produced significantly higher levels of IFN-gamma, and decreased levels of IL-4 and IL-5, than mice infected with parasites alone. Finally, we determined if IFN-gamma might augment vaccine induced immunity. We found that s.c. immunization with soluble leishmanial Ag, the bacterial adjuvant, Corynebacterium parvum and IFN-gamma could protect mice against L. major infection, and that this protection was associated with induction of Th1 responses. From these data we conclude that levels of IFN-gamma at the time of infection or immunization dramatically alters the type of response elicited: high levels of IFN-gamma favor Th1 type responses, whereas low levels promote a Th2 response.     

Different cytokines are required for induction and maintenance of the Th2 type response in DBA/2 mice resistant to infection with Leishmania major

Experimental cutaneous leishmaniasis is a useful model in studying the mechanism regulating immune responses between T helper type 1 (Th1) and Th2. Mice susceptible to Leishmania major infection such as BALB/c (H-2(d)) are associated with the induction of the disease-promoting Th2 response, while the resistant mice such as DBA/2 (H-2(d)) develop the protective Th1 response. To understand the induction mechanism of Th1 and Th2 responses, it is necessary to establish an immunization scheme by which the induction of each Th response can be easily and experimentally controlled. Adjuvants are known to enhance the immune responses through the combined effect of several factors: prolonged release of antigen, migration of cells, mitogenic effect and so forth. When the genetically resistant DBA/2 mice were immunized twice with soluble leishmanial antigen (SLA), emulsified in incomplete Freund's adjuvant (IFA) before L. major inoculation, these mice mounted a Th2 cell response and suffered from progressive infection. While IL-4 and IL-13 were upregulated early after the infection in both healer and non-healer groups of mice, IL-5 and IL-10 were upregulated only in non-healer mice. From these results, IL-5 and IL-10 appear to have an important role, at least in the early phases of the infection, rather than IL-4 and IL-13 in establishing the disease-promoting Th2 response in leishmaniasis. Further, IL-9 was found to be expressed in both BALB/c and DBA/2 mice immunized with IFA/SLA. This cytokine may support the establishment of a Th2 response in these mice. Therefore it is suggested that Th2 cytokines play different roles between priming and maintaining the Th2 immune response after the infection.     

An IFN-gamma-independent proinflammatory role of IL-18 in murine streptococcal cell wall arthritis

IL-18 is a member of the IL-1 family of proteins that exerts proinflammatory effects. It was formally known as IFN-gamma-inducing factor and is a pivotal cytokine for the development of Th1 responses. Apart from Th1 immune-stimulatory activity, IL-18 induces the production of proinflammatory cytokines such as TNF-alpha and IL-1 in vitro. The goal was to investigate the role of endogenous IL-18 in murine streptococcal cell wall (SCW)-induced arthritis. Furthermore, we investigated whether IL-18 neutralization had an impact on local TNF and IL-1 production. C57BL/6, BALB/c, and IFN-gamma-deficient mice were injected with 2 mg of rabbit anti-murine IL-18 Abs shortly before induction of arthritis by intra-articular injection of 25 microg of SCW fragments into the right knee joint. Suppression of joint swelling was noted on days 1 and 2 of SCW arthritis after blockade of endogenous IL-18. Analysis of local cytokine concentrations showed that IL-18, TNF-alpha, and IL-1ss levels were decreased. Severe inhibition of chondrocyte proteoglycan synthesis was seen in the vehicle-treated control animals, whereas a reversal of the inhibition of chondrocyte proteoglycan synthesis was found in the anti-IL-18-exposed animals. Blockade of endogenous IL-18 in IFN-gamma-deficient mice showed results similar to those found in wild-type animals, identifying a role for IL-18 that is IFN-gamma independent. The present study indicates that IL-18 is a proinflammatory cytokine during the onset of murine SCW arthritis, and this inflammatory role of IL-18 is IFN-gamma independent.     

New Lactococcus strain with immunomodulatory activity: enhancement of Th1-type immune response

Few studies exist dealing with the probiotic activity of lactococci, which are commonly used as starter bacteria in the manufacture of many kinds of fermented dairy products. Fifteen strains of the genus Lactococcus were examined for their probiotic activities, such as immunomodulatory effects. Six strains induced the production of cytokines (IL-12, IL-6, and TNF-alpha) in macrophage-like cell line J774.1, and the highest induction was observed with Lactococcus lactis subsp. lactis G50. The cytokine induction in the J774.1 cell line was almost entirely sustained after heat-killing of the strain. Spleen cells from BALB/c mice fed G50 culture produced more IL-12 and IFN-gamma and slightly less IL-4 and IL-6 than the control (i.e., without strain G50), indicating that strain G50 can enhance Th1-type immune response in vivo. The effect of the oral administration of strain G50 on antibody response in mice was also investigated. Mice were immunized with ovomucoid (OVM), a potent egg allergen, and the antibody level in the serum was then determined. The total IgE antibody level in the group treated with strain G50 was significantly lower than that of the control. The response of OVM-specific IgG1 and IgE antibodies tended to be low in the group that was administered strain G50, compared with the response of the control group. These results suggest that strain G50 has an ability to suppress the Th2 response. Thus, Lactococcus lactis subsp. lactis G50 is a potential probiotic strain for the suppression of hypersensitive reactions caused by the Th2 response.     

Reconstitution of Leishmania immunity in severe combined immunodeficient mice using Th1- and Th2-like cell lines.

Leishmania major disseminates in genetically susceptible BALB/c mice to cause fatal disease. Progressive infection has been linked to the failure of parasite-specific Th1, IFN-gamma-producing, CD4+ T lymphocytes to expand and direct macrophage activation and control of intracellular parasitism. In contrast, Th2 CD4+ cell expansion accompanies disease progression. Immunomodulation using CD4 cell depletion at the time of infection results in control of infection and Th1 CD4+ cell expansion. A Th1-like cell line, H1A, was established from the draining lymph nodes of an anti-CD4-pretreated BALB/c mouse infected with L. major, H1A was CD4, TCR(+)-alpha/beta, and released IL-2 and IFN-gamma in response to parasite Ag. A Th2-like cell line, U1A, was established from the lymph node cells of an infected BALB/c mouse that was also CD4, TCR(+)-alpha/beta but released IL-4 and IL-5 after stimulation. Mice with severe combined immunodeficiency were reconstituted with H1A and U1A before infection with L. major. Non-reconstituted mice were unable to restrict parasite growth. Mice reconstituted with H1A healed infection, whereas mice reconstituted with U1A suffered exacerbation of disease. Analysis of spleen cells by flow cytometry confirmed the reconstitution of CD4+ cells in both instances, and stimulation with mitogen established that the lymphokine profile of the donor cells had been maintained during 6 to 8 wk of infection. Histologic analysis of the lesions confirmed migration of donated cells to sites of infection. Neutralization of IFN-gamma in H1A-reconstituted mice and IL-4 in U1A-reconstituted mice reversed the disease phenotype mediated by the two cell lines. These data demonstrate the capacity of CD4+ T cells alone to modulate both positively and negatively the course of leishmaniasis in a lymphokine-dependent manner.     

Endogenous IFN-gamma production is induced and required for protective immunity against pulmonary chlamydial infection in neonatal mice

Chlamydia trachomatis infection in neonates, not adults, has been associated with the development of chronic respiratory sequelae. Adult chlamydial infections induce Th1-type responses that subsequently clear the infection, whereas the neonatal immune milieu in general has been reported to be biased toward Th2-type responses. We examined the protective immune responses against intranasal Chlamydia muridarum challenge in 1-day-old C57BL/6 and BALB/c mice. Infected C57BL/6 pups displayed earlier chlamydial clearance (day 14) compared with BALB/c pups (day 21). However, challenged C57BL/6 pups exhibited prolonged deficits in body weight gain (days 12-30) compared with BALB/c pups (days 9-12), which correlated with continual pulmonary cellular infiltration. Both strains exhibited a robust Th1-type response, including elevated titers of serum antichlamydial IgG2a and IgG2b, not IgG1, and elevated levels of splenic C. muridarum-specific IFN-gamma, not IL-4, production. Additionally, elevated IFN-gamma, not IL-4 expression, was observed locally in the infected lungs of both mouse strains. The immune responses in C57BL/6 pups were significantly greater compared with BALB/c pups after chlamydial challenge. Importantly, infected mice deficient in IFN-gamma or IFN-gamma receptor demonstrated enhanced chlamydial dissemination, and 100% of animals died by 2 wk postchallenge. Collectively, these results indicate that neonatal pulmonary chlamydial infection induces a robust Th1-type response, with elevated pulmonary IFN-gamma production, and that endogenous IFN-gamma is important in protection against this infection. The enhanced IFN-gamma induction in the immature neonatal lung also may be relevant to the development of respiratory sequelae in adult life.     

Helicobacter pylori-induced mucosal inflammation is Th1 mediated and exacerbated in IL-4, but not IFN-gamma, gene-deficient mice

To elucidate the pathogenesis of Helicobacter pylori-associated gastritis, we studied immune responses of C57BL/6J wild-type (WT), SCID, and gene deficient (IFN-gamma-/- and IL-4-/-) mice following infection with a pathogenic isolate of H. pylori (SPM326). During early infection in WT mice, mononuclear and polymorphonuclear cells accumulated in the gastric lamina propria, and the numbers of cells in the inflamed mucosa expressing IFN-gamma, but not IL-4, mRNA rose significantly (p < 0.005), consistent with a local Th1 response. Splenic T cells from the same infected WT mice produced high levels of IFN-gamma, no detectable IL-4, and low amounts of IL-10 following in vitro H. pylori urease stimulation, reflecting a systemic Th1 response. Infected C57BL/6J SCID mice did not develop gastric inflammation despite colonization by many bacteria. Infected C57BL/10J and BALB/c mice also did not develop gastric inflammation and displayed a mixed Th1/Th2 splenic cytokine profile. These data imply a major role for the Th1 cytokine IFN-gamma in H. pylori-associated gastric inflammation in C57BL/6J mice. Compared with WT animals, infected IL-4-/- animals had more severe gastritis and higher levels of IFN-gamma production by urease-stimulated splenocytes (p < 0.01), whereas IFN-gamma-/- mice exhibited no gastric inflammation and higher levels of IL-4 production by stimulated splenocytes. These findings establish C57BL/6J mice as an important model for H. pylori infection and demonstrate that up-regulated production of IFN-gamma, in the absence of the opposing effects of IL-4 (and possibly IL-10), plays a pivotal role in promoting H. pylori-induced mucosal inflammation.     

Tyk2 negatively regulates adaptive Th1 immunity by mediating IL-10 signaling and promoting IFN-gamma-dependent IL-10 reactivation

The Jak, Tyk2, is activated in response to IL-12 and IFN-alphabeta and promotes IFN-gamma production by Th1-type CD4 cells. Mice deficient in Tyk2 function have been previously shown to be resistant to autoimmune arthritis and septic shock but are acutely susceptible to opportunistic pathogens such as Toxoplasma gondii. In this study, we show that Tyk2, in addition to mediating the biological effects of IL-12 and IFN-alphabeta, is an important regulator for the signaling and expression of the immunosuppressive cytokine IL-10. In the absence of Tyk2, Ag-reactive CD4 cells exhibit impaired IL-10 synthesis following rechallenge of T. gondii vaccine-primed mice. The impaired IL-10 reactivation leads to unopposed antimicrobial effector mechanisms which results in a paradoxically superior protection of immune Tyk2(-/-) mice against virulent T. gondii challenge. We further demonstrate that Tyk2 indirectly controls CD4 IL-10 reactivation by signaling for maximal IFN-gamma secretion. The unexpected role of IFN-gamma in mediating IL-10 reactivation by Th1 cells provides compelling evidence that conditions driving Th1 responses establish a negative feedback loop, which will ultimately lead to its autoregulation. Thus, Tyk2 can be viewed as a dual-function Jak, mediating both pro and anti-inflammatory cytokine responses.     

BALB/c mice bearing a transgenic IL-12 receptor beta 2 gene exhibit a nonhealing phenotype to Leishmania major infection despite intact IL-12 signaling

In BALB/c mice infected with Leishmania major, early secretion of IL-4 leads to a Th2-type response and nonhealing. We explored the role of IL-4-induced down-regulation of the IL-12Rbeta2 chain in the establishment of this Th2 response. First, we showed that the draining lymph nodes of resistant C57BL/6 mice infected with L. major were enriched in CD4+/IL-12Rbeta2 chain+ cells producing IFN-gamma. Next, we demonstrated that BALB/c background mice bearing an IL-12Rbeta2-chain transgene manifested a nonhealing phenotype similar to wild-type littermates despite the persistence of their ability to undergo STAT4 activation. Finally, we found that such transgenic mice display more severe infection than wild-type littermates when treated with IL-12 7 days after infection, and under this condition, the mice display increased Leishmania Ag-induced IL-4 secretion. These studies indicate that although CD4+/IL-12Rbeta2 chain+ T cells are important components of the Th1 response, maintenance of IL-12Rbeta2 chain expression is not sufficient to change a Th2 response to a Th1 response in vivo and thus to allow BALB/c mice to heal L. major infection.     

Differential production of Th1- and Th2-derived cytokines does not determine the genetically controlled or vaccine-induced rate of cure in murine visceral leishmaniasis

Recent studies with models of cutaneous leishmaniasis have provoked much interest in the role of CD4+ T cell subsets in determining the outcome of infectious disease. In Leishmania major infections, cure vs progressive disease correlates with the expansion of Th1-like or Th2-like CD4+ populations, respectively. We have investigated whether similar responses are associated with the differential patterns of infection seen in models of visceral leishmaniasis, caused by L. donovani. Splenic lymphocytes from infected Lsh congenic C57BL/10 (Lshs;H-2b) and B10.L-Lshr (Lshr;H-2b) mice and MHC congenic non-curing B10.D2/n (Lshs;H-2d) mice were examined for the production of cytokines representative of these CD4+ populations (IL-2, IL-3, IL-4, IL-5, and IFN-gamma). In all three strains examined, there was no evidence for the production of Th2-restricted cytokines. In addition, levels of serum IgE were depressed during the early phase of infection, indicative of in vivo IFN-gamma production. In the non-curing B10.D2/n strain, late phase of infection was associated with the decreased ability to produce cytokines in response to Ag and not with the production of IL-4 or IL-5 in response to Ag or mitogen. Serum IgE levels were also not raised above levels seen in uninfected controls. C57BL/10 mice were vaccinated with SDS-PAGE fractionated amastigote Ag bound to nitrocellulose and cytokine levels determined at various times after infection. The protocol used for vaccination was able to induce significant modulation of the course of infection in this strain and it was clear that IFN-gamma production in vitro provided an excellent correlate of rate of cure. Occasional individuals produced low levels of IL-5 in culture in response to parasite Ag, but this did not correlate with disease progression. Together, these data suggest that over-expansion of Th2-type cells and production of their specific cytokines (IL-4 and IL-5) is not a contributing factor to the variable long term course of L. donovani infection in these strains of mice.