IL-18 regulates intestinal mastocytosis and Th2 cytokine production independently of IFN-gamma during Trichinella spiralis infection

Expulsion of the gastrointestinal nematode Trichinella spiralis is associated with pronounced mastocytosis mediated by a Th2-type response involving IL-4, IL-10, and IL-13. Here we demonstrate that IL-18 is a key negative regulator of protective immune responses against T. spiralis in vivo. IL-18 knockout mice are highly resistant to T. spiralis infection, expel the worms rapidly and subsequently develop low levels of encysted muscle larvae. The increased speed of expulsion is correlated with high numbers of mucosal mast cells and an increase in IL-13 and IL-10 secretion. When normal mice were treated with rIL-18 in vivo, worm expulsion was notably delayed, and the development of mastocytosis and Th2 cytokine production was significantly reduced. The treatment had no effect on intestinal eosinophilia or goblet cell hyperplasia but specifically inhibited the development of mastocytosis. Addition of rIL-18 to in vitro cultures of bone marrow-derived mast cells resulted in a significant reduction in cell yields as well as in the number of IL-4-secreting mast cells. In vivo treatment of T. spiralis-infected IFN-gamma knockout mice with rIL-18 demonstrated that the inhibitory effect of IL-18 on mastocytosis and Th2 cytokine secretion is independent of IFN-gamma. Hence, IL-18 plays a significant biological role as a negative regulator of intestinal mast cell responses and may promote the survival of intestinal parasites in vivo.     

Reciprocal regulatory effects of IFN-gamma and IL-4 on the in vitro development of human Th1 and Th2 clones.

The effects exerted on the in vitro development of purified protein derivative (PPD)-specific or Dermatophagoides pteronyssinus group I (Der p I)-specific T cell lines (TCL) and T cell clones (TCC) by IL-4 or IFN-gamma addition or neutralization in human PBMC cultures were examined. PBMC from two normal individuals, which were stimulated with PPD and then cultured in IL-2 alone, developed into PPD-specific TCL and TCC able to produce IFN-gamma and IL-2 but not IL-4 and IL-5 (Th1-like). IFN-gamma or anti-IL-4 antibody addition in bulk cultures before cloning did not influence the PPD-specific TCL profile of cytokine production. In contrast, the addition of IL-4 resulted in the development of PPD-specific TCL and TCC able to produce not only IFN-gamma and IL-2 but also IL-4 and IL-5. PBMC from one atopic Der p I-sensitive patient, which were stimulated with Der p I and then cultured in IL-2 alone, developed into Der p I-specific TCL and TCC able to produce IL-5 and large amounts of IL-4 but no IFN-gamma (Th2-like). The addition in bulk cultures, before cloning, of either IFN-gamma or anti-IL-4 antibody markedly inhibited the development of Der p I-specific T cells into IL-4- and IL-5-producing TCL. Accordingly, the development into Der p I-specific Th2-like TCC was significantly reduced by the addition of IFN-gamma in bulk culture and was virtually suppressed by the presence of both IFN-gamma and anti-IL-4 antibody. These data suggest that the presence or the absence of IL-4 and IFN-gamma in bulk cultures of PBMC before cloning may have strong regulatory effects on the in vitro development of human CD4+ T cells into Th1 or Th2 clones.     

Shift in Th1 (IL-2 and IFN-gamma) and Th2 (IL-10 and IL-4) cytokine mRNA balance within two new histological main-types of rheumatoid-arthritis (RA).

Cytokines are the main mediators of inflammation in rheumatoid arthritis (RA). Thus, Th2 cytokines--such as IL-4 and IL-10--have protective properties to this disease. In opposite, the Th1 cytokines--such as IL-2 and IFN-gamma--are supporting proinflammatory microenvironment in joints from patients with RA. The imbalance of Th1/Th2 cytokine steady state may play an important role in the pathogenesis of rheumatoid arthritis. The evaluation of this imbalance leads up to the possibility of pathohistological discrimination in this disease. In this context, we investigated Th1- (IFN-gamma, IL-2) and Th2 (IL-10, IL-4)-cell-derived cytokine mRNA expression in two novel pathohistological main-types of RA synovial membrane (SM). These main-types are characterized by different tissue-infiltrating inflammatory cells and different extent of SM destruction. Our findings showed that expression of IL-10 mRNA was an outcome of histological main-type I (p<0.001), whereas expression of IFN-gamma and IL-2 were mainly associated with pathohistological main-type II (p<0.005, p<0.05). Surprisingly, IL4 was not differential expressed and could be associated with another special T cell subset in this disease. These results suggest that Th1/Th2 balance is biased to Th2 cytokines within main-type I and Th1 cytokines in main-type II.     

The roles of IL-10 and TGF-beta in controlling IL-4 and IFN-gamma production during experimental Fasciola hepatica infection

Hosts infected with Fasciola hepatica experience immunosuppression during the acute and chronic phases of the disease. This immunosuppression may allow parasite survival in the face of an ongoing immune response. In bovine hosts early IL-4 and continued IgG1 production is one of the few remaining features of the characteristic type 0/2 helper (Th0/2) response present in the chronic stage of disease. Here we demonstrate elevated levels of parasite-specific, in vitro peripheral blood mononuclear cell (PBMC)-derived transforming growth factor (TGF)-β1 from the early phases of infection and increasing levels of IL-10 as the infection becomes chronic. In vitro neutralisation of these cytokines during culture of PBMCs from experimentally-infected cattle increased IL-4 and IFN-γ production in response to parasite-specific and non-specific stimulation. At 4 weeks p.i. neutralisation of TGF-β results in an increase in parasite driven IL-4, while also having a greater role, compared with IL-10, in influencing specific and non-specific IFN-γ. At 12 weeks p.i. ex vivo parasite driven IL-4 was not restored by inhibiting either IL-10 or TGF-β. However IL-10 influenced both parasite-specific and non-specific IFN-γ production at this time. This highlights the roles of IL-10 and TGF-β in fasciolosis, however the cellular sources of these have yet to be defined. This suggests that suppression of IFN-γ production by parasite molecules occurs during infection and it is possible that the suppression of IFN-γ production may mediate parasite survival in this disease.     

Role of IFN-gamma in Th1 differentiation: IFN-gamma regulates IL-18R alpha expression by preventing the negative effects of IL-4 and by inducing/maintaining IL-12 receptor beta 2 expression

Two key events occur during the differentiation of IFN-gamma-secreting Th1 cells: up-regulation of IL-12Rbeta2 and IL-12-driven up-regulation of IL-18Ralpha. We previously demonstrated that IL-12-driven up-regulation of IL-18Ralpha expression is severely impaired in IFN-gamma(-/-) mice. However, it was unclear from these studies how IFN-gamma influenced IL-18Ralpha since IFN-gamma alone had no direct effect on IL-18Ralpha expression. In the absence of IL-4, IL-12-dependent up-regulation of IL-18Ralpha/IL-12Rbeta2 was independent of IFN-gamma. However, in the presence of IL-4, IFN-gamma functions to limit the negative effects of IL-4 on both IL-18Ralpha and IL-12Rbeta2. Neutralization of IL-4 restored IL-12-driven up-regulation of IL-18Ralpha/IL-12Rbeta2 in an IFN-gamma-independent fashion. In the absence of both IL-12 and IL-4, IFN-gamma up-regulates IL-12beta2 expression and primes IFN-gamma-producing Th1 cells. When T cells were primed in the presence of IL-4, no correlation was found between the levels of expression of the IL-18Ralpha or the IL-12Rbeta2 and the capacity of these cells to produce IFN-gamma, suggesting that IL-4 may also negatively affect IL-12-mediated signal transduction and thus Th1 differentiation. These data clarify the role of IFN-gamma in regulation of IL-18Ralpha/IL-12Rbeta2 during both IL-12-dependent and IL-12-independent Th1 differentiation.     

Healthy individuals that control a latent infection with Mycobacterium tuberculosis express high levels of Th1 cytokines and the IL-4 antagonist IL-4delta2

The majority of healthy individuals exposed to Mycobacterium tuberculosis will not develop disease and identifying what constitutes "protective immunity" is one of the holy grails of M. tuberculosis immunology. It is known that IFN-gamma is essential for protection, but it is also apparent that IFN-gamma levels alone do not explain the immunity/susceptibility dichotomy. The controversy regarding correlates of immunity persists because identifying infected but healthy individuals (those who are immune) has been problematic. We have therefore used recognition of the M. tuberculosis virulence factor early secretory antigenic target 6 to identify healthy, but infected individuals from tuberculosis (TB)-endemic and nonendemic regions (Ethiopia and Denmark) and have compared signals for cytokines expressed directly ex vivo with the pattern found in TB patients. We find that TB patients are characterized by decreased levels of Th1 cytokines and increased levels of IL-10 compared with the healthy infected and noninfected community controls. Interestingly, the healthy infected subjects exhibited a selective increase of message for the IL-4 antagonist, IL-4delta2, compared with both TB patients or noninfected individuals. These data suggest that long-term control of M. tuberculosis infection is associated not just with elevated Th1 responses but also with inhibition of the Th2 response.     

Increased nonobese diabetic Th1:Th2 (IFN-gamma:IL-4) ratio is CD4+ T cell intrinsic and independent of APC genetic background

Autoreactive CD4(+) T cells play a major role in the pathogenesis of autoimmune diabetes in nonobese diabetic (NOD) mice. We recently showed that the non-MHC genetic background controlled enhanced entry into the IFN-gamma pathway by NOD vs B6.G7 T cells. In this study, we demonstrate that increased IFN-gamma, decreased IL-4, and decreased IL-10 production in NOD T cells is CD4 T cell intrinsic. NOD CD4(+) T cells purified and stimulated with anti-CD3/anti-CD28 Abs generated greater IFN-gamma, less IL-4, and less IL-10 than B6.G7 CD4(+) T cells. The same results were obtained in purified NOD.H2(b) vs B6 CD4(+) T cells, demonstrating that the non-MHC NOD genetic background controlled the cytokine phenotype. Moreover, the increased IFN-gamma:IL-4 cytokine ratio was independent of the genetic background of APCs, since NOD CD4(+) T cells generated increased IFN-gamma and decreased IL-4 compared with B6.G7 CD4(+) T cells, regardless of whether they were stimulated with NOD or B6.G7 APCs. Cell cycle analysis showed that the cytokine differences were not due to cycle/proliferative differences between NOD and B6.G7, since stimulated CD4(+) T cells from both strains showed quantitatively identical entry into subsequent cell divisions (shown by CFSE staining), although NOD cells showed greater numbers of IFN-gamma-positive cells with each subsequent cell division. Moreover, 7-aminoactinomycin D and 5-bromo-2'-deoxyuridine analysis showed indistinguishable entry into G(0)/G(1), S, and G(2)/M phases of the cell cycle for both NOD and B6.G7 CD4(+) cells, with both strains generating IFN-gamma predominantly in the S phase. Therefore, the NOD cytokine effector phenotype is CD4(+) T cell intrinsic, genetically controlled, and independent of cell cycle machinery.     

IL-13 induces disease-promoting type 2 cytokines, alternatively activated macrophages and allergic inflammation during pulmonary infection of mice with Cryptococcus neoformans

In the murine model of Cryptococcus neoformans infection Th1 (IL-12/IFN-gamma) and Th17 (IL-23/IL-17) responses are associated with protection, whereas an IL-4-dependent Th2 response exacerbates disease. To investigate the role of the Th2 cytokine IL-13 during pulmonary infection with C. neoformans, IL-13-overexpressing transgenic (IL-13Tg(+)), IL-13-deficient (IL-13(-/-)), and wild-type (WT) mice were infected intranasally. Susceptibility to C. neoformans infection was found when IL-13 was induced in WT mice or overproduced in IL-13Tg(+) mice. Infected IL-13Tg(+) mice had a reduced survival time and higher pulmonary fungal load as compared with WT mice. In contrast, infected IL-13(-/-) mice were resistant and 89% of these mice survived the entire period of the experiment. Ag-specific production of IL-13 by susceptible WT and IL-13Tg(+) mice was associated with a significant type 2 cytokine shift but only minor changes in IFN-gamma production. Consistent with enhanced type 2 cytokine production, high levels of serum IgE and low ratios of serum IgG2a/IgG1 were detected in susceptible WT and IL-13Tg(+) mice. Interestingly, expression of IL-13 by susceptible WT and IL-13Tg(+) mice was associated with reduced IL-17 production. IL-13 was found to induce formation of alternatively activated macrophages expressing arginase-1, macrophage mannose receptor (CD206), and YM1. In addition, IL-13 production led to lung eosinophilia, goblet cell metaplasia and elevated mucus production, and enhanced airway hyperreactivity. This indicates that IL-13 contributes to fatal allergic inflammation during C. neoformans infection.     

Flow cytometric detection of type 1 (IL-2, IFN-gamma) and type 2 (IL-4, IL-5) cytokines in T-helper and T-suppressor/cytotoxic cells in rheumatoid arthritis, allergic asthma and atopic dermatitis.

Type 1 cytokines (a.o. IL-2 and IFN-gamma) play an important role in the pathogenesis of rheumatoid arthritis. On the other hand, IgE-mediated diseases such as allergic asthma and atopic dermatitis show a type 2 cytokine (amongst others IL-4 and IL-5) profile.This study examined simultaneously the intracellular production of IL-2, IFN-gamma, IL-4 and IL-5 in T-lymphocytes of patients with rheumatoid arthritis during treatment with methotrexate or salazopyrin, patients with allergic asthma or atopic dermatitis under stable treatment, compared to healthy controls.A three-colour flow cytometric analysis was used for cytokine detection in T-helper cells and T-suppressor/cytotoxic cells.Compared to controls, patients with symptomatic atopic dermatitis showed an increased number of IL-4-producing T-helper lymphocytes in basal circumstances (P=0.001), in contrast to asymptomatic allergic asthma patients. Compared to controls, rheumatoid arthritis patients, treated with salazopyrin, showed an increased number of IL-2-producing T-helper and T-suppressor/cytotoxic lymphocytes after in vitro stimulation with PMA and ionomycin (P=0.01). In contrast, rheumatoid arthritis patients, treated with methotrexate, a more potent disease modifying drug, did not show this type 1 cytokine profile. A positive correlation was found between the number of IFN-gamma producing T-helper cells and disease activity (Ritchie Index and number of swollen joints) in both rheumatoid arthritis patient groups.Active atopic dermatitis patients showed a type 2 cytokine profile, whereas stable asthma patients with lower disease activity did not show a predominance of type 2 cytokines. Rheumatoid arthritis patients under treatment with salazopyrin had a type 1 cytokine profile, which could not be demonstrated in patients treated with methotrexate. This imbalance between type 1 and type 2 cytokines in different immune mediated disorders can be related with treatment and the grade of disease activity. These results stress the need for further investigation of the influence of therapy on cytokine profiles.     

Serum antibody response and nasal lymphoid tissue (NALT) structure in the absence of IL-4 or IFN-gamma

Immunization via the nasal route is effective for inducing not only mucosal immunity but also antibody (Ab) response in serum. Nasal lymphoid tissue (NALT) is important for induction of systemic immunity. It remains controversial which T effector cell response is important for serum Ab response after nasal immunization. We investigated serum Ab responses and NALT structures in interleukin (IL)-4 gene targeted (IL-4(-/-)) and interferon (IFN)-gamma gene targeted (IFN-gamma(-/-)) mice. Mice were immunized via nostrils with ovalbumin (OVA) and cholera toxin as adjuvant and serum Ab titers were measured 1 week after final antigen challenge. OVA-specific IgG titers in sera of IL-4(-/-) mice indicated a Th(1) type response, whereas titers in IFN-gamma(-/-) mice and wild-type mice indicated a Th(2) type response. Enhanced serum Ab responses were observed in IL-4(-/-) mice but not IFN-gamma(-/-) mice. OVA-specific Ab-forming cells were detected in the cervical draining lymph nodes but were rare or absent in and around the NALT of all strains of mice. Numbers of OVA-specific Ab-forming cells in cervical lymph nodes were significantly higher in IL-4(-/-) mice than in wild-type and IFN-gamma(-/-) mice. Germinal centers of lymphoid follicles were present in NALT of IL-4(-/-) and other mice. Immunohistochemistry for B and T cell markers revealed that NALT of all mice had approximately the same cellular compositions. Although the absence of IL-4 had no effect on NALT structure, IL-4 may suppress induction of serum Ab responses by nasal immunization.     

Effect of IL-12 and soluble IL-4 receptor on the herpesvirus infection in human SCID chimeras whose Th2 cells predominate

Th2 cytokines, commonly detected in burn patients, have been shown as inhibitors for the generation of Th1 cells that are essential for the host's resistance against herpes simplex virus type 1 (HSV-1) infection. In this study, the possibility of immunological treatment through the regulation of Th1/Th2 responses was examined in two kinds of human severe combined immunodeficiency (SCID) chimera models reflecting human immune functions. SCID mice injected with a mixture of PBMC from a healthy donor and Th2 cells experimentally generated from the same healthy PBMC (Th2 SCID chimeras) were more susceptible to HSV-1 infection when compared with SCID mice injected with healthy donor PBMC (healthy SCID chimeras). When Th2 SCID chimeras were individually treated with human IL-12 (hIL-12) or human soluble IL-4 receptor (hsIL-4R), hIFN-gamma was not produced in their sera after antihuman CD3 mAb stimulation. However, hIFN-gamma production in sera of Th2 SCID chimeras treated with the combination therapy of hIL-12 and hsIL-4R was recovered at levels observed in healthy SCID chimeras. When Th2 SCID chimeras infected with HSV-1 were treated with saline, hIL-12, hsIL-4R or a combination of hIL-12 and hsIL-4R, 13%, 13%, 25% or 100% of them survived, respectively. Also, Th1 responses (hIFN-gamma production) were demonstrated in Th2 SCID chimeras that became resistant against HSV-1 infection after the combination treatment. These results suggest that individuals whose Th2 cells predominated may be immunologically controlled by the combination treatment between a Th1 response inducer and a Th2 response inhibitor.     

Regulatory roles of IL-2 and IL-4 in H4/inducible costimulator expression on activated CD4+ T cells during Th cell development

We found a tight correlation among the levels of H4/inducible costimulator (ICOS) expression, IL-4 production, and GATA-3 induction, using activated CD4(+) T cells obtained from six different murine strains. BALB/c-activated CD4(+) T cells expressed approximately 10-fold more H4/ICOS on their surfaces and produced approximately 10-fold more IL-4 upon restimulation than C57BL/6-activated CD4(+) T cells. BALB/c naive CD4(+) T cells were shown to produce much higher amounts of IL-2 and IL-4 upon primary stimulation than C57BL/6 naive CD4(+) T cells. Neutralization of IL-4 with mAbs in culture of BALB/c naive CD4(+) T cells strongly down-regulated both H4/ICOS expression on activated CD4(+) T cells and IL-4 production upon subsequent restimulation. Conversely, exogenous IL-4 added to the culture of BALB/c or C57BL/6 naive CD4(+) T cells up-regulated H4/ICOS expression and IL-4 production upon restimulation. In addition, retroviral expression of GATA-3 during the stimulation of naive CD4(+) T cells from C57BL/6 or IL-4(-/-) mice increased H4/ICOS expression on activated CD4(+) T cells. A similar effect of IL-2 in the primary culture of BALB/c naive CD4(+) T cells appeared to be mediated by IL-4, the production of which was regulated by IL-2. These data suggest that IL-4 induced by IL-2 is critical to the maintenance of high H4/ICOS expression on BALB/c-activated CD4(+) T cells.     

Analysis of Th1 and Th2 cells in murine gut-associated tissues. Frequencies of CD4+ and CD8+ T cells that secrete IFN-gamma and IL-5

After Ag and/or mitogen stimulation, cloned mouse Th1 and Th2 cells produce different cytokines that contribute to induction of particular B cell isotype responses. In this regard, IL-5 produced by Th2 cells has been shown to enhance IgA synthesis in LPS-triggered splenic (SP) B cell or in unstimulated Peyer's patch (PP) B cell cultures. This raises the possibility that Th2 cells may occur in higher frequency in gut-associated tissues, because B cells in these areas are committed to IgA synthesis. We have used an ELISPOT assay to detect individual T cells producing IFN-gamma or IL-5. For the IL-5 assay, the mAb TRFK-5 and biotinylated TRFK-4 were used in coating and detection, respectively, whereas the mAb R4-6A2 and biotinylated XMG 1.2 were similarly used for enumeration of IFN-gamma-specific spot forming cells (SFC). Specificity of each assay was tested by using Con A-activated, cloned Th1 (H66-61) or Th2 (CDC-25) cells, where the Th1 cells only produced IFN-gamma SFC and the Th2 cells only gave IL-5-specific spots. Further, preincubation of biotinylated TRFK-4 or XMG 1.2 with rIL-5 or IFN-gamma, respectively, abrogated the formation of specific spots when tested with Con A-activated SP CD4+ T cells. Both IFN-gamma and IL-5 were produced de novo, because treatment of T cells with cycloheximide inhibited both IFN-gamma and IL-5 SFC. We have assessed the numbers of T cells spontaneously secreting these cytokines in PP and in lamina propria and intraepithelial lymphocyte (LPL and IEL) populations. Moderate levels of IL-5 SFC occurred in the IEL subset, whereas higher levels existed in the LPL population. Although significant numbers of IFN-gamma SFC (Th1-type) were also seen in LPLs, the frequency of IL-5 SFC was always higher (Th1:Th2 in LPL = 1:3). In IELs, equal numbers of IFN-gamma and IL-5 SFC were seen. Interestingly, CD8+ IEL T cells produced these two cytokines. In contrast, T cells freshly isolated from PP, an IgA inductive site, contained smaller numbers of IL-5- or IFN-gamma-secreting cells and SP T cells had essentially no SFC. When PP or SP T cells were stimulated with Con A, significant and approximately equal numbers of IFN-gamma- and IL-5-producing cells appeared.(ABSTRACT TRUNCATED AT 250 WORDS)     

Timing of IFN-beta exposure during human dendritic cell maturation and naive Th cell stimulation has contrasting effects on Th1 subset generation: a role for IFN-beta-mediated regulation of IL-12 family cytokines and IL-18 in naive Th cell differentiation

Type I IFNs, IFN-alpha and IFN-beta, are early effectors of innate immune responses against microbes that can also regulate subsequent adaptive immunity by promoting antimicrobial Th1-type responses. In contrast, the ability of IFN-beta to inhibit autoimmune Th1 responses is thought to account for some of the beneficial effects of IFN-beta therapy in the treatment of relapsing remitting multiple sclerosis. To understand the basis of the paradoxical effects of IFN-beta on the expression of Th1-type immune responses, we developed an in vitro model of monocyte-derived dendritic cell (DC)-dependent, human naive Th cell differentiation, in which one can observe both positive and negative effects of IFN-beta on the generation of Th1 cells. In this model we found that the timing of IFN-beta exposure determines whether IFN-beta will have a positive or a negative effect on naive Th cell differentiation into Th1 cells. Specifically, the presence of IFN-beta during TNF-alpha-induced DC maturation strongly augments the capacity of DC to promote the generation of IFN-gamma-secreting Th1 cells. In contrast, exposure to IFN-beta during mature DC-mediated primary stimulation of naive Th cells has the opposite effect, in that it inhibits Th1 cell polarization and promotes the generation of an IL-10-secreting T cell subset. Studies with blocking mAbs and recombinant cytokines indicate that the mechanism by which IFN-beta mediates these contrasting effects on Th1 cell generation is at least in part by differentially regulating DC expression of IL-12 family cytokines (IL-12 and/or IL-23, and IL-27) and IL-18.     

Antigen-specific activation of effector macrophages by IFN-gamma producing (TH1) T cell clones. Failure of IL-4-producing (TH2) T cell clones to activate effector function in macrophages

IFN-gamma-producing (TH1) and IL-4-producing (TH2) clones were assayed for their ability to directly induce cytostatic activity in macrophages generated from splenic myeloid precursors (M phi-c). In the presence, but not in the absence, of antigen, TH1 clones activated the M phi-c to inhibit the growth of P815 tumor cells in vitro. TH2 clones were not able to activate such effector activity in the M phi-c. The M phi-c did effectively present Ag to the TH2 clones as evidenced by the proliferation of TH2 cells cultured with Ag in the presence, but not in the absence, of M phi-c. Therefore, although both TH1 and TH2 were activated by cognate interaction with antigen presenting M phi-c, only TH1:M phi-c interactions displayed reciprocity resulting in activation of the M phi-c. TH1-derived lymphokines or rIFN-gamma, in the presence of LPS, could activate proteose-peptone elicited M phi, resident peritoneal M phi, and M phi-c whereas neither TH2-derived lymphokines nor rIL4 could induce detectable activity in any of the 3 M phi populations. IFN-gamma, in the absence of LPS, could activate the elicited M phi and to a lesser and more variable degree, the resident M phi Only the M phi-c consistently required both IFN-gamma and LPS for induction of cytostatic activity. Since M phi-c consistently required at least two signals for activation, the ability of TH1-derived lymphokines to synergize with TH2 cells in M phi activation was examined. TH2 could activate the Ag-presenting M phi-c in the presence of IFN-gamma. The ability of added IFN-gamma to synergize with TH2 indicates that the cognate interaction between TH2 and antigen presenting M phi-c does result in delivery of at least one of the signal required for M phi activation.     

Cutting edge: ectopic expression of the IL-12 receptor-beta 2 in developing and committed Th2 cells does not affect the production of IL-4 or induce the production of IFN-gamma

The IL-12 receptor-beta 2 (IL-12R beta 2) chain is expressed on Th1 cells and lost upon differentiation to the Th2 phenotype. This has been suggested as the basis for commitment of Th1 cells, because early differentiated Th2 cells do not reverse their phenotype and do not produce IFN-gamma on restimulation in the presence of IL-12. In this study, we ectopically expressed the IL-12 receptor-beta 2 (IL-12R beta 2) bicistronically with enhanced green fluorescent protein by retroviral infection in developing and committed Th2 cells. Restimulation of Th2 cells expressing this ectopic IL-12R beta 2 in the presence of IL-12 led to levels of IL-4 production similar to those in control Th2 cells. The expression of IL-12R beta 2 in Th2 cells did not lead to significant levels of IFN-gamma production, although IL-12-mediated STAT signaling and proliferation were restored. Thus, although the IL-12R beta 2 and IL-12-dependent STAT4 activation are required for Th1 responses, activation of this pathway is not sufficient to restore a Th1 phenotype in developing or committed Th2 cells.