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.     

Human dendritic cells discriminate between viable and killed Toxoplasma gondii tachyzoites: dendritic cell activation after infection with viable parasites results in CD28 and CD40 ligand signaling that controls IL-12-dependent and -independent T cell production of IFN-gamma

We studied how the interaction between human dendritic cells (DC) and Toxoplasma gondii influences the generation of cell-mediated immunity against the parasite. We demonstrate that viable, but not killed, tachyzoites of T. gondii altered the phenotype of immature DC. DC infected with viable parasites up-regulated the expression of CD40, CD80, CD86, and HLA-DR and down-regulated expression of CD115. These changes are indicative of DC activation induced by T. gondii. Viable and killed tachyzoites had contrasting effects on cytokine production. DC infected with viable T. gondii rather than DC that phagocytosed killed parasites induced secretion of high amounts of IFN-gamma by T cells from T. gondii-seronegative donors. IFN-gamma production in response to DC infected with viable parasites required CD28 and CD40 ligand (CD40L) signaling. In addition, this IFN-gamma response was dependent in part on IL-12 secretion. Production of IL-12 p70 occurred after interaction between T cells and DC infected with viable T. gondii, but not after incubation of T cells with DC plus killed tachyzoites. IL-12 synthesis was inhibited by blockade of CD40L signaling. IL-12-independent IFN-gamma production required CD80/CD86-CD28 interaction and, to a lesser extent, CD40-CD40L signaling. Taken together, T. gondii-induced activation of human DC is associated with T cell production of IFN-gamma through CD40-CD40L-dependent release of IL-12 and through CD80/CD86-CD28 and CD40-CD40L signaling that mediate IFN-gamma secretion even in the absence of bioactive IL-12.     

IL-18-induced expression of intercellular adhesion molecule-1 in human monocytes: involvement in IL-12 and IFN-gamma production in PBMC

IL-18 time- and concentration-dependently upregulated the expression of intercellular adhesion molecule-1 (ICAM-1) in a monocyte population in human PBMC as determined by FACS analysis while the expression of CD11a, CD18, CD29, CD44, and CD62L in monocytes and that of ICAM-1, CD11a, CD18, CD29, CD44, and CD62L in T cells was not influenced by IL-18. IL-18 in the same concentration range stimulated the production of IL-12, TNF-alpha, and IFN-gamma in culture of PBMC; however, IL-18-induced expression of ICAM-1 in monocytes was not inhibited by anti-IL-12, anti-TNF-alpha, or anti-IFN-gamma Ab, suggesting the independence of the upregulating effect of IL-18 on endogenous IL-12, TNF-alpha, and IFN-gamma production. IL-18 also induced the aggregation of PBMC, which was prevented by anti-ICAM-1 and anti-LFA-1 Abs. On the other hand, anti-ICAM-1 and anti-LFA-1 Abs inhibited IL-18-induced production of three cytokines, IL-12, IFN-gamma, and TNF-alpha, by 60 and 40%, respectively. These results strongly suggested that the IL-18-induced upregulation of ICAM-1 and the subsequent adhesive interaction through ICAM-1 on monocytes and LFA-1 on T/NK cells generate an additional stimulatory signaling as well as an efficient paracrine environment for the IL-18-initiated cytokine cascade.     

IL-4 induces in vivo production of IFN-gamma by NK and NKT cells

Although IL-4 and IFN-gamma often have opposite effects and suppress each other's production by T cells, IL-4 can stimulate IFN-gamma production. To characterize this, we injected mice with IL-4 and quantified IFN-gamma production with the in vivo cytokine capture assay. IL-4 induced Stat6-dependent IFN-gamma production by NK and, to a lesser extent, NKT cells, but not conventional T cells, in 2-4 h. Increased IFN-gamma production persisted at a constant rate for >24 h, but eventually declined, even with continuing IL-4 stimulation. This eventual decline in IFN-gamma production was accompanied by a decrease in NK and T cell numbers. Consistent with a dominant role for NK cells in IL-4-stimulated IFN-gamma secretion, IL-4 induction of IFN-gamma was B and T cell-independent; suppressed by an anti-IL-2Rbeta mAb that eliminates most NK and NKT cells; reduced in Stat4-deficient mice, which have decreased numbers of NK cells; and absent in Rag2/gamma(c)-double-deficient mice, which lack T, B, and NK cells. IL-4-induced IFN-gamma production was not affected by neutralizing IL-12p40 and was increased by neutralizing IL-2. IL-13, which signals through the type 2 IL-4R and mimics many IL-4 effects, failed to stimulate IFN-gamma production and, in most experiments, suppressed basal IFN-gamma production. Thus, IL-4, acting through the type 1 IL-4R, induces Stat6-dependent IFN-gamma secretion by NK and NKT cells. This explains how IL-4 can contribute to Th1 cytokine-associated immune effector functions and suggests how IL-13 can have stronger proallergic effects than IL-4.     

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.     

Dominant role for TL1A/DR3 pathway in IL-12 plus IL-18-induced IFN-gamma production by peripheral blood and mucosal CCR9+ T lymphocytes

The TNF-like cytokine TL1A augments IFN-gamma production by anti-CD3 plus anti-CD28 and IL-12/IL-18-stimulated peripheral blood (PB) T cells. However, only a small subset of PB T cells respond to TL1A stimulation with IFN-gamma production. PB CCR9+ T cells represent a small subset of circulating T cells with mucosal T cell characteristics and a Th1/Tr1 cytokine profile. In the current study, we show that TL1A enhanced IFN-gamma production by TCR- or CD2/CD28-stimulated CCR9(+)CD4+ PB T cells. However, TL1A had the most pronounced effect on augmenting IFN-gamma production by IL-12/IL-18-primed CCR9(+)CD4+ PB T cells. TL1A enhanced both the percentage and the mean fluorescence intensity of IFN-gamma in CCR9(+)CD4+ T cells as assessed by intracellular cytokine staining. IL-12 plus IL-18 up-regulated DR3 expression in CCR9(+)CD4+ T cells but had negligible effect on CCR9(-)CD4+ T cells. CCR9(+)CD4+ T cells isolated from the small intestine showed a 37- to 105-fold enhancement of IFN-gamma production when TL1A was added to the IL-12/IL18 cytokine combination. Cell membrane-expressed TL1A was preferentially expressed in CCR9(+)CD4+ PB T cells, and a blocking anti-TL1A mAb inhibited IFN-gamma production by cytokine-primed CCR9(+)CD4+ T cells by approximately 50%. Our data show that the TL1A/DR3 pathway plays a dominant role in the ultimate level of cytokine-induced IFN-gamma production by CCR9+ mucosal and gut-homing PB T cells and could play an important role in Th1-mediated intestinal diseases, such as Crohn's disease, where increased expression of IL-12, IL-18, TL1A, and DR3 converge in the inflamed intestinal mucosa.     

Blockade of TLR9 agonist-induced type I interferons promotes inflammatory cytokine IFN-gamma and IL-17 secretion by activated human PBMC

Type I interferons (IFN) (IFN-alpha/beta) are recognized as both inhibitors and effectors of autoimmune disease. In multiple sclerosis, IFN-beta therapy appears beneficial, in part, due to its suppression of autoimmune inflammatory Th cell responses. In contrast, in systemic lupus erythematosus (SLE) triggering of plasmacytoid DC (pDC) Toll-like receptors (TLRs) by autoimmune complexes (autoICs) results in circulating type I IFN that appear to promote disease by driving autoantigen presentation and autoantibody production. To investigate how pDC-derived type I IFN might regulate Th cells in SLE, we examined a model in which sustained pDC stimulation by autoICs is mimicked by pretreating normal human PBMC with TLR9 agonist, CpG-A. Subsequently, PBMC Th cells are activated with superantigen, and APC are activated with CD40L. The role of CpG-A/TLR9-induced type I IFN in regulating PBMC is determined by blocking with virus-derived soluble type I IFN receptor, B18R. In summary, pretreatment with either rhIFN-alpha/beta or CpG-A inhibits PBMC secretion of superantigen-induced IFN-gamma and IL-17, and CD40L-induced IL-12p70 and IL-23. B18R prevents these effects. Data indicate that CpG-A-induced type I IFN inhibit IL-12p70-dependent PBMC IFN-gamma secretion by enhancing IL-10. Our results suggest that in SLE, circulating type I IFN may potentially act to inhibit inflammatory cytokine secretion.     

A role for CD40-CD40 ligand interactions in the generation of type 1 cytokine responses in human leprosy

The interaction of CD40 ligand (CD40L) expressed by activated T cells with CD40 on macrophages has been shown to be a potent stimulus for the production of IL-12, an obligate signal for generation of Th1 cytokine responses. The expression and interaction of CD40 and CD40L were investigated in human infectious disease using leprosy as a model. CD40 and CD40L mRNA and surface protein expression were predominant in skin lesions of resistant tuberculoid patients compared with the highly susceptible lepromatous group. IL-12 release from PBMC of tuberculoid patients stimulated with Mycobacterium leprae was partially inhibited by mAbs to CD40 or CD40L, correlating with Ag-induced up-regulation of CD40L on T cells. Cognate recognition of M. leprae Ag by a T cell clone derived from a tuberculoid lesion in the context of monocyte APC resulted in CD40L-CD40-dependent production of IL-12. In contrast, M. leprae-induced IL-12 production by PBMC from lepromatous patients was not dependent on CD40L-CD40 ligation, nor was CD40L up-regulated by M. leprae. Furthermore, IL-10, a cytokine predominant in lepromatous lesions, blocked the IFN-gamma up-regulation of CD40 on monocytes. These data suggest that T cell activation in situ by M. leprae in tuberculoid leprosy leads to local up-regulation of CD40L, which stimulates CD40-dependent induction of IL-12 in monocytes. The CD40-CD40L interaction, which is not evident in lepromatous leprosy, probably participates in the cell-mediated immune response to microbial pathogens.     

Synergistic effects of IL-4 and IL-18 on IL-12-dependent IFN-gamma production by dendritic cells

Mouse splenic dendritic cells (DCs) produce IFN-gamma in response to IL-12. In the present study, we analyzed effects of Th1 and Th2 cytokines on IFN-gamma production by DCs. IL-18 produced by DCs and macrophages acts in an autocrine manner and augments IL-12-induced IFN-gamma production by DCs as also observed in T and NK cells. Surprisingly, IL-4, a Th2 cytokine, also acts synergistically with IL-12 on IFN-gamma production by DCs. In addition, IL-4 markedly enhances IFN-gamma production when DCs are stimulated through CD40 or MHC class II. These results indicate that both Th1 and Th2 cytokines act on DCs during T cell-DC interaction upon Ag presentation. p38 mitogen-activated protein kinase is constitutively activated in mature DCs and is required for IFN-gamma production by DCs. IL-18 but not IL-4 or IL-12 further activates the p38 mitogen-activated protein kinase activity, suggesting that IL-4 and IL-18 enhance IFN-gamma production through distinct intracellular signal transduction pathways in DCs.     

IL-12Rbeta2-deficient mice of a genetically resistant background are susceptible to Leishmania major infection and develop a parasite-specific Th2 immune response

The cytokine IL-12 plays a critical role in inducing the production of IFN-gamma from T and NK cells and in the polarization of T cells towards the Th1 phenotype. IL-12 is comprised of two subunits (IL-12p40 and IL-12p35) that together form the biologically active p70 molecule, and IL-12 functions via binding to a heterodimeric receptor (IL-12Rbeta1 and IL-12Rbeta2). Previous studies utilizing mice deficient for either the IL-12 cytokine or the IL-12-induced signaling molecule STAT4 have established a critical role for IL-12 during infection with Leishmania major. However, these studies warrant careful re-interpretation in light of the recent discovery of the IL-12-related cytokine, IL-23, which utilizes the IL-12p40 chain in combination with an IL-12p35-related molecule, called p19, and a receptor comprised of the IL-12Rbeta1 chain plus a unique chain referred to as IL-23R. We analyzed the course of L. major infection in mice deficient for the IL-12-specific IL-12Rbeta2 subunit in order to assess the role of IL-12 signaling without disruption of the IL-23 pathway. After infection with L. major, IL-12Rbeta2KO mice of a resistant background (C57Bl/6) developed large cutaneous lesions similar to those developed by susceptible BALB/c mice. Draining lymph node cells from L. major-infected IL-12Rbeta2KO mice released the Th2 cytokines IL-4 and IL-5 after in vitro stimulation with Leishmania lysate but were completely devoid of IFN-gamma, consistent with a default towards a strong parasite-specific Th2 response. L. major-infected IL-12Rbeta2KO mice were also devoid of parasite-specific IgG2a antibodies, and interestingly, their footpad lesions ulcerated earlier than those of susceptible BALB/c mice.     

Impaired accumulation and function of memory CD4 T cells in human IL-12 receptor beta 1 deficiency

Defects in IL-12 production or IL-12 responsiveness result in a vulnerability to infection with non-viral intracellular organisms, but the immunological mechanisms responsible for this susceptibility remain poorly understood. We present an immunological analysis of a patient with disseminated Salmonella enteritidis and a homozygous splice acceptor mutation in the IL-12Rbeta1-chain gene. This mutation resulted in the absence of IL-12Rbeta1 protein on PBMC and an inability of T cells to specifically bind IL-12 or produce IFN-gamma in response to either IL-12 or IL-23. The accumulation of memory (CD45R0(high)) CD4 T cells that were CCR7(high) (putative central memory cells) was normal or increased for age. Central memory CD4 T cells of the patient and age-matched controls were similar in having a low to undetectable capacity to produce IFN-gamma after polyclonal stimulation. In contrast, the patient had a substantial decrease in the number of CCR7(neg/dull) CD45R0(high) memory CD4 T cells (putative effector memory cells), and these differed from control cells in having a minimal ability to produce IFN-gamma after polyclonal stimulation. Importantly, tetanus toxoid-specific IFN-gamma production by PBMC from the patient was also significantly reduced compared with that in age-matched controls, indicating that signaling via the IL-12Rbeta1-chain is generally necessary for the in vivo accumulation of human memory CD4 T cells with Th1 function. These results are also consistent with a model in which the IL-12Rbeta1 subunit is necessary for the conversion of central memory CD4 T cells into effector memory cells.     

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

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

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.     

The development of a Th1-type response and resistance to Leishmania major infection in the absence of CD40-CD40L costimulation.

CD40-CD40L interactions have been shown to be essential for the production of IL-12 and IFN-gamma and control of L. major infection. In contrast, C57BL/6 mice deficient in CD28 develop a dominant Th1-type response and heal infection. In this study, we investigate the effects of a deficiency in both CD40L and CD28 molecules on the immune response and the course of L. major infection. We compared infection in mice genetically lacking CD40L (CD40L(-/-)), CD28 (CD28(-/-)), or both (CD40L(-/-)CD28(-/-)), and in C57BL/6 mice, all on a resistant background. Although CD40L(-/-) mice failed to control infection, CD28(-/-) and CD40L(-/-)CD28(-/-) mice, as well as C57BL/6 mice, spontaneously resolved their infections. Healing mice had reduced numbers of lesion parasites compared with nonhealing CD40L(-/-) mice. At wk 9 of infection, we detected similar levels of IL-4, IFN-gamma, IL-12p40, and IL-12Rbeta2 mRNA in draining lymph nodes of healing C57BL/6, CD28(-/-), and CD40L(-/-)CD28(-/-) mice, whereas CD40L(-/-) mice had increased mRNA levels for IL-4 but reduced levels for IFN-gamma, IL-12p40, and IL-12Rbeta2. In a separate experiment, blocking of the CD40-CD40L pathway using Ab to CD40L led to an exacerbation of infection in C57BL/6 mice, but had little or no effect on infection in CD28(-/-) mice. Together, these results demonstrate that in the absence of CD28 costimulation, CD40-CD40L interaction is not required for the development of a protective Th1-type response. The expression of IL-12p40, IL-12Rbeta2, and IFN-gamma in CD40L(-/-)CD28(-/-) mice further suggests the presence of an additional stimulus capable of regulating IL-12 and its receptors in absence of CD40-CD40L interactions.     

Modulation of CLA, IL-12R, CD40L, and IL-2Ralpha expression and inhibition of IL-12- and IL-23-induced cytokine secretion by CNTO 1275

Cytokines interleukin (IL)-12 and IL-23 are implicated in the pathogenesis of psoriasis. IL-12 causes differentiation of CD4+ T cells to interferon-gamma (IFN-gamma)-producing T helper 1 (Th1) cells, while IL-23 induces differentiation to IL-17-producing pathogenic Th17 cells. The effects of the monoclonal antibody to IL-12/23 p40 subunit (CNTO 1275) on IL-12 receptor (IL-12R) expression, markers associated with skin homing, activation, and cytokine secretion were investigated in vitro using human peripheral blood mononuclear cells (PBMCs) from healthy donors. PBMCs were activated in the presence or absence of recombinant human (rh) IL-12 or rhIL-23, with or without CNTO 1275. CNTO 1275 inhibited upregulation of CLA, IL-12R, IL-2Ralpha and CD40L expression and also inhibited IL-12- and IL-23-induced IFN-gamma, IL-17A, tumor necrosis factor (TNF)-alpha, IL-2, and IL-10 secretion. Thus, the therapeutic effect of CNTO 1275 may be attributed to the IL-12/23 neutralization, resulting in decreased expression of skin homing and activation markers, and IL-12- and IL-23-induced cytokine secretion.     

IL-23 compensates for the absence of IL-12p70 and is essential for the IL-17 response during tuberculosis but is dispensable for protection and antigen-specific IFN-gamma responses if IL-12p70 is available

IL-12p70 induced IFN-gamma is required to control Mycobacterium tuberculosis growth; however, in the absence of IL-12p70, an IL-12p40-dependent pathway mediates induction of IFN-gamma and initial bacteriostatic activity. IL-23 is an IL-12p40-dependent cytokine containing an IL-12p40 subunit covalently bound to a p19 subunit that is implicated in the induction of CD4 T cells associated with autoimmunity and inflammation. We show that in IL-23 p19-deficient mice, mycobacterial growth is controlled, and there is no diminution in either the number of IFN-gamma-producing Ag-specific CD4 T cells or local IFN-gamma mRNA expression. Conversely, there is an almost total loss of both IL-17-producing Ag-specific CD4 T cells and local production of IL-17 mRNA in these mice. The absence of IL-17 does not alter expression of the antimycobacterial genes, NO synthase 2 and LRG-47, and the absence of IL-23 or IL-17, both of which are implicated in mediating inflammation, fails to substantially affect the granulomatous response to M. tuberculosis infection of the lung. Despite this redundancy, IL-23 is required to provide a moderate level of protection in the absence of IL-12p70, and this protection correlates with a requirement for IL-23 in the IL-12p70-independent induction of Ag-specific, IFN-gamma-producing CD4 T cells. We also show that IL-23 is required for the induction of an IL-17-producing Ag-specific phenotype in naive CD4 T cells in vitro and that absence of IL-12p70 promotes an increase in the number of IL-17-producing Ag-specific CD4 T cells both in vitro and in vivo.     

In vitro analysis of interferon gamma (IFN-gamma) and interleukin-12 (IL-12) production and their effects in ileal Crohn's disease

Crohn's disease is an inflammatory disease of the gut in which tumour necrosis factor (TNF) and T helper 1 (Th1) cytokines (interleukin (IL)-12, interferon (IFN)-gamma) are thought to play a major role. After the successes obtained with neutralisation of TNF, interest is now growing for therapy aiming at neutralisation of Th1-associated cytokines. Since cytokines are linked in a delicate network, in vitro cultures of ileal lamina propria mononuclear cells (LPMC) were set up for evaluation of a) IFN-gamma and IL-12 production, b) effects of rhIFN-gamma and rhIL-12 and c) effects of anti-IFN-gamma and anti-IL-12 on pro-inflammatory cytokines and IL-10 production. LPMC were isolated from surgical specimens of a total of 27 Crohn's disease and 17 caecum carcinoma (control) patients. Cells were stimulated with CD40L (which triggers myeloid CD40-expressing cells) or anti-CD3 +CD80 (which triggers T cells). LPMC from involved ileal, Crohn's disease produced, in both non-stimulated and stimulated conditions, more IFN-gamma and IL-12p70 than LPMC from non-involved tissue or from control patients. rhIFN-gamma significantly enhanced TNF production in both controls and in ileal Crohn's disease patients, while rhIL-12 enhanced IFN-gamma but not TNF production. LPMC from involved tissue were more sensitive to IL-12 than control LPMC. LP-T cell-dependent activation of monocytes was then studied by co-culture of anti-CD3/CD80-stimulated LPMC with fresh monocytes, which resulted in high IL-12, IFN-gamma, TNF and IL-10 production. The data show that neutralisation of either IL-12 or IFN-gamma with mAb in these cultures also affects secretion of the reciprocal cytokine and (in the case of anti-IL-12) also that of the anti-inflammatory cytokine IL-10. However, no effect of anti-IL-12 or anti-IFN-gamma on production of TNF, a cytokine with an important pathogenic role in Crohn's disease, could be found. Therapies aiming at neutralisation of IFN-gamma or IL-12 are therefore unlikely to replace anti-TNF, but they might provide an additive or synergistic effect.