Depressed interleukin-12 (IL-12), but not IL-18, production in response to a 30- or 32-kilodalton mycobacterial antigen in patients with active pulmonary tuberculosis

The secreted 30-kDa antigen (Ag) of Mycobacterium tuberculosis directly stimulates Th1-type protective cytokine responses in healthy tuberculin reactors but not in patients with active tuberculosis (TB). To examine the cytokine profiles attributable to Th1 suppression associated with active TB, interleukin-12 (IL-12), IL-18, and IL-10 production in response to a 30- or 32-kDa Ag in 16 patients with active pulmonary TB and 24 healthy controls was investigated by enzyme-linked immunosorbent assay. In TB patients, production of IL-12 p40, as well as gamma interferon (IFN-gamma), by 30- or 32-kDa Ag-stimulated peripheral blood mononuclear cells (PBMC) was significantly decreased compared with that in healthy tuberculin reactors. There were no significant differences in IL-18 production between patients and controls early during stimulation (16 h). However, PBMC from patients showed significantly enhanced IL-18 proteins after 96 h of stimulation. Similarly, higher IL-10 production was observed in the TB patients than in healthy tuberculin reactors. After 2 months of anti-TB therapy, the mean IFN-gamma and IL-12 p40 production and the mean blastogenic responses were significantly increased in PBMC in the 10 TB patients who were followed up. Our findings provide evidence that depressed IL-12 in response to the 30- or 32-kDa Ag is involved in the immunopathogenesis of human active pulmonary TB.     

The production of tumour necrosis factor-alpha is decreased in peripheral blood mononuclear cells from multidrug-resistant tuberculosis patients following stimulation with the 30-kDa antigen of Mycobacterium tuberculosis

The clearance of intracellular bacteria requires the appropriate induction of proinflammatory cytokines and chemokines to recruit macrophages and T cells to the site of infection. In this study, we investigated the production of tumour necrosis factor (TNF)-alpha, interleukin (IL)-8 and interferon (IFN)-gamma by the peripheral blood mononuclear cells (PBMC) of patients with multidrug-resistant tuberculosis (MDR-TB) in response to in vitro stimulation with the 30-kDa antigen of Mycobacterium tuberculosis. The results were compared with those from cases of newly diagnosed TB (N-TB) and TB with treatment failure (TF-TB), and healthy tuberculin reactors (HTR). The most significantly depressed TNF-alpha levels were found in MDR-TB patients. IFN-gamma production was depressed significantly in all groups of TB patients compared with the HTR group. TNF-alpha secretion in response to the 30-kDa antigen was unchanged by coculturing with recombinant human interferon (rhIFN)-gamma, and was increased dramatically following IL-10 neutralization with an anti-human IL-10 antibody. The IL-8 levels were depressed significantly in MDR-TB patients compared with N-TB patients, but were similar to the IL-8 levels in TF-TB patients. Furthermore, rhTNF-alpha directly increased IL-8 secretion, and neutralizing antibody to TNF-alpha inhibited IL-8 production by the PBMC of MDR-TB patients that were stimulated with the 30-kDa antigen. Taken together, these data suggest that the PBMC of MDR-TB patients typically show TNF-alpha depression in response to the 30-kDa antigen, and this effect is modulated by IL-10. In addition, we highlight the role of TNF-alpha in IL-8 secretion in MDR-TB patients.     

IL-18 production in human pulmonary and pleural tuberculosis

Interleukin-18 (IL-18) has multiple important pro-inflammatory effects, including the induction of interferon-gamma (IFN-gamma) in various diseases. In this study, we investigated the IL-18-producing activities in human pulmonary and pleural tuberculosis (TB) in response to purified protein derivative (PPD) antigen (Ag) from Mycobacterium tuberculosis. The most significant IL-18 production was found in chronic refractory TB (CRTB) patients. However, IFN-gamma production in CRTB patients was significantly less than that in healthy tuberculin reactors or in patients with tuberculous pleurisy (TBP). Elevated levels of both IL-18 and IFN-gamma were found in pleural fluids from TBP patients. In vitro production of IL-18 was dramatically decreased following an 18 h stimulation with PPD. However, IFN-gamma was markedly increased in pleural mononuclear cells from TBP patients after in vitro stimulation with PPD. The mesothelial cell type was the main source of pro-IL-18 in pleural cells from TBP patients, suggesting an important role for these cells in TBP. Taken together, these data indicate that IL-18 is elevated in peripheral blood mononuclear cells from CRTB patients, as well as at the site of TBP, indicating a possible role for IL-18 in both protective immunity and pathologic responses in human TB.     

In vitro kinetics of allergen- and microbe-induced IL-4 and IFN-gamma mRNA expression in PBMC of pollen-allergic patients

BACKGROUND: According to a hypothesis allergens induce Th2 responses in allergic patients, and microbes induce Th1 responses. We studied the kinetics of in vitro allergen-, tuberculin (PPD)- and tetanus toxin (TT)-induced IFN-gamma and IL-4 mRNA expression in peripheral blood mononuclear cell (PBMC) cultures of pollen-allergic patients and healthy controls. METHODS: PBMC of 10 birch or timothy pollen-allergic patients and of 13 healthy controls were stimulated in vitro with allergen (birch or timothy), PPD or TT. Pellets and supernatants were collected at 24, 48, 72 and 96 h after stimulation. IFN-gamma and IL-4 production was measured by enzyme linked immunosorbent assay and mRNA expression using RT-PCR and time-resolved fluorometry. RESULTS: Allergen induced IFN-gamma production and mRNA expression in PBMC more in allergic patients than in healthy controls. Also allergen induced IL-4 mRNA expression more in allergic patients than in healthy controls. PPD induced IFN-gamma mRNA expression both in allergic patients and healthy controls, whereas IFN-gamma production was induced only in healthy controls and IL-4 was not induced at all. TT induced IFN-gamma mRNA expression in both groups, IFN-gamma production in allergic patients, and IL-4 mRNA expression in both allergic patients and healthy controls. CONCLUSIONS: In vitro stimulation with allergen induced both IFN-gamma and IL-4 mRNA expression of PBMC in allergic patients. These observations challenge the clearcut division of microbe-specific Th1 and allergen-specific Th2 responses in peripheral blood.     

IL-13 production by allergen-stimulated T cells is increased in allergic disease and associated with IL-5 but not IFN-gamma expression.

Interleukin-13 (IL-13) shares many, but not all, of the properties of the prototypic T-helper type 2 (Th2) cytokine IL-4, but its role in allergen-driven T-cell responses remains poorly defined. We hypothesized that allergen stimulation of peripheral blood T cells from patients with atopic disease compared with non-atopic controls results in elevated IL-13 synthesis in the context of a 'Th2-type' pattern. Freshly isolated peripheral blood mononuclear cells (PBMC) obtained from sensitized atopic patients with allergic disease, and non-atopic control subjects, were cultured with the allergens Phleum pratense (Timothy grass pollen) or Dermatophagoides pteronyssinus (house dust mite) and the non-allergenic recall antigen Mycobacterium tuberculosis purified protein derivative (PPD). Supernatant concentrations of IL-13, along with IL-5 and interferon-gamma (IFN-gamma) (Th2- and Th1-type cytokines, respectively) were determined by enzyme-linked immunosorbent assay (ELISA). Allergen-induced IL-13 and IL-5 production by T cells from patients with allergic disease was markedly elevated (P = 0.0075 and P = 0.0004, respectively) compared with non-atopic controls, whereas IFN-gamma production was not significantly different. In contrast to allergen, the prototypic Th1-type antigen M. tuberculosis PPD induced an excess of IFN-gamma over IL-13 and IL-5 production, and absolute concentrations of cytokines were not affected by the presence or absence of atopic disease. Addition of exogenous recombinant IFN-gamma or IL-12, cytokines known to inhibit Th2-type responses, significantly inhibited allergen-driven production of both IL-13 and IL-5, but not T-cell proliferation, whereas exogenous IL-4 did not significantly affect production of IL-13 or IL-5. We conclude that allergen-specific T cells from atopic subjects secrete elevated quantities of IL-13 compared with non-atopic controls, in the context of a Th2-type pattern of cytokine production.     

Depressed interleukin-12 production by peripheral blood mononuclear cells after in vitro stimulation with the 30-kDa antigen in recurrent pulmonary tuberculosis patients

Some patients develop recurrent tuberculosis (R-TB), even after successfully completing initial anti-tubercular treatment. Although R-TB may be caused by relapse or exogenous reinfection, little is known about the underlying host responses associated with R-TB. This study investigated the profile of cytokines [interferon (IFN)-gamma, interleukin (IL)-12, tumor necrosis factor (TNF)-alpha, IL-6, and IL-10] present in peripheral blood mononuclear cells (PBMCs) of 17 R-TB patients after stimulation with the 30-kDa antigen (Ag) or purified protein derivative (PPD) Ag of Mycobacterium tuberculosis. These data were compared with data obtained from 15 patients with newly diagnosed pulmonary TB (N-TB), 22 patients with treatment failure (TF-TB), and 19 healthy tuberculin reactors (HTR). N-TB and R-TB patients were enrolled in this study within 1 month of beginning anti-tubercular chemotherapy. ELISA results showed that IFN-gamma production following stimulation with the 30-kDa Ag was significantly lower in each group of TB patients than in the HTR controls. In addition, patients with R-TB showed the most significant IL-12 depression among the subject groups after in vitro stimulation with either Ag. Furthermore, a significant decrease in TNF-alpha and IL-10 levels was observed in R-TB patients relative to N-TB patients. However, there was no statistical difference in TNF-alpha and IL-10 production between R-TB patients, TF-TB patients, and HTR controls. Our findings suggest that the underlying mechanisms of cytokine regulation might differ between N-TB and R-TB patients, and that decreased IL-12 production in response to the 30-kDa or PPD Ag might be involved in the immunopathogenesis of human R-TB.     

Interaction of Mycobacterium tuberculosis-Induced Transforming Growth Factor β1 and Interleukin-10

Mycobacterium tuberculosis is associated with the activation of cytokine circuits both at sites of active tuberculosis in vivo and in cultures of mononuclear cells stimulated by M. tuberculosis or its components in vitro. Interactive stimulatory and/or inhibitory pathways are established between cytokines, which may result in potentiation or attenuation of the effects of each molecule on T-cell responses. Here we examined the interaction of transforming growth factor beta1 (TGF-beta1) and interleukin-10 (IL-10) in purified protein derivative (PPD)-stimulated human mononuclear cell cultures in vitro. TGF-beta1 induced monocyte IL-10 (but not tumor necrosis factor alpha) production (by 70-fold, P < 0.02) and mRNA expression in the absence but not in the presence of PPD. Both exogenous recombinant (r) IL-10 and rTGF-beta1 independently suppressed the production of PPD-induced gamma interferon (IFN-gamma) in mononuclear cells from PPD skin test-positive individuals. Synergistic suppression of IFN-gamma in cultures containing both rTGF-beta1 and rIL-10 was only seen when the responder cell population were peripheral blood mononuclear cells (PBMC) and not monocyte-depleted mononuclear cells and when PBMC were pretreated with rTGF-beta1 but not with rIL-10. Suppression of PPD-induced IFN-gamma in PBMC containing both rTGF-beta1 (1 ng/ml) and rIL-10 (100 pg/ml) was 1.5-fold higher (P < 0.05) than cultures containing TGF-beta1 alone and 5.7-fold higher (P < 0.004) than cultures containing IL-10 alone. Also, neutralization of endogenous TGF-beta1 and IL-10 together enhanced PPD-induced IFN-gamma in PBMC in a synergistic manner. Thus, TGF-beta1 and IL-10 together potentiate the downmodulatory effect on M. tuberculosis-induced T-cell production of IFN-gamma, and TGF-beta1 alone enhances IL-10 production. At sites of active M. tuberculosis infection, these interactions may be conducive to the suppression of mononuclear cell functions.     

Increased circulating interleukin-12 (IL-12) p40 in pulmonary sarcoidosis

In sarcoidosis, a T helper 1 (Th1) response is an essential event and the up-regulation of interleukin-12 (IL-12) has been detected in affected disease sites. In order to investigate the clinical usefulness of circulating IL-12, we measured the serum concentrations of IL-12 by ELISA and performed immunohistochemistry using specific MoAbs for IL-12 in the lungs and scalene lymph nodes of patients with sarcoidosis. The serum concentration of IL-12 p40 was detectable in all 45 patients with pulmonary sarcoidosis and 18 normal controls, whereas that of IL-12 p70 was undetectable. The serum concentrations of IL-12 p40 in pulmonary sarcoidosis were significantly higher than those of the normal controls, especially in cases with abnormal intrathoracic findings detected by chest roentogenogram. The serum concentrations of interferon-gamma (IFN-gamma) also increased compared with those of normal controls and there was a significant positive correlation between the serum concentrations of IL-12 p40 and IFN-gamma. Furthermore, serum angiotensin-converting enzyme (ACE) and lysozyme, which are known to be useful markers for disease activity in sarcoidosis, correlated well with the serum concentrations of IL-12 p40. The positive 67Ga scan group (for lung field) had significantly elevated serum IL-12 p40 levels compared with those of the negative group. No bioactivity of IL-12 p70 was detected in three sarcoid cases sera by using the IL-12 responsive cell line. Finally, the immunohistochemical approach revealed that IL-12 p40 was expressed in the epithelioid cells and macrophages of sarcoid lungs and lymph nodes. We concluded that the production of IL-12 p40 was far greater in the sera and we have demonstrated this to be a useful clinical marker for disease activity and the Th1 response in pulmonary sarcoidosis.     

The effect of IL-18 on IL-12-induced CD30 expression and IL-4 and IFN-gamma production by allergen and PPD specific T cells

CD30 is expressed on activated T cells that, as has been suggested, preferentially produce IFN-gamma. Interleukin 12 increases antigen-induced CD30 expression on T cells and IFN-gamma production. Synthesis of IFN-gamma can be augmented further by IL-18. The aim of our study was to investigate whether IL-18 affects the IL-12 induced CD30 expression and cytokine production by allergen or PPD specific T cells. Mononuclear cells of healthy or atopic volunteers were stimulated with PPD or allergen, respectively, to obtain specific T cell lines. T cells were restimulated with appropriate antigen and antigen-presenting cells in the presence of IL-12, IL-18 or a combination of these cytokines. After 3 days, expression of CD30 was investigated on CD4 and CD8 T cells and IFN-gamma and IL-4 cytokine production was estimated in the culture supernatants. Flow cytometric analyses showed no effect of IL-18 on CD30 expression during IL-12 co-stimulation. At the same time after the optimal stimulation for CD30 expression, the levels of IFN-gamma were high in PPD-stimulated cell lines but have not been up-regulated by IL-18. IFN-gamma levels were much lower in allergen-stimulated T cells and although they were up-regulated by IL-12 there was no additional or synergistic effect from IL-18. IL-18, however, increased production of IL-4 in allergen-stimulated cell lines. Our studies provide new information about IL-18 activity on human cells and question its exclusive role in Th1 mediated responses.     

Interleukin-12 p40/p70 ratio and in vivo responsiveness to IFN-alpha treatment in chronic hepatitis C.

To evaluate the relationship between cytokine balance and responsiveness to interferon-alpha (IFN-alpha), we investigated the production of IFN-gamma, interleukin-10 (IL-10), IL-12 p70, and IL-12 p40 by peripheral blood mononuclear cell (PBMC) cultures from patients with chronic hepatitis C (CHC) before and after 1 year of IFN-alpha treatment. Before the therapy, responder (R) patients exhibited lower IFN-gamma release, higher IL-10 production, and higher values of the IL12 p40/p70 ratio compared with nonresponders (NR). Increased sensitivity to the effects of IL-12 and IL-10, as well as higher IL-12-dependent IFN-gamma secretion, were also found in the R subset. After IFN-alpha therapy, an increase in IFN-gamma production and a decrease in the IL-12 p40/p70 ratio were observed in R patients, whereas opposite results were obtained in the NR group. Finally, the therapy induced downregulation of IL-10 production and cell responsiveness to recombinant IL-12 in all patients. These findings imply that predominance of a T helper 2 (Th2) cytokine profile in CHC patients favors the beneficial effects of IFN-alpha, thus suggesting a therapeutic role for Th1-driven stimulation of immune response. The findings also stress the primary importance of the IL-12 p40 and p70 balance in the modulation of immune responses to hepatitis C virus (HCV).     

In vitro responsiveness to IL-18 in combination with IL-12 or IL-2 by PBMC from patients with bronchial asthma and atopic dermatitis

Interleukin (IL)-18 is a proinflammatory cytokine and is now recognized as an important regulator of both helper T cells (Th) 1 and 2 cytokine production. An increased IL-18 secretion has been reported in patients with allergic disorders. It is predominantly produced by activated macrophages, and synergizes with IL-12 and IL-2 to induce IFN-gamma synthesis, thereby promoting Th1 cytokine response. Paradoxically, IL-18, by itself, strongly induces immunoglobulin (Ig) E and allergic inflammation, indicating a role for IL-18 in promoting Th2 response. We investigated the inducing effect in vitro of combining IL-18 and Il-12 or Il-2 on Th1- and Th2-type cytokines production by peripheral blood mononuclear cells (PBMC) from patients with allergic diseases. PBMC derived from 44 allergic patients [23 bronchial asthma (BA) and 21 atopic dermatitis (AD)] and 20 healthy controls were cultured with IL-18 in the presence of phytohemagglutinin (PHA) and IL-12 or IL-2. The levels of IFN-gamma, IL-13, and IL-4 in the culture supernatants were measured using enzymatic immunoassaying. IFN-gamma production was detected in all cultures from nonallergic controls stimulated with IL-18 in the presence of IL-12; however, the results for five BA patients and five AD patients were under the detection limit for IFN-gamma. In collaboration with IL-2, IL-18 was able to induce IFN-gamma production by PBMCs from all nonallergic controls and all allergic patients, with the exception of one AD patient. Synergistic induction of IL-13 production was found in cultures with IL-18 + IL-2, and the IL-13 induction was significantly increased in BA patients when compared with that in nonallergic controls (P = 0.006). The stimulation by IL-18, even in combination with IL-2, failed to induce IL-4 production by PBMC from both nonallergic controls and allergic patients. Although the induction of IFN-gamma by IL-18 + IL-12 was impaired in around a quarter of the allergic patients, the impairment of the IFN-gamma production was completely restored by IL-2 in the presence of IL-18. Thus, IL-18 enhances IFN-gamma production through an IL-12-dependent pathway and exhibits synergism when combined with IL-2 in terms of enhanced IL-13 and IFN-gamma production, suggesting the involvement of IL-18/IL-12/IL-2 pathway in modulating Th1/Th2 cytokine response.     

Dynamic changes in pro- and anti-inflammatory cytokine profiles and gamma interferon receptor signaling integrity correlate with tuberculosis disease activity and response to curative treatment

Pro- and anti-inflammatory cytokines and their signaling pathways play key roles in protection from and pathogenesis of mycobacterial infection, and their balance and dynamic changes may control or predict clinical outcome. Peripheral blood cells' capacity to produce proinflammatory (tumor necrosis factor alpha [TNF-alpha], interleukin-12/23p40 [IL-12/23p40], and gamma interferon [IFN-gamma]) and anti-inflammatory (IL-10) cytokines in response to Mycobacterium tuberculosis or unrelated stimuli (lipopolysaccharide, phytohemagglutinin) was studied in 93 pulmonary tuberculosis (TB) patients and 127 healthy controls from Indonesia. Their cells' ability to respond to IFN-gamma was examined to investigate whether M. tuberculosis infection can also inhibit IFN-gamma receptor (IFN-gammaR) signaling. Although there was interindividual variability in the observed responses, the overall results revealed that M. tuberculosis-induced TNF-alpha and IFN-gamma levels showed opposite trends. Whereas TNF-alpha production was higher in active-TB patients than in controls, IFN-gamma production was strongly depressed during active TB, correlated inversely with TB disease severity, and increased during therapy. By contrast, mitogen-induced IFN-gamma production, although lower in patients than in controls, did not change during treatment, suggesting an M. tuberculosis-specific and reversible component in the depression of IFN-gamma. Depressed IFN-gamma production was not due to decreased IL-12/IL-23 production. Importantly, IFN-gamma-inducible responses were also significantly depressed during active TB and normalized during treatment, revealing disease activity-related and reversible impairment in IFN-gammaR signaling in TB. Finally, IFN-gamma/IL-10 ratios significantly correlated with TB cure. Taken together, these results show that M. tuberculosis-specific stimulation of IFN-gamma (but not TNF-alpha) production and IFN-gammaR signaling are significantly depressed in active TB, correlate with TB disease severity and activity, and normalize during microbiological TB cure. The depression of both IFN-gamma production and IFN-gammaR signaling may synergize in contributing to defective host control in active TB.     

APC-dependent impairment of T cell proliferation in aging: role of CD28- and IL-12/IL-15-mediated signaling

The age-related impairment of phytohaemagglutinin (PHA)-triggered peripheral blood mononuclear cell (PBMC) proliferation was paralleled by an expansion of CD28 (-) T lymphocytes with a poor capacity to undergo lectin-induced blastogenesis. However, both CD28 (-) and CD28 (+) T cells isolated from aged individuals exhibited a significant reduction of proliferative response to PHA in comparison with young controls, this implies that the CD28-mediated signaling is not the only defective pathway in the elderly. Thus, PBMC or T cell subsets plus monocytes from aged donors were stimulated with PHA and assayed for the production of, or the response to cytokines known to regulate T cell functions. Results can be so summarized: (i). interleukin (IL)-2 as well as IL-10 release was unaffected by age; (ii). in both groups of subjects, IL-15 concentrations were similar to those spontaneously released by PBMC; (iii). surprisingly, IL-12 p70 and IL-12 p40 production by PBMC was markedly increased in the aged group; (iv) in spite of this finding and of the experimental outcome that IFN-gamma synthesis was almost completely dependent on IL-12. PBMC from old individuals did not release higher amounts of IFN-gamma in comparison with young controls; (v). moreover, only a slight increase in IFN-gamma production was observed in PBMC cultures from the aged group as a result of IL-12 and/or IL-15 costimulation; (vi) at the same time, even though IL-12 as well as IL-15 were necessary for an efficient T cell proliferation, the addition of exceeding doses of cytokines proved to be ineffective in enhancing the proliferative outcome of PBMC or of both CD28 (+) and CD28 (-) T cells in the aged group. Taken together, the data outline the role of CD28 and IL-12/IL-15 signaling impairment in T cell proliferative deficiency during senescence.     

Intrathecal production of interleukin-12 and gamma interferon in patients with bacterial meningitis.

To assess the role of interleukin-12 (IL-12) and gamma interferon (IFN-gamma) in children with bacterial meningitis, bioactive IL-12 (p70) and the inactive subunit p40 and IFN-gamma were measured in serum and cerebrospinal fluid (CSF) from 35 children with bacterial meningitis and 10 control subjects. The production of IFN-gamma is induced by IL-12 with tumor necrosis factor alpha (TNF-alpha) as a costimulator and inhibited by IL-10. CSF concentrations of IL-12 p40 as well as those of IFN-gamma were markedly elevated, whereas IL-12 p70 was hardly detectable. Detectable CSF levels of IFN-gamma correlated positively with IL-12 p40 (r = 0.40, P = 0.02) and TNF-alpha (r = 0.46, P = 0.04) but not with IL-6, IL-8, or IL-10. In contrast to CSF levels of TNF-alpha, IL-12, and IL-10, those of IFN-gamma were significantly higher in patients with pneumococcal meningitis than in children with meningitis caused by Haemophilus influenzae and Neisseria meningitidis, presumably because of a high CSF TNF-alpha/IL-10 ratio in the former. We suggest that IL-12- and TNF-alpha-induced IFN-gamma production may contribute to the natural immunity against microorganisms in the CSF compartment during the acute phase of bacterial meningitis.     

Both IL-12 and IL-18 contribute to small intestinal Th1-type immunopathology following oral infection with Toxoplasma gondii, but IL-12 is dominant over IL-18 in parasite control

Oral infection of C57BL/6 mice with Toxoplasma gondii results in small intestinal Th1-type immunopathology mediated by local production of IFN-gamma, TNF-alpha, and NO. To analyze whether the proinflammatory cytokines IL-12 and IL-18 play a role in the induction of immunopathology, IL-12p35/p40(-/-) and IL-18(-/-) mice were orally infected with T. gondii. Wild-type mice developed massive necrosis in their small intestines and died 7-10 days post infection. Even though IL-12p35/40(-/-) mice did not develop the necrosis they all died between day 9 and 11 after infection. In contrast, 50% of IL-18(-/-) mice died during the acute phase of infection. Compared to wild-type mice, IL-12p35/p40(-/-) but not IL-18(-/-) mice showed significantly higher parasite numbers in their small intestines and significantly higher numbers of parasite-associated inflammatory foci in their livers. IFN-gamma production was similar in infected wild-type and IL-18(-/-) mice but significantly decreased in IL-12p35/p40(-/-) mice. Treatment of mice with anti-IL-12- or anti-IL-18 antibodies after infection prevented the development of intestinal necrosis. These results reveal that both IL-12 and IL-18 play an important role in the development of intestinal immunopathology following oral infection with T. gondii. However, IL-12 is dominant over IL-18 in the host defense against parasite replication. Therefore, neutralization of IL-18 (rather than TNF-alpha, IL-12, and IFN-gamma) may be a safe strategy for the treatment of Th1-associated diseases.     

IL-12 receptor deficiency revisited: IL-23-mediated signaling is also impaired in human genetic IL-12 receptor beta1 deficiency

IFN-gamma and IL-12 are crucial cytokines for cell-mediated immunity against intracellular pathogens. We have previously shown that human IL-12Rbeta1-deficiency leads to impaired IL-12 responsiveness and unusual susceptibility to infections due to mycobacteria and salmonellae. IL-23 is a cytokine with functions that partially overlap with those of IL-12. IL-23 consists of IL-12p40 and a novel p19 protein, and binds to a receptor complex comprising IL-12Rbeta1 and IL-23R. Thus, IL-12Rbeta1-deficiency may impair both IL-12- and IL-23 signaling, and both may contribute to the immunological phenotypes. To examine whether IL-12Rbeta1 is essential for IL-23 signaling in human T cells, we have studied IL-23 responsiveness of four IL-12Rbeta1-deficient individuals. Whereas IL-23 promoted IFN-gamma production by CD4(+) and CD8(+) T cells in controls, IL-12Rbeta1-deficient T cells lacked IL-23-induced IFN-gamma secretion, but responded normally to IL-2, IL-4, IL-15 and IL-18. We also show that induction of IFN-gamma production by IL-23 depends upon TCR-ligation and is enhanced by CD28-costimulation. Furthermore, IL-23 cooperates with IL-12 and IL-18 in promoting IFN-gamma production in controls, but not in patients. We conclude that IL-12Rbeta1-deficiency impairs IL-12- and IL-23-dependent signaling in human T cells. The syndrome caused by IL-12Rbeta1-deficiency thus needs to be reinterpreted as resulting from defective IL-12-as well as IL-23-mediated immunity.     

IL-24 modulates IFN-gamma expression in patients with tuberculosis

IL-24 is a newly described member of the IL-10 family. We previously demonstrated that PBMC from TB patients exhibited low levels of IL-24 and IFN-gamma compared to subjects with latent tuberculosis infection (LTBI). In order to investigate the role of IL-24 in IFN-gamma expression in TB patients, we stimulated PBMC from individuals with LTBI or TB patients with the Mtb-specific antigen, early secretory antigenic target-6 (ESAT-6) and measured cytokine expression using quantitative real-time PCR (qPCR). Exogenous IL-24 increased IFN-gamma expression in PBMC obtained from TB patients while neutralization of IL-24 reduced IFN-gamma expression in PBMC from subjects with LTBI. Exogenous IL-24 enhanced IFN-gamma expression by increasing expression of IL-12 family cytokines, including IL-12alpha, IL-12beta, IL-23alpha and IL-27, and by reducing FOXP3 expression in PBMC from TB patients. This is the first demonstration that IL-24 may play an important role in IFN-gamma expression following infection with Mtb.     

Production of interleukin-18 and interleukin-12 in patients suffering from chronic hepatitis C virus infection before antiviral therapy

Interleukin-12 and -18 (IL-12 and IL-18) are known to enhance the cytotoxic T-lymphocyte response synergistically, but their precise involvement in hepatitis C virus (HCV) infection is not well known, especially for IL-18. Enzyme-linked immunosorbent assay (ELISA) was used to study the production of these cytokines in plasma and peripheral blood mononuclear cells (PBMCs) stimulated by lipopolysaccharide (LPS) of patients infected chronically with HCV before initiation of antiviral therapy. Fifty-six patients and 40 healthy controls were evaluated. Patients infected with genotype 1 or with genotype other than genotype 1 HCV had significantly a high production of plasma IL-12 compared with controls (P < 0.05). However, patients infected with genotype 1 HCV had lower levels of PBMC IL-18 than were founded in the controls (P < 0.05); plasma IL-18 also tended to be lower in this group of patients than in the controls, although nonsignificantly. Plasma IL-18 was related to hepatic histological activity (P < 0.05). The data suggest a relationship between these two cytokines and some features of HCV infection, so that their respective production in relation to the outcome of the infection deserves further study.