The increased mucosal mRNA expressions of complement C3 and interleukin-17 in inflammatory bowel disease

Recent studies have demonstrated that the complement system participates in the regulation of T cell functions. To address the local biosynthesis of complement components in inflammatory bowel disease (IBD) mucosa, we investigated C3 and interleukin (IL)‐17 mRNA expression in mucosal samples obtained from patients with IBD. The molecular mechanisms underlying C3 induction were investigated in human colonic subepithelial myofibroblasts (SEMFs). IL‐17 and C3 mRNA expressions in the IBD mucosa were evaluated by real‐time polymerase chain reaction. The C3 levels in the supernatant were determined by enzyme‐linked immunosorbent assay. IL‐17 and C3 mRNA expressions were elevated significantly in the active lesions from ulcerative colitis (UC) and Crohn's disease (CD) patients. There was a significant positive correlation between IL‐17 and C3 mRNA expression in the IBD mucosa. IL‐17 stimulated a dose‐ and time‐dependent increase in C3 mRNA expression and C3 secretion in colonic SEMFs. The C3 molecules secreted by colonic SEMFs were a 115‐kDa α‐chain linked to a 70‐kDa β‐chain by disulphide bonds, which was identical to serum C3. The IL‐17‐induced C3 mRNA expression was blocked by p42/44 mitogen‐activated protein kinase (MAPK) inhibitors (PD98059 and U0216) and a p38 MAPK inhibitor (SB203580). Furthermore, IL‐17‐induced C3 mRNA expression was inhibited by an adenovirus containing a stable mutant form of IκBα. C3 and IL‐17 mRNA expressions are enhanced, with a strong correlation, in the inflamed mucosa of IBD patients. Part of these clinical findings was considered to be mediated by the colonic SEMF response to IL‐17.     

In vivo demonstration of T lymphocyte migration and amelioration of ileitis in intestinal mucosa of SAMP1/Yit mice by the inhibition of MAdCAM-1

The aetiology of Crohn's disease (CD) remains unknown. Since SAMP1/Yit mice have been reported to develop CD-like spontaneous enteric inflammation, such mice have been studied as an animal model of CD. In this study, using this model we examined T lymphocyte migration in microvessels of intestinal mucosa in vivo and the expression of adhesion molecules by immunohistochemistry. Fluorescence-labelled T lymphocytes isolated from AKR/J (control) mice were injected into the tail veins of recipient mice, and T lymphocyte migration in the postcapillary venules of Peyer's patches, submucosal microvessels, and villus capillaries of the terminal ileum was monitored using an intravital microscope. Adhesion of T lymphocytes was significantly increased in 35 week old SAMP1/Yit mice compared with that in AKR/J or 15 week old SAMP1/Yit mice. Immunohistochemical study showed increased infiltration of CD4, CD8 and beta7-integrin-positive cells and increased expression of MAdCAM-1 and VCAM-1 in the terminal ileum of SAMP1/Yit mice. Antibodies against MAdCAM-1 and VCAM-1 significantly inhibited adhesion of T lymphocytes to microvessels of the terminal ileum, and anti-MAdCAM-1 antibody showed stronger suppressive effect than the anti-VCAM-1 antibody. Periodical administration of anti-MAdCAM-1 antibody twice a week for 7 weeks significantly ameliorated ileitis of SAMP1/Yit mice, but submucosal hypertrophy was not significantly suppressed. Anti-VCAM-1 antibody treatment failed to show significant resolution of ileitis. In addition, anti-MAdCAM-1 antibody treatment also attenuated established ileitis. The results demonstrate that, although MAdCAM-1 and VCAM-1 play an important role in T lymphocyte-endothelial cell interactions in SAMP1/Yit mice, MAdCAM-1 may be a more appropriate target for therapeutic modulation of chronic ileitis.     

Expression of IL-27 in human Th1-associated granulomatous diseases

Interleukin (IL)‐27 is a newly described member of the IL‐12 family. It is a heterodimeric cytokine composed of two subunits, p28 and Epstein–Barr virus‐induced gene 3 (EBI3). In vitro studies have shown that IL‐27 is mainly produced by activated monocytes and dendritic cells. It induces the proliferation of naïve CD4‐positive T cells and synergizes with IL‐12 for interferon‐γ (IFN‐γ) production. Knock‐out mice for the IL‐27 receptor (WSX‐1/TCCR) have impaired Th1 responses and form abnormal granulomas when injected with bacillus Calmette‐Guérin. However, the expression profile of IL‐27 in vivo is currently unknown. To investigate the potential role of IL‐27 in the development of a Th1 response in humans in vivo, this study has analysed the in situ expression of IL‐27 subunits in three types of granulomatous disease (tuberculosis, sarcoidosis, and Crohn's disease), each characterized by a Th1 response. Tissue sections from patients with tuberculosis (n = 9), sarcoidosis (n = 8), or Crohn's disease (n = 7) were analysed by immunohistochemistry with anti‐EBI3 and anti‐p28 antibodies, in parallel with control tissues (control reactive lymph nodes, n = 14, and control intestinal tissues, n = 11). In granulomatous tissues, EBI3 and p28 co‐expression was detected in epithelioid and multinucleate giant cells in granulomas. In addition, sinus or tissue macrophages, endothelial cells, and plasma cells were found to co‐express EBI3 and p28. These data support a possible role for IL‐27 in human Th1 responses. Copyright © 2004 John Wiley & Sons, Ltd.     

The proportion of Th1 cells, which prevail in gut mucosa, is decreased in inflammatory bowel syndrome

T lymphocytes and their cytokines have an important role in the regulation of immune responses in the gut and in the pathogenesis of intestinal inflammation such as in Crohn's disease. The aim of this study was to analyse the Th1/Th2 cytokine profile (IFN-gamma, IL-2, IL-4 and IL-10) in intraepithelial lymphocytes (IEL) and lamina propria lymphocytes (LPL) in Crohn's disease (CD) and ulcerative colitis (UC) in relation to healthy controls (C). Colonic and ileal biopsy specimens were obtained from controls (n = 13) and patients with CD (n = 32). Colonic biopsies were obtained from patients with UC (n = 11). Intracytoplasmic IFN-gamma, IL-2, IL-4 and IL-10 were determined by flow cytometry after PMA-ionomycin stimulation in IEL and LPL. In colonic LPL, a significant proportional decrease of IFN-gamma and IL-2 producing CD3+ cells was observed in patients with CD and UC compared to controls. In ileal LPL, a similar tendency was found although differences were not significant. In IEL no differences in cytokine profiles could be observed. Flow cytometric analysis of intracytoplasmic cytokines at single cell level showed a proportional decrease of IFN-gamma and IL-2 producing T cells in colonic lamina propria in patients with inflammatory bowel disease.     

Blockade of PSGL-1 attenuates CD14+ monocytic cell recruitment in intestinal mucosa and ameliorates ileitis in SAMP1/Yit mice

The pathogenesis of Crohn's disease (CD) is not known. However, monocytes and macrophages are thought to play important roles in the development of mucosal inflammation. Therefore, in this study, we examined the role of monocyte-endothelial cell interactions in senescence-accelerated mouse P1 (SAMP1)/Yit mice, a murine model of spontaneous ileitis. Fluorescence-labeled CD14+ monocytic cells isolated from the spleen and mesenteric lymph nodes of AKR/J (control) mice were injected into the tail veins of recipient (AKR/J and SAMP1/Yit) mice, and migration in the postcapillary venules (PCV) of Peyer's patches, submucosal venules, and villus microvessels of the terminal ileum was monitored by using an intravital microscope. Rolling and adhesion of CD14+ monocytic cells in the PCV of Peyer's patches and microvessels of the terminal ileum were increased in SAMP1/Yit mice. An immunohistochemical study showed increased expression of P-selectin glycoprotein-1 (PSGL-1), P-selectin, and vascular cell adhesion molecule-1 in the terminal ileum of SAMP1/Yit mice. Antibodies against these three adhesion molecules significantly inhibited adhesion of CD14+ monocytic cells to the PCV of Peyer's patches and microvessels of the terminal ileum, treatment with an anti-PSGL-1 monoclonal antibody (mAb) showing the strongest suppressive effect. Anti-PSGL-1 mAb also attenuated T cell adhesion in microvessels of intestinal mucosa. In addition, periodical administration of an anti-PSGL-1 mAb for 7 weeks significantly ameliorated ileitis of SAMP1/Yit mice. The results suggest that PSGL-1-P-selectin interaction plays an important role in monocyte-endothelial cell interactions and the development of ileitis in a murine model of CD and that the blockade of this adhesion molecule may be a novel strategy for treating CD.     

Epstein-Barr virus (EBV) infection and expression of the interleukin-12 family member EBV-induced gene 3 (EBI3) in chronic inflammatory bowel disease

Herpesviruses have been suggested as possible etiological agents of ulcerative colitis and Crohn's disease. Recently, increased numbers of Epstein-Barr virus (EBV)-infected cells have been detected in ulcerative colitis as compared to Crohn's disease. Interestingly, expression levels of the EBV-induced gene 3 (EBI3), a molecule belonging to the interleukin (IL)-12 family, have also been reported to be elevated in ulcerative colitis as compared to Crohn's disease. To test the hypothesis that these observations might be interrelated, ileocolic resection specimens were examined from 16 patients with ulcerative colitis and from 20 patients with Crohn's disease. The presence of EBV-infected cells and of EBI3-expressing cells was determined quantitatively by in situ hybridisation and immunohistochemistry, respectively. Larger number of EBV-infected cells were seen in areas of active inflammation of ulcerative colitis and Crohn's disease as compared to areas of inactive inflammation. However, there was no statistically significant difference between ulcerative colitis and Crohn's disease. Numbers of EBI3-expressing cells were increased in areas of active inflammation of ulcerative colitis and Crohn's disease but again there was no statistically significant difference between the two diseases. Double labelling experiments showed that EBI3 expression occurred only in a small minority of EBV-infected cells in ulcerative colitis and Crohn's disease. These results suggest that increased numbers of EBV-infected cells in areas of active inflammatory bowel disease (IBD) are secondary to influx or local proliferation of inflammatory cells and do not contribute significantly to local production of EBI3. Assessment of the possible role of EBI3 of the pathogenesis of ulcerative colitis or Crohn's disease requires information regarding the expression of other IL-12 family members.     

Distinct expression of interleukin (IL)‐36α, β and γ, their antagonist IL‐36Ra and IL‐38 in psoriasis,rheumatoid arthritis and Crohn's disease

Interleukin (IL)‐36α, IL‐36β and IL‐36γ are expressed highly in skin and are involved in the pathogenesis of psoriasis, while the antagonists IL‐36Ra or IL‐38, another potential IL‐36 inhibitor, limit uncontrolled inflammation. The expression and role of IL‐36 cytokines in rheumatoid arthritis (RA) and Crohn's disease (CD) is currently debated. Here, we observed that during imiquimod‐induced mouse skin inflammation and in human psoriasis, expression of IL‐36α, γ and IL‐36Ra, but not IL‐36β and IL‐38 mRNA, was induced and correlated with IL‐1β and T helper type 17 (Th17) cytokines (IL‐17A, IL‐22, IL‐23, CCL20). In mice with collagen‐induced arthritis and in the synovium of patients with RA, IL‐36α, β, γ, IL‐36Ra and IL‐38 were all elevated and correlated with IL‐1β, CCL3, CCL4 and macrophage colony‐stimulating factor (M‐CSF), but not with Th17 cytokines. In the colon of mice with dextran sulphate sodium‐induced colitis and in patients with CD, only IL‐36α, γ and IL‐38 were induced at relatively low levels and correlated with IL‐1β and IL‐17A. We suggest that only a minor subgroup of patients with RA (17–29%) or CD (25%) had an elevated IL‐36 agonists/antagonists ratio, versus 93% of patients with psoriasis. By immunohistochemistry, IL‐36 cytokines were produced by various cell types in skin, synovium and colonic mucosa such as keratinocytes, CD68⁺ macrophages, dendritic/Langerhans cells and CD79α⁺ plasma cells. In primary cultures of monocytes or inflammatory macrophages (M1), IL‐36β and IL‐36Ra were produced constitutively, but IL‐36α, γ and IL‐38 were produced after lipopolysaccharide stimulation. These distinct expression profiles may help to explain why only subgroups of RA and CD patients have a potentially elevated IL‐36 agonists/antagonists ratio.     

Interleukin-2 primes eosinophil degranulation in hypereosinophilia and Wells' syndrome

Patients with hypereosinophilia frequently suffer from eosinophil-mediated damages of the heart, lungs, skin, and other organs, while some do not. The reason(s) for this difference is not known. We observed that eosinophils from most patients with hypereosinophilia express the alpha-chain of the IL-2 receptor (CD25), and that IL-2 enhances platelet-activating factor-stimulated release of eosinophil cationic protein from CD25-expressing but not from CD25-negative eosinophils. Such a "priming" effect has previously been described for eosinophil hematopoietins. These data suggest that patients with increased eosinophil surface CD25 expression are at higher risk of eosinophil degranulation and subsequent tissue damage when IL-2 is present at inflammatory sites.     

Interleukin-1beta induces in vivo tolerance to lipopolysaccharide in mice

Endotoxin or lipopolysaccharide (LPS) tolerance may be partially due to the secretion of potent anti-inflammatory cytokines following severe Gram-negative infections, or by low doses of LPS. In this work, we describe the effects of interleukin-1 (IL-1) and tumour necrosis factor alpha (TNF-), two early cytokines secreted after LPS exposure, in the induction of LPS tolerance. Our results demonstrate that mice treated with three daily doses of 100 ng of IL-1 were tolerant to LPS-induced shock. However, TNF- was unable to induce an LPS refractory state. Given the fact that 100 ng of IL-1 increase the plasma levels of glucocorticoids, we evaluated whether a daily injection of dexamethasone (DEX) alone was able to reproduce the LPS-like tolerant state. However, no signs of LPS refractoriness were detected, except when DEX was administered concomitantly with a dose of IL-1 that does not induce corticosterone secretion (12 ng/mouse). This dose was found to induce in vitro up-regulation of the glucocorticoid receptors (GcR) of peritoneal macrophages following 24 h of treatment. In addition, we demonstrate that IL-1 is capable of inducing the down-regulation of Toll-like receptor 4 (TLR4), a crucial molecule in the signal transduction of LPS. Taken together, our results indicate that IL-1 can generate tolerance to LPS in vivo, and suggest that the regulation of mechanisms of the down-regulation of TLR4, as well as those involved in the expression of GcR and/or in the secretion of glucocorticoids, would be crucial for these effects.     

Expression of interleukin (IL)‐19 and IL‐24 in inflammatory bowel disease patients: a cross‐sectional study

Interleukin (IL)‐19 and IL‐24 belong to the IL‐20 subfamily, and are involved in host defence against bacteria and fungi, tissue remodelling and wound healing. Nevertheless, no previous studies have explored their expression in Mexican mestizo patients with inflammatory bowel disease (IBD). The aim of the study was to characterize and to enumerate peripheral and tissue IL‐19‐ and IL‐24‐producing cells, as well as gene expression in patients with IBD with regard to its clinical activity. We studied a total of 77 patients with ulcerative colitis (UC), 36 Crohn's disease (CD) and 33 patients as control group (without endoscopic evidence of intestinal inflammation). Gene expression was measured by real‐time–polymerase chain reaction (RT–PCR). Protein expression was detected in biopsies by immunohistochemistry and in freshly isolated peripheral blood mononuclear cells by flow cytometry. IL‐19 and IL‐24 gene expression was elevated significantly in patients with active IBD versus the inactive disease and non‐inflammatory control groups (P < 0·05). However, IL‐19‐ and IL‐24‐producing cells were only increased in active CD versus active UC and non‐inflammatory tissues (P < 0·05). IL‐19 was produced conspicuously by circulating B cells and monocytes in patients with inactive disease (P < 0·05). Conversely, IL‐24 was noticeably synthesized by peripheral B cells, CD4⁺ T cells, CD8⁺ T cells and monocytes in patients with active disease. In conclusion, IL‐19‐ and IL‐24‐producing cells in active CD patients were increased compared with active UC and non‐inflammatory tissues. These cytokines could significantly shape and differentiate inflammatory process, severity and tolerance loss between UC and CD pathophysiology.     

Impaired Th1 responses in mice deficient in Epstein-Barr virus-induced gene 3 and challenged with physiological doses of Leishmania major

Protection against Leishmania major is dependent on IL-12 release from L. major-infected dendritic cells (DC) that induce IFN-gamma-producing Th1/Tc1 cells. IL-27, a novel member of the IL-12 family, is a heterodimer composed of p28 and IL-12p40-related Epstein-Barr virus-induced gene 3 (EBI3), and was shown to be produced by DC. In this study, we utilized EBI3-deficient mice to investigate the role of IL-27 in leishmaniasis using physiological low-dose infections that mimic natural transmissions. Lesions in EBI3(-/-) mice were significantly larger between weeks 3 and 10 post infection, reaching up to approximately threefold increased lesion volumes compared to wild types. In parallel, dermal lesions of EBI3(-/-) mice contained greater parasite numbers, reaching a peak load that was 2-log higher than in C57BL/6 mice. However, lesions in EBI3(-/-) and wild-type mice resolved after 12 weeks. At early time points, the antigen-specific cytokine response in EBI3(-/-) lymph nodes showed increased levels of IL-4, IL-10 and IL-13 and decreased IFN-gamma production. IL-27 production was restricted to the DC population, since the majority of EBI3 expression in lymph nodes of infected mice was found in CD11c(+) cells. In conclusion, our data show that DC-derived IL-27 is critical for the timely initiation of efficient anti-parasite Th1 immunity early in infections.     

Involvement of interleukin 18 in Crohn's disease: evidence from in vitro analysis of human gut inflammatory cells and from experimental colitis models

An imbalance of immunoregulatory factors and/or cells contributes to uncontrolled mucosal T cell activation and inflammation in Crohn's disease (CD). Bioactive interleukin (IL)-18 has been shown to be produced by macrophages in CD lesions. We report here that T cells freshly isolated from inflamed tissue of CD patients (and not T cells from control intestinal tissue) were responsive to IL-18. In the presence of IL-18, these T cells produced more interferon (IFN)-gamma and less IL-10. To analyse further the role of IL-18 in this disease, an acute and a chronic model of murine colitis were used. IL-18 mRNA was significantly enhanced in trinitrobenzene sulphonic acid (TNBS) induced colitis, and treatment with IL-18 binding protein (IL-18BPa), which neutralizes IL-18 bioactivity, significantly reduced the severity of colitis. However, IL-18BPa did not affect the course of chronic colitis in CD45RBhighCD4+ T cell reconstituted SCID mice. Production of IFN-gamma in lamina propria mononuclear cell cultures from IL-18BPa-treated SCID mice was decreased, but at the same time fewer lamina propria CD4+ T cells harvested from IL-18BPa-treated mice compared to non-treated mice were in apoptosis. We conclude that IL-18 clearly has a modulatory role in the inflammatory cascade of CD and experimental colitis by affecting IFN-gamma and IL-10 production, and apoptosis. In view of the divergent effects of IL-18 neutralization in the two different murine colitis models, it is unlikely that IL-18 is at the top of this cascade.     

Neuroprotective effects of enriched environment in MPTP-treated SAMP8 mice

Neuroprotective effects of enriched environment (EE) have been well established. Recent study suggests that exposure to EE can protect dopaminergic neurons against MPTP-induced Parkinsonism. After 64 female SAMP8 mice were reared in EE and standard environment (SE) for 3 months, the effects of EE and SE were compared on behavioural change, tyrosine hydroxylase (TH) immunoreaction positive neuron and dopaminetransporter (DAT) expression in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP)-treated SAMP8. EE mice showed decreased spontaneous activity compared with SE mice. But EE + MPTP mice showed less decreased spontaneous activity compared with SE + MPTP mice. Otherwise, EE mice showed increased percentage of entries into the open arms and percentage of time spent in the open arms. Furthermore, EE mice demonstrated reduced neurotoxicity, with less decreased TH mRNA and protein expression in Substantia Nigra (SN) after MPTP administration compared with SE mice. SE mice showed a 53.77% loss of TH-positive neurons, whereas EE mice only showed a 42.28% loss. Moreover, EE mice showed decreased DAT mRNA and protein expression compared with SE mice. These data demonstrate that EE can protect dopaminergic neurons against MPTP-induced neuronal damage, which suggest that the probability of developing Parkinson's disease (PD) may be related to life environment.     

CXCR1-binding chemokines in inflammatory bowel diseases: down-regulated IL-8/CXCL8 production by leukocytes in Crohn's disease and selective GCP-2/CXCL6 expression in inflamed intestinal tissue

Crohn's disease (CD) and ulcerative colitis (UC) are inflammatory bowel diseases (IBD) that are characterized by chronic intestinal inflammation and a constant influx of leukocytes mediated by pro-inflammatory cytokines and chemokines. The intestinal expression of the CXCR1-binding chemokines IL-8/CXCL8 and GCP-2/CXCL6 and the participation of immunocompetent cells in IBD were evaluated. IL-8 production by peripheral blood mononuclear cells (PBMC) from IBD patients, stimulated with endotoxin, plant lectin or double-stranded RNA, was significantly lowered in patients with CD, but not in UC patients or healthy subjects. The reduced chemokine production by PBMC from IBD patients was both IL-8 and CD specific, but not inducer dependent. In serum, most chemokines remained undetectable, while the levels of those that were measurable remained unaltered in IBD patients. GCP-2, but not ENA-78/CXCL5, nor IL-8, were highly expressed by endothelial cells in inflamed intestinal tissue of IBD patients. In contrast, stimulated endothelial cell cultures produced more IL-8 than GCP-2. The selective GCP-2 staining of endothelial cells at sites of ulcerations suggests that GCP-2, despite its low production capacity in vitro, plays a role in IBD that is different from that of structurally (ENA-78) and functionally (IL-8) related ELR(+) CXC chemokines. Thus, the chemokine network shows complementarity rather than redundancy.     

Questioning the Th1/Th2 paradigm in reproduction: peripheral levels of IL-12 are down-regulated in miscarriage patients

PROBLEM: It has been postulated that a T helper (Th)1 response is associated with pregnancy failure, whereas a Th2 response contributes to pregnancy maintenance. However, this Thl/Th2 dichotomy has recently been hypothesized to be an oversimplification. To prove this novel hypothesis, we investigated the levels of the Th1-inducer cytokine interleukin (IL)-12 in immunocompetent cells of patients with normal pregnancies (NP) and spontaneous abortion (SA). METHODS: Presence of intracellular IL-12 was evaluated in CD8+ and CD56-blood and decidual lymphocytes as well as in monocytes and granulocytes by flow cytometry from NP and SA individuals. IL-12 serum levels were measured by enzyme-linked immunosorbent assay (ELISA). We further investigated the effect of recombinant human (rh) IL-12 on the production of interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha in peripheral leukocytes ex vivo. RESULTS: In patients suffering from SA we observed lower percentages of IL-12 in lymphocytes, monocytes and granulocytes derived from peripheral blood and decidua, compared with women with normally progressing pregnancies. No differences could be observed when evaluating the levels of IL-12 in the granulocyte population. The IL-12 serum levels were below the ELISA sensitivity limit. Ex vivo stimulation of the peripheral blood cells with increasing doses of IL-12 resulted in a significant decrease of IFN-gamma+, whereas levels of TNF-alpha+ in lymphocytes were unaffected. CONCLUSIONS: The classical Th1/Th2 paradigm appears to be insufficient to exclusively explain the causes of pregnancy loss. Our current results render us to requestion the role of Th1 cytokines during pregnancy and suggest some protective function of the Th1-inducer cytokine IL-12.     

Deregulated cytokine network and defective Th1 immune response in multiple myeloma

Intracellular cytokine production by peripheral blood mononuclear cells (PBMC) was analysed in 51 patients with multiple myeloma (MM), 22 with monoclonal gammopathy of undetermined significance (MGUS) and 20 healthy subjects, as a parameter of immunological dysfunction in MM. An increased proportion of T cells and HLA-DR+ cells producing IL-6 was observed in MM patients with active disease (at diagnosis and relapsing) compared with patients in remission and with MGUS, whereas no difference of IFN-gamma+, IL-2+ PBMC between patients and controls was evident. Determination of serum cytokine levels demonstrated that the imbalanced IL-6 production by T cells and the defective anti-tumour Th1 cell activity were related to elevated levels of IL-6 and IL-12. In vitro studies of PHA- and anti-CD3/anti-CD28 MoAbs stimulation of PBMC demonstrated the ability of lymphocytes from MM patients to differentiate towards the Th1 subset in the presence of rIL-12. By contrast, addition of exogenous rIL-6 impaired IFN-gamma production by rIL-12-prompted T cells. Inhibition of Th1 polarization of the immune response by IL-6 was direct on T cells and not mediated by dendritic cells (DC). Evaluation of the ability of MM-derived DC to stimulate cell proliferation of allogenic T lymphocytes and produce IL-12 in vitro, in fact, suggested that MM-derived DC were functionally active. Taken as a whole, these results indicate that a deregulated cytokine network occurs in active MM. They also suggest that increased IL-6 production by peripheral T lymphocytes contributes to the immune dysfunction observed in MM, and enables tumour cells to escape immune surveillance by preventing the anti-tumour Th1 immune response.