MCS-18, a novel natural product isolated from Helleborus purpurascens, inhibits dendritic cell activation and prevents autoimmunity as shown in vivo using the EAE model

Here we report for the first time that MCS-18, a novel natural product isolated from Helleborus purpurascens, is able to inhibit the expression of typical molecules of mature dendritic cells (DC) such as CD80, CD86, and especially of CD83 subsequently leading to a clear and dose-dependent inhibition of the DC-mediated T-cell stimulation. Furthermore, MCS-18 impeded the formation of the typical DC/T-cell clusters, which are essential to induce potent immune responses. Interestingly, MCS-18 also inhibited CCR7 expression on DC which subsequently lead to a dose-dependent block of the CCL19-mediated DC migration. MCS-18 not only inhibited the DC-mediated T-cell stimulation but also the anti-CD3/anti-CD28-mediated T-cell stimulation. Strikingly, MCS-18 also strongly reduced the paralysis associated with the experimental autoimmune encephalomyelitis (EAE), which is a murine model for human multiple sclerosis, in a prophylactic as well as in a "real" therapeutic setting. Even when the EAE was induced for a second time, the MCS-18-treated animals were still protected, suggesting that MCS-18 induces a long-lasting suppressive effect. In addition, and very important for the potential practical application in humans, MCS-18 was also active when administered orally. MCS-18 treatment almost completely reduced leukocyte infiltration in the brain and in the spinal cord. In conclusion, using in vitro as well in vivo assays we were able to show that MCS-18 exerts a strong immunosuppressive activity with remarkable potential for the therapy of diseases characterized by a pathologically over-activated immune system.     

Inhibition of the proteasome influences murine and human dendritic cell development in vitro and in vivo

Dendritic cells (DC) are the most potent antigen-presenting cells (APC) known today and are designated as nature′s adjuvant since they are the only antigen-presenting cell type capable of inducing naïve T cell responses in vivo. In order to become potent T cell stimulators DC have to mature. This mature DC phenotype is characterized amongst other characteristics by the up-regulation of co-stimulatory molecules such as CD40, CD80, CD86 and the cell surface expression of CD83. Inhibition of their expression blocks the immune responses in vitro and in vivo, and thus represents an interesting strategy to control undesired and/or over-activated immune responses such as in autoimmune disorders, transplant rejections and allergies. Here we investigated the in vitro and in vivo effects of the proteasome inhibitor Velcade^® in respect to DC phenotype and DC functions in murine and human DC. Interestingly, in vitro, DC maturation as well as DC-mediated T cell stimulation and cytokine production was impaired. Furthermore, administration of the inhibitor in vivo resulted in a reduced mature phenotype of ex vivo generated murine DC. Thus, inhibition of the proteasome interferes with DC maturation and subsequently with DC-mediated T cell stimulation events.     

CNI-1493 mediated suppression of dendritic cell activation in vitro and in vivo

The tetravalent guanylhydrazone CNI-1493 (CNI-1493) has been shown to inhibit macrophage activation, reduce systemic inflammation as well as proinflammatory cytokine production. Here we report for the first time that CNI-1493 also influences the biology of dendritic cells (DC). In order to become potent T cell stimulators of DC have to mature. Interestingly, when CNI-1493 was added to the maturation stimulus the expression of a typical DC-maturation marker i.e. CD83 was reduced. Subsequent functional in vitro analyses showed that DC-mediated T-cell stimulation was clearly reduced in CNI-1493-treated DC, underlining the functional impact that CNI-1493 on DC biology. Furthermore, the effect of CNI-1493 was analyzed in vivo using the experimental autoimmune encephalomyelitis (EAE) model in C57BL/6 mice. Interestingly, in a prophylactic treatment regimen CNI-1493 prevented the paralysis associated with EAE almost completely. In addition, when applied in an early therapeutic setting CNI-1493 also reduced the clinical EAE symptoms. In summary, we show for the first time, that in addition to the earlier reported effects on macrophages, CNI-1493 also influences the function and biology of DC. Since DC are the only antigen-presenting cells (APC) known today to be able to prime naive T cells, the findings reported herein are highly relevant for the therapeutic application of CNI-1493.     

Human plasmacytoid-derived dendritic cells and the induction of T-regulatory cells

Suppression by T-regulatory (Tr) cells is essential for the induction of T-cell tolerance and the prevention of autoimmune diseases, organ rejection, and graft-versus-host disease. Increasing attention has been devoted to understand the role of dendritic cells (DC) in the control of Tr-cell differentiation. Here we review the recent evidence that cluster designation (CD)40-ligand activated plasmacytoid-derived DCs (DC2) have the ability to induce primary Tr-cell differentiation. We propose that in addition to the regulatory functions of immature myeloid DC, Tr-cell induction by DC2 represents a nonredundant mechanism for the safeguard of peripheral T-cell tolerance. DC2 can be used as tool to drive potent antigen specific Tr-cell differentiation and expansion in vitro and in vivo.     

CD40/CD40L interaction is essential for the induction of EAE in the absence of CD28-mediated co-stimulation

CD28 provides a co-stimulatory signal critical for optimal T cell activation. We and others have shown that the B7/CD28 co-stimulatory pathway is a major regulatory pathway for the control of immune responses. Experimentally induced models of autoimmunity have been shown to be prevented or reduced in intensity in mice deficient for CD28. Here, we show that EAE and accompanying neuroantigen-specific immune responses are drastically reduced in the absence of CD28. However, we go on to show that EAE can be induced in CD28-deficient mice following two immunizations. After re-immunization, CD28-deficient mice develop severe EAE with myelin-specific responses equal to those of wildtype controls, and extensive demyelination in the spinal cord. Treatment of CD28-deficient mice with anti-CD40L at the time of immunization significantly reduced DTH responses and prevented the development of EAE following two immunizations, indicating a critical role for CD40/CD40L signaling in the absence of CD28. Taken together, our results indicate that CD28-mediated co-stimulation does not regulate immunological anergy. Instead, CD28 appears to adjust the threshold for activation and expansion of autoreactive cells.     

CD25 as an immune regulatory molecule expressed on myeloid dendritic cells

CD25 (alpha-chain of IL-2 receptor) on dendritic cells (DC) has been previously regarded as an activation marker. DC that concomitantly express surface CD25 and co-stimulatory molecules were considered to be fully mature. While both murine and human DC can express CD25, they do not express the beta-chain of the IL-2 receptor, which is indispensable for the execution of IL-2 signaling. The biological function of CD25 during the DC maturation therefore still remains undefined. In this review we focus on recent findings, describing CD25 expression and secretion by human myeloid regulatory DC. These DC co-express CD25 and the immunoregulatory enzyme indoleamine 2,3-dioxygenase (IDO) and inhibit T-cell function. CD25, expressed and secreted by such DC may capture IL-2 and thereby suppress T-cell proliferation, by this means providing an accessory mechanism of DC-mediated immune suppression. We also discuss the implication of DC-derived CD25 for human disease in both cancer and chronic infection.     

Costimulation of CD3/TcR complex with either integrin or nonintegrin ligands protects CD4+ allergen-specific T-cell clones from programmed cell death

An optimal stimulation of CD4⁺ cells in an immune response requires not only signals transduced via the TcR/CD3 complex, but also costimulatory signals delivered as a consequence of interactions between T-cell surface-associated costimulatory receptors and their counterparts on antigen-presenting cells ‘APC). The intercellular adhesion molecule-1 ‘ICAM-1, CD54) efficiently costimulates proliferation of resting, but not antigen-specific, T cells. In contrast, CD28 and CD2 support interleukin ‘IL)-2 synthesis and proliferation of antigen-specific T cells more efficiently than those of resting T cells. The molecular basis for this differential costimulation of T cells is poorly understood. Cypress-specific T-cell clones ‘TCC) were generated from four allergic subjects during in vivo seasonal exposure to the allergen. Purified cypress extract was produced directly from fresh collected pollen and incubated with the patients' mononuclear cells. Repeated allergen stimulation was performed in T-cell cultures supplemented with purified extract and autologous APC. The limiting-dilution technique was then adopted to generate allergen-specific TCC, which were also characterized by their cytokine secretion pattern as ThO ‘IL-4 plus interferon-gamma) or Th2 ‘IL-4). Costimulation-induced proliferation or apoptosis was measured by propidium iodide cytofluorometric assay. By cross-linking cypress-specific CD4⁺ and CD8⁺ T-cell clones with either anti-CD3 or anti-CD2, anti-CD28, and anti-CD54 monoclonal antibodies, we demonstrated that CD4+ clones ‘with ThO- or Th2-type cytokine production pattern) undergo programmed cell death only after anti-CD3 stimulation, whereas costimulation with either anti-CD54 or anti-CD28 protects target cells from apoptosis. The costimulation-induced protection from apoptotic death was associated with a significant rise in IL-4 secretion in both Th0 and Th2-type clones. In contrast, cypress-specific Th0 CD8⁺ clones were more susceptible to stimulation-induced apoptosis via either anti-CD3 or anti-CD2, alone or in combination with anti-CD54 or anti-CD28, thus displaying only slight but nonsignificant modifications in the pattern of IL-4 secretion. The death-promoting costimulatory effects were not observed with highly purified normal resting CD4⁺ or CD8⁺ lymphocytes. Taken together, these results suggest that TcR engagement by an allergen in the context of functionally active APC induces activation-dependent cell death of some, perhaps less specific, cells, and this may be an important homeostatic mechanism through which functional expansion of allergen-specific T cells is regulated during an ongoing immune response.     

Role of B70/B7-2 in CD4+ T-cell immune responses induced by dendritic cells.

Dendritic cells (DC) are potent antigen-presenting cells (APC). However, the molecular basis underlying this activity remains incompletely understood. To address this question, we generated murine monoclonal antibodies (mAb) against human peripheral blood-derived DC. One such antibody, designated IT209, stained differentiated DC and adherent monocytes, but failed to stain freshly isolated peripheral blood mononuclear cells (PBMC). The antigen recognized by IT209 was identified as B70 (B7-2; also recently identified as CD86). Using this mAb we studied the role of B70 in CD4+ T-cell activation by DC in vitro. IT209 partly inhibited the proliferative response of CD4+ T cells to allogeneic DC and to recall antigens, such as tetanus toxoid (TT) and purified protein derivative (PPD) of tuberculin, presented by autologous DC. More importantly, the mAb had a potent inhibitory effect on the primary response of CD4+ T cells to autologous DC pulsed with human immunodeficiency virus (HIV) gp160 or keyhole limpet haemocyanin (KLH). Adherent monocytes, despite their expression of B70, failed to induce T-cell responses to these antigens. IT209-mediated inhibition of CD4+ T-cell responses was equivalent to that produced by anti-CD25 mAb, whereas an anti-CD80 mAb was only marginally inhibitory and did not augment the effect of IT209. These findings indicate that the B70 antigen plays an important role in DC-dependent CD4+ T-cell activation, particularly in the induction of primary CD4+ T-cell responses to soluble antigens. However, since activated monocytes, despite their expression of B70, failed to prime naive T cells to these antigens, our results suggest that additional molecules contribute to the functions of DC in CD4+ T-cell activation.     

Bidirectional NK/DC interactions promote CD4 expression on NK cells, DC maturation, and HIV infection

Interactions between natural killer (NK) and dendritic cells (DCs) are integral to immune response development, potentially leading to bidirectional NK/DC activation. We demonstrate that autologous NK/DC interactions induce CD4 expression on NK cells, influencing degranulation. Cell contact is required, with high NK:DC ratios and mature DCs most effectively inducing CD4 expression. CD4(+) NK cells, in turn, mediate DC maturation via contact-dependent and independent pathways, more effectively maturing DCs than CD4(-) NK cells. Bidirectional NK/DC interactions also impact HIV infection, as NK-matured DCs effectively deliver infectious HIV to T cells, via trans-infection. DC-induced CD4 expression also renders NK cells susceptible to HIV infection. Focusing on NK/DC interactions, DCs can transfer infectious virus and enhance HIV infection of CD4(+) NK cells, strongly suggesting that these interactions influence HIV pathogenesis. Findings provide new insight regarding NK/DC interactions, defining a mechanism by which cellular interactions in the absence of pathogens promote DC-mediated amplification of HIV infection.     

Adherent dendritic cells expressing high levels of interleukin-10 and low levels of interleukin-12 induce antigen-specific tolerance to experimental autoimmune encephalomyelitis

We have previously shown that tolerance can be induced against acute experimental autoimmune encephalomyelitis (EAE) in Lewis rats by bone marrow-derived dendritic cells (DC) that have been pulsed in vitro with encephalitogenic myelin basic protein peptide 68-86 (MBP 68-86), and injected subcutaneously into healthy rats prior to immunization with MBP 68-86 plus complete Freund's adjuvant. To elucidate better the properties of tolerogenic DC, we here compared plastic-adherent DC with floating, non-adherent DC, which were cultured for 7 days in the presence of granulocyte-macrophage colony-stimulating factor plus interleukin-4 (IL-4). Adherent DC expressed high levels of IL-10 mRNA and protein, and low levels of IL-12 mRNA and showed high expression of CD54 compared with floating DC. Proliferation, nitrite concentration and capacity for antigen presentation were lower in adherent DC than in floating DC. There were no differences between adherent and floating DC regarding expression of CD11c, OX62, major histocompatibility complex class II, CD80, or CD86. Most importantly, we observed that adherent DC induced tolerance to EAE in vivo when injected subcutaneously into Lewis rats prior to immunization, while floating DC did not. Adherent DC-mediated tolerance to EAE was associated with augmented proliferation, nitric oxide production and frequency of apoptotic cells as well as with up-regulation of transforming growth factor-beta (TGF-beta) -expressing cells in T-cell areas of lymph nodes. Tolerance induction by adherent DC seems to be related to a nitric oxide-apoptosis pathway and to up-regulation of TGF-beta-expressing cells.     

Influence of CD26 and integrins on the antigen sensitivity of human memory T cells

The antigen sensitivity of class II MHC-restricted human CD4 T-cell clones is demonstrated to increase gradually with time after restimulation. This is manifested in a requirement of less antigen in culture, as well as decreased numbers of peptide-MHC complexes per APC for T-cell activation, and in an increased resistance to inhibition by class II MHC blockade. The increase in antigen sensitivity is accompanied by increased cellsurface expression of CD26, LFA-1, and VLA-1, whereas the expression of TCR and a series of other cell-surface molecules remains unchanged. Using appropriate monoclonal antibodies, we have shown that CD26 and LFA-1 contribute directly to the increased antigen sensitivity of “late-stage” T-cell clones. The late-memory T-cell phenotype established in this study is shown to occur also among T cells activated in vivo. We suggest that increasing the antigen sensitivity via antigen-nonspecific molecules is a physiologic mechanism for maintaining T-cell memory in face of decreasing antigen concentration, and for ensuring preferential activation of memory T cells upon repeated encounter with antigen.     

Adhesive substrate-modulation of adaptive immune responses

While it is well-known that adsorbed proteins on implanted biomaterials modulate inflammatory responses, modulation of dendritic cells (DCs) via adhesion-dependent signaling has only been begun to be characterized. In this work, we demonstrate that adhesive substrates elicit differential DC maturation and adaptive immune responses. We find that adhesive substrates support similar levels of DC adhesion and expression of stimulatory and co-stimulatory molecules. Conversely, DC morphology and differential production of pro- and anti-inflammatory cytokines (IL-12p40 and IL-10, respectively) is adhesive substrate-dependent. For example, DCs cultured on collagen and vitronectin substrates generate higher levels of IL-12p40, whereas DCs cultured on albumin and serum-coated tissue culture-treated substrates produce the higher levels of IL-10 compared to other substrates. Additionally, our results suggest substrate-dependent trends in DC-mediated allogeneic CD4(+) T-cell proliferation and T-helper cell type responses. Specifically, we show that substrate-dependent modulation of DC IL-12p40 cytokine production correlates with CD4(+) T-cell proliferation and T(h)1 type response in terms of IFN-gamma producing T-helper cells. Furthermore, our results suggest substrate-dependent trends in DC-mediated stimulation of IL-4 producing T-cells, but this T(h)2 type response is not dependent on DC production of IL-10 cytokine. This work has impact in the rational design of biomaterials for diverse applications such as tissue-engineered constructs, synthetic particle-based vaccines and the ex vivo culture of DCs for immunotherapies.     

Human bone marrow stromal cells hamper specific interactions of CD4 and CD8 T lymphocytes with antigen-presenting cells

Bone marrow stromal cells (BMSCs) may inhibit T-cell functions in vitro and thus have been proposed as immunoregulators to control in vivo graft-versus-host disease (GVHD) in haploidentical hemopoietic stem cell transplants. To better investigate this phenomenon, we used a defined experimental system in which responding T cells are antigen-specific and devoid of alloreactivity against BMSC from a different subject. Thus, we established antigen-specific human CD4 and CD8 T-cell lines as the readout system. Antigen-dependent proliferation was reduced with both T-cell subsets cultured on confluent BMSCs, and also on confluent human skin fibroblasts (HSF) inhibited T-cell proliferation with similar efficiency. Morphological observations of the cocultures showed impairment of physical interactions between T-cell and antigen-presenting cells in the presence of BMSC, with lack of formation of antigen-dependent clusters of T cells and antigen-presenting cells (APCs). In contrast, no effects were seen with BMSC-conditioned medium. Since suppression was seen only with confluent mesenchymal cells, this phenomenon may not be relevant in vivo, where BMSCs are at low frequency. In addition, if the reported suppressive effect of BMSCs on GVHD in vivo is confirmed, a different in vitro system should be envisaged to better understand and exploit the underlying mechanism.     

MCS-18, a novel natural plant product prevents autoimmune diabetes

There is still a vital need for new therapies in order to prevent or treat type I diabetes. In this respect, we report that MCS-18 a novel natural product isolated from the plant Helleborus purpurascens (i.e. Christmas rose) is able to increase diabetes free survival using the NOD-mouse model, which is accompanied with a diminished IFN-γ secretion of splenocytes. In the animal group which has been treated with MCS-18 during week 8 and week 12 of age 70% of the animals showed a diabetes free survival at week 30, whereas in contrast in the untreated animals less than 10% were free of diabetes. MCS-18 treatment significantly reduced islet T-cell infiltrates as well as the rate of T-cell proliferation. Periinsular infiltrates in the MCS-18 treated animals showed a significantly enhanced number of Foxp3(+) CD25(+) T cells, indicating the increased presence of regulatory T cells. These studies show that MCS-18 exerts an efficient immunosuppressive activity with remarkable potential for the therapy of diseases characterized by pathological over-activation of the immune system.     

T-cell Ig and mucin domain-containing protein (Tim)-2 regulates murine allergic conjunctivitis during the effector phase

T-cell Ig and mucin domain-containing protein (Tim)-2 is associated with Th2-dependent immune responses. Here, we investigated whether administration of anti-Tim-2 Abs affects the development of murine experimental allergic conjunctivitis (EC), a Th2-mediated disease. While treatment with anti-Tim-2 Abs in vivo during the induction phase did not affect the severity of EC, treatment during the effector phase augmented EC. The in vitro stimulation of ragweed (RW)-primed splenocytes with RW in the presence of anti-Tim-2 Abs induced significantly more IL-5 and IL-13 production but significantly less IFN-γ production compared with the control splenocytes treated with normal rat IgG. In addition, the transfer of the anti-Tim-2 Ab-treated splenocytes induced significantly more severe EC than the control splenocytes. Thus, Tim-2 negatively regulates the Th2 differentiation of Ag-primed T-cells and the development of EC during the effector phase.     

Anti-CD52 blocks EAE independent of PD-1 signals and promotes repopulation dominated by double-negative T cells and newly generated T and B cells

Lymphocyte depletion using anti-CD52 antibody effectively reduces relapses of multiple sclerosis (MS). To begin to understand what mechanisms might control this outcome, we examined the effect of a murine-CD52-specific mAb on the depletion and repopulation of immune cells in mice with experimental autoimmune encephalomyelitis (EAE), a model of MS. We tested whether the tolerance-promoting receptor programmed cell death protein-1 (PD-1) is required for disease remission post anti-CD52, and found that PD-1-deficient mice with a more severe EAE were nevertheless effectively treated with anti-CD52. Anti-CD52 increased the proportions of newly generated T cells and double-negative (DN) T cells while reducing newly generated B cells; the latter effect being associated with a higher expression of CD52 by these cells. In the longer term, anti-CD52 caused substantial increases in the proportion of newly generated lymphocytes and DN T cells in mice with EAE. Thus, the rapid repopulation of lymphocytes from central lymphoid organs post anti-CD52 may limit further disease. Furthermore, these data identify DN T cells, a subset with immunoregulatory potential, as a significant hyperrepopulating subset following CD52-mediated depletion.     

CD4-mediated functional activation of human CD4+CD25+ regulatory T cells

Naturally occurring CD4(+)CD25(+)FoxP3(+) regulatory T cells (CD25(+) Tregs) constitute a specialized population of T cells that is essential for the maintenance of peripheral self-tolerance. The immune regulatory function of CD25(+) Tregs depends upon their activation. We found that anti-CD4 antibodies activate the suppressive function of human CD25(+) Tregs in a dose-dependent manner. We demonstrate that CD4-activated CD25(+) Tregs suppress the proliferation of CD4(+) and CD8(+) T cells, their IL-2 and IFN-gamma production as well as the capacity of CD8(+) T cells to re-express CD25. By contrast, anti-CD4 stimulation did not induce suppressive activity in conventional CD4(+) T cells. These results identify CD4 as a trigger for the suppressive function of CD25(+) Tregs and suggest a possible CD4-mediated exploitation of these cells.     

p150/95 (CD11c/CD18) expression is required for the development of experimental autoimmune encephalomyelitis

p150/95 (CD11c/CD18, CR4) is a member of the beta(2)-integrin family of adhesion molecules and is considered an important phagocytic receptor. The role of p150/95 in the development of central nervous system demyelinating diseases, including multiple sclerosis, remains unexplored. To determine p150/95-mediated mechanisms in experimental autoimmune encephalomyelitis (EAE), we performed EAE using CD11c-deficient (CD11c(-/-)) mice. EAE in CD11c(-/-) mice was significantly attenuated and characterized by markedly reduced spinal cord T-cell infiltration and interferon-gamma production by these cells. Adoptive transfer of antigen-restimulated T cells from wild-type to CD11c(-/-) mice produced significantly attenuated EAE, whereas transfer of CD11c(-/-) antigen-restimulated T cells to control mice induced a very mild, monophasic EAE. T cells from MOG(35-55) peptide-primed CD11c(-/-) mice displayed an unusual cytokine phenotype with elevated levels of interleukin (IL)-2, IL-4, and IL-12 but reduced levels of interferon-gamma, tumor necrosis factor-alpha, IL-10, IL-17, and transforming growth factor-beta compared with control mice. Overall, CD11c(-/-) T cells from primed mice proliferated comparably to that of control T cells on MOG(35-55) restimulation. Our results indicate that expression of p150/95 is critical on both T cells as well as other leukocytes for the development of demyelinating disease and may represent a novel therapeutic target for multiple sclerosis.     

Co-stimulation with 4-1BB ligand allows extended T-cell proliferation, synergizes with CD80/CD86 and can reactivate anergic T cells

Activation of T cells requires co-stimulation, in addition to signals through the antigen-receptor complex. Antigen encounter without adequate co-stimulation results in T-cell desensitization or anergy, a mechanism of peripheral tolerance and an apparent obstacle to cancer immunotherapy. One important co-stimulatory pathway involves CD28 engagement by CD80 or CD86. However, other ligand-receptor pairs can also provide co-stimulation and may have important functions modulating the immune response. Previous reports indicated that co-stimulation using 4-1BB ligand (4-1BBL) or agonistic anti-4-1BB antibodies could prolong T-cell responses, avoid activation-induced cell death and promote anti-tumour responses in mice. To further investigate the potential for cancer immunotherapy, we studied the effects of CD80/CD86 and 4-1BBL in repeated stimulation of human T cells and asked whether 4-1BBL might be capable of reversing anergy. We expressed CD80, CD86 and 4-1BBL in A549 lung carcinoma cells using adenovirus vectors and co-cultured these with human T cells stimulated with anti-CD3 antibody. Proliferation co-stimulated by CD80 or CD86 was transient; however, 4-1BBL-co-stimulated cultures continued to proliferate for up to 5 weeks, with repeated stimulation. Combined co-stimulation with CD80/CD86 and 4-1BBL also allowed continuous proliferation at a faster rate than either signal alone. Co-stimulation with 4-1BBL did not suppress expression of the inducible, inhibitory CD80/CD86R, CTLA-4. Significantly, we show that T cells that had become non-responsive to anti-CD3, either alone or together with CD80/CD86 co-stimulation, and thus were anergic, could be reactivated to proliferate when costimulated with 4-1BBL, either alone or combined with CD80/CD86.     

Infection with prevalent clinical strains of Mycobacterium tuberculosis leads to differential maturation of monocyte derived dendritic cells

The link between innate and adaptive host immune response to Mycobacterium tuberculosis (M.tb) is driven by dendritic cells (DC). In this study, we examined the ability of prevalent clinical strains from south India (S7, S10) and laboratory strain H37Rv (Rv) to induce maturation of monocyte derived dendritic cells (MoDC). The phenotypic and functional changes of DC upon infection with different strains of M.tb were evaluated. It was observed that S7 and Rv strains partially hampered the maturation of MoDC as reflected by the low expression of maturation markers and co-stimulatory markers when compared to LPS stimulated MoDC. In contrast, strain S10 infected DC showed a marked increase in the expression of these markers. The functional property was investigated by the ability of infected MoDC to induce T-cell proliferation and to stimulate secretion of IFN-γ by CD4⁺T-cells. It was found that Rv and S7 infected MoDC were less efficient in inducing T-cell proliferation. The secretion of IL-12 by Rv and S7 infected MoDC was also found to be significantly lesser than LPS stimulated MoDC. On the other hand, S10 infected MoDC showed enhanced T-cell stimulation and cytokine secretion. Together these results indicate that there is a substantial variability in the capacity of M.tb clinical strains to induce maturation of DC which may be dependent upon their virulence.