Reciprocal control of T helper cell and dendritic cell differentiation.
It is not known whether subsets of dendritic cells provide different cytokine microenvironments that determine the differentiation of either type-1 T helper (TH1) or TH2 cells. Human monocyte (pDC1)-derived dendritic cells (DC1) were found to induce TH1 differentiation, whereas dendritic cells (DC2) derived from CD4+CD3-CD11c- plasmacytoid cells (pDC2) induced TH2 differentiation by use of a mechanism unaffected by interleukin-4 (IL-4) or IL-12. The TH2 cytokine IL-4 enhanced DC1 maturation and killed pDC2, an effect potentiated by IL-10 but blocked by CD40 ligand and interferon-gamma. Thus, a negative feedback loop from the mature T helper cells may selectively inhibit prolonged TH1 or TH2 responses by regulating survival of the appropriate dendritic cell subset. (+info)
Expression of stromelysin-3 in atherosclerotic lesions: regulation via CD40-CD40 ligand signaling in vitro and in vivo.
Stromelysin-3 is an unusual matrix metalloproteinase, being released in the active rather than zymogen form and having a distinct substrate specificity, targeting serine proteinase inhibitors (serpins), which regulate cellular functions involved in atherosclerosis. We report here that human atherosclerotic plaques (n = 7) express stromelysin-3 in situ, whereas fatty streaks (n = 5) and normal arterial specimens (n = 5) contain little or no stromelysin-3. Stromelysin-3 mRNA and protein colocalized with endothelial cells, smooth muscle cells, and macrophages within the lesion. In vitro, usual inducers of matrix metalloproteinases such as interleukin-1, interferon-gamma, or tumor necrosis factor alpha did not augment stromelysin-3 in vascular wall cells. However, T cell-derived as well as recombinant CD40 ligand (CD40L, CD154), an inflammatory mediator recently localized in atheroma, induced de novo synthesis of stromelysin-3. In addition, stromelysin-3 mRNA and protein colocalized with CD40L and CD40 within atheroma. In accordance with the in situ and in vitro data obtained with human material, interruption of the CD40-CD40L signaling pathway in low density lipoprotein receptor-deficient hyperlipidemic mice substantially decreased expression of the enzyme within atherosclerotic plaques. These observations establish the expression of the unusual matrix metalloproteinase stromelysin-3 in human atherosclerotic lesions and implicate CD40-CD40L signaling in its regulation, thus providing a possible new pathway that triggers complications within atherosclerotic lesions. (+info)
Minimal cross-linking and epitope requirements for CD40-dependent suppression of apoptosis contrast with those for promotion of the cell cycle and homotypic adhesions in human B cells.
Eight different CD40 mAb shared with soluble trimeric CD40 ligand (sCD40LT) the capacity to rescue germinal center (GC) B cells from spontaneous apoptosis and to suppress antigen receptor-driven apoptosis in group I Burkitt's lymphoma cells. Three mAb (G28-5, M2 and M3) mimicked sCD40LT in its ability to promote strong homotypic adhesion in resting B cells, whereas others (EA5, BL-OGY/C4 and 5C3) failed to stimulate strong clustering. Binding studies revealed that only those mAb that promoted strong B cell clustering bound at, or near to, the CD40L binding site. While all eight mAb and sCD40LT were capable of synergizing with IL-4 or phorbol ester for promoting DNA synthesis in resting B cells, co-stimulus-independent activation of the cells into cycle through CD40 related directly to the extent of receptor cross-linking. Thus, mAb which bound outside the CD40L binding site synergized with sCD40LT for promoting DNA synthesis; maximal levels of stimulation were achieved by presenting any of the mAb on CD32 transfectants in the absence of sCD40LT or by cross-linking bound sCD40LT with a second antibody. Monomeric sCD40L, which was able to promote rescue of GC B cells from apoptosis, was unable to drive resting B cells into cycle. These studies demonstrate that CD40-dependent rescue of human B cells from apoptosis requires minimal cross-linking and is essentially epitope independent, whereas the requirements for promoting cell cycle progression and homotypic adhesion are more stringent. Possible mechanisms underlying these differences and their physiological significance are discussed. (+info)
TRANCE, a TNF family member, is differentially expressed on T cell subsets and induces cytokine production in dendritic cells.
TNF-related activation-induced cytokine (TRANCE) is a member of the TNF family recently identified in activated T cells. We report here that TRANCE mRNA is constitutively expressed in memory, but not naive, T cells and in single-positive thymocytes. Upon TCR/CD3 stimulation, TRANCE mRNA and surface protein expression are rapidly up-regulated in CD4+ and CD8+ T cells, which can be further enhanced on CD4+ T cells by CD28-mediated costimulation. However, TRANCE induction is significantly suppressed when cells are stimulated in the presence of IL-4, but is not modified in the presence of IFN-alpha, IFN-gamma, TGF-beta, TNF-alpha, or IL-2. High levels of TRANCE receptor expression are found on mature dendritic cells (DCs). In this study we show that activated T and B cells also express TRANCE receptor, but only at low levels. TRANCE, however, does not exert any significant effect on the proliferation, activation, or survival of those cells. In DCs, TRANCE induces the expression of proinflammatory cytokines (IL-6, IL-1) and T cell growth and differentiation factors (IL-12, IL-15) in addition to enhancing DC survival. Moreover, TRANCE cooperates with CD40 ligand or TNF-alpha to further increase the viability of DCs, suggesting that several TNF-related molecules on activated T cells may cooperatively regulate the function and survival of DCs to enhance T cell-mediated immune responses. (+info)
N-acetyl-L-cysteine inhibits primary human T cell responses at the dendritic cell level: association with NF-kappaB inhibition.
N-acetyl-L-cysteine (NAC) is an antioxidant molecule endowed with immunomodulatory properties. To investigate the effect of NAC on the induction phase of T cell responses, we analyzed its action on human dendritic cells (DC) derived from adherent PBMC cultured with IL-4 and granulocyte-macrophage CSF. We first found that NAC inhibited the constitutive as well as the LPS-induced activity of the transcription factor NF-kappaB. In parallel, NAC was shown to down-regulate the production of cytokines by DC as well as their surface expression of HLA-DR, CD86 (B7-2), and CD40 molecules both at the basal state and upon LPS activation. NAC also inhibited DC responses induced by CD40 engagement. The inhibitory effects of NAC were not due to nonspecific toxicity as neither the viability of DC nor their mannose receptor-mediated endocytosis were modified by NAC. Finally, we found that the addition of NAC to MLR between naive T cells and allogeneic DC resulted in a profound inhibition of alloreactive responses, which could be attributed to a defect of DC as APC-independent T cell responses were not inhibited by NAC. Altogether, our results suggest that NAC might impair the generation of primary immune responses in humans through its inhibitory action on DC. (+info)
Lymphocyte activation gene-3, a MHC class II ligand expressed on activated T cells, stimulates TNF-alpha and IL-12 production by monocytes and dendritic cells.
Lymphocyte activation gene-3 (LAG-3) is an MHC class II ligand structurally and genetically related to CD4. Although its expression is restricted to activated T cells and NK cells, the functions of LAG-3 remain to be elucidated. Here, we report on the expression and function of LAG-3 on proinflammatory bystander T cells that are activated in the absence of TCR engagement. LAG-3 is expressed at high levels on human T cells cocultured with autologous monocytes and IL-2 and synergizes with the low levels of CD40 ligand (CD40L) expressed on these cells to trigger TNF-alpha and IL-12 production by monocytes. Indeed, anti-LAG-3 mAb inhibits both IL-12 and IFN-gamma production in IL-2-stimulated cocultures of T cells and autologous monocytes. Soluble LAG-3Ig fusion protein markedly enhances IL-12 production by monocytes stimulated with infra-optimal concentrations of sCD40L, whereas it directly stimulates monocyte-derived dendritic cells (DC) for the production of TNF-alpha and IL-12, unravelling an enhanced responsiveness to MHC class II engagemenent in DC as compared with activated monocytes. Thus similar to CD40L, LAG-3 may be involved in the proinflammatory activity of cytokine-activated bystander T cells and most importantly it may directly activate DC. (+info)
Regulation of interleukin (IL)-12 receptor beta2 subunit expression by endogenous IL-12: a critical step in the differentiation of pathogenic autoreactive T cells.
The interleukin (IL)-12 receptor (R)beta2 subunit is the critical molecule involved in maintaining IL-12 responsiveness and controlling T helper cell type 1 lineage commitment. We demonstrate that IL-12 and interferon (IFN)-gamma play separate, but complementary, roles in regulating IL-12Rbeta2 expression on antigen-specific CD4(+) T cells. These results are consistent with our previous observation that IL-12 can promote autoimmune disease through IFN-gamma-independent as well as -dependent pathways. Therefore, we compared the induction of IL-12 by, and the expression of the IL-12Rbeta2 subunit on, myelin basic protein (MBP)-specific T cells from experimental allergic encephalomyelitis (EAE)-susceptible SJL (H-2(s)) mice and from EAE- resistant B10.S mice (H-2(s)). B10.S mice had an antigen-specific defect in their capacity to upregulate the IL-12Rbeta2 subunit. Defective expression was not secondary to the production of suppressive cytokines, but to a failure of B10.S MBP-specific T cells to upregulate CD40 ligand expression and to induce the production of IL-12. IL-12Rbeta2 expression as well as encephalitogenicity of these cells could be restored by the addition of IL-12. These results suggest that the development of immunotherapies that target the IL-12Rbeta2 subunit may be useful for the treatment of autoimmune diseases. (+info)
Bone marrow-derived cells are required for the induction of a pulmonary inflammatory response mediated by CD40 ligation.
The expression of inflammatory mediators by various cells following in vitro CD40 ligation is well known. However, knowledge of the role and interaction with these cells in the establishment and maintenance of in vivo immune-mediated inflammation is limited. In this report, a chimeric mouse model based on CD40 knockout and wild-type mice was used to assess the role of bone marrow (BM)-derived and non-BM-derived cells in a CD40-mediated pulmonary inflammation response. CD40+ BM-derived cells were required for initial cell recruitment, pulmonary edema, and weight loss associated with this response. The structural CD40+ non-BM-derived cells of the lung, such as fibroblasts, epithelial cells, and endothelial cells, could not by themselves establish any level of pulmonary inflammation. However, both the CD40+ BM-derived cells and the structural CD40+ non-BM-derived cells of the lung were required to maximize the level of pulmonary inflammation. Both B cells and T cells played a contributing role in macrophage recruitment and pulmonary edema but neither contributed to the inflammation-associated weight loss. These experiments indicate that CD40+ BM-derived cells were critical to the induction of pulmonary inflammation and that alveolar macrophages, B cells, and T cells contributed to selective aspects of the response. (+info)