Impairment of antigen-presenting cell function in mice lacking expression of OX40 ligand.
(41/1635)
OX40 expressed on activated T cells is known to be an important costimulatory molecule on T cell activation in vitro. However, the in vivo functional significance of the interaction between OX40 and its ligand, OX40L, is still unclear. To investigate the role of OX40L during in vivo immune responses, we generated OX40L-deficient mice and a blocking anti-OX40L monoclonal antibody, MGP34. OX40L expression was demonstrated on splenic B cells after CD40 and anti-immunoglobulin (Ig)M stimulation, while only CD40 ligation was capable of inducing OX40L on dendritic cells. OX40L-deficient and MGP34-treated mice engendered apparent suppression of the recall reaction of T cells primed with both protein antigens and alloantigens and a significant reduction in keyhole limpet hemocyanin-specific IgG production. The impaired T cell priming was also accompanied by a concomitant reduction of both T helper type 1 (Th1) and Th2 cytokines. Furthermore, antigen-presenting cells (APCs) derived from the mutant mice revealed an impaired intrinsic APC function, demonstrating the importance of OX40L in both the priming and effector phases of T cell activation. Collectively, these results provide convincing evidence that OX40L, expressed on APCs, plays a critical role in antigen-specific T cell responses in vivo. (+info)
Characterisation of CTL directed towards non-inherited maternal alloantigens in human cord blood.
(42/1635)
Allogeneic cord blood transplantation (CBT), especially from unrelated donors, is being increasingly used for treating paediatric patients with both malignant and non-malignant disorders. Recent clinical and experimental evidence suggests that human cord blood mononuclear cells (CBMC) may acquire in utero a state of tolerance towards non-inherited maternal antigens (NIMA). In order to better define this phenomenon, we measured, by means of a limiting dilution assay (LDA), the frequency of NIMA-specific CTL precursors (CTLp) in cord blood samples obtained from 13 healthy neonates. The immunophenotype of the effector cells recovered from LDA was also analysed. Data concerning both CTLp frequency and phenotype of effector cells were compared with those obtained stimulating CBMC with cells of paternal origin (NIPA) and adult PBMC with allogeneic targets. Results showed that cytotoxic cells directed towards cells of maternal origin could be detected in all cord blood samples tested. Phenotype analysis demonstrated that NIPA elicit the expansion of CD3+/CD8bright T cells, a phenotype associated with alloreactive CTL. By contrast, NIMA preferentially stimulated the expansion of CD3-/CD8dim+ cells, a phenotype associated with NK cells, which are known to be able, in certain clinical conditions, to kill allogeneic haematopoietic cells without causing GVHD. Thus, our results indicate that, when evaluated in a limiting dilution condition, NIMA-reactive cord blood cells are detectable and a preferential expansion of NK cells is observed. (+info)
Umbilical cord blood T lymphocytes are induced to apoptosis after being allo-primed in vitro.
(43/1635)
In this study, the immunity of umbilical cord blood (UCB) T lymphocytes against allo-antigens was investigated by a standard MLC. No significant difference, between the UCB T cells or peripheral blood (PB) mature T cells, was observed in the primary responses (stimulation index (SI), 51.8 +/- 14.8 and 46.5 +/- 15.0, respectively). In contrast, in the secondary response, the SI obtained with the CD4 T cells from UCB decreased dramatically (16.3 +/- 6.4), while it increased with the CD4 T cells from PB (118.5 +/- 21.7). UCB (CD4 and CD8) T cells separately showed much higher frequencies of apoptosis after a primary allo-priming, compared with PB CD4 and CD8 T cells (CD4, UCB 30.5% vs PB 0.8%; CD8, UCB 32% vs PB 1.3%). The higher apoptotic level of the UCB CD4 T cells was confirmed by a second, ELISA-based, Tunel assay (OD values, UCB CD4 1.93 +/- 0.31 vs PB CD4 0.59 0.9; P < 0.01). Those apoptotic steps were not attributed to the amount of cytokine (IL-2, 4 and IFN-gamma) production, which was found to be similar in both cases. In conclusion, UCB lymphocytes are much more likely to be induced to apoptosis by allo-priming than adult lymphocytes. This supports their possible, successful engraftment across barriers of HLA incompatibility. (+info)
Cytomegalovirus immune globulin intravenous (human) administration modulates immune response to alloantigens in sensitized renal transplant candidates.
(44/1635)
One of the important parameters for prolonged waiting time for potential renal transplant recipients is the presence of preformed antibodies to human leucocyte antigen (HLA) antigens, which is often caused by previous transplants, pregnancy or transfusions. In vivo administration of specific and unselected polyclonal intravenous immunoglobulin (IVIGs) preparations have been shown to inhibit anti-HLA alloantibodies in highly sensitized patients. We sought to determine whether Cytogam (Medimmune Inc., Gaithersburg, MD, USA), a hyperimmune anticytomegalovirus immunoglobulin would (1) effect either in vitro or in vivo alloreactivity, and (2) whether Cytogam therapy could reduce the titre of preformed anti-HLA antibodies in highly sensitized patients. Alloreactivity was assessed by mixed lymphocyte reaction (MLR) and cytotoxic T lymphocyte (CTL) assay. A complement dependent microlymphocytotoxicity assay was done to assess for panel reactive antibody (PRA) status and the presence of anti-idiotypic antibodies in the Cytogam preparation. The MLR was inhibited by Cytogam in vitro in a dose-dependent fashion ranging from 31-92%. Significant inhibition of the MLR responses was not observed in recipients who received Cytogam in vivo (50 mg/kg). This could be a result of adminstration of a low dose of IVIG. However, CTL activity against the alloantigens in all individuals assessed was significantly inhibited after in vivo administration of Cytogam. Three of five individuals experienced a decrease of 5-32% in the PRA status at 4 weeks post administration of Cytogam. Cytogam also blocked the anti-HLA antibody titres in a microlymphocytotoxicity assay, suggesting the presence of anti-idiotypic antibodies. Our study was based on a single prophylactic dose of Cytogam (50 mg/kg), however, higher dose administration could be feasible by removing more fluid at dialysis, but should be given intradialytically to avoid volume overload. Overall, our results suggest that Cytogam can modulate the in vivo and in vitro T cell responses against the alloantigens. (+info)
In vivo rapid reduction of alloantigen-activated CD8+ mature cytotoxic T cells by inhibitors of acidification of intracellular organelles, prodigiosin 25-C and concanamycin B.
(45/1635)
Prodigiosin (PrG) 25-C and concanamycin B (CMB) are immunosuppressants that specifically inhibit the induction of cytotoxic T cells (CTL) without affecting the function of B cells and helper T cells in vivo. Both compounds inhibit acidification of intracellular organelles and induce destruction of cytotoxic granules and degradation of perforin in vitro. Here we show that a single intraperitoneal (i.p.) injection of PrG 25-C, and of CMB, into mice eliminates cytotoxic activity 7 days after alloantigen stimulation (when mature CTL activity has been detected in control mice), with minimal effect on the alloantigen-specific antibody titre in serum. FK506 did not suppress the cytotoxic activity with this administration schedule. Suppression was accompanied by a decrease in the CD8+ population and in perforin expression of spleen cells induced by alloantigen stimulation. The suppression of CTL activity and decrease in CD8+ cell number was detected as early as 7 hr after the injection of compounds. These results suggest that inhibitors of acidification of intracellular organelles suppress CTL activity in vivo by reducing the number of mature CD8+ CTL. (+info)
Development and analysis of various clonal alloantigen-dependent cytotoxic cell lines from channel catfish.
(46/1635)
To determine the phenotypes of cytotoxic cells in channel catfish, clonal alloantigen-dependent leukocyte lines were established from mixed leukocyte cultures. Each clone was analyzed for expression of TCR alpha and beta genes by RT-PCR and for target cell specificity by 51Cr-release assay. Based on the above criteria, the following five different cell types were identified among the 19 clones analyzed: 1) TCR alphabeta+ allospecific cytotoxic cells, 2) TCR alphabeta+ nonspecific cytotoxic cells, 3) allospecific TCR alphabeta+ noncytotoxic cells, 4) TCR alphabeta- nonspecific cytotoxic cells, and 5) TCR alphabeta- allospecific cytotoxic cells. The demonstration of cloned, TCR alphabeta+, allospecific cytotoxic effectors provides the strongest evidence to date for the existence of cytotoxic T cells in fish. (+info)
Blockade of CD28-B7, but not CD40-CD154, prevents costimulation of allogeneic porcine and xenogeneic human anti-porcine T cell responses.
(47/1635)
Despite increasing use of swine in transplantation research, the ability to block costimulation of allogeneic T cell responses has not been demonstrated in swine, and the effects of costimulatory blockade on xenogeneic human anti-porcine T cell responses are also not clear. We have compared the in vitro effects of anti-human CD154 mAb and human CTLA4IgG4 on allogeneic pig T cell responses and xenogeneic human anti-pig T cell responses. Both anti-CD154 mAb and CTLA4IgG4 cross-reacted on pig cells. While anti-CD154 mAb and CTLA4IgG4 both inhibited the primary allogeneic pig MLRs, CTLA4IgG4 (7.88 microg/ml) was considerably more inhibitory than anti-CD154 mAb (100 microg/ml) at optimal doses. Anti-CD154 mAb inhibited the production of IFN-gamma by 75%, but did not inhibit IL-10 production, while CTLA4IgG4 completely inhibited the production of both IFN-gamma and IL-10. In secondary allogeneic pig MLRs, CTLA4IgG4, but not anti-CD154 mAb, induced Ag-specific T cell anergy. CTLAIgG4 completely blocked the indirect pathway of allorecognition, while anti-CD154 mAb blocked the indirect response by approximately 50%. The generation of porcine CTLs was inhibited by CTLA4IgG4, but not by anti-CD154 mAb. Human anti-porcine xenogeneic MLRs were blocked by CTLA4IgG4, but only minimally by anti-CD154 mAb. Finally, CTLA4IgG4 prevented secondary xenogeneic human anti-porcine T cell responses. These data indicate that blockade of the B7-CD28 pathway was more effective than blockade of the CD40-CD154 pathway in inhibiting allogeneic pig T cell responses and xenogeneic human anti-pig T cell responses in vitro. These findings have implications for inhibiting cell-mediated immune responses in pig-to-human xenotransplantation. (+info)
Calcitonin gene-related peptide decreases expression of HLA-DR and CD86 by human dendritic cells and dampens dendritic cell-driven T cell-proliferative responses via the type I calcitonin gene-related peptide receptor.
(48/1635)
These studies were performed to establish whether functional receptors for calcitonin gene-related peptide (CGRP) are present on human dendritic cells (DCs) and to investigate potential immunomodulatory effects of CGRP on DCs other than Langerhans cells. Reverse transcriptase-PCR revealed expression of mRNA for a type 1 CGRP receptor by mature and immature blood-derived DCs. Sequence analysis confirmed the identity of the type 1 CGRP receptor (CGRP-R1). Addition of CGRP (10-7 M) to mature and immature DCs resulted in mobilization of intracellular calcium. Treatment of immature DCs with CGRP (10-7 M), before and after maturation in monocyte-conditioned medium, resulted in decreased cell surface expression of HLA-DR MHC class II and the costimulatory molecule, CD86. Treatment of immature DCs with CGRP (10-7 M) also resulted in decreased expression of CD86, but expression of HLA-DR was unchanged. When CGRP-treated mature DCs were used to stimulate allogeneic T cells, proliferative responses were dampened (approximately 50%), especially at low DC:T cell ratios (1:360). This effect was not observed with CGRP-treated, immature DCs. In contrast, CGRP-treated mature or immature DCs were no less efficient than untreated DCs in driving syngeneic T cell-proliferative responses to staphylococcal enterotoxin B. We conclude that mature and immature DCs express type 1 CGRP receptors and that signaling through these receptors may dampen mature DC-driven T cell proliferation most likely via down-regulation of CD86 and HLA-DR. (+info)