Recent convincing data have shown that naturally occurring CD8+CD122+ T cells are also regulatory T cells. Paradoxically, CD8+CD122+ T cells have been well described as memory T cells. Given their critical role in tolerance versus long-term immunity, it is important to reconcile this profound dichotomy. In this study, we reported that CD8+CD122+ T cells contain both programmed death-1 (PD-1)− and PD-1+ populations. It was CD8+CD122+PD-1+ T cells, but not their PD-1− counterparts, that suppressed T cell responses in vitro and in vivo. This suppression was largely dependent on their production of IL-10. Moreover, the costimulatory signaling of both CD28 and PD-1 is required for their optimal IL-10 production. In contrast, Ag-specific CD8+CD122+PD-1− T cells were bona fide memory T cells. Thus, CD8+CD122+ T cells can be either regulatory T or memory T cells, depending on their PD-1 expression and Ag specificity. This study reconciles previously contradictory findings and has important implications for tolerance induction.

The constitutive expression of PD-L1 in the testis is an important mechanism underlying testicular immune privilege and long-term survival of intratesticular islet allografts.

Memory T cells respond faster and more vigorously than their naive counterparts and are critical for adaptive immunity. However, it is unknown whether and how memory T cells react in the face of irrelevant Ags. It is generally accepted that bystander memory T cells are neutral in immune responsiveness. In this study, we present the first evidence that bystander central memory (TCM), but not effector memory (TEM), CD8+ T cells suppress allograft rejection as well as T cell proliferation in the draining lymph nodes (DLN) of recipient mice. Both bystander TCM and naive T cells, but fewer TEM cells, migrated to DLN, whereas TCM cells exhibited faster turnover than their naive counterparts, suggesting that bystander TCM cells have an advantage over their naive counterparts in suppression. However, bystander TEM cells migrated to inflammatory graft sites, but not DLN, and yet failed to exert their suppression. These findings indicate that bystander memory T cells need to migrate to lymph nodes to exert their suppression by inhibiting responder T cell activation or homeostatic proliferation. Moreover, the suppression mediated by bystander TCM cells was largely dependent on IL-15, as IL-15 was required for their homeostatic proliferation and TCM-mediated suppression of allograft rejection. This suppression also required the presence of TGFβ1, as TCM cells expressed TGFβ1 while neutralizing TGFβ1 abolished their suppression. Thus, bystander TCM, but not TEM, CD8+ T cells are potent suppressors rather than bystanders. This new finding will have an impact on cellular immunology and may have clinic implications for tolerance induction.

Memory T cells are resistant to the conventional costimulatory blockade and therefore impede tolerance induction. However, their migratory, survival, and functional requirements for chemokines are not well understood. We herein examine the role for MCP-1 or CCL2 in the generation, migration, and function of memory CD8+ T cells. We found that overall generation of both central memory (TCM) and effector memory (TEM) CD8+ T cells was severely impaired in the absence of MCP-1. Importantly, the survival of TEM, but not TCM, CD8+ cells was reduced without MCP-1, whereas the homeostatic proliferation of TCM, but not TEM, CD8+ cells was weakened in MCP-1−/− mice. However, once they were generated in the absence of MCP-1, in vitro function of both subsets of memory cells remained intact as determined by their proliferation and IFN-γ production. Interestingly, the migration of TCM, but not TEM, CD8+ cells to inflammatory sites was significantly delayed without MCP-1, whereas both subsets of memory cells underwent comparable expansion and apoptosis with or without MCP-1 during the effector phase. Moreover, the function to eliminate a graft of TCM, but not TEM, CD8+ cells was impaired without MCP-1. Thus, this study demonstrates that MCP-1 plays an important role in not only migration but also generation and survival of memory T cells. This finding provides new insight into the requirement of chemokines for the generation, survival, and function of differential subsets of memory T cells and may have clinic implications for tolerance induction.

Dendritic cell-derived indoleamine 2,3-dioxygenase (IDO) suppresses naive T cell proliferation and induces their apoptosis by catalyzing tryptophan, and hence is essential for the maintenance of peripheral tolerance. However, it is not known whether memory T cells are subject to the regulation by IDO-mediated tryptophan catabolism, as memory T cells respond more rapidly and vigorously than their naive counterparts and are resistant to conventional costimulatory blockade. In this study, we present the evidence that memory CD8+ T cells are susceptible to tryptophan catabolism mediated by IDO. We found that overexpression of IDO in vivo attenuated the generation of both central memory CD8+ T cells (TCM) and effector memory CD8+ T cells (TEM) while suppressing IDO activity promoted their generation. Moreover, IDO overexpression suppressed the effector function of TCM cells or TCM cell-mediated allograft rejection as well as their proliferation in vivo. Interestingly, TCM cells were resistant to apoptosis induced by tryptophan catabolism. However, IDO overexpression did not suppress the effector function of TEM cells or TEM cell-mediated allograft rejection, suggesting that TEM cells, unlike TCM cells, do not require tryptophan for their effector function once they are generated. This study provides insight into the mechanisms underlying the differential regulation of memory T cell responsiveness and has clinical implications for vaccination or tolerance induction.

Cigarette smoke causes cancer and increases the vulnerability of smokers to infections. Epidemiologic studies have shown that smoking is one of major risk factors for late allograft rejection. Despite statistical data that associate smoking with allograft rejection, no any study has been conducted to prove that cigarette smoke directly causes allograft rejection in a cause-effect manner. In particular, investigation into immunologic mechanisms underlying smoke-related allograft rejection is lacking. Here we found that second hand smoke (SHS) hindered long-term islet allograft survival induced by CD154 costimulatory blockade plus donor-specific splenocyte transfusion (DST), although it failed to alter acute islet allograft rejection. SHS did not directly interfere with vigorously alloreactive T-cell proliferation in vivo and in vitro. Neither naturally occurring nor induced CD4+CD25+ Treg cell numbers were significantly reduced by SHS. However, SHS suppressed mRNA and protein expression of indoleamine 2, 3-dioxygenase (IDO) and its activity upon transplantation while IDO overexpression in islet allografts restored their long-term survival induced by CD154 blockade. Therefore, SHS prevents long-term allograft survival by inhibiting IDO expression and activity. Thus, our study for the first time demonstrates that SHS shortens allograft survival in a cause-effect manner and unveils a novel immunologic mechanism underlying smoking-related allograft rejection.

BackgroundInsulin-producing cell clusters (IPCCs) have recently been generated in vitro from adipose tissue-derived stem cells (ASCs) to circumvent islet shortage. However, it is unknown how long they can survive upon transplantation, whether they are eventually rejected by recipients, and how their long-term survival can be induced to permanently cure type 1 diabetes. IPCC graft survival is critical for their clinical application and this issue must be systematically addressed prior to their in-depth clinical trials.Methodology/Principal FindingsHere we found that IPCC grafts that differentiated from murine ASCs in vitro, unlike their freshly isolated islet counterparts, did not survive long-term in syngeneic mice, suggesting that ASC-derived IPCCs have intrinsic survival disadvantage over freshly isolated islets. Indeed, β cells retrieved from IPCC syngrafts underwent faster apoptosis than their islet counterparts. However, blocking both Fas and TNF receptor death pathways inhibited their apoptosis and restored their long-term survival in syngeneic recipients. Furthermore, blocking CD40-CD154 costimulation and Fas/TNF signaling induced long-term IPCC allograft survival in overwhelming majority of recipients. Importantly, Fas-deficient IPCC allografts exhibited certain immune privilege and enjoyed long-term survival in diabetic NOD mice in the presence of CD28/CD40 joint blockade while their islet counterparts failed to do so.Conclusions/SignificanceLong-term survival of ASC-derived IPCC syngeneic grafts requires blocking Fas and TNF death pathways, whereas blocking both death pathways and CD28/CD40 costimulation is needed for long-term IPCC allograft survival in diabetic NOD mice. Our studies have important clinical implications for treating type 1 diabetes via ASC-derived IPCC transplantation.

Abstract. Capsaicin, the main constituent in chili, is an extremely spicy vanillin alkaloid and is found in several Capsicum species in China. Traditionally, it has been used to treat inflammatory diseases such as allergic rhinitis, neuralgia after shingles, refractory female urethral syndrome, spontaneous recalcitrant anal pruritus, and solid tumors. Constant stimulation of the body by inflammatory factors can lead to chronic inflammation. Capsaicin possesses anti-inflammatory activity; however, the underlying mechanism is unknown. We investigated the effect of capsaicin on the secretion of macrophage inflammatory factors in a lipopolysaccharide-induced inflammation model using 56 healthy, SPF grade, BALB/c mice. To this end, mice peritoneal macrophages were isolated and stimulated with lipopolysaccharide (1 μg/mL) and capsaicin (25, 50, 75, or 100 μg/mL) for 24 h. At all concentrations tested, capsaicin significantly promoted the phagocytosis of neutral red dye by macrophages. Furthermore, the gene expression and secretion of inflammatory cytokines significantly increased after induction with lipopolysaccharide (P<0.01); the interleukin (IL)-6 level was 204 μg/mL, tumor necrosis factor (TNF)-α level was 860 μg/mL, and nitric oxide (NO) level was 19.8 μg/mL. However, the treatment with capsaicin reduced their levels (P<0.01) and protein expression of lipopolysaccharide-induced extracellular signal-related kinase 1/2 and p65 (P<0.05). Overall, capsaicin reduced the secretion of inflammatory cytokines (P<0.01), interleukins, TNF-α (P<0.01), and NO by inhibiting the nuclear factor-kappa B and microtubule-associated protein kinase signaling pathways, and thereby reduced lipopolysaccharide-induced inflammatory response in macrophages.