Mechanisms of Tolerance Induction in Liver Transplantation: Lessons Learned from Fetomaternal Tolerance, Autoimmunity and Tumor Immunity

Since the first published report of experimental kidney transplantation in dogs in 1902, there were many experimental and clinical trials of organ transplantation, with many sacrifices. After the establishment of the surgical technique and the discovery of immunosuppressive drugs, transplantation became the definitive treatment strategy for patients with terminal organ failure. However, this is not a common therapy method due to the difficulty of solving the fundamental issues behind organ transplantation, including the shortage of donor graft, potential risks of transplant surgery and economic capability. The pre- and post-transplant management of recipients is another critical issue that may affect transplant outcome. Most liver transplant recipients experience post-transplant complications, including infection, acute/chronic rejection, metabolic syndrome and the recurrence of hepatocellular carcinoma. Therefore, the early prediction and diagnosis of these complications may improve overall and disease-free survival. Furthermore, how to induce operational tolerance is the key to achieving the ultimate goal of transplantation. In this review, we focus on liver transplantation, which is known to achieve operational tolerance in some circumstances, and the mechanical similarities and differences between liver transplant immunology and fetomaternal tolerance, autoimmunity or tumor immunity are discussed.

CD3+CD56+ and CD3-CD56+ lymphocytes in the cerebrospinal fluid of persons with HIV-1 subtypes B and C

The transactivator of transcription (Tat) is a HIV regulatory protein which promotes viral replication and chemotaxis. HIV-1 shows extensive genetic diversity, HIV-1 subtype C being the most dominant subtype in the world. Our hypothesis is the frequency of CSF CD3+CD56+ and CD3-CD56dim is reduced in HIV-1C compared to HIV-1B due to the Tat C30S31 substitution in HIV-1C. 34 CSF and paired blood samples (PWH, n = 20; PWoH, n = 14) were studied. In PWH, the percentage of CD3+CD56+ was higher in CSF than in blood (p < 0.001), comparable in both compartments in PWoH (p = 0.20). The proportion of CD3-CD56dim in CSF in PWH was higher than PWoH (p = 0.008). There was no subtype differences. These results showed CNS compartmentalization of NKT cell response in PWH.

The Role of Type I and Type II NKT Cells in Materno-Fetal Immunity

NKT cells represent a small but significant immune cell population as being a part of and bridging innate and adaptive immunity. Their ability to exert strong immune responses via cytotoxicity and cytokine secretion makes them significant immune effectors. Since pregnancy requires unconventional maternal immunity with a tolerogenic phenotype, investigation of the possible role of NKT cells in materno-fetal immune tolerance mechanisms is of particular importance. This review aims to summarize and organize the findings of previous studies in this field. Data and information about NKT cells from mice and humans will be presented, focusing on NKT cells characteristics during normal pregnancy in the periphery and at the materno-fetal interface and their possible involvement in female reproductive failure and pregnancy complications with an immunological background.

Is there a Role of Intravenous Immunoglobulin in Immunologic Recurrent Pregnancy Loss?

Recurrent pregnancy loss (RPL) commonly refers to three or more miscarriages that occur before 20 weeks of pregnancy. The immunological cause of RPL could be either an auto- or alloimmune-related event or both. Because of the discovery of immunological abnormalities in RPL patients in clinical practice, several immunomodulatory therapies were introduced to maintain the immune balance at the maternal-fetal interface. Intravenous immunoglobulin (IVIg) is one of the immunomodulators. In recent years, several studies have analyzed the therapeutic effect of IVIg on RPL patients with antiphospholipid syndrome (APS) or unexplained RPL. However, their results are controversial. IVIg can be used in RPL patients with APS who have previously failed in other treatments. It is recommended that IVIg infusion could be considered used before conception in RPL patients who have cellular immune abnormalities such as increased natural killer (NK) cell counts, NK cell cytotoxicity, or increased T helper (Th)1/Th2 ratio, depending on the cut-off values of each hospital. The aim of this review was to summarize the mechanisms, efficacy, pharmacokinetics, and side effects associated with passive immunization using IVIg in immunologic RPL, according to the literature published in recent years. We hope that more obstetricians will be able to understand the timing and indication of IVIg properly in immunologic RPL patients and effectively enhance pregnancy outcomes for mothers and neonates.

Unveiling the pathophysiology of gestational diabetes: Studies on local and peripheral immune cells

Gestational diabetes mellitus (GDM) has been associated with impaired maternal immune response. Our aim was to review the available literature linking immune cells profile to GDM, in order to comprehend the role that different subpopulations play in the development of this pathology. We searched in PubMed for studies published in the last decade on circulating levels and placenta expression of immune cells on GDM. We identified 18 studies with several differences regarding the study design, clinical characteristics, number of participants, cell subpopulation and type of sample. Most studies assessed only one subpopulation either in peripheral blood or placenta and did not analyse functional properties of the cells. The most frequently evaluated immune cells were T lymphocytes, especially regulatory T (Tregs), and natural killer (NK) cells in the peripheral blood, and placental macrophages. No studies analysing B cells were identified, and only one study each evaluating γδT cells, dendritic cell (DC) and monocytes was found. Although there are controversies, at least one study reported positive association between GDM and CD4⁺ (activated), Tregs, Th17 and γδT cells; neutrophil/lymphocyte; NK cell (cytotoxic); macrophages; and monocytes. The number of studies is still small, so caution should be exercised in interpreting the data, and further research is required to validate these findings and establish the role of adaptive and innate immune cells in GDM pathophysiology.

Inhibition of endocytic lipid antigen presentation by common lipophilic environmental pollutants

Environmental pollutants as non-heritable factors are now recognized as triggers for multiple human inflammatory diseases involving T cells. We postulated that lipid antigen presentation mediated by cluster of differentiation 1 (CD1) proteins for T cell activation is susceptible to lipophilic environmental pollutants. To test this notion, we determined whether the common lipophilic pollutants benzo[a]pyrene and diesel exhaust particles impact on the activation of lipid-specific T cells. Our results demonstrated that the expression of CD1a and CD1d proteins, and the activation of CD1a- and CD1d-restricted T cells were sensitively inhibited by benzo[a]pyrene even at the low concentrations detectable in exposed human populations. Similarly, diesel exhaust particles showed a marginal inhibitory effect. Using transcriptomic profiling, we discovered that the gene expression for regulating endocytic and lipid metabolic pathways was perturbed by benzo[a]pyrene. Imaging flow cytometry also showed that CD1a and CD1d proteins were retained in early and late endosomal compartments, respectively, supporting an impaired endocytic lipid antigen presentation for T cell activation upon benzo[a]pyrene exposure. This work conceptually demonstrates that lipid antigen presentation for T cell activation is inhibited by lipophilic pollutants through profound interference with gene expression and endocytic function, likely further disrupting regulatory cytokine secretion and ultimately exacerbating inflammatory diseases.

Natural killer cells in placentation and cancer: Implications for hypertension during pregnancy

Hypertension during pregnancy is the most common medical condition encountered during gestation. Despite this, knowledge of the mechanisms that underlie the disease and the development of new therapies are limited. Hypertension during pregnancy and some forms of cancer confer an increased risk to the development of cardiovascular disease later in life; one mechanism which may link these conditions is the involvement of natural killer (NK) cells. Whilst immunology and immunotherapy are well-developed areas in oncology; the complex mechanisms of the immune system in health and disease at the maternal-fetal interface are less well-defined. Natural killer (NK) cells have emerged as key immune cells involved in physiology and pathology of pregnancy. These small lymphocytes are present in the decidua (the uterine-specific uNK cells) and are distinct from peripheral NK cells. The uNK cell population plays a vital role in mediating trophoblast invasion and affecting decidual vascular remodelling whereas the role of the peripheral NK cell population during pregnancy is less well-defined. This review will give an overview of NK cell biology followed by a discussion of the current evidence for the role of uterine and peripheral NK cells at the maternal-fetal interface in health and disease. Furthermore, examples of NK cell research from cancer biology will be employed to inform future directions of research. By combining this knowledge from oncology where the field of immunotherapy has now matured into clinical trials; it is hopeful that new mechanisms can be elucidated to generate targets for similar therapeutic strategies for women with hypertensive pregnancies where interventions are needed.

Immune regulatory network in successful pregnancy and reproductive failures

Maternal immune system must tolerate semiallogenic fetus to establish and maintain a successful pregnancy. Despite the existence of several strategies of trophoblast to avoid recognition by maternal leukocytes, maternal immune system may react against paternal alloantigenes. Leukocytes are important components in decidua. Not only T helper (Th)1/Th2 balance, but also regulatory T (Treg) cells play an important role in pregnancy. Although the frequency of Tregs is elevated during normal pregnancies, their frequency and function are reduced in reproductive defects such as recurrent miscarriage and preeclampsia. Tregs are not the sole population of suppressive cells in the decidua. It has recently been shown that regulatory B10 (Breg) cells participate in pregnancy through secretion of IL-10 cytokine. Myeloid derived suppressor cells (MDSCs) are immature developing precursors of innate myeloid cells that are increased in pregnant women, implying their possible function in pregnancy. Natural killer T (NKT) cells are also detected in mouse and human decidua. They can also affect the fetomaternal tolerance. In this review, we will discuss on the role of different immune regulatory cells including Treg, γd T cell, Breg, MDSC, and NKT cells in pregnancy outcome.

Immune Regulation in Pregnancy: A Matter of Perspective?

The maternal immune system is complex and governed by multiple hormonal and metabolic factors, including those provided to the mother via the fetus. Understanding of the balance between maternal tolerance and protection of the fetus may require thinking from multiple theoretical approaches to the general problem of immune activation and tolerance. This article provides a brief review of the immune system, with aspects relevant to pregnancy. The references include reviews that expand on the elements discussed. The article also uses different models of immune system activation and tolerance to provide a theoretical understanding of the problem of maternal tolerance.

Immune Regulation in Pregnancy: A Matter of Perspective?

The maternal immune system is complex and governed by multiple hormonal and metabolic factors, including those provided to the mother via the fetus. Understanding of the balance between maternal tolerance and protection of the fetus may require thinking from multiple theoretical approaches to the general problem of immune activation and tolerance. This article provides a brief review of the immune system, with aspects relevant to pregnancy. The references include reviews that expand on the elements discussed. The article also uses different models of immune system activation and tolerance to provide a theoretical understanding of the problem of maternal tolerance.

Interleukin-15 enhances the expansion and function of natural killer T cells from adult peripheral and umbilical cord blood

Invariant natural killer T cells (iNKT cells) are innate-like non-conventional T cells restricted by the CD1d molecule that are unique in their ability to play a pivotal role in immune regulation. Deficient iNKT function has been reported in patients receiving umbilical cord blood (UCB) transplantation. We sought to determine the effect of interleukin (IL)-15 on α-galactosylceramide (α-GalCer)-expanded iNKT cell function from UCB and adult peripheral blood (APB) mononuclear cells (MNCs). Fresh APB and UCB MNCs were cultured with IL-15 (50 ng/ml) in the presence or absence of α-GalCer (100 ng/ml) for 10 days. Cells were harvested for examination of cell yield, apoptosis, cytokine production and cytotoxic function of Vα24(+)/Vβ11(+) iNKT cells. We observed that α-GalCer-expanded APB and UCB iNKT cells and such expansion was further enhanced with IL-15. The percentage of CD3(+)CD56(+) NKT-like cells in both APB and UCB MNCs was increased with IL-15 but not with α-GalCer. Apoptosis of UCB iNKT cells was ameliorated by IL-15. Although APB and UCB iNKT cells secreted lower IFN-γ, it could be enhanced with IL-15. The expression of perforin in APB iNKT cells can also be enhanced with IL-15. UCB Vα24(+)Vβ11(+) iNKT cells further augmented K562 cytotoxicity mediated by IL-15. Taken together, these results demonstrated the relative functional deficiencies of α-GalCer induced UCB iNKT cells, which can be ameliorated by IL-15. Our findings suggest a therapeutic benefit of IL-15 immunotherapy during the post-UCB transplant period when iNKT function remains poor.

Tim-3 expression on peripheral monocytes and CD3+CD16/CD56+natural killer-like T cells in patients with chronic hepatitis B

Hepatitis B virus (HBV) infection is one of the major causes of chronic liver inflammation. Tim-3 acts as a negative regulatory molecule and plays a critical role in immune tolerance. In the current study, we investigated Tim-3 expression on peripheral monocytes and CD3+CD16/CD56+ natural killer like T (NKT-like) cells in chronic hepatitis B (CHB) patients. Peripheral blood mononuclear cells (PBMCs) were isolated from 52 CHB patients and 60 healthy controls. Tim-3+CD14+ cells and Tim-3+CD3+CD16/CD56+ cells were analyzed by flow cytometry. Results showed that expression of Tim-3 was significantly increased on both the monocytes and NKT-like cells in CHB patients than in controls (P = 0.002 and P < 0.001, respectively). Tim-3 levels on monocytes and NKT-like cells were further upregulated in patients with acute-on-chronic liver failure (ACLF). In addition, we assessed the correlation of Tim-3 expression with levels of alanine aminotransferase (ALT) and tumor necrosis factor alpha (TNF-α). Data revealed that Tim-3 expression on both monocytes and NKT-like cells was positively correlated with level of ALT (r = 0.59, P < 0.001, and r = 0.60, P < 0.001, respectively), whereas Tim-3 expression on NKT-like cells was negatively correlated with serum level of TNF-α (r = -0.54, P < 0.001) in CHB patients. Our results suggest that Tim-3 may play important roles in the pathogenesis of CHB.

Intravenous immunoglobulin treatment increased live birth rate in a Spanish cohort of women with recurrent reproductive failure and expanded CD56(+) cells

PROBLEM

Natural killer (NK, CD3(-)CD56(+)/CD16(+)) and NKT-like cells (CD3(+)CD56(+)/CD16(+)) activity is considered among the key factors for reproductive success. In the absence of immunological screening, beneficial effects of intravenous immunoglobulin (IVIG) in preventing recurrent reproductive failure (RRF) have not been reported. Here, we analyse the IVIG influence on pregnancy success in women with RRF and circulating NK or/and NKT-like cells expansion.

METHOD OF STUDY

One hundred fifty-seven women with previous recurrent miscarriage and/or recurrent implantation failure after in vitro fertilization were consecutively studied. Sixty-four patients with CD56(+) cell expansion, no apparent underlying disease and who maintained their desire to conceive were selected. Forty of them received IVIG during pregnancy.

RESULTS

Overall, the clinical pregnancy rate for the women under IVIG therapy was 92.5% and the live birth rate was 82.5%. Significantly lower pregnancy and live birth rates (25% and 12.5%, respectively) were observed for the patients with recurrent pregnancy loss and NK/NKT-like cells expansion without IVIG. After three cycles of IVIG, NK cell percentages decreased significantly and these values persisted throughout gestation.

CONCLUSION

Intravenous immunoglobulin therapy for women with RRF and NK or NKT-like cell expansion was a safe and beneficial therapeutic strategy that associated with high clinical pregnancy and live birth rates.

Stimulation of dopamine receptor D5 expressed on dendritic cells potentiates Th17-mediated immunity

Dendritic cells (DCs) are responsible for priming T cells and for promoting their differentiation from naive T cells into appropriate effector cells. Emerging evidence suggests that neurotransmitters can modulate T cell-mediated immunity. However, the involvement of specific neurotransmitters or receptors remains poorly understood. In this study, we analyzed the role of dopamine in the regulation of DC function. We found that DCs express dopamine receptors as well as the machinery necessary to synthesize, store, and degrade dopamine. Notably, the expression of D5R decreased upon LPS-induced DC maturation. Deficiency of D5R on the surface of DCs impaired LPS-induced IL-23 and IL-12 production and consequently attenuated the activation and proliferation of Ag-specific CD4(+) T cells. To determine the relevance of D5R expressed on DCs in vivo, we studied the role of this receptor in the modulation of a CD4(+) T cell-driven autoimmunity model. Importantly, D5R-deficient DCs prophylactically transferred into wild-type recipients were able to reduce the severity of experimental autoimmune encephalomyelitis. Furthermore, mice transferred with D5R-deficient DCs displayed a significant reduction in the percentage of Th17 cells infiltrating the CNS without differences in the percentage of Th1 cells compared with animals transferred with wild-type DCs. Our findings demonstrate that by contributing to CD4(+) T cell activation and differentiation to Th17 phenotype, D5R expressed on DCs is able to modulate the development of an autoimmune response in vivo.

Cord blood Vα24-Vβ11 natural killer T cells display a Th2-chemokine receptor profile and cytokine responses

Background

The fetal immune system is characterized by a Th2 bias but it is unclear how the Th2 predominance is established. Natural killer T (NKT) cells are a rare subset of T cells with immune regulatory functions and are already activated in utero. To test the hypothesis that NKT cells are part of the regulatory network that sets the fetal Th2 predominance, percentages of Vα24⁺Vβ11⁺ NKT cells expressing Th1/Th2-related chemokine receptors (CKR) were assessed in cord blood. Furthermore, IL-4 and IFN-γ secreting NKT cells were quantified within the single CKR⁺ subsets.

Results

Cord blood NKT cells expressed the Th2-related CCR4 and CCR8 at significantly higher frequencies compared to peripheral blood NKT cells from adults, while CXCR3⁺ and CCR5⁺ cord blood NKT cells (Th1-related) were present at lower percentages. Within CD4^negCD8^neg (DN) NKT cells, the frequency of IL-4 producing NKT cells was significantly higher in cord blood, while frequencies of IFN-γ secreting DN NKT cells tended to be lower. A further subanalysis showed that the higher percentage of IL-4 secreting DN NKT cells was restricted to CCR3⁺, CCR4⁺, CCR5⁺, CCR6⁺, CCR7⁺, CCR8⁺ and CXCR4⁺ DN subsets in cord blood. This resulted in significantly decreased IFN-γ /IL-4 ratios of CCR3⁺, CCR6⁺ and CCR8⁺ cord blood DN NKT cells. Sequencing of VA24AJ18 T cell receptor (TCR) transcripts in sorted cord blood Vα24Vβ11 cells confirmed the invariant TCR alpha-chain ruling out the possibility that these cells represent an unusual subset of conventional T cells.

Conclusions

Despite the heterogeneity of cord blood NKT cells, we observed a clear Th2-bias at the phenotypic and functional level which was mainly found in the DN subset. Therefore, we speculate that NKT cells are important for the initiation and control of the fetal Th2 environment which is needed to maintain tolerance towards self-antigens as well as non-inherited maternal antigens.

Bisphenol A in combination with TNF-alpha selectively induces Th2 cell-promoting dendritic cells in vitro with an estrogen-like activity

Bisphenol A (BPA) is a monomer used in manufacturing a wide range of chemical products, including epoxy resins and polycarbonate. BPA, an important endocrine disrupting chemical that exerts estrogen-like activities, is detectable at nanomolar levels in human serum worldwide. The pregnancy associated doses of 17beta-estradiol (E2) plus tumor-necrosis factor-alpha (TNF-alpha) induce distorted maturation of human dendritic cells (DCs) that result in an increased capacity to induce T helper (Th) 2 responses. The current study demonstrated that the presence of BPA during DC maturation influences the function of human DCs, thereby polarizing the subsequent Th response. In the presence of TNF-alpha, BPA treatment enhanced the expression of CC chemokine ligand 1 (CCL1) in DCs. In addition, DCs exposed to BPA/TNF-alpha produced higher levels of IL-10 relative to those of IL-12p70 on CD40 ligation, and preferentially induced Th2 deviation. BPA exerts the same effect with E2 at the same dose (0.01-0.1 microM) with regard to DC-mediated Th2 polarization. These findings imply that DCs exposed to BPA will provide one of the initial signals driving the development and perpetuation of Th2-dominated immune response in allergic reactions.

Cytokine-dependent modification of IL-12p70 and IL-23 balance in dendritic cells by ligand activation of Valpha24 invariant NKT cells

CD1d-restricted invariant NKT (iNKT) cells play crucial roles in various types of immune responses, including autoimmune diseases, infectious diseases and tumor surveillance. The mechanisms underlying their adjuvant functions are well understood. Nevertheless, although IL-4 and IL-10 production characterize iNKT cells able to prevent or ameliorate some autoimmune diseases and inflammatory conditions, the precise mechanisms by which iNKT cells exert immune regulatory function remain elusive. This study demonstrates that the activation of human iNKT cells by their specific ligand alpha-galactosylceramide enhances IL-12p70 while inhibiting the IL-23 production by monocyte-derived dendritic cells, and in turn down-regulating the IL-17 production by memory CD4(+) Th cells. The ability of the iNKT cells to regulate the differential production of IL-12p70/IL-23 is mainly mediated by a remarkable hallmark of their function to produce both Th1 and Th2 cytokines. In particular, the down-regulation of IL-23 is markedly associated with a production of IL-4 and IL-10 from iNKT cells. Moreover, Th2 cytokines, such as IL-4 and IL-13 play a crucial role in defining the biased production of IL-12p70/IL-23 by enhancement of IL-12p70 in synergy with IFN-gamma, whereas inhibition of the IFN-gamma-promoted IL-23 production. Collectively, the results suggest that iNKT cells modify the IL-12p70/IL-23 balance to enhance the IL-12p70-induced cell-mediated immunity and suppress the IL-23-dependent inflammatory pathologies. These results may account for the long-appreciated contrasting beneficial and adverse consequence of ligand activation of iNKT cells.

NKT cells at the maternal-fetal interface

Establishment of the maternal-fetal interface is characterized by the influx of maternal NK cells, macrophages, and T cells into the decidua. Although a great deal has been learned about the function of NK cells in the decidua, comparatively little is known of decidual T cell function. NKT cells are an unusual T cell subset capable of producing both Th1-like and Th2-like cytokines. Unlike conventional alphabeta T cells that recognize peptides in the context of MHC molecules, NKT cells recognize glycolipids presented by the MHC class I-like molecule, CD1d. Recent reports have demonstrated that NKT cells and CD1d are present at the maternal-fetal interface. Moreover, activation of NKT cells can have dramatic effects on pregnancy. In this article, we will review basic aspects of NKT cell biology and summarize the recent literature on NKT cells at the maternal-fetal interface.