HLA-G gene polymorphism in human placentas: possible association of G*0106 allele with preeclampsia and miscarriage

The expression and functional activity of membrane-bound human leukocyte antigen-G1 are influenced by the 3'-untranslated region

Human Leukocyte Antigen (HLA)-G is an immunosuppressive molecule acting on both the innate and adaptive immune system. A 14 bp insertion/deletion polymorphism (rs66554220) in the 3'-untranslated region (3'UTR) of the HLA-G gene has been associated with a number of diseases, pregnancy complications, and graft rejection after organ transplantation. We have investigated the effect of HLA-G polymorphism in the 3'UTR on the processing and stability of the membrane-bound HLA-G1 (mHLA-G1) isoform, as well as its functional significance. Different HLA-G1 cDNA sequences were transduced into the human K562 cell line. Flow cytometry, immunohistochemistry, and ELISA were used to examine HLA-G1 protein expression. A quantitative RT-PCR assay was used to quantify transduced HLA-G1 DNA and mRNA transcript levels. Stability of mRNA and functional significance of HLA-G were investigated via Actinomycin D and NK cytotoxicity assays, respectively. Human leukocyte antigen-G mRNA from the 14 bp insertion K562-G1 cells showed a higher degree of stability than the other constructs, and increased mHLA-G1 expression relative to transductants lacking the 14 bp sequence. In line with this, transductants carrying the 14 bp insertion were the most efficient in inhibiting NK cytotoxicity but showed a lower soluble HLA-G1 per mHLA-G1 ratio than the HLA-G1 K562 cells lacking the 14 bp insertion. Our data suggest 3'UTR polymorphism may play an important role in HLA-G regulation with implications on a range of diseases.

The maternal HLA-G 1597ΔC null mutation is associated with increased risk of pre-eclampsia and reduced HLA-G expression during pregnancy in African-American women

The non-classical major histocompatibility complex molecule, human leukocyte antigen (HLA)-G, is thought to contribute to maternal immune tolerance and successful placentation during pregnancy. Genetic polymorphisms in HLA-G are known to influence expression levels as well as the relative expression of individual protein isoforms. As diminished or aberrant HLA-G expression patterns may contribute to the development of certain pregnancy complications, we sought to investigate the association between functional HLA-G polymorphisms and the risk of pre-eclampsia (PE) in African-American women. The association between maternal and fetal genotype at six HLA-G polymorphisms and risk of PE was assessed in 372 pregnancies (314 normotensive; 58 pre-eclamptic). We observed an elevated risk of PE (P = 0.00027) in pregnancies where the mother carried the 1597ΔC allele, a null allele that abolishes expression of full-length HLA-G isoforms. Furthermore, the frequency of the maternal 1597ΔC allele was highest in the subset of pre-eclamptic pregnancies that were delivered preterm, suggesting an association between the null allele and the severity of PE. We then replicated the association between higher maternal 1597ΔC allele frequency and increased severity of PE (P = 0.038) in an independent sample of 533 African-American women. Finally, to investigate the mechanistic basis of this association, we measured circulating soluble HLA-G (sHLA-G) concentrations in maternal serum collected during pregnancy in 51 healthy, normotensive African-American control women and found significantly lower levels in women carrying the 1597ΔC allele (P = 0.012). These results demonstrate that maternal HLA-G genotype is significantly associated with risk of PE in African-American women and is predictive of circulating sHLA-G levels during pregnancy.

Role of HLA-G and other immune mechanisms in pregnancy

Pregnancy loss (abortion) and pre-eclampsia represent the most common disorders in pregnant women. Besides infection, there are anatomical, endocrinological, genetic and immunological factors that can induce pregnancy disorders. Because the exact mechanisms of physiological pregnancy maintenance are still not clearly understood, the search for genes and proteins fulfilling this role is still in progress. One of the immune molecules that plays a beneficial role in pregnancy is the nonclassical HLA-G molecule. The molecule is mainly expressed on trophoblast cells in the foetal placenta and induces the immune tolerance of the foetus via its interaction with inhibitory receptors on maternal NK cells and CD8+ T lymphocytes. In relation to pregnancy disorders, associations between HLA-G polymorphism, HLA-G level and HLA-G function were described. Thus, the HLA-G molecule can be used as a new diagnostic marker and, potentially, for the future therapy of pregnancy disorders.

HLA-G haplotype structure shows good conservation between different populations and good correlation with high, normal and low soluble HLA-G expression

HLA-G molecule has considerable impact in various clinical fields, therefore many studies attempted to predict its expression based on HLA-G genotype. These studies have focused on polymorphisms in either the coding region or in one of the two untranslated regions (UTR) of the gene. The aim of our study was to determine if HLA-G haplotype defined based on SNPs 5' and 3'UTR could be used to predict soluble HLA-G expression in unstimulated individuals. Our findings showed that HLA-G haplotype structure was well conserved between distant populations and that the defined haplotypes were correlated with high, normal and low HLA-G soluble secretors. In conclusion, we showed that this genotyping strategy based on the use of a few selected SNPs rather than isolated SNP analysis allows reliable HLA-G expression in all populations. This strategy could be useful in a number of clinical settings, e.g., predicting graft compatibility immunogenetic laboratories.

HLA-G polymorphisms and soluble HLA-G protein levels in women with recurrent pregnancy loss from Basrah province in Iraq

HLA-G is a nonclassical, class I major histocompatibility complex (MHC) gene that exhibits immunomodulatory properties and likely plays a role in the maintenance of successful pregnancy. In this study, we investigated the role of HLA-G polymorphisms on risk for recurrent pregnancy loss (RPL) and on circulating levels of soluble (s)HLA-G in Iraqi women. DNA and plasma were obtained from blood samples collected at 9-12 weeks gestation from 50 women with RPL and 50 healthy pregnant women in Basrah province, Iraq. As measured by ELISA, median sHLA-G levels were significantly lower in the RPL cases compared to healthy controls (21.4 vs. 38.8 U/ml, respectively; P=0.025), and decreased with increasing maternal age (P=0.0051). However, HLA-G allele and haplotype frequencies did not differ significantly between cases and controls (P values ≥0.12 for all tests). In contrast, homozygosity for the C allele (CC) at a tri-allelic promoter polymorphism, -725C/G/T, was associated with lower concentrations of sHLA-G compared to the CG or CT genotypes (median levels 21.1 vs. 40.1 vs. 42.6 U/ml, respectively; P=0.0089). These results demonstrate that HLA-G genotype influences circulating sHLA-G levels during pregnancy but is not significantly associated with risk of RPL.

Simple methods for the detection of HLA-G variants in coding and non-coding regions

The non-classical human leukocyte antigen (HLA)-G plays a crucial role in the induction of tolerance at the feto-maternal interface as well as in transplantation, cancer, inflammation, and autoimmune diseases. To understand gene regulation and the impact of polymorphic sites on the function, simple and easy feasible approaches are needed for the detection of HLA-G variants in coding and non-coding regions. Here we summarize a set of methods for the identification of variants in the exon 2-4, in the 3' untranslated region and in the gene promoter region of the HLA-G gene.

Barriers of the Human Organism and Their Achilles’ Heels

The human body is covered by barriers separating it from the external and internal surroundings. The “milieu enterieur” has to be stabilised in spite of the variable external and internal conditions of toxic, osmotic, microbial and climatic environmental circumstances. This first line of barriers is composed of skin and mucous membranes of complicated structures.

A second line of barrier system is present in our organisms. Certain organs have to be separated from the immune system and other parts of the body because of evolutionary reasons (eye-bulb and testicles) because of unique proteins “unknown” for the acquired immune system. The blood-brain barrier (BBB) is providing enhanced safety circumstances for the central nervous system. The second line of barriers is represented by the special properties of the capillary endothelial system.

The maternal-fetal barrier is the most complex. At the maternal fetal interface two individuals of two different haplotypes has to be live 9 months separated by a very complicated dynamic barrier.

The placenta is the organ, which is separating the maternal and fetal tissues. Similar to others the bidirectional transport of gasses, metabolites, cells, proteins, regulatory substances, are transported by active or passive transcellular and intercellular mechanisms.

The fetal immune system develops immunotolerance to all maternal cells and antigens transferred transplacentally. The problem is to mitigate the maternal immune system to tolerate the paternal haplotype of the fetus. In the case of normal pregnancy a complex series of physiological modifications can solve the problem without harmful consequences to the mother and fetus.

The outermost contact cells of trophoblasts express instead of HLA-class Ia and class II antigens non-variable HLA-C, HLA-E, HLA-F and HLA-G antigens. The first consequence of this is reduction of the activity of maternal natural killer cells and maternal dendritic cells;

Progesteron, micro-RNA and mediators influence the development of T effector-cells. The production of soluble HLA-G(5 and 6) and IL-10 supports the differentiation of Th-2 CD4⁺ helper cells, reducing the ability of maternal cells to kill fetal cells.

Series of receptors and costimulators are expressed by the different lines of semi-allogenic trophoblast cells to bind HLA-G and mitigate maternal immune response;

The maternal immunotolerance is further facilitated by the activation of CD4⁺CD25^brightFoxp3⁺ regulatory T (T_REG) cells.

Infections have to be prevented during pregnancy. The cells of placenta express 10 Toll-like receptors a group of pattern recognition receptors responsible for innate immunity. The interferon level is also higher in the placental tissues than in the somatic fetal or maternal cells.

The complement system is also adapted to the requirements of the pregnancy and fetal damage is inhibited by the production of “assymmetric IgG antibodies” under hormonal and placental-regulation. These modifications prevent the activation of complement, cytotoxic activity, opsonising ability, antigen clearance and precipitating activity of the molecules.

The Achilles’ heels of the different barriers are regularly found by virus infections. Lamina cribrosa of the blood-brain barrier, optical nerve of the eyes, etc. the risk factors of the maternal-fetal barrier has been summarised in Table 1.1.

Pathogenesis of preeclampsia: the genetic component

Preeclampsia (PE) is one of the main causes of maternal and fetal morbidity and mortality in the world, causing nearly 40% of births delivered before 35 weeks of gestation. PE begins with inadequate trophoblast invasion early in pregnancy, which produces an increase in oxidative stress contributing to the development of systemic endothelial dysfunction in the later phases of the disease, leading to the characteristic clinical manifestation of PE. Numerous methods have been used to predict the onset of PE with different degrees of efficiency. These methods have used fetal/placental and maternal markers in different stages of pregnancy. From an epidemiological point of view, many studies have shown that PE is a disease with a strong familiar predisposition, which also varies according to geographical, socioeconomic, and racial features, and this information can be used in the prediction process. Large amounts of research have shown a genetic association with a multifactorial polygenic inheritance in the development of this disease. Many biological candidate genes and polymorphisms have been examined in their relation with PE. We will discuss the most important of them, grouped by the different pathogenic mechanisms involved in PE.

The genetics of pre-eclampsia and other hypertensive disorders of pregnancy

Hypertension is the most frequent medical complication occurring during pregnancy. In this chapter, we aim to address the genetic contribution to these disorders, with specific focus on pre-eclampsia. The pathogenic mechanisms underlying pre-eclampsia remain to be elucidated; however, immune maladaptation, inadequate placental development and trophoblast invasion, placental ischaemia, oxidative stress and thrombosis are all thought to represent key factors in the development of disease. Furthermore, all of these components have genetic factors that may be involved in the pathogenic changes occurring. The familial nature of pre-eclampsia has been known for many years and, as such, extensive genetic research has been carried out in this area using strategies that include candidate gene studies and linkage analysis. Interactions between fetal and maternal genotypes, the effect of environmental factors, and epistasis will also be considered.

The importance of HLA-G expression in embryos, trophoblast cells, and embryonic stem cells

The nonclassical HLA-G molecule is a trophoblast-specific molecule present in almost every pregnancy. It differs from classical HLA class I molecules by the low degree of allelic variants and the high diversity of protein structures. HLA-G is reported to be a tolerogenic molecule that acts on cells of both innate and adaptive immunity. At the maternal-fetal interface HLA-G seems to be responsible largely for the reprogramming of local maternal immune response. This review will focus on the HLA-G gene expression profile in pregnancy, in preimplantation embryos, and in human embryonic stem cells with emphasis on the structural diversity of the HLA-G protein and its potential functional and diagnostic implications.

HLA-G polymorphism patterns show lack of detectable association with recurrent spontaneous abortion

Human leukocyte antigen-G (HLA-G) is a class I non-classical molecule that is predominantly expressed on the extravillous cytotrophoblasts at foetal-maternal interface during pregnancy. We recruited 143 recurrent spontaneous abortion (RSA) and 150 control couples for the study. DNA-based typing of the HLA-G was carried out to explore if we can validate the patterns of association reported elsewhere or find association of novel HLA-G alleles with RSA in the Indian population. We also evaluated the role of allele sharing in couples with RSA. We did not find association of any of the HLA-G alleles with RSA in our study. There is a general trend of increase in sharing among the RSA couples, but the increase is not significant. The results suggest that the HLA-G alleles or the allele sharing by couples may not play a significant role in the manifestation of RSA in the Indian context albeit more studies are required before making any definitive statement.

Implications of the polymorphism of HLA-G on its function, regulation, evolution and disease association

The HLA-G gene displays several peculiarities that are distinct from those of classical HLA class I genes. The unique structure of the HLA-G molecule permits a restricted peptide presentation and allows the modulation of the cells of the immune system. Although polymorphic sites may potentially influence all biological functions of HLA-G, those present at the promoter and 3′ untranslated regions have been particularly studied in experimental and pathological conditions. The relatively low polymorphism observed in the MHC-G coding region both in humans and apes may represent a strong selective pressure for invariance, whereas, in regulatory regions several lines of evidence support the role of balancing selection. Since HLA-G has immunomodulatory properties, the understanding of gene regulation and the role of polymorphic sites on gene function may permit an individualized approach for the future use of HLA-G for therapeutic purposes.

Soluble human leukocyte antigen-G isoforms in maternal plasma in early and late pregnancy

PROBLEM

Human Leukocyte Antigen (HLA)-G is a class Ib gene located in the human major histocompatibility complex (MHC). Several lines of investigation indicate that the HLA-G molecule is involved in the maternal acceptance of the semi-allogenic fetus during pregnancy and in the development of tolerance. Expression of soluble HLA-G (sHLA-G) is positively correlated with successful in vitro fertilization (IVF) treatments, and aberrant expression of HLA-G in certain complications of pregnancy, such as pre-eclampsia and spontaneous abortion, has been reported. The main purpose of this study was to investigate the levels of different soluble HLA-G isoforms in maternal plasma in early and late pregnancy.

METHOD OF STUDY

Soluble HLA-G (sHLA-G) can be detected in maternal blood, and in this study, two different isoforms of sHLA-G, namely sHLA-G1 generated by shedding of membrane-bound HLA-G1 and HLA-G generated by specific HLA-G transcripts, have been investigated early [median of 16.4 weeks of gestation (GW)] and late (median: 38.9 GW) in pregnancy in an original cohort of 580 pregnant Caucasian women.

RESULTS

Lower concentrations of sHLA-G1 were found late in pregnancy (>32 GW) in a group of women with severe pre-eclampsia compared with controls with uncomplicated pregnancies (P = 0.029, P(C) = 0.09; Mann-Whitney; Logistic regression analysis: P = 0.024, OR = 0.920, 95% CI: 0.855-0.989). However, this was not the case with HLA-G5, and significantly more of the cases with severe pre-eclampsia had detectable plasma HLA-G5 compared with that of the control group (P = 0.013, P(C) = 0.04; Mann-Whitney). Similar findings were not observed in women with gestational hypertension or existing hypertension continuing into pregnancy. Furthermore, there was a trend toward lower maternal plasma sHLA-G1 in a group of women with premature birth (<37 GW) compared with that of the control group (P = 0.028, P(C) = 0.17; Mann-Whitney). On the contrary, HLA-G5 was lower in the control group compared with that in the premature group (P = 0.004, P(C) = 0.02; Mann-Whitney).

CONCLUSION

This study shows in line with other published studies that a high, detectable soluble HLA-G concentration in maternal plasma or serum is not mandatory for a successful pregnancy. However, complications during pregnancy, such as (severe) pre-eclampsia, spontaneous abortion, IUGR, and premature birth, are associated with a low or undetectable level of soluble HLA-G in the maternal blood circulation. Also, this study indicates that sHLA-G1 is the interesting soluble HLA-G isoform in pre-eclampsia, and that low or undetectable levels of HLA-G5 at the end of pregnancy seem to be associated with an uncomplicated normal pregnancy, whereas in severe pre-eclampsia and possibly other pregnancy complications, such as preterm birth and IUGR, the level of HLA-G5 is higher.

Contribution of interferon-gamma receptor 1 gene polymorphisms to pre-eclampsia in China

PROBLEM

As gene polymorphisms of cytokines receptors have been found to significantly influence cell responses to cytokines, the aim of this study was to test the hypothesis that IFN-gamma receptor 1 (IFNGR1) gene polymorphisms may contribute to the pathogenesis of pre-eclampsia.

METHOD OF STUDY

One hundred and sixty-four pre-eclamptic patients (121 patients with mild pre-eclampsia and 43 patients with severe pre-eclampsia) and 171 controls were included. Polymorphisms of the IFNGR1 gene at positions -611, -270, +56 and +95 were genotyped with the matrix-assisted laser desorption/ionization time of flight mass spectrometry.

RESULTS

This study showed a positive association between -56C/C genotype (OR = 1.7; 95% CI = 1.1-2.7) and pre-eclampsia. Although the genotype frequencies (except for -56C/C) of the two polymorphisms were comparable between cases and controls, higher frequency of the -611A/-56C haplotype (OR = 1.450; 95% CI = 1.070-1.966) was noticed in patients versus controls. All patients and controls were homozygous for the -270T/T and +95T/T genotypes. Specifically, the frequency of the -56C allele (OR = 1.838; 95% CI = 1.127-2.995) was higher among patients with severe pre-eclampsia.

CONCLUSION

The IFNGR1 gene polymorphisms may contribute to the pathogenesis of pre-eclampsia in our population.

Implication of expression of osteopontin and its receptor integrin alphanubeta3 in the placenta in the development of preeclampsia

To investigate the expression of osteopontin (OPN) and its receptor integrin alphanubeta3 in the placental tissue from pregnant women complicated with preeclampsia, the expression of OPN and alphanubeta3 in the placenta of the pregnant women with preeclampsia and healthy pregnant women was detected by immunohistochemistry, Western blotting and RT-PCR. Our results showed that OPN and alphanubeta3 protein were expressed in the placenta from normal pregnant woman and those with preeclampsia. OPN was located in the placental syncytiotrophoblasts and the cytoplasm of capillary endothelial cells and integrin alphanubeta3 was mainly expressed on the surface of trophoblast cells. Expression of OPN and integrin alphanubeta3 in the placental tissue from preeclampsia subjects was significantly lower than that from the control group (P<0.05). Compared with the control group, expression of OPN in the placental tissue from preeclampsia group was significantly lower (P<0.05) but there was no significant difference in the expression of alphanu and beta3 between the preeclampsia group and the controls. It is concluded that OPN and its receptor integrin alphanubeta3 may be involved in the pathogenesis of preeclampsia.

Lack of association between HLA-G 14-bp polymorphism and systemic lupus erythematosus in a Han Chinese population

HLA-G is a non-classical HLA-class Ib molecule with multiple immunoregulatory properties. A 14-bp insertion/deletion polymorphism in the HLA-G gene has been suggested to influence the expression of HLA-G and to associate with certain pathological conditions, including autoimmune diseases. We investigated the influence of the 14-bp insertion/deletion polymorphism in the HLA-G gene on disease susceptibility in systemic lupus erythematosus by genotyping this polymorphism in 231 patients with systemic lupus erythematosus and 367 healthy controls and analyzing the levels of soluble HLA-G in a subset of patients with systemic lupus erythematosus and healthy subjects from a Han Chinese population. No statistically significant differences were observed in the frequencies of the 14-bp insertion/deletion HLA-G alleles or genotypes between controls and patients with systemic lupus erythematosus. However, a significant increased expression of soluble HLA-G was noted in patients with systemic lupus erythematosus (mean value = 230.2 U/ml vs 118.3 U/ml in controls, p = 0.0001). Moreover, patients with high levels of soluble HLA-G presented with higher disease activity and had more neurological involvement. Our results do not support the HLA-G 14-bp insertion/deletion polymorphism as a genetic factor influencing systemic lupus erythematosus susceptibility. It is possible that the expression of soluble HLA-G in systemic lupus erythematosus is enhanced as part of a mechanism to try to restore the tolerance process towards auto-antigens and to counteract inflammation. However, the participation of this molecule in the pathological process of the disease also could not be excluded. Lupus (2009) 18, 1259—1266.

Possible gene-gene interaction of KIR2DL4 with its cognate ligand HLA-G in modulating risk for preeclampsia

Preeclampsia (PE) is a leading cause of maternal and fetal mortality and morbidity that occurs only during pregnancy. Pregnancy is the only physiological situation where killer-cell immunoglobulin-like receptors (KIRs) may meet cognate nonself variants of human leukocyte antigen (HLA) allotypes. We previously reported that presence of fetal HLA-G*0106 was significantly associated with risk for PE in multigravid pregnancies. We have now tested the KIR2DL4 receptor gene for association with PE, as well as for its interaction with HLA-G in modulating disease risk, in a case-control study of 83 PE and 240 normotensive pregnancies. No significant association was observed between alleles of KIR2DL4 and PE in both maternal and fetal groups, either among primigravid or multigravid pregnancies. Alleles of KIR2DL4 and HLA-G were then analyzed together to determine whether particular variant ligand-receptor combinations were associated with an increased risk for PE. Gene-gene interaction analyses suggest that the presence of fetal HLA-G*0106 in combination with maternal KIR2DL4*006 is significantly associated with PE risk in multigravid pregnancies (P < .001). These data provide the first preliminary evidence suggesting that although KIR2DL4 itself is not associated with PE, it may modulate the effect of HLA-G*0106 on risk for PE.

Human leukocyte antigen-G polymorphism in relation to expression, function, and disease

Human leukocyte antigen-G (HLA-G) is a nonclassical class Ib molecule belonging to the major histocompatibility complex. HLA-G appears to play a role in the suppression of immune responses and contribute to long-term immune escape or tolerance. The focus of this review is polymorphism in the HLA-G gene and protein and its possible importance in expression, function, and disease associations.

HLA-G: a human pregnancy-related immunomodulator

In human pregnancies mothers and their embryo/fetuses are invariably genetically different. Thus, attenuation of the adaptive maternal immune response, which is programmed to reject 'foreign' entities, is required for pregnancy to be initiated and maintained. Unexpectedly, given the propensity of the immune system to dispose of non-self entities, at least 50% of expected human pregnancies reliably go forward. This indicates that to a large extent, effective systems of tolerance have evolved. Although overlapping and redundant mechanisms of tolerance have been identified, production of HLA-G by trophoblast cells derived from the external trophectoderm layer of the blastocyst appears to be of major importance. At this point in time, no pregnancies in which all of the proteins derived from the HLA-G gene are absent have as yet been reported. Many studies have shown that both membrane-bound and soluble isoforms of the proteins derived from this HLA class Ib gene are produced by placental trophoblast cells, with consequences that include but are not restricted to immune suppression at the maternal-fetal interface. Here we report new studies that are leading to a better understanding of the HLA-G proteins, their unique structures, unusual modes of regulation, diverse functions, and potential for use in diagnostic and therapeutic procedures related to suboptimal fertility in women.

Tolerance versus immune response -- microRNAs as important elements in the regulation of the HLA-G gene expression

HLA-G is a class Ib HLA which has gained much attention due to its multiple functions on the immune system. HLA-G exerts several immunomodulatory effects, being beneficially implicated in embryo implantation and fetal survival but, conversely, being potentially detrimental in tumors and viral infections. Such a two-edged sword behavior suggest that HLA-G expression is under tight regulation. However, to date, little is known about the regulation of this gene and previous works have been unable to well correlate HLA-G regulation at the mRNA level with the polymorphic variants at the genomic level. Here we present the hypothesis that an element, which was until now neglected, might play a role in HLA-G expression regulation: MicroRNAs might participate in the regulation of the HLA-G gene expression through a putative microRNA binding site at its 3' UTR region. Inside the 20 nt region of this microRNA binding site lies a C/G polymorphism, which was shown to be responsible for differential microRNA binding affinity and translation suppression. The role of microRNA binding on the regulation of HLA-G gene expression (and therefore on tolerance versus immune response) can be easily tested through relatively simple steps: Confirming the expression of those three complementary microRNAs in human cells which express HLA-G, followed by examination of the correlation between HLA-G mRNA and protein production controlling for HLA-G genotypes and microRNA levels; finally, selective inhibition of microRNA activity with anti-sense oligos restoring HLA-G production would access microRNA influence on HLA-G expression which, if confirmed, might help in the development of strategies to the management of several conditions in which HLA-G is involved, including pregnancy complications, transplantation, and cancer.