Lack of MHC-G4 and soluble (G5, G6) isoforms in the higher primates, Pongidae

Evolution and molecular interactions of major histocompatibility complex (MHC)-G, -E and -F genes

Classical HLA (Human Leukocyte Antigen) is the Major Histocompatibility Complex (MHC) in man. HLA genes and disease association has been studied at least since 1967 and no firm pathogenic mechanisms have been established yet. HLA-G immune modulation gene (and also -E and -F) are starting the same arduous way: statistics and allele association are the trending subjects with the same few results obtained by HLA classical genes, i.e., no pathogenesis may be discovered after many years of a great amount of researchers’ effort. Thus, we believe that it is necessary to follow different research methodologies: (1) to approach this problem, based on how evolution has worked maintaining together a cluster of immune-related genes (the MHC) in a relatively short chromosome area since amniotes to human at least, i.e., immune regulatory genes (MHC-G, -E and -F), adaptive immune classical class I and II genes, non-adaptive immune genes like (C2, C4 and Bf) (2); in addition to using new in vitro models which explain pathogenetics of HLA and disease associations. In fact, this evolution may be quite reliably studied during about 40 million years by analyzing the evolution of MHC-G, -E, -F, and their receptors (KIR—killer-cell immunoglobulin-like receptor, NKG2—natural killer group 2-, or TCR-T-cell receptor—among others) in the primate evolutionary lineage, where orthology of these molecules is apparently established, although cladistic studies show that MHC-G and MHC-B genes are the ancestral class I genes, and that New World apes MHC-G is paralogous and not orthologous to all other apes and man MHC-G genes. In the present review, we outline past and possible future research topics: co-evolution of adaptive MHC classical (class I and II), non-adaptive (i.e., complement) and modulation (i.e., non-classical class I) immune genes may imply that the study of full or part of MHC haplotypes involving several loci/alleles instead of single alleles is important for uncovering HLA and disease pathogenesis. It would mainly apply to starting research on HLA-G extended haplotypes and disease association and not only using single HLA-G genetic markers.

HLA-G: Function, polymorphisms and pathology

HLA-G immune modulatory genes and molecules are presently being studied by a widespread number of research groups. In the present study, we do not aim to be exhaustive since the number of manuscripts published every year is overwhelming. Instead, our aim is pointing out facts about HLA-G function, polymorphism and pathology that have been confirmed by several different researchers, together with exposing aspects that may have been overlooked or not sufficiently remarked in this productive field of study. On the other hand, we question whether performing mainly studies on HLA-G and disease associations is going to give a clear answer in the future, since 40 years of study of classical HLA molecules association with disease has still given no definite answer on this issue.

HLA-G/C, miRNAs, and their role in HIV infection and replication

In recent years, a number of different mechanisms regulating gene expressions, either in normal or in pathological conditions, have been discovered. This review aims to highlight some of the regulatory pathways involved during the HIV-1 infection and disease progression, focusing on the novel discovered microRNAs (miRNAs) and their relation with immune system's agents. Human leukocyte antigen (HLA) family of proteins plays a key role because it is a crucial modulator of the immune response; here we will examine recent findings, centering especially on HLA-C and -G, novel players lately discovered to engage in modulation of immune system. We hope to provide novel perspectives useful to find out original therapeutic roads against HIV-1 infection and AIDS progression.

Evolution of killer cell Ig-like receptor (KIR) genes: definition of an orangutan KIR haplotype reveals expansion of lineage III KIR associated with the emergence of MHC-C

Orangutan (Pongo pygmaeus) MHC-C appears less evolved than human HLA-C: Popy-C is not fixed and its alleles encode only one (C1) of the two motifs for killer cell Ig-like receptor (KIR) ligands. To assess the structure and complexity of the orangutan KIR locus, the complete nucleotide sequence of an orangutan KIR haplotype was determined. The PopyKIR locus is flanked by LILR and FCAR and consists of seven genes and pseudogenes, two novel and five corresponding to known cDNA. Distinguishing all KIRs in this rapidly evolving KIR locus from the KIR3DX1 gene is an LTR33A/MLT1D element in intron 3. These two forms of KIR represent lineages that originated by duplication of a common ancestor. The conserved, framework regions of primate KIR loci comprise the 5' part of a lineage V KIR, the 3' part of a pseudogene, the complete 2DL4 gene, and the 3' part of a lineage II KIR. Although previously defined PopyKIR2DL4 alleles contain premature termination codons, the sequenced haplotype's PopyKIR2DL4 allele encodes a full-length protein. A model for KIR evolution is proposed. Distinguishing the orangutan KIR haplotype from the proposed common ancestor of primate KIR haplotypes is an increased number to give three lineage III KIR genes in the centromeric part of the locus, the site for most human lineage III genes encoding HLA-C specific KIR. Thus, expansion of lineage III KIR is associated with emergence of MHC-C.

14th International HLA and Immunogenetics Workshop: Report on non-classical class I genes

Non-classical class I genes are encoding for cell surface proteins that have largely yet unknown functions. Although some of these proteins (human leukocyte antigens E, F and G) have been shown to present peptides, their polymorphism is very restricted at the peptide-binding region. In the present Workshop, several papers were presented addressing detection, evolutive and functional issues of these proteins. The general inhibitory immunological function of these proteins is put forward.

HLA-G in human reproduction: aspects of genetics, function and pregnancy complications

The non-classical human leukocyte antigen (HLA) class Ib genes, HLA-E, -G and -F, are located on chromosome 6 in the human major histocompatibility complex (MHC). HLA class Ib antigens resemble the HLA class Ia antigens in many ways, but several major differences have been described. This review will, in particular, discuss HLA-G and its role in human reproduction and in the human MHC. HLA-G seems to be important in the modulation of the maternal immune system during pregnancy and thereby the maternal acceptance of the semiallogenic fetus. Recent findings regarding aspects of HLA-G polymorphism, the possible significance of this polymorphism in respect to HLA-G function and certain complications of pregnancy (such as pre-eclampsia and recurrent spontaneous abortions (RSA)) are discussed together with possible importance to IVF. Finally, aspects of a possible role of HLA-G in organ transplantation and in inflammatory or autoimmune disease, and of HLA-G in an evolutionary context, are also briefly examined.

Evolutionary relationships of major histocompatibility complex class I genes in simian primates

New World monkeys (NWMs) occupy a critical phylogenetic position in elucidating the evolutionary process of major histocompatibility complex (MHC) class I genes in primates. From three subfamilies of Aotinae, Cebinae, and Atelinae, the 5'-flanking regions of 18 class I genes are obtained and phylogenetically examined in terms of Alu/LINE insertion elements as well as the nucleotide substitutions. Two pairs of genes from Aotinae and Atelinae are clearly orthologous to human leukocyte antigen (HLA) -E and -F genes. Of the remaining 14 genes, 8 belong to the distinct group B, together with HLA-B and -C, to the exclusion of all other HLA class I genes. These NWM genes are classified into four groups, designated as NWM-B1, -B2, -B3, and -B4. Of these, NWM-B2 is orthologous to HLA-B/C. Also, orthologous relationships of NWM-B1, -B2, and -B3 exist among different families of Cebidae and Atelidae, which is in sharp contrast to the genus-specific gene organization within the subfamily Callitrichinae. The other six genes belong to the distinct group G. However, a clade of these NWM genes is almost equally related to HLA-A, -J, -G, and -K, and there is no evidence for their orthologous relationships to HLA-G. It is argued that class I genes in simian primates duplicated extensively in their common ancestral lineage and that subsequent evolution in descendant species has been facilitated mainly by independent loss of genes.

Dialogue materno-fœtal et implantation embryonnaire humaine : des concepts qui évoluent

Multiple immunogical mechanisms allow fetal allograft tolerance. In this review, we first describe the maternal and embryological side in order to expose the dangers for the embryo enabling the development of materno-fetal strategies that will allow fetal survival and growth.

HLA-G genotype is associated with fetoplacental growth

The human leukocyte antigen (HLA)-G is expressed by extravillous cytotrophoblast cells in the feto-maternal contact zone. Polymorphisms have been described in the HLA-G gene and have been linked with differences in HLA-G mRNA alternative splicing patterns and protein expression. Differences in the isoform profile or the degree of HLA-G expression may influence cytokine production and, thereby, placental and fetal growth. Associations between a 14 bp deletion polymorphism in the 3'UTR part of the HLA-G gene and birth weight in relation to gestational age and placental weight were studied in 47 pregnancies complicated with preeclampsia and 87 with no preeclampsia. An HLA-G genotype homozygous for the presence of the 14 bp sequence polymorphism was significantly associated with increased birth weight in relation to gestational age (one-way analysis of variance; 2 degrees of freedom: p = 0.02) and with placental weight at birth (>38 weeks of gestation; +14 bp/+14 bp vs others; unpaired t-test: p = 0.03). There was also a slightly higher placental ratio in the offspring with the +14 bp/+14 bp genotype. The implications of these findings are discussed in relation to certain complications of pregnancy and in an evolutionary perspective.

Evolutionary Relationships of Major Histocompatibility Complex Class I Genes in Simian Primates

New World monkeys (NWMs) occupy a critical phylogenetic position in elucidating the evolutionary process of major histocompatibility complex (MHC) class I genes in primates. From three subfamilies of Aotinae, Cebinae, and Atelinae, the 5′-flanking regions of 18 class I genes are obtained and phylogenetically examined in terms of Alu/LINE insertion elements as well as the nucleotide substitutions. Two pairs of genes from Aotinae and Atelinae are clearly orthologous to human leukocyte antigen (HLA) -E and -F genes. Of the remaining 14 genes, 8 belong to the distinct group B, together with HLA-B and -C, to the exclusion of all other HLA class I genes. These NWM genes are classified into four groups, designated as NWM-B1, -B2, -B3, and -B4. Of these, NWM-B2 is orthologous to HLA-B/C. Also, orthologous relationships of NWM-B1, -B2, and -B3 exist among different families of Cebidae and Atelidae, which is in sharp contrast to the genus-specific gene organization within the subfamily Callitrichinae. The other six genes belong to the distinct group G. However, a clade of these NWM genes is almost equally related to HLA-A, -J, -G, and -K, and there is no evidence for their orthologous relationships to HLA-G. It is argued that class I genes in simian primates duplicated extensively in their common ancestral lineage and that subsequent evolution in descendant species has been facilitated mainly by independent loss of genes.

HLA-G Molecules: from Maternal–Fetal Tolerance to Tissue Acceptance

Over the past few years, HLA-G, the non-classical HLA class I molecule, has been the center of investigations that have led to the description of its specific structural and functional properties. Although located in the HLA class I region of chromosome six, the HLA-G gene may be distinguished from other HLA class I genes by its low polymorphism and alternative splicing that generates seven HLA-G proteins, whose tissue-distribution is restricted to normal fetal and adult tissues that display a tolerogeneic function toward both innate and acquired immune cells. We review these points, with special emphasis on the role of HLA-G in human pathologies, such as cancer, viral infection, and inflammatory diseases, as well as in organ transplantation.

A brief review of recent data on some cytokine expressions at the materno-foetal interface which might challenge the classical Th1/Th2 dichotomy

Focussing attention on cytokines at the materno-foetal interface represents one of the major advances made in the field. This owes much to the visionary views of Tom Wegmann, and to the changes brought about in the field by immunotrophism and Th1/Th2 paradigms. We review these briefly and also point out some emerging problems.However, a certain number of newly discovered cytokines do not fit into the classical Th1/Th2 dichotomy. Yet, by their capacity to activate or downregulate NK cells, by their action on adhesion molecules, and by their regulatory effects on the vascularisation process, they are of possible interest within the materno-foetal relationship. Therefore, as a first step, we have undertaken a systematic study of the expression of IL-11, IL-12, IL-13, IL-15, IL-16, IL-17 and IL-18 in the uterus, the peri-implantation embryo, and later on decidual and placental tissues throughout pregnancy. These cytokines were detected in every case, with, in each case, a precise localisation, which will be detailed, and which indeed suggests important regulatory functions, especially during implantation. In some cases, as will be shown in the peri-implantation uterus, those cells are perfectly expressed by uterine GMG-NK-like cells. Comparative ELISAs and quantitative RT-PCR have been or are being conducted, but already the expression patterns that are observed, and the very precise window of appearance that is observed for some of the GMG NK-like cells, either around or in the implanting embryo, as well as the complexity of the respective distributions, strongly suggest that, as useful as it certainly was for a while, the Th1/Th2 paradigm must now be considered as an over-simplification. Rather, the existing data point to sequential windows and are suggestive of a system where an extreme complexity is allied to very precise timing and tuning. They also suggest that the materno-foetal relationship is not simply maternal tolerance of a foreign tissue, but a series of intricate mutual cytokine interactions governing selective immune regulation and also control of the adhesion and vascularisation processes during this dialogue.

Evolution of MHC-G in humans and primates based on three new 3'UT polymorphisms

MHC-G is a class Ib (non-classical) major histocompatibility complex (MHC) whose functional and evolutionary characteristics are still under scrutiny. The study of noncoding sequences in the MHC genes may provide important phylogenetic information. In this work we have sequenced the MHC-G exon 8, which encodes for the 3'UT region, in different species of primates. It has been shown that: (1) a previously described 14 base pair (bp) deletion polymorphism is human-specific and the HLA-G alleles may be classified according to its absence or presence; (2) another newly described 3 bp deletion/insertion polymorphism is also human-specific; and (3) another newly described 51 bp deletion polymorphism is common to Pongidae and humans, but is not found in other primates belonging to the Cercopithecinae family. A hypothesis on the evolutionary pathway of this gene is put forward in the light of these findings.