Association of maternal killer-cell immunoglobulin-like receptors and parental HLA-C genotypes with recurrent miscarriage

NK gene complex and chromosome 19 loci enhance MHC resistance to murine cytomegalovirus infection

An H-2(k) MHC locus is critical for murine cytomegalovirus (MCMV) resistance in MA/My mice and virus control is abolished if H-2(k) is replaced with H-2(b) MHC genes from MCMV-susceptible C57L mice. Yet, H-2(k) resistance varies with genetic background; thus, modifiers of virus resistance must exist. To identify non-MHC resistance loci, spleen and liver MCMV levels and genome-wide genotypes were assessed in (C57L x MA/My) and (MA/My x C57L) F(2) offspring (representing 550 meioses). Significantly, a non-Mendelian frequency of MHC genotypes was observed for offspring of the latter cross. Quantitative trait loci (QTL) and their interaction potential in MCMV resistance were assessed in R/qtl; QTL on chromosomes 17, 6, and 19 affected MCMV levels in infected animals. A chromosome 6 QTL was linked with the NK gene complex and acted in an additive fashion with an H-2(k) MHC QTL to mitigate spleen MCMV levels. We provide biological confirmation that this chromosome 6 QTL provided MCMV control independent of H-2(k) via NK cells. Importantly, both chromosome 6 and 19 QTLs contribute to virus control independent of H-2(k). Altogether, MHC and non-MHC MCMV-resistance QTL contribute in early resistance to MCMV infection in this genetic system.

Recurrent first trimester pregnancy loss: revised definitions and novel causes

PURPOSE OF REVIEW

First trimester pregnancy loss affects up to 15% of clinically recognized pregnancies. Whereas most couples will proceed to have successful subsequent pregnancies, 2-4% will suffer recurrent losses, often with no identifiable cause. In fact, up to 40-50% of patients suffering recurrent pregnancy loss (RPL) will have no identifiable cause for their losses. Whereas the high incidence of spontaneous fetal aneuploidy will ensure that this number will never fall to zero, its level suggests that additional causes and appropriate diagnostic testing await discovery. The definition, diagnostic work-up and appropriate interventions among patients with RPL remain controversial. Here, we will review those papers published in the last 1-2 years that improve our understanding of the definition of RPL, that confirm the utility of present testing paradigms or that pose novel causes and diagnostic approaches to patients with a history of RPL.

RECENT FINDINGS

Standard definitions of RPL have been suggested by the American Society of Reproductive Medicine. Suggested potential diagnostic testing for RPL has been expanded to include male factors and new paradigms that address placental function, including the role of vascular endothelial growth factor, thrombosis and maternal-fetal immunology.

SUMMARY

Standardized definitions for RPL and standardized approaches to initiating the RPL work-up will aid in study design and improve the applicability and implications of published findings. Appropriate investigation of novel causes for RPL may decrease the percentage of patients carrying the diagnosis of unexplained RPL.

Genetic association of phase I and phase II detoxification genes with recurrent miscarriages among North Indian women

Allelic variants of the detoxification genes that have impaired biotransformation functions may increase susceptibility to reproductive toxicity leading to endometriosis, recurrent miscarriage (RM) or poor pregnancy outcome. In the present study, we have investigated CYP1A1, CYP2D6, GSTT1, GSTP1 and GSTM1, which are involved in the phase I and phase II detoxification systems, in relation to their role in the etiology of unexplained RMs. In a case-control study, we have investigated 200 females with RM and 300 age and ethnically matched healthy controls with successful reproductive history from North India. The frequencies of phase I wild-type genotypes of CYP1A1 and CYP2D6 in RM cases were 0.56 and 0.60, whereas in controls these were 0.68 and 0.65, respectively (both P < 0.05). The GSTM1 null-genotype frequencies were 0.66 and 0.84 among RM cases and controls, respectively, the GSTT1 null-genotype frequencies were 0.52 and 0.45 (P < 0.005) and the GSTP1 variant allele frequencies were 0.23 and 0.20, respectively. In conclusion, we observed significant protective effects of phase I wild-type genotypes and association of the GSTT1 null genotype with RM. Through combined analyses we have highlighted the importance of the balance of phase I/phase II detoxification systems, in the etiology of RM.

Co-evolution of KIR2DL3 with HLA-C in a human population retaining minimal essential diversity of KIR and HLA class I ligands

Natural killer (NK) cells contribute to immunity and reproduction. Guiding these functions, and NK cell education, are killer cell Ig-like receptors (KIR), NK cell receptors that recognize HLA class I. In most human populations, these highly polymorphic receptors and ligands combine with extraordinary diversity. To assess how much of this diversity is necessary, we studied KIR and HLA class I at high resolution in the Yucpa, a small South Amerindian population that survived an approximate 15,000-year history of population bottleneck and epidemic infection, including recent viral hepatitis. The Yucpa retain the three major HLA epitopes recognized by KIR. Through balancing selection on a few divergent haplotypes the Yucpa maintain much of the KIR variation found worldwide. HLA-C*07, the strongest educator of C1-specific NK cells, has reached unusually high frequency in the Yucpa. Concomitantly, weaker variants of the C1 receptor, KIR2DL3, were selected and have largely replaced the form of KIR2DL3 brought by the original migrants from Asia. HLA-C1 and KIR2DL3 homozygosity has previously been correlated with resistance to viral hepatitis. Selection of weaker forms of KIR2DL3 in the Yucpa can be seen as compensation for the high frequency of the potent HLA-C*07 ligand. This study provides an estimate of the minimal KIR-HLA system essential for long-term survival of a human population. That it contains all functional elements of KIR diversity worldwide, attests to the competitive advantage it provides, not only for surviving epidemic infections, but also for rebuilding populations once infection has passed.

The developmental role of natural killer cells at the fetal-maternal interface

Natural killer (NK) cells have been extensively studied in their traditional roles in host defense against tumor or virally infected cells. Uterine NK cells are of 2 distinct subsets: endometrial NK (eNK) cells, found in the uterus during the menstrual cycle, and decidual NK (dNK) cells, found in the decidua during pregnancy. This review will explore the immunosurveillance and cytotoxicity profiles of NK cells, the inert nature of eNK cells, and the role of dNK cells as builders at the maternal-fetal interface that create a pregnancy-favorable environment by inducing angiogenesis, trophoblast invasion, and vascular remodeling.

The genetic and evolutionary balances in human NK cell receptor diversity

In primates and cattle two ancient killer-cell immunoglobulin-like receptor (KIR) lineages independently evolved to become diverse NK cell receptors. In mice, KIR genes were sidelined to the X chromosome, a possible consequence of pathogen-mediated selection on the receptor for IgA-Fc. In humans, KIR uniquely form two omnipresent haplotype groups (A and B), postulated here to play complementary and necessary roles in immune defense and reproduction. The basis of KIR3DL1/S1 polymorphism is three ancient lineages maintained by long-term balancing selection and present in all human populations. Conserved and variable NK cell receptors produce structurally diverse NK cell receptor repertoires within a defined range of missing-self-response.

Association between von Willebrand factor gene polymorphism and preeclampsia

AIMS

The aims of this study were to assess whether the Msp I polymorphism of von Willebrand factor (vWF)(intron 19) gene differs between patients with preeclampsia and normal pregnancies in Chinese Han population, and to study the relationship between the Msp I polymorphism in the vWF(intron 19) gene and severity of preeclampsia symptoms within the preeclampsia group.

METHODS

In this case-control study, peripheral blood samples of 70 patients with preeclampsia and 82 normal pregnancies were genotyped for the Msp I polymorphism in vWF(intron 19) gene on the basis of a hospital-based study. The genotyping was performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and direct sequencing techniques.

RESULTS

The genotype frequencies for M+/M+, M+/M- and M-/M- were 22.9, 45.7 and 31.4% in patients with preeclampsia, and 1.2, 36.6 and 62.2% in normal pregnancies, respectively. The frequency of the M+ allele in patients with preeclampsia was significantly higher than in normal pregnancies (45.7 vs. 19.5%).

CONCLUSIONS

The Msp I polymorphism in intron 19 (M+ allele) of vWF gene is associated with the development and the severity of preeclampsia, and may be a susceptibility factor for preeclampsia.

Influence of activating and inhibitory killer immunoglobulin-like receptors on predisposition to recurrent miscarriages

BACKGROUND

Understanding of the immune events and mechanisms occurring at the feto-maternal interface is likely to help in understanding the ability of the fetus to survive within the maternal body. Evidence supporting extensive roles of natural killer cells during pregnancy gives rise to a possibility that these NK cells can be mis-regulated and involved in fetal allograft rejection. Killer immunoglobulin-like receptors (KIR) play an important role in regulating the NK cell activity through their activating and inhibiting isoforms. Since there exists a considerable, genetically determined variation in the repertoire of KIR receptors between different individuals, a particular maternal KIR repertoire may predispose to recurrent miscarriages (RMs).

METHODS

Gene-specific PCR amplification (PCR-SSP) was used to determine the individual KIR genotypes in women experiencing RM and controls.

RESULTS

A higher prevalence of activating KIR genes was seen in patients than in controls. Among women experiencing RM, the BB genotypes were more prevalent (P < 0.0001, OR = 4.4, 95% CI = 2.89-6.69) compared with controls.

CONCLUSIONS

Our results indicate that the balance between inhibitory and activating receptor-mediated signals present in natural killer cells is inclined toward a more activating state that may contribute to pregnancy loss.

A study of natural killer cell lectin-like receptor K1 gene (KLRK1/NKG2D) region polymorphisms in a European population sample

Recent evidence has reinforced the belief in immunosurveillance as a powerful mechanism against cancer development. The natural killer (NK) cell has been recognized as a potent agent of cancer immunosurveillance. A Japanese cohort study correlated natural cytotoxic activity levels with subsequent cancer development and identified NK cell lectin-like receptor K1 gene (KLRK1/NKG2D) polymorphisms as genetic markers of cancer predisposition. In the present study, we genotyped 82 reference cell lines and 388 newborn samples at 10 KLRK1 region variants by TaqMan((R)) allelic discrimination assays and showed that the same polymorphisms occur at similar frequencies in Europeans. The same haplotype block that has been associated with lower natural cytotoxic activity also occurred with the highest frequency in our sample. We further detected evidence suggestive of natural selection at some of the loci analyzed and more importantly, sex specificity of this selection. It appeared that heterozygosity at loci forming a haplotype block was unfavorable for boys. Given the relevance of NK cells in fetal survival, this finding has potential implications in the study of genetics of maternofetal recognition. Our preliminary findings are of marginal statistical significance and should be replicated in a larger sample. We believe that our results will increase awareness of the involvement of KLRK1 in cancer immunosurveillance and possibly in prenatal selection.

Human natural killer receptors, co-receptors, and their ligands

In the last 20 years, the study of human natural killer (NK) cells has moved from the first molecular characterizations of very few receptor molecules to the identification of a plethora of receptors displaying surprisingly divergent functions. Our laboratory has contributed to the description of inhibitory receptors and their signaling pathways, important in fine regulation in many cell types, but unknown until their discovery in the NK cells. Inhibitory function is central to regulating NK-mediated cytolysis, with different molecular structures evolving during speciation to assure its persistence. Only in the last ten years has it become possible to characterize the NK triggering receptors mediating natural cytotoxicity, leading to an appreciation of the existence of a cellular interaction network between effectors of both natural and adaptive immunity. This report reviews the contemporary history of molecular studies of receptors and ligands involved in NK cell function, characterizing the ligands of the triggering receptor and the mechanisms for finely regulating their expression in pathogen-infected or tumor cells.

Unique receptor repertoire in mouse uterine NK cells

Uterine NK (uNK) cells are a prominent feature of the uterine mucosa and regulate placentation. NK cell activity is regulated by a balance of activating and inhibitory receptors, however the receptor repertoire of mouse uNK cells is unknown. We describe herein two distinct subsets of CD3(-)CD122(+) NK cells in the mouse uterus (comprising decidua and mesometrial lymphoid aggregate of pregnancy) at mid-gestation: a small subset indistinguishable from peripheral NK cells, and a larger subset that expresses NKp46 and Ly49 receptors, but not NK1.1 or DX5. This larger subset reacts with Dolichus biflores agglutinin, a marker of uNK cells in the mouse, and is adjacent to the invading trophoblast. By multiparametric analysis we show that the phenotype of uNK cells is unique and unprecedented in terms of adhesion, activation, and MHC binding potential. Thus, the Ly49 repertoire and the expression of other differentiation markers strikingly distinguish uNK cells from peripheral NK cells, suggesting that a selection process shapes the receptor repertoire of mouse uNK cells.

The Yin and Yang of HLA and KIR in human disease

Killer cell immunoglobulin-like receptors (KIR) are expressed on natural killer (NK) cells and subsets of T cells. The KIR genes are polymorphic and the KIR gene complex is polygenic with varying numbers of inhibitory and activating receptors. HLA class I molecules serve as ligands for the KIR. Interactions of the independently segregating KIR and HLA loci are important for recognition of targets by NK cells as well as NK cell 'licensing'. Several disease association studies indicate a role for interactions between these loci in infectious diseases, autoimmune/inflammatory disorders, cancer and reproduction. Emerging functional data supports a mechanism based on a continuum of inhibition to activation through various compound KIR-HLA genotypes in diseases.

NK receptor interactions with MHC class I molecules in pregnancy

Both HLA class I molecules and their receptors on Natural Killer cells, the KIR molecules, are highly polymorphic. It is generally believed that this variation is driven in response to the role of these receptors and counter-receptors in resistance to disease. Uterine NK cells are the major maternal leukocyte population present within the decidua, and they express KIR2D receptors for HLA-C, the only polymorphic class I molecule on trophoblast. Genetic and functional data suggest that the maternal KIR/fetal HLA-C interaction in pregnancy may affect the delivery of an optimal blood supply to mother and fetus. The drive for novelty in HLA-C and KIR2D allelic diversity may relate not only to survival from infections but also to reproductive success.

Preeclampsia: a danger growing in disguise

Preeclampsia occurs in 3-14% of pregnancies and is defined by maternal hypertension with proteinurea, generally associated with edema, coagulation abnormalities, and disseminated intravascular coagulation. The conditions can lead to eclampsia, characterized by hyperreflexia and convulsions. Several organs are afflicted by the condition, most importantly the liver and kidneys. The direct cause of preeclampsia is unknown, but the initial events are linked to abnormalities of placentation. This implies abnormalities in trophoblast invasion and in physiological alterations of placental vessels required for adequate perfusion of the placenta, which leads to ischemia. The mechanisms that link the ischemic placenta to endothelial lesions and to stimulation of vasoconstrictors and inhibition of vasodilators are still subject of speculation. The only treatment of preeclampsia is delivery. Lowering of blood pressure and prevention of eclampsia with magnesium sulfate is indicated in severe preeclampsia. Despite numerous studies attempting to elucidate the exact etiopathogenesis of this complex multifactorial disease, prediction or prevention methods of preeclampsia are not available.