Study On The Correlation Between Killer Cell Immunoglobulin-like Receptors Genes And Preelampsia

Preeclampsia is one of the common complications of pregnancy, which is the leading cause of perinatal both fetal and maternal morbidity and mortality. Although the etiology of preeclampsia is always the heat of obstetric researches, so far there is no hypothesis which can explain the pathgenesis of the disease perfectly . At present , it is thought of that the susceptibility of preeclampsia is increased by multi-gene inheritance background and the influence of environments. During the pregnancy, the balance of immunity between maternal and fetus is destroyed which will result in trophocyte infiltration disability and poor placentation , and substituted of reduction of plancetal perfusion and dysmetabolism; then endothelial cells will be injured and the disproportion of vasoactive substance will induce hyperkinesias of systemic small arteries, all of above will finally lead to the occurrence of preeclampsia.Natural killer cells can discriminate self from non-self and play an important role in innate immunity. Killer cell immunoglobulin-like receptors (KIR) are a diverse family of receptors expressing on NK cells. When KIR band with specific HLA class I alleles of target cells , the stimulatory and inhibitory signals can be transferred from KIR to NK cells, thus the function of NK cells are regulated. So KIRs are very important to NK cells, that NK cells'function depend on existence of KIRs. Especially, recent research indicate interaction of KIR2DL4 and its specific ligand produce a marked effect infeto-materna immune tolerance during pregnancy, and the fuctional disorder between them can lead to happenning of pathological pregnancy. The genomic region that encodes KIRs exhibits extensive variability among individuals due to differences in gene content , gene copy number,and allelic polymorphism,which may be associated with the genetic predisposition of preelampsia. Until now, there is no elaborate report about the KIR and the preeclampsia.We detected of the KIR gene polymorphism of 71 patients of preeclampsia and 100 healthy pregnant women by sequence specific primer polymerase chain reaction (PCR-SSP), and analyzed the differences of KIR gene frenquency , genotype, haplotype and the arithmetic mean of KIR gene between two groups in detail .We also quantified KIR2DL4mRNA level in placentas from preeclampsia and gestational normal pregnancies using real time RT-PCR combining the 2-⊿⊿CT Method, respectively. Finally, we selected 40 preeclampsia patients and 38 healthy pregnant women to detected single nucleotide polymorphisms (SNPs) in the gene coding and joint areas between introns and extrons by directly sequencing techniques of KIR2DL4 genomic DNA , we also carried on the linkage disquilibrium analysis for all the SNP we found, and built some haplotypes according to the result of linkage disquilibrium analysis. Then to find the association of KIR2DL4 gene polymorphism with preelampsia , we carried on case-control study of all alleles, genotypes and haplotypes of KIR2DL4 gene.In this study ,all of 18 KIR genes were observed in both patients and controls. Generally, three framework genes(KIR2DL4,3DL2,3DL3) were present in all individuals. There were no difference between cases and controls in gene frequences ,haplotypes and the arithmetic mean of KIR gene. Distributions of some relatively activating KIR genotypes shew a significant association with preeclampsia. Real-time RT-PCR showed that KIR2DL4 mRNA can be measured both in placenta of women with preeclampsia and normal pregnancy and the level of preeclampsia was significantly lower than that of normal pregnancy, only as much as 0.276 times that of controls. We identified 18 polymorphisms, of which, 7 were first reported , and 6 SNPs were in joint areas between introns and extrons ,and one synonymous SNP was in the seventh exon of KIR2DL4 gene. But no significant differences in genotype distributions or allele frequencies were observed in these SNPs between cases and controls .Distributions of haplotypic frenquencies of the SNPs did not show a significant association between any of the haplotyes and preeclampsiaWe discussed the correlativity between KIR and preeclampsia, at gene level. Distributions of some relatively activating KIR genotypes showed a significant association with preeclampsia, which indicated that the polymorphism of KIR genes might be associated with the genetic predisposition of preelampsia. And because the expression of KIR2DL4 mRNA in the placentas of cases was significantly lower than control group, we speculated that the decreasing of KIR2DL4 expression in placenta might take part in the pathogenesis of preeclampsia through destroy the feto-maternal immune tolerance. We got the relative quantity of the expression of our aim gene KIR2DL4 to the expression of house keeper gene TBP , by the method of real time RT-PCR (SYBR Green I dye method) combining the 2-⊿⊿CT Method ,and we find the method was available, easy operation and good specificity .And we found neither SNP nor haplotype of KIR2DL4 associated with preeclampsia in our study , so the further research of KIR2DL4 would be necessary .