Biomedical subjects

Raja Rajalingam

Publications and source records attributed to Raja Rajalingam.

9 recordsLinked to original sources

PubMed2006

Receptor-ligand analyses define minimal killer cell Ig-like receptor (KIR) in humans.

Interactions between inhibitory killer cell immunoglobulin-like receptors (iKIR) and human leukocyte antigen (HLA) class I molecules regulate natural killer (NK) cell responses to eliminate infected and transformed cells while maintaining tolerance to healthy cells. Unlinked polymorphic gene families encode KIR receptors and HLA class I ligands and their independent segregation results in a variable number and type of iKIR + HLA pairs inherited in individuals. The diversity in the co-inheritance of iKIR + HLA pairs and activating KIR (aKIR) genes in 759 unrelated individuals from four ethnic populations was analyzed. Every individual studied inherited a minimum of one iKIR + HLA pair; suggesting that major histocompatibility complex class I-dependent inhibitory KIR signaling is essential for human NK cell function. In contrast, 13.4% of the study group lacked all aKIR genes. Twenty percent of the study group carried only one of the four iKIR + HLA pairs. Interestingly, 3% of the study group carrying only KIR2DL3 + HLA-C1 as an iKIR + HLA pair lacked aKIR genes. These data suggest that a single iKIR can constitute the minimal KIR repertoire for human NK cells. Genotypes carrying an equal number of iKIR + HLA pairs and aKIR genes represented 20% of the study group. The remaining individuals had either a dominant inhibitory KIR genotype (iKIR + HLA > aKIR) or a dominant activating KIR genotype (iKIR + HLA < aKIR). Genotypes encoding these imbalanced inhibitory and activating interactions may contribute to susceptibility or resistance to human diseases.

Epitope Mapping↗

PubMed2004

Domain shuffling has been the main mechanism forming new hominoid killer cell Ig-like receptors.

The killer cell Ig-like receptor (KIR) gene family encodes MHC class I-specific receptors, which regulate NK cell responses and are also expressed on subpopulations of T cells. KIR haplotypes vary in gene content, which, in combination with allelic polymorphism, extensively diversifies the KIR genotype both within and between human populations. Species comparison indicates that formation of new KIR genes and loss of old ones are frequent events, so that few genes are conserved even between closely related species. In this regard, the hominoids define a time frame that is particularly informative for understanding the processes of KIR evolution and its potential impact on killer cell biology. KIR cDNA were characterized from PBMC of three gorillas, and genomic DNA were characterized for six additional individuals. Eleven gorilla KIR genes were defined. With attainment of these data, a set of 75 KIR sequences representing five hominoid species was assembled, which also included rhesus monkey, cattle, and rodent KIR. Searching this data set for recombination events, and phylogenetic analysis using Bayesian methods, demonstrated that new KIR were usually the result of recombination between loci in which complete protein domains were shuffled. Further phylogenetic analysis of the KIR sequences after removal of confounding recombined segments showed that only two KIR genes, KIR2DL4 and KIR2DL5, have been preserved throughout hominoid evolution, and one of them, KIR2DL4, is also common to rhesus monkey and hominoids. Other KIR genes represent recombinant forms present in a minority of species, often only one, as exemplified by 8 of the 11 gorilla KIR genes.

Animals↗

PubMed2004

Human leukocyte antigen A29 subtypes associated with birdshot retinochoroidopathy.

PURPOSE: To determine whether birdshot retinochoroidopathy is associated with subtypes of the human leukocyte antigen (HLA)-A29 other than HLA-A*2902. DESIGN: Experimental study. METHODS: High-resolution DNA typing of HLA-A29 subtypes was performed on blood from 20 subjects with birdshot retinochoroidopathy using polymerase chain reaction-based typing methods. Results were compared with published controls. RESULTS: Four of 20 subjects (20%) had the HLA-A*2901 allele; two were homozygous for HLA-A*29, and both had the HLA-A*2901 and HLA-A*2902 alleles. Among 18 subjects with only one HLA-A*29 allele, the HLA-A*2902 allele was found in 16 (89%) and the HLA-A*2901 allele was found in two (11%). No subject was found to have HLA-A*2903, HLA-A*2904, HLA-A*2905, or HLA-A*2906. CONCLUSIONS: Both HLA-A*2901 and HLA-A*2902 are associated with birdshot retinochoroidopathy. Our data do not support the previous suggestion that the HLA-A29.1 serotype may be protective against development of birdshot retinochoroidopathy. Additional studies will be required to determine whether the other, less common subtypes are associated with the disease. HLA-A29 subtype testing is not required for the clinical evaluation of HLA-A29-positive patients with birdshot retinochoroidopathy.

Chorioretinitis↗

PubMed2004

Anti-HLA class I antibody-mediated activation of the PI3K/Akt signaling pathway and induction of Bcl-2 and Bcl-xL expression in endothelial cells.

Anti-human leukocyte antigen (HLA) antibodies (Ab) have long been implicated in the process of acute and chronic allograft rejection, yet their mechanism(s) of action is not well understood. The aim of this study was to determine whether ligation of HLA class I molecules by anti-HLA Ab on the surface of human endothelial cells (EC) activates the PI3 Kinase (PI3K)/Akt signaling pathway and downstream target proteins of the cell death apparatus. We report that Ab ligation of major histocompatibility complex (MHC) class I molecules on the surface of EC triggers phosphorylation of Akt, PI3K, and recruitment of PI3K and Akt into a signaling unit with focal adhesion kinase. Signaling through class I also stimulated phosphorylation of Bad and upregulated expression of Bcl-2 and Bcl-xL. Pretreatment of EC with the PI3K inhibitor wortmannin blocked class I-mediated expression of Bcl-2, but not Bcl-xL, suggesting a role for the PI3K/Akt signaling pathway in regulation of class I-induced Bcl-2 expression. The intracellular events initiated by class I ligation were influenced by the concentration of the anti-HLA Ab with the lowest tested concentrations of Ab stimulating the highest level of Akt phosphorylation, Bcl-xL and Bcl-2 expression. Consistent with the in vitro experiments, analysis of biopsy samples from heart transplant recipients with evidence of Ab-mediated rejection exhibited increased Bcl-2 expression on the vascular endothelium. These results suggest that exposure of the graft endothelium to low concentrations of anti-HLA Ab may promote cell survival by transducing signals resulting in upregulation of cell survival genes.

Androstadienes↗

PubMed2004

A sequencing-based typing method for HLA-DQA1 alleles.

Sequencing-based typing (SBT) is the most comprehensive method for characterizing human leukocyte antigen gene polymorphisms. Development of a SBT method for DQA1 is hampered because of a deletion of codon 56 in nearly half of the known DQA1 alleles. Sequence electropherograms of heterozygous samples comprising a deletion allele and a non-deletion allele display misalignment after codon 56 because of a three base-pair shift in the deletion allele. To overcome this problem, we have designed three group-specific primer sets to selectively amplify the deletion alleles from the nondeletion alleles. DNA samples are initially polymerase chain reaction (PCR)-typed using these primer sets along with an internal positive control primer set specific to growth hormone gene 1 (hGH1). The positive group-specific PCR reactions were selectively repeated without hGH1 control primers, and the amplicons were used as template in sequencing reactions. The sequence data were analyzed to obtain DQA1 types using ABI MatchTools software as well as the newly available Conexio Genomics Assign SBT Genotyping Software. The method was validated using a panel of reference DNA from the University of California, Los Angeles, International DNA Exchange Program. We conclude that the present SBT method is a technically simple and robust procedure to characterize the sequence polymorphisms in exon 2 of DQA1 gene.

Alleles↗

PubMed2004

HLA-DRB1 and -DQB1 alleles in mestizo patients with Vogt-Koyanagi-Harada's disease in Southern California.

We evaluated human leukocyte antigen (HLA)-DRB1 and -DQB1 alleles as genetic markers for Vogt-Koyanagi-Harada (VKH) disease in Mestizo patients in Southern California. Mestizo individuals with VKH disease (n = 29) at two institutions were evaluated. Typing of HLA-DRB1 and DQB1 genes was performed using DNA-based techniques. Gene frequencies were compared to Mestizo individuals living in Southern California. All patients had HLA-DRB1*01, DRB1*04, DQB1*03 or DQB1*05, or a combination of these genes. The gene frequency of combined HLA-DR4 alleles was increased when compared to controls. The frequencies of HLA-DRB1*0404 and DRB1*0407 were increased compared to controls, but were not significant after Bonferroni correction. Three patients had the HLA-DRB1*0410 allele; this allele was not found in controls. All HLA-DRB1*01 positive patients had the DRB1*0102 subtype. No HLA-DQB1 allele was significantly increased compared to controls. This study is the first to identify a possible association between HLA-DRB1*0404 and VKH disease, as well as to find DRB1*0102 and DRB1*0410 in Mestizo patients.

Alleles↗

PubMed2002

Predominance of group A KIR haplotypes in Japanese associated with diverse NK cell repertoires of KIR expression.

Genomic DNA from a panel of 41 healthy unrelated Japanese individuals was typed for the presence or absence of 16 KIR genes and pseudogenes. Only eight different KIR genotypes were found. Group A haplotypes outnumbered group B haplotypes in frequency by approximately 3:1, with individuals having two group A haplotypes accounting for 56% of the panel. The frequency of A haplotypes in the Japanese is higher than that observed in other populations. Flow cytometric comparison of KIR expression in 19 panel members showed considerable diversity in NK cell repertoire, which was also seen within the group of individuals having two A haplotypes. This diversity is likely due to allelic polymorphism in expressed genes of the A haplotype. In comparison to other populations, the Japanese appear less heterogeneous in KIR genotype as assessed by gene content.

Adult↗

PubMed2002

Distinctive KIR and HLA diversity in a panel of north Indian Hindus.

HLA and KIR are diverse and rapidly evolving gene complexes that work together in human immunity mediated by cytolytic lymphocytes. Understanding their complex immunogenetic interaction requires study of both HLA and KIR diversity in the same human population. Here a panel of 72 unrelated north Indian Hindus was analyzed. HLA- A, B, C, DRB1, DQA1, and DQB1 alleles and their frequencies were determined by sequencing or high-resolution typing of genomic DNA; KIR genotypes were determined by gene-specific typing and by allele-level DNA typing for KIR2DL1, 2DL3, 2DL5, 3DL1, and 3DL2. From HLA analysis, the north Indian population is seen to have several characteristics shared either with Caucasian or East Asian populations, consistent with the demographic history of north India, as well as specific features, including several alleles at high frequency that are rare or absent in other populations. A majority of the north Indian KIR gene profiles have not been seen in Caucasian and Asian populations. Most striking is a higher frequency of the B group of KIR haplotypes, resulting in equal frequencies for A and B group haplotypes in north Indians. All 72 members of the north Indian panel have different HLA genotype and different KIR genotype.

Alleles↗

PubMed2002

Conservation and variation in human and common chimpanzee CD94 and NKG2 genes.

To assess polymorphism and variation in human and chimpanzee NK complex genes, we determined the coding-region sequences for CD94 and NKG2A, C, D, E, and F from several human (Homo sapiens) donors and common chimpanzees (Pan troglodytes). CD94 is highly conserved, while the NKG2 genes exhibit some polymorphism. For all the genes, alternative mRNA splicing variants were frequent among the clones obtained by RT-PCR. Alternative splicing acts similarly in human and chimpanzee to produce the CD94B variant from the CD94 gene and the NKG2B variant from the NKG2A gene. Whereas single chimpanzee orthologs for CD94, NKG2A, NKG2E, and NKG2F were identified, two chimpanzee paralogs of the human NKG2C gene were defined. The chimpanzee Pt-NKG2CI gene encodes a protein similar to human NKG2C, whereas in the chimpanzee Pt-NKG2CII gene the translation frame changes near the beginning of the carbohydrate recognition domain, causing premature termination. Analysis of a panel of chimpanzee NK cell clones showed that Pt-NKG2CI and Pt-NKG2CII are independently and clonally expressed. Pt-NKG2CI and Pt-NKG2CII are equally diverged from human NKG2C, indicating that they arose by gene duplication subsequent to the divergence of chimpanzee and human ancestors. Genomic DNA from 80 individuals representing six primate species were typed for the presence of CD94 and NKG2. Each species gave distinctive typing patterns, with NKG2A and CD94 being most conserved. Seven different NK complex genotypes within the panel of 48 common chimpanzees were due to differences in Pt-NKG2C and Pt-NKG2D genes.

Alleles↗