A specific amino acid motif of HLA-DRB1 mediates risk and interacts with smoking history in Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disease in which genetic risk has been mapped to HLA, but precise allelic associations have been difficult to infer due to limitations in genotyping methodology. Mapping PD risk at highest possible resolution, we performed sequencing of 11 HLA genes in 1,597 PD cases and 1,606 controls. We found that susceptibility to PD can be explained by a specific combination of amino acids at positions 70-74 on the HLA-DRB1 molecule. Previously identified as the primary risk factor in rheumatoid arthritis and referred to as the "shared epitope" (SE), the residues Q/R-K/R-R-A-A at positions 70-74 in combination with valine at position 11 (11-V) is highly protective in PD, while risk is attributable to the identical epitope in the absence of 11-V. Notably, these effects are modified by history of cigarette smoking, with a strong protective effect mediated by a positive history of smoking in combination with the SE and 11-V (P = 10-4; odds ratio, 0.51; 95% confidence interval, 0.36-0.72) and risk attributable to never smoking in combination with the SE without 11-V (P = 0.01; odds ratio, 1.51; 95% confidence interval, 1.08-2.12). The association of specific combinations of amino acids that participate in critical peptide-binding pockets of the HLA class II molecule implicates antigen presentation in PD pathogenesis and provides further support for genetic control of neuroinflammation in disease. The interaction of HLA-DRB1 with smoking history in disease predisposition, along with predicted patterns of peptide binding to HLA, provide a molecular model that explains the unique epidemiology of smoking in PD

HLA Class I and Class II Conserved Extended Haplotypes and Their Fragments or Blocks in Mexicans: Implications for the Study of Genetic Diversity in Admixed Populations

Major histocompatibility complex (MHC) genes are highly polymorphic and informative in disease association, transplantation, and population genetics studies with particular importance in the understanding of human population diversity and evolution. The aim of this study was to describe the HLA diversity in Mexican admixed individuals. We studied the polymorphism of MHC class I (HLA-A, -B, -C), and class II (HLA-DRB1, -DQB1) genes using high-resolution sequence based typing (SBT) method and we structured the blocks and conserved extended haplotypes (CEHs) in 234 non-related admixed Mexican individuals (468 haplotypes) by a maximum likelihood method. We found that HLA blocks and CEHs are primarily from Amerindian and Caucasian origin, with smaller participation of African and recent Asian ancestry, demonstrating a great diversity of HLA blocks and CEHs in Mexicans from the central area of Mexico. We also analyzed the degree of admixture in this group using short tandem repeats (STRs) and HLA-B that correlated with the frequency of most probable ancestral HLA-C/−B and -DRB1/−DQB1 blocks and CEHs. Our results contribute to the analysis of the diversity and ancestral contribution of HLA class I and HLA class II alleles and haplotypes of Mexican admixed individuals from Mexico City. This work will help as a reference to improve future studies in Mexicans regarding allotransplantation, immune responses and disease associations

Spherotech-EDTA combined serum treatment reduces background more effectively as compared to One Lambda Adsorb Out™ and LIFECODES Serum Cleaner in Luminex-based solid-phase immunoassays for HLA antibody detection

Spherotech (SPT) microparticles capture non-specific binding materials present in test serum, and EDTA removes the so called” prozone effect”. This study presents a novel approach of combined SPT-EDTA serum treatment prior to Luminex HLA antibody testing to remove high background, and prozone effect in a single step process, and compared the efficacy of SPT-EDTA serum pre-treatment with AdsorbOut (ADS) and Serum Cleaner (SC) to reduce background in solid phase immunoassays (SPI). A total of 21 serum samples with a history of elevated negative control (NC) values ≥500, and 20 samples with normal NC values were included to assess the potential adverse effects. A problem of high background was noted in 25% of our samples in SPI. We observed 80% effectiveness in reducing NC values <500 with SPT-EDTA serum pre-treatment compared to 72%, and 67% for ADS and SC-treated sera, respectively. Interestingly, we found a strong correlation in antibody-binding levels between SPT versus ADS; and ADS versus SC-treated sera for both phenotype and single antigen bead assays (p < 0.001). No adverse effect was noted on NC, positive control (PC) values, PC/NC ratios in the upfront use of SPT-EDTA as compared to EDTA alone. Our data revealed that combined SPT-EDTA treated sera is more effective than ADS, and SC in reducing high background in SPI. Taken together, SPT-EDTA serum treatment prior to Luminex HLA Ab testing is cost-effective, our laboratory saves nearly 30% of the annual total cost for Ab testing and improved test turnaround time by two business days