Molecular-genetic investigation into host susceptibility and variability to HIV/AIDS in the South African population

Pretorius, Gideon Stephan (2003-12)

Thesis (PhD)--University of Stellenbosch, 2003.

Thesis

ENGLISH ABSTRACT: The risk of human immunodeficiency virus type-1 (HIV-1) infection and rate of progression towards development of the acquired immunodeficiency syndrome (AIDS) is determined by a combination of viral characteristics, immune function and host genetic variation. Although mutations of the chemokine and chemokine co-receptor genes and allelic variation of the major histocompatibility complex (MHC) have been studied extensively, variation in these host genetic factors does not explain the differences in HIV/AIDS susceptibility in all cases. This study represents the first analysis of new candidate genes implicated in iron metabolism and immune function in relation to HIV-1 disease in the African context. Both case-control association studies and genotype-phenotype correlations were performed to determine the potential functional significance of genetic variants that may be involved, either directly or indirectly, in susceptibility to HIV-1 disease in the South African population. Genotyping was performed to identify potentially important polymorphisms in the solute carrier family 11 member 1 (SLC11A 1), haemochromatosis (HFE) and protein-tyrosine phosphatase receptor-type C (PTPRC/CD45) genes in HIV-seropositive versus HIVseronegative individuals. This was followed by HLA-B27 genotyping in HIV-1 infected individuals with known disease status to determine the potential impact of combined genotypes for different mutations identified in the same study cohort. Preferential association with any of the mutations screened for in the CCR5, SLC 11A1, HFE or CD45 genes were not detected in HLA-B27 positive individuals identified. These findings were in accordance with the independent protective role of HLA-B27 in relation to disease progression in HIV-1 infected individuals. Although differences in allelic distribution were not significant between the study groups, an apparently African-specific mutation 32A~G, identified in an exonic splicing silencer element (ESS-1) of the CD45 gene, appeared to predominate in HIV-1 infected subjects with WHO Class I disease status and slow progression to AIDS. This mutation was present in 35.7% (5/14) of HIV-seropositive individuals with WHO Class I disease status, whilst absent in 22 HIV-seropositive patients with rapid disease progression. This finding may be related to differences in proportions of both CD4+ and CD8+ subsets observed following flow cytometry (FACs) analys.s in two HIV-seropositive individuals with mutation 32A~G, compared with an HIV-seropositive individual without this mutation. Analysis of the iron-related SLC11A1 and HFE genes did not reveal significant associations with modified risk of HIV-1 infection or progression to AIDS in our predominantly African study population. However, the effect of the virus on iron metabolism was demonstrated for the first time at the DNA level. Haemoglobin levels were significantly reduced in both HIV-seropositive (P=O.004) and HIV-seronegative (P=O.02) Black Africans with mutation IVS3-48c~g in the HFE gene, compared with mutationnegative individuals in both groups. Since this effect was more pronounced in HIV-infected individuals compared with controls, presence of the HFE mutation seems to result in an even stronger effect on haemoglobin levels, which may be related to the acute phase response following virus infection. This effect possibly results from genetic variation in a nearby gene involved in innate immunity, most likely in the HLA region on chromosome 6. It therefore seems possible that genetic variation in any of the host molecules involved in response to infection could contribute to clinical outcome. The significance of the multitude of host genetic factors investigated in this study, or previously implicated in susceptibility to HIV-1 infection and disease progression, revealed a complex interrelationship between the host and HIV-1. In some instances the disease process following HIV-1 infection depends on combined effects of different mutations occurring in the same individual, while independent effects of specific genes in conjunction with environmental influences may explain diverse clinical outcomes in others.

AFRIKAANSE OPSOMMING: Die risiko vir menslike immuniteitsgebrek virus tipe-1 (MIV-1) infeksie en die progressietempo vir ontwikkeling van die verworwe immuniteits gebrek sindroom (VIGS) word hoofsaaklik deur fn kombinasie van virale eienskappe, immuunfunksie en gasheer genetiese variasie bepaal. Alhoewel mutasies van die chemokien en chemokien koreseptor gene en alleliese variasie van die major weefsel-verenigbaarheidskompleks (MWVK) reeds omvattend bestudeer is, verklaar variasie van hierdie gasheer genetiese faktore nie noodwendig verskille in vatbaarheid vir MIVNIGS in alle gevalle nie. Hierdie studie verteenwoordig die eerste analise van nuwe kandidaatgene, geïmpliseer in yster metabolisme en immuunfunksie in die konteks van MIV-1 siekte in Swart bevolkingsgroepe. Beide gevalle-kontrole assosiasie-studies en genotipe-fenotipe korrelasies is uitgevoer om moontlik betekenisvolle verwantskappe met genetiese variante te bepaal, wat moontlik direk of indirek betrokke mag wees in vatbaarheid vir MIV-1 siekte in die Suid Afrikaanse populasie. Genotipering van die solute draer familie 11 lid 1 (SLC11A1), hemochromatose (HFE) en protein-tirosien fosfatase reseptor-tipe C (PTFRC/CD45) gene is uitgevoer in beide MIVseropositiewe en MIV-seronegatiewe individue. Daaropvolgend is genotipering van die menslike leukosien antigeen-B27 (MLA-B27) uitgevoer in MIV-1 geïnfekteerde individue met bekende siekte-status, om die potensiële impak van gekombineerde genotipes te bepaal vir verskillende mutasies wat in dieselfde studie populasie geïdentifiseer is. Voorkeur-assosiasie is nie waargeneem vir enige van die mutasies waarvoor geanaliseer is in die CCR5, SLC11A1, HFE of CD45 gene nie. Hierdie bevinding is in ooreenstemming met die onafhanklike rol van MLA-B27 in verwantskap met siekte progressie in MIV-1 geïnfekteerde individue. Alhoewel die alleelverspreiding van In Afrika-spesifieke mutasie 32A~GI wat in In eksoniese splytingsdemper-element (ESS-1) van die CD45 geen geïdentifiseer is, nie statisties betekenisvolle verskille getoon het tussen studiegroepe nie, is die mutasie oorheersend waargeneem in MIV-1 geïnfekteerde individue met WGO Klas I siektestatus en stadige progressie na VIGS. Hierdie mutasie was teenwoordig in 35.7% (5/14) van HIV-seropositiewe individue met WGO Klas I siekte-status, terwyl dit afwesig was in 22 HIV-seropositiewe pasiënte met vinnige siekteprogressie. Hierdie bevinding mag moontlik verband hou met verskille in verhoudings van beide die CD4+ en CD8+ substelle, soos waargeneem gedurende vloei sitometriese (VAS, FACs) analise in twee HIV-seropositiewe individue met mutasie 32A---+G, in vergelyking met en HIV-seropositiewe individu sonder hierdie mutasie. Analise van die yster-verwante SLC11A 1 en HFE gene het nie betekenisvolle assosiasies opgelewer met gemodifiseerde risiko vir MIV-1 siekte of progressie na VIGS in die hoofsaaklik Swart studie-populasie nie. Die effek van die virus op ystermetabolisme is wel vir die eerste keer op DNS vlak gedemonstreer. Hemoglobien vlakke was betekenisvol verlaag in beide MIV-seropositiewe (P=O.004) en MIV-seronegatiewe (P=O.02) Swart individue met die HFE geen IVS3-48C---+G mutasie, in vergelyking met mutasie-negatiewe individue in beide groepe. Aangesien hierdie effek meer uitgesproke was in MIVgeïnfekteerde individue as in kontroles, blyk dit dat die teenwoordigheid van die HFE mutasie die hemoglobienvlakke tot engroter mate beïnvloed weens die akute fase respons wat verband hou met die virusinfeksie. Hierdie effek kan moontlik toegeskryf word aan genetiese variasie in ennaasliggende geen wat in aangebore immuniteit betrokke is, heel moontlik in die MLA gebied van chromosoom 6. Dit wil dus voorkom asof genetiese variasie in enige van die gasheer molekules betrokke by respons op infeksie kan bydra tot die kliniese uitkoms. Die belangrike rol van die veelvuldige gasheer genetiese faktore wat in hierdie studie bestudeer is, of wat voorheen geïmpliseer is in vatbaarheid vir MIV-1 infeksie en siekte progressie, het enkomplekse inter-verwantskap tussen gasheer en MIV-1 geopenbaar. In sommige gevalle is die siekte-proses na MIV-1 infeksie afhanklik van gekombineerde effekte van verskillende mutasies in dieselfde individu, terwylonafhanklike effekte van spesifieke gene tesame met omgewings-invloede uiteenlopende kliniese uitkomste in ander mag verklaar.

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