Variation in ABCB1 and its effect on immune recovery with antiretrovirals

• Main Author: Du Plooy, Ingrid Marie
• Format: Others
• Language: en
• Published: 2012
• Subjects: Genetics; Pharmacology; Drugs (physiological effect); Variation (biology)
• Online Access: http://hdl.handle.net/10539/11243

Ph.D., Faculty of Science, University of the Witwatersrand, 2011 === The ABCB1 gene encodes P-glycoprotein, a transmembrane protein that regulates the efflux of drugs in the cells and may affect the response to antiretroviral drugs. ABCB1 polymorphisms affect the function or expression of P-gp. The 3435T allele has been associated with decreased protein production, but is in linkage disequilibrium with other polymorphisms. HIV is prevalent in Southern Africa, and characterization of ABCB1 variation may provide insight into its role in antiretroviral immune response. The aim was to determine if there was any association between ABCB1 variation, relative mRNA levels and immune response. Seven known polymorphisms were characterized for linkage disequilibrium and haplotype analysis, regions upstream of the gene were sequenced for bioinformatic analysis, the relative amounts of mRNA were determined, and CD4+ and viral load data was analyzed for association. Sequencing revealed six novel variations: T-137G, C-233T and G-298A upstream of exon 1, T108G and G153A in exon 2, and A111G in intron 26. The frequencies of the -129T (0.85), 1236T (0.70), 2677G (0.77), IVS 25+3050G (0.86), IVS 25+5231T (0.51), 3435C (0.88) and IVS 26+80T (0.89) polymorphisms were different and LD was lower compared to other populations. The haplotype frequencies were different to other populations and the genetic structure was probably a result of multiple recombination or mutation events. The viral load counts at the second measurement after baseline (time point 2) were significantly different from baseline for the 2677GG and 2677GA genotypes, and the -129T allele was associated with a lower proportional decrease in viral load at 8 the second measurement. The IVS 25+3050GG, 3435CC and IVS 26+80TT genotypes have been associated with lower mean relative mRNA levels. In conclusion, the genetic structure of the southern African populations is different from other populations and that genetic association and functional studies derived from other populations would be irrelevant in this population. A larger sample size and functional studies would be required to attempt to resolve the molecular mechanisms of the ABCB1 gene and to confirm the findings of association between ABCB1 polymorphisms and immune response.