Investigation of Mycobacterium tuberculosis protein expression and analysis of humoral immune responses of TB patients

[摘要] ENGLISH ABSTRACT:New agents for the diagnosis, prevention and treatment of tuberculosis are urgentlyrequired. Yet, despite extensive tuberculosis research over recent years, no new drugs,vaccines or diagnostics have been identified to date. It is widely speculated that the majorobstacle to the identification of new therapies is the lack of understanding of the hostpathogeninteraction.This study has investigated whether patterns of antigen expression correlate withmolecular epidemiological data and strain virulence through the analysis of protein expressionand antigen recognition profiles of different M tuberculosis clinical isolates. Usingpolyacrylamide gel electrophoresis, enzyme-linked immunosorbent assay, and Westernblotting, protein expression and antigen recognition by two genotypically different clinicalstrains that differed in their frequency in the study population have been compared. Inaddition to differences in protein expression and antigen recognition between the clinicalstrains and the reference strain H37Rv, protein expression differences between the clinicalstrains themselves were observed which may relate to strain frequency and virulence.Differential protein expression by M tuberculosis strains, may explain theheterogeneous host humoral immune response and why no fully effective serodiagnostic testhas been developed to date. To explore this hypothesis, the potential of serodiagnosis in thiscommunity, where patients are infected with a wide variety of genotypically distinct strains,was investigated. IgG levels to three mycobacterial antigens showed that serodiagnosis of TBis possible in this community, despite infection by a wide variety of genotypically differentM tuberculosis strains. Disease episode affected antibody levels, suggesting that care shouldbe taken when evaluating serological diagnosis for repeat episode patients.This study has shown that M tuberculosis protein expression is dynamic and that thebacillus presents a hypervariabie array of antigens to the host immune system. It is likely thatdifferent antigens become immunodominant as antituberculosis chemotherapy progresses, andthat these differentially expressed antigens may be tracked as predictors of treatment outcome.This hypothesis was tested by correlating Ag85-specific IgG with treatment response, asassessed by sputum smear conversion after two months of antimycobacterial chemotherapy.No significant correlation between antibody levels and treatment responses was observed,suggesting that antibodies may not be useful surrogate markers or that the incorrect antibodytype or mycobacterial antigen were selected. Results were consistent with previous findingswhere patient-to-patient variation dictated the host humoral response.The results obtained in this study have demonstrated that although bacteriologicalfactors may influence strain prevalence due to antigen variation and immune evasion, bothbacteriological and host factors affect humoral immunity. Differential protein expression byM tuberculosis strains has potentially important implications for serodiagnosis and thedevelopment of subunit or DNA vaccines, by suggesting that multi-antigen cocktails shouldbe used. Differential protein expression may also explain why patients do not developadequate protective immunity and are susceptible to reinfection.

[发布机构] Stellenbosch University