The impact of B-cell activation on the T-cell immune response to Mycobacterium tuberculosis

Van Rensburg, Ilana Claudia (2016-12)

Thesis (MSc)--Stellenbosch University, 2016.

Thesis

ENGLISH SUMMARY: The host immune response to tuberculosis is extremely complex, and in order to fully elucidate this, one has to thoroughly study the host response by considering all immune cells and phases of infection. T-cells have always been at the forefront of tuberculosis research due to its production of interferon-gamma and other pro-inflammatory cytokines. However, our increased understanding of B-cells show that these cells display non-humoral functions, such as production of cytokines and the expression of death-inducing ligands. These additional functions indicate that B-cells have a role to play during infection with Mycobacterium tuberculosis. We hypothesize that B-cells utilise these additional functions, like the production of cytokine, to modulate T-cell phenotype and function during exposure to Mycobacterium tuberculosis. Individuals with newly diagnosed untreated tuberculosis were recruited for the study, and were followed up during treatment. Controls recruited included healthy exposed/infected and uninfected controls, as well as other lung disease controls. Peripheral blood was collected from all these individuals. In order to evaluate B-cell gene regulation, transcriptional analysis was performed. Secondly, B-cell phenotypic characterization was done using flow cytometry and secreted cytokines evaluated using the Luminex platform. Furthermore, to assess the interaction between B- and T-cells, autologous B- and T-cells were co-cultured under various stimulation conditions, and the cells and cytokine production (Interferon-gamma, Tumour Necrosis Factor-alpha and Interleukin-2) analysed using flow cytometry. The results indicate that there is decreased activation of B-cells during active tuberculosis, and this is restored during anti-TB treatment. Transcriptional and phenotypic analysis show that there is a decline in FasL expression by B-cells during tuberculosis (compared to controls), and that the expression is enhanced following successful treatment. A potential function underlying FasL regulation could involve the induction of apoptosis of infected T-cells as a means to rid the body of pathogens. Furthermore, co-culture experiments show that B-cells are able to induce cytokine production by both CD4+ and CD8+ T-cells in the context of Mycobacterium tuberculosis exposure. These results could prove significant as B-cells may serve as a target for new vaccines or modified TB treatment. Current interventions are aimed at enhancing T-cell responses in order to combat infection. However, if B-cells are able to modulate T-cell responses, then these cells could be used to indirectly enhance the T-cell responses needed to eliminate the bacteria.

AFRIKAANSE OPSOMMING: Die gasheer immuun reaksie tot tuberkulose is uiters kompleks, en om dit ten volle te verstaan, moet 'n deeglike studie van die gasheer reaksie gedoen word deur alle immuunselle en fases van infeksie te oorweeg. T-selle was nog altyd aan die voorpunt van tuberkulose navorsing as gevolg van die produksie van interferon-gamma en ander pro-inflammatoriese sitokiene. Met ‘n toename in ons begrip van B-selle is dit duidelik dat hierdie selle nie-humorale funksies vertoon, soos onder andere die produksie van sitokiene en die uitdrukking van die dood induserende ligande. Hierdie bykomende funksies dui aan dat B-selle 'n rol het om te speel gedurende infeksie met Mikobakterium tuberkulose. Ons hipotese is dat B-selle hierdie bykomende funksies, soos die produksie van sitokiene gebruik, om T-sel fenotipe en funksie te moduleer tydens blootstelling aan Mikobakterium tuberkulose. Individue met nuut gediagnoseerde onbehandelde tuberkulose was gewerf vir die studie, en is opgevolg tydens behandeling. Gesonde kontrole wat blootgestel/besmet is en onbesmette kontrole, sowel as kontroles met ander longsiekte was ook gewerf. Perifere bloed is gekollekteer vanaf al hierdie individue. Om B-sel geenregulering te evalueer, is transkripsionele analise uitgevoer. Tweedens is B-sel fenotipiese karakterisering gedoen met behulp van vloeisitometrie en die vlakke van geproduseerde sitokiene geëvalueer met behulp van die Luminex platform. Om die interaksie tussen B- en T-selle te bepaal, is hierdie selle in kultuur saamgekweek onder verskillende stimulasie kondisies, en die selle en sitokiene produksie (Interferon-gamma, Tumor Nekrose Faktor-alfa en Interleukien-2 ) ontleed met behulp van vloeisitometrie. Die resultate dui daarop dat die aktivering van B-selle afneem tydens aktiewe tuberkulose, en dat dit herstel tydens anti-TB behandeling. Transkripsionele en fenotipiese analise toon dat daar 'n afname in FasL uitdrukking is deur die B-selle tydens tuberkulose (in vergelyking met die kontrole), en dat die uitdrukking bevorder word na suksesvolle behandeling. 'n Potensiële funksie sluit in dat FasL regulasie die inlywing van apoptose van besmette T-selle betrek as 'n manier waardeer die liggaam ontslaee raak van patogene. Verder, kwekings eksperimente toon dat B-selle in staat is om sitokien produksie deur beide CD4+ en CD8 + T-selle in die konteks van blootstelling aan Mikobakterium tuberkulose kan verander. Hierdie resultate dui aan dat B-selle as 'n teiken vir nuwe entstowwe of TB behandeling kan dien. Huidige ingrypings is gemik op die verbetering van T-sel reaksies ten einde infeksie te bekamp. Indien B-selle in staat is om T-sel reaksies te moduleer, kan hierdie selle gebruik word om die T-sel reaksie indirek te verbeter om sodoende die bakterieë uit te skakel.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100431
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