Immune regulation in children and adults in a community with a high incidence of tuberculosis

Adams, Joanita Frances Ann (1998-12)

Thesis (MScMedSc) -- Stellenbosch University, 1998.



ENGLISH ABSTRACT: There is a progressive maturation of the immune system from infancy to adulthood. The immature immune system in early life is characterised by impaired macrophage function and antigen presentation as well as a higher naIve to memory T cell ratio with subsequent diminished IFN-y production. Children with tuberculosis often present with lymphadenopathy, the complications thereof or with systemic spread of the organisms. Adults generally manifest with pronounced systemic effects (such as weight loss and high fever) and immunopathology (such as cavitation and fibrosis). We hypothesised that the immunopathology in adults may be due to enhanced cytokine production in comparison to children. The first aim of this study was therefore to measure cytokine responses in healthy children and adults. Cytokine responses in patients with tuberculosis will be examined in future studies. Peripheral blood mononuclear cells (PBMC) were isolated from whole blood obtained from 9 healthy children and 9 healthy adults. The cells were cultured in serum-free medium, unstimulated or polyclonally stimulated with Phytohaemagglutinin (PHA). Supernatants were harvested after which IFN-y, IL-2, TNF-a., IL-4 and IL-IO production was determined by means of ELISA analysis. Ri'J"A was ~ubsequently extracted from the cells followed by RT-PCR analysis for the semiquantitative determination of mRNA levels of these cytokines. PBMC isolated from healthy children produced significantly less IFN-y protein than adults. Futhermore, IFN-y production in the adults seemed to be trimodally distributed. No significant differences could be found in the production of IL-2, TNF-a, IL-4 and IL-] O. Although children produced low levels of IFN-y protein, their IFN-y, TNF-a, IL-2, IL-4 and IL-IO mRNA levels were comparable to that of adults. Tuberculosis is a major cause of mortality and morbidity, particularly in the third world. Ravensmead and Uitsig, two adjacent suburbs in the Western Cape, have a tuberculosis incidence of> I 000/100000 population. Also, up to 90 % of the children in the Western Cape have been reported to be infested by intestinal parasites such as Ascaris lumbricoides and Trichurius trichl/ria. Infection with M tuberculosis indut:es a Th 1 Stellenbosch University iv In:.,c response, while intestinal parasites elicit a Th2 immune response. Th2 dominance induced by intestinal parasite infestations could predispose individuals to an enhanced susceptibility to M. tuberculosis. The second aim of this study was to investigate serum IgE levels, surrogate markers for Th2 activation, in the community. The serum 19B levels were subsequently correlated to the tuberculosis incidence per enumerator sub-district (ESD), crowding, female literacy and socio-economic levels. Similarly, the tuberculosis incidence per ESD was correlated with the above mentioned parameters. A significant positive correlation was found between tuberculosis incidence and the serum 19E levels in the community. However, further studies are needed to determine if intestinal parasites are the main cause of the high 19B levels in the community and to dCh111ine if parasite loads or Th2 dominance are causally linked to the incidence of tuberculosis. Correlation between serum 19E levels and tuberculosis incidence with the other parameters were significant, except in the case of crowding. The third aim of this study was to measure serum IgE and specific 19E levels against Ascaris and common allergens on presentation of tuberculosis and again after completion of successful treatment. Significant declines in serum 19B and Ascaris specific 19B levels were observed after completion of tuberculosis treatment. This down regulation of IgE levels may be due to an up regulation of ThI responses in patients following successful treatment for tuberculosis.

AFRIKAANSE OPSOMMING: Die immuunsisteem matureer toenemend vanaf kinderjare tot en met volwassewording. Die onvolwasse immuunsisteem van jong kinders word gekenmerk deur verswakte makrofaag-funksionering en antigeenpresentering, sowe) as 'n verhoogde naiwe tot geheue T-sel verhouding met gevolglikc verminderde IFN-y produksie. Kinders met tuberkulose presenteer gewoonlik met Iimfadenopatie, komplikasies daarvan of met gedissemineerde siekte. Volwassenes presenteer met sistemiese gevolge (soos gewigsverlies en hoe koors) en immunopatologie (soos kavitasie en fibrose). Ons hipotese is dat die immunopatologie in volwassenes die gevolg is van 'n verhoogde sitokienproduksie in vergelyking met kinders. Die eerste doelwit van die studie was om sitokienproduksie in gesonde kinders en volwassenes te meet. Sitokienproduksie in tuberkulose pasiente sal in 'n opvolgstudie bepaal word. Perifere bloed mononukleere selle was geisoleer vanuit heel bloed verkry vanaf 9 gesonde kinders en 9 gesonde volwassenes. Die selle was gekweek, ongestimuleer of gestimuleer met Phytohaemagglutinien (PHA). Supernatante was geoes vir die bepaling van IFN-y, IL-2, IL-4, IL-I0 en TNF-a. produksie, deur gebruik te maak van ELISA analise. RNA was gevolglik vanaf die selle ge-ekstraheer vir die tru-transkriptase polimeerketting reaksie analise, waartydens sitokien mRNA vlakke op 'n semi-kwantitatiewe wyse bepaal was. Perifere bloed mononukleere selle geisoleer vanaf die kinders het minder IFN-y geproduseer as die van volwassenes. Hierdie verminderde produksie was hoogs betekenisvol. Dit wou voorkom asof die IFN-y produksie deur volwassenes trimodaal versprei was. Geen betekenisvolle verskille tussen kinders en volwassenes kon gevind word in die produksie van IL-2, IL-4, IL-IO en TNF-a nie. Alhoewel kinders minder IFN-y proteien geproduseer het, het hulle IFN-y, IL-2, IL-4, IL-JO en TNF-a mRNA produksie met vlakke van volwassenes ooreengestem. Tuberkulose speel 'n groat rol in morbiditeit en mortaliteit in veral die derde wereld. Ravensmead en Uitsig, twee aangrensende voorstede in die Wes-Kaap, het 'n tuberkulose voorkomssyfer van> 1 000/1 00000 populasie. Verder, is tot 90 % van die kinders in die Stellenbosch University VI Wes-Kaap gei'nfesteer met intestinale parasiete soos Ascaris Ilimbricoides en Trichllrills trichllria. M. tuberculosis infeksie induseer 'n Thl immuunrespons, terwyl intestinale parasiete 'n Th2 immuunrespons uitlok. 'n Dominante Th2 respons mag moontlik individue predisponeer tot 'n verhoogde vatbaarheid vir M. tuberculosis. Gevolglik was die tweede doelwit van die studie om serum IgE vlakke as surrogaat merkers vir Th2 aktivering in die gemeenskap bestudeer. Die serum IgE vlakke was gevolglik gekorreleer met die tuberkulose voorkoms per opnemerssensusgebied (OSG), saamdringing, vroulike geletterdheid en sosio-ekonomiese vlakke. Die tuberkulose voorkoms per OSG, is op dieselfde wyse gekorreleer met die bogenoemde parameters. 'n Betekenisvolle positiewe korrelasie is gevind tussen tuberkulose voorkoms en serum IgE vlakke in die gemeenskap. Verdere stuciies is egter nodig om te bepaal of intestinale parasiete weI die oorsaak van die hoe IgE vlakke in die gemeenskap is en of parasiet ladings of Th2 dominansie oorsaaklik verbind kan word aan die tuberkulose voorkoms. Die derde doelwit van die studie was om serum 19E en spesifieke IgE vlakke teen Ascaris en algemene allergene te meet met presentering van tuberkulose en weer na voltooing van suksesvolle behandeling. 'n Betekenisvolle afname in serum 19E en Ascaris spesifieke 19E vlakke is waargeneem na vohooing van tuberkulose behandeling. Die afregulering van 19E vlakke kan moontlik toegeskryf word aan die opregulering van Th1 response in pasi"ente na voltooing van suksesvolle behandeling van tuberkulose.

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