Thesis (MScMedSc)--Stellenbosch University, 2012. / Includes bibliography / ENGLISH ABSTRACT: Infection is a major cause of morbidity and mortality in infants within the first few months of life. Susceptibility to infectious disease in this vulnerable population is more prevalent in resource-limited regions, with a higher disease burden. Due to certain deficiencies in their adaptive immune system, neonates rely predominantly on their innate immune system for protection against infection, a vital component in the early host defence against pathogens. Several studies have described differences in neonatal innate toll-like receptor-mediated responses compared to adult counterparts, though very little is known about these receptor responses within resource-limited settings. To address this issue, we assessed the longitudinal development of cytokine-specific responses of TLR4 and TLR7/8 in monocytes, myeloid dendritic cells and plasmacytoid dendritic cells in infants from a resource-limited setting, South Africa, within the first 12 months of life and compared it to adults. Contrary to previously published literature, we observed heightened production of TH-1 cytokines: we showed increased responsiveness to TLR4 and TLR7/8 stimulation in infants at two and six weeks of age, which may be due to vaccination administered at birth. Unexpectedly, the hyper-inflammatory response persisted at six months in response to the LPS (TLR4) stimulus. This increased response at six months may be attributed to decreased passive immunity through infant weaning as well as increased exposure to microbial pathogens in this setting. Maturation of most cytokine responses was reached at twelve months for the TLR4 receptor, and at six months for the TLR7/8 receptor. The first year of life represents a critical period for maturation of the immune response. Data from this study point towards an elevated response within the first six months of life. This heightened response reflects both an ability to mount a sufficient TH-1 response in infancy, but more likely, the increased exposure to microbial stimuli in the environment. Thus, we speculate that these age-specific inflammatory responses may influence the outcome of immune responses to various vaccines administered, which may result in altered responsiveness to immunisation in infancy. / AFRIKAANSE OPSOMMING: Die hoof oorsaak vir morbiditeit en mortaliteit in babas binne die eerste paar maande van hul lewe word toegeskryf aan infeksie. In hulpbron beperkte gebiede, gekenmerk deur `n groter siektelas, is daar `n verhoogde vatbaarheid vir infeksie in hierdie kwesbare populasie. As gevolg van sekere gebreke in die verworwe immuunstelsel, maak pasgebore babas hoofsaaklik staat op hul aangebore immuunstelsel vir beskerming teen infeksie, ’n belangrike komponent vir die vroeë verdediging teen patogene. Verskeie studies het al die verskille in toll-tipe reseptor (TTR) bemiddelde reaksies tussen pasgebore babas en volwassenes vergelyk, maar nie veel is bekend oor hierdie reaksies in areas waar hulpbronne beperk is nie. Om hierdie kwessie aan te spreek is die longitudinale ontwikkeling van sitokien-spesifieke reaksies van die TTR4 en TTR7/8 reseptore van monosiete, miëloïede en plasmasitoïede dendritiese selle van babas in die hulpborn beperkte land Suid-Afrika, oor die eerste 12 maande geëvalueer en dit vergelyk met volwassenes. In teenstelling met vorige literatuur, het hierdie studie ’n polarisasie tot TH-1-sitokien produksie gevind: verhoogde reaktiwiteit van die TTR4 en TTR7/8 is gevind in babas van twee en ses weke oud, wat gedeeltelik as gevolg van die inenting kan wees wat toegedien was na geboorte. Hierdie hiper-inflammatoriese reaksie teen die TTR4 stimulus (Lipopolisakkaried (LPS), het teen verwagting voortgeduur tot op ses maande en kan toegeskryf word aan die vermindering van passiewe immuniteit deur spening, sowel as die toenemende blootstelling aan mikrobiese patogene in die omgewing. Maturasie vir die meerderheid van die sitokiene reaksies, is bereik op 12 maande vir TTR4, en op ses maande vir TTR7/8. Die eerste lewensjaar is ‘n kritiese periode vir die ontwikkeling van die immuunstelsel. Data van hierdie studie dui op ‘n verhoogde reaksie binne die eerste ses maande van ‘n baba se lewe. Hierdie verhoogde reaksie dui op die vermoë om `n voldoende TH-1 reaksie te ontlok, maar meer waarskynlik, verhoogde blootstelling aan mikrobiese stimuli in die omgewing. Dus spekuleer ons dat hierdie ouderdom-spesifieke reaksies dalk die uitkoms van die immuunreaksie teen verskeie entstof toediening kan beïnvloed in babas.