Les infections respiratoires et plus particulièrement la pneumonie représentent la première cause de mortalité infantile dans le monde. L’essor des technologies de diagnostic moléculaire a permis de mettre en évidence une étiologie très hétérogène des infections respiratoires ainsi qu’un taux élevé de co-infection virale et bactérienne dont l’impact clinique reste difficile à évaluer. La recherche translationnelle menée au cours de ce projet de thèse avait pour objectif de décrire l’étiologie des infections respiratoires ainsi que l’impact des co-infections sur la modulation de la réponse immunitaire innée. Nous avons développé un modèle d’étude in-vitro d’infection successive de cellules présentatrice d’antigènes (CPA) humaines par le virus Influenza (IAV) et Streptococcus pneumoniae (SP) et étudié la modulation de la réponse inflammatoire. Les résultats obtenus démontrent que la co-infection des CPA par ces deux pathogènes majeurs de la pneumonie impacte fortement sur leur viabilité et induit une dérégulation importante de la réponse inflammatoire. Au cours de la co-infection, la chémokine pro-inflammatoire IP-10 est exprimée de manière synergique suggérant un rôle jusqu’à présent non décrit de cette chémokine dans la pathogénèse de la pneumonie. Nous avons également démontré que les micro-ARNs (dont le miR-200a-3p) participent activement à la régulation de la réponse inflammatoire, en ciblant des régulateurs de la voie de signalisation JAK-STAT (SOCS-6) et indirectement la voie de synthèse d’IP-10. Récemment, nous avons évalué la réponse inflammatoire d’enfants âgés de moins de 5 ans hospitalisés pour une pneumonie, en partenariat avec les équipes médicales et scientifiques du Paraguay via le réseau GABRIEL. Ce volet d’étude confirme 1) une étiologie variée de la pneumonie chez l’enfant et 2) un taux d’IP-10 sérique significativement plus élevé chez les enfants co-infectés et présentant une pneumonie très sévère. / Respiratory infections, especially pneumonia are the leading cause of death among children under 5 years-old worldwide. Advances in molecular diagnostic have highlighted heterogeneous etiologies of respiratory infections with a high proportion of viral and bacterial co-infections whose clinical impact remain difficult to assess. The translational research conducted during this thesis aimed to describe the etiology of respiratory infections and the impact of viral and bacterial co-infections on the innate immunity.We have developed an in-vitro study model of sequential infection of antigen presenting cells (APC) by the human influenza virus and Streptococcus pneumoniae and studied the modulation of the inflammatory response. The results show that APC co-infection by those two major pathogens of pneumonia strongly impacts cells viability and induces a significant deregulation of the inflammatory response. During co-infection, pro-inflammatory chemokine IP-10 is synergistically expressed suggesting a role so far undescribed for this chemokine in the pathogenesis of pneumonia. We also demonstrated that micro-RNAs (including miR-200a-3p) actively participate in the regulation of the inflammatory response by targeting the signaling pathway regulators JAK-STAT (SOCS-6) and indirectly IP-10 signalling pathway.Recently, we evaluated the inflammatory response of children aged under 5 hospitalized for pneumonia, in partnership with medical and scientific teams of Paraguay involved in the GABRIEL network. This study confirmed 1) a varied etiology of childhood pneumonia and 2) a significant elevated IP-10 serum level among children with very severe pneumonia caused by mixed viral and bacterial co-infections.

Les deux formes d'inflammation pulmonaire en réanimation sont la pneumonie et le syndrome de détresse respiratoire aiguë (SDRA). Nous avons conçu un test diagnostique rapide basé sur l'autofluorescence des neutrophiles alvéolaires. S'appuyant sur une étude expérimentale, puis sur une étude clinique randomisée, nous avons montré que les sondes d'intubation avec ballonnets coniques diminuaient les micro-inhalations sans prévenir l'incidence des pneumonies post-opératoire. Une grande variabilité des pressions des ballonnets coniques pose la question de leur effet délétère. La thérapie cellulaire basée sur les cellules souches mésenchymateuses (CSM) est prometteuse. L'étude des effets thérapeutiques des vésicules extracellulaires issues de CSM (VE-CSM) constitue un nouvel axe de recherche. Dans 2 modèles murins de SDRA, puis dans un modèle de poumons humains ex vivo, nous avons démontré des effets thérapeutiques des VE-CSM. Nous avons ensuite étudié les lymphocytes T régulateurs (Treg) pulmonaires et systémiques dans le SDRA. Cette étude a montré un déficit quantitatif plutôt que fonctionnel de la population Treg pulmonaire dans le SDRA, avec une cinétique évoquant un recrutement des Treg circulants vers le compartiment pulmonaire au cours de la maladie. En conclusion, nos travaux ont développé de nouvelles stratégies diagnostiques et préventives des pneumonies de réanimation, afin de réduire leur impact en termes de morbi-mortalité. Les bénéfices thérapeutiques des CSM et des VE-CSM dans le SDRA expérimental, ainsi que l'altération du phénotype Treg observé chez nos patients, ouvrent de nouveaux champs de recherche vers le développement d'immunothérapies innovantes. / Pneumonia and acute respiratory distress syndrome (ARDS) are two facets of severe acute lunginflammation, often met in intensive care unit (ICU). Rapid diagnosis of pneumonia remains essential inorder to optimize their management. We worked on setting up a quick test diagnosis based on theintensity of alveolar neutrophils autofluorescence. The validation of this test in a multicenter cohort isunderway. Preventing microaspiration across the cuff remains a priority to prevent pneumonia inmechanically ventilated patients. Based on the results of an ex vivo study followed by a clinicalrandomized trial, we showed that tapered-cuff endotracheal tube prevented microaspiration in the exvivo model, without lowering intraoperative microaspirations and postoperative pneumonia rate aftermajor vascular surgery. Both studies yielded similar results concerning the higher variation of cuffpressureover time, which leads to the question of their safety of use in terms of potential resultingtracheal wall ischemia.Pneumonia represents 80% of the cause of ARDS, which can be viewed as lung uncontrolledinflammatory response. Cell-based therapy using mesenchymal stem cells (MSC) is a growing field ofresearch in ARDS therapy. Despite numerous beneficial effects in ARDS, their capacity of self-renewalpoints them out as a potential cancer inducer in the mid-long term. In this context, evaluating thetherapeutic effects of extracellular vesicles-released from MSC (EV-MSC) represents a novel approach.We showed therapeutic effects of EC-CSM in two murine model of ARDS induced by endotoxin or liveEscherichia coli bacteria, and in another ex vivo human lung preparation.We then focused our research on temporal and compartmental dynamics of regulatory T cells(Treg) phenotypes in ARDS patients. This prospective observational clinical study showed that Early ARDSwas characterized with an alveolar compartment fully polarized towards pro-inflammatory state andneutrophils chemotaxis. In lung compartment, and compared to control patients, ARDS patients showeda quantitative Tregs deficiency, which partially recovered over time, while activation markers wereoverexpressed in both Tregs and effectors T cells (Teff). Conversely, patients with ARDS had a higherproportion of systemic Tregs compared to controls. Significant increased proportion in circulating Th1,Th22, and ILC1 subsets, and decreased proportion in ILC3 subsets were also found in ARDS patientscompared to controls.In conclusion, we developed novel strategies to diagnose and prevent pneumonia in ICU, whichremains essential to improve patients’ outcomes. Therapeutic effects of MSC and EV-MSC, as well asTreg phenotype alterations pave the way for development of novel immunoregulatory therapies.

La grippe est une infection respiratoire aiguë, due au virus Influenza, qui touche en moyenne chaque hiver 2,5 millions de personnes. C'est un enjeu de santé publique majeur par son impact économique et en santé humaine. Les traitements actuellement disponibles contre le virus Influenza repose sur des antiviraux ciblant la neuraminidase (inhibiteur de la neuraminidase). Jusqu'en 2007 moins de 5% des souches de virus Influenza circulantes dans le monde étaient résistantes à ces INA. Contre toute attente, l'hiver 2007/2008 a été marqué par l'émergence simultanée d'une nouvelle souche apparentée au virus A/Brisbane/59/2007(H1N1) et d'une augmentation massives des résistances à l'Oseltamivir. Nous avons caractérisés les propriétés enzymatiques des souches sensibles et résistantes isolées dans la communauté au cours des saisons 2007/2008, 2008/2009 pour les comparer à un panel de souches de référence des virus A(H1N1). Les résultats obtenus soulignent la particularité des propriétés enzymatiques de la NA de A/Brisbane/59/2007(H1N1) et le rôle de la balance HA-NA dans la diffusion mondiale de cette souche résistante en l'absence de pression de sélection La pandémie de 2009 au virus A(H1N1)pdm09 a été l'occasion de décrire le rôle de l'infection respiratoire basse, virale isolée ou dans le cadre d'une co-infection bactérienne, dans les patients décédés d'un syndrome de détresse respiratoire. La forte proportion de pneumonies virales observées dans les études épidémiologiques réalisées au cours de la pandémie de 2009/2010 et de la saison 2010/2011 suggère la présence de facteurs de virulence permettant au virus A(H1N1)pdm09 de se lier aux récepteurs présents au niveau de l'appareil respiratoire bas. Nous avons étudié l'impact du polymorphisme en position 222 de la HA du virus A(H1N1)pdm09 sur les propriétés de liaison de la HA à son récepteur, sur la balance HA-NA et, in fine, sur le phénotype des virus in vitro et in vivo. Nos résultats montrent que les substitutions D222G, D222E et D222N de la HA du virus A(H1N1)pdm09 favorisent la liaison aux acides sialiques présents au niveau de l'alvéole pulmonaire. Cette propriété pourrait expliquer la plus forte pathogénicité pulmonaire de ce virus. Par ailleurs nos résultats montrent également une association entre l'équilibre de la balance HA-NA et le profil de réplication de ces souches in vitro / Influenza is responsible of 2,5 million cased of respiratory infection, each winter, in France. It is a main human health threat and a main public health concern. The current treatment of flu relies on antiviral drug targeting viral proteins that can induce the appearance of resistant virus. Until 2007, less than 5% of all circulating Influenza strains were resistant to neuraminidase inhibitors. Against all odds, Oseltamivir resistant A/Brisbane/59/2007(H1N1) emerged and spread during 2007/2008 and 2008/2009 season. To understand the driving force of this emergence we tested clinical strains from 2007 to 2011 for Oseltamivir and Zanamivir resistance, sequenced their HA and NA gene, and compared their NA enzymatic properties with A(H1N1) reference strain from 1977 to 2007. Our results showed that A/Brisbane/59/2007 displayed a high affinity compare with NA of previous A(H1N1) reference strains. Moreover these results suggested that HA-NA balance underlie the worldwide emergence of the Oseltamivir resistance without any selection pressure. The A(H1N1)pdm09 pandemic highlighted the importance of lower tract respiratory infection in the severe influenza case. The high proportion of viral pneumonia observed during the 2009 pandemic and the following season suggest that A(H1N1)pdm harbored a virulence factor that allowed the virus replication in the lower respiratory tracts. We studied the effect of HA 222 polymorphism on HA properties, HA-NA balance and in vitro and in vivo Influenza phenotype. Our results demonstrated that G222, E222 or N222 HA mutation increased the binding of A(H1N1)pdm09 mutation to the lower respiratory tract receptor. This may explain the A(H1N1)pdm09 increase pathogenicity. Moreover our results show than an optimal HA-NA balance is link to an efficient replication profile in vitro

L'émergence de bactéries résistantes à plusieurs classes d'antibiotiques rend difficile le traitement des pneumonies nosocomiales. Notre objectif était d'évaluer de nouvelles stratégies thérapeutiques et hypothèses physiopathologiques dans des modèles murins de pneumonie.Dans un premier modèle de pneumonie aigue létale à A. baumannii chez le rat, nous avons comparé la virulence de 2 souches nosocomiales, l'une sensible (ABCS) et l'autre résistante (ABCR) à la colistine. Nous avons montré une diminution de la mortalité, du compte bactérien pulmonaire, de l'incidence des bactériémies et des lésions histologiques pulmonaires chez les animaux infectés avec ABCR, ceci confirmant la baisse de virulence associée à l'acquisition de la résistance à la colistine. Dans un second travail, nous avons développé un modèle de pneumonie chronique à P. aeruginosa chez le rat et montré que des aérosols de squalamine permettaient une diminution de la charge bactérienne pulmonaire et du nombre de lésions histologiques de pneumonie. Au cours d'un troisième travail, nous avons évalué l'effet inhibiteur du quorum sensing d'une lactonase in vitro et dans un modèle de pneumonie aigue létale à P. aeruginosa chez le rat. Nous avons constaté une diminution de l'activation de gènes de virulence et de la synthèse de biofilm bactérien in vitro. Ceci était associé à une diminution de la mortalité de 75 à 20 % chez les animaux traités.ConclusionsCe travail de thèse nous a permis de montrer le potentiel thérapeutique de 2 molécules dans des pneumonies à P. aeruginosa et d'illustrer la perte de virulence associée à la résistance à la colistine dans une souche clinique d'A. baumannii. / The emergence multi-drug resistant bacteria hardens the treatment of nosocomial pneumonia. Our objective was to evaluate new therapeutic strategies and pathophysiological hypotheses in murine models of pneumonia.In a first model of acute lethal pneumonia with A. baumannii in rats, we compared the virulence of two hospital strains, one susceptible (ABCS) and the other resistant (ABCR) to colistin. We showed a reduction in mortality, pulmonary bacterial count, incidence of bacteremia and pulmonary histological lesions in animals infected with ABCR. This confirms the impaired virulence associated with the acquisition of resistance to colistin. In a second study, we developed a model of chronic pneumonia with P. aeruginosa in rats and showed thataerosols of squalamine permitted a reduction in pulmonary bacterial load and the number of histological lesions of pneumonia. In a third study, we evaluated the quorum quenching effects of a lactonase in vitro and in a model of acute lethal P. aeruginosa pneumonia in rats. We found a decrease in virulence gene activation and bacterial biofilm synthesis in vitro. This was associated with a decreased mortality from 75 to 20% in the treated animals.ConclusionsIn this work, we described the therapeutic potential of 2 molecules in P. aeruginosa pneumonia and illustratesd the loss of virulence associated with resistance to colistin in a clinical strain of A. baumannii.

Streptococcus pneumoniae é o principal causador da pneumonia bacteriana. As vacinas atualmente disponíveis contêm polissacarídeo capsular conjugado ou não com proteínas carreadoras. No entanto, elas apresentam elevado custo ou proteção reduzida nos grupos de risco (crianças abaixo de 5 anos de idade e idosos). Proteínas de superfície de S. pneumoniae, como a PsaA e PspA, são consideradas fortes candidatas vacinais. Com o objetivo de se desenvolver uma vacina de ampla cobertura e baixo custo contra pneumococos, os genes psaA e pspA foram clonados em vetores de expressão em E. coli, pAE e pET e as proteínas expressas foram purificadas por cromatografias de afinidade e de troca aniônica. O rendimento de proteína recombinante obtido com a construção baseada em pET foi 3 vezes maior que o obtido com pAE. Condições de cultivo foram estabelecidas utilizando meio definido com indução por IPTG e/ou por lactose. As cepas recombinantes estão adequadas para serem usadas em estudos para escalonamento da produção em biorreatores. / Streptococcus pneumoniae is the main causative agent of bacterial pneumonia. The current vaccines available contain capsular polysaccharide conjugated or not with carrier proteins. However these are either too expensive or do not protect the high-risk groups. Surface proteins of S. pneumoniae, such as PsaA and PspA, are considered strong vaccine candidates. With the aim of developing a broad-coverage and low-cost vaccine against pneumococcus, the psaA and pspA genes were cloned in E. coli expression vectors, pAE and pET and the expressed proteins were purified through affinity and anion exchange chromatography. The yield of the recombinant protein obtained with the construction based in pET was 3-fold higher than that obtained with pAE. Culture conditions were established using defined media with IPTG and/or lactose induction. The recombinant strains are now ready to undergo studies for scale-up of production in bioreactors.

Ziel dieser Publikation soll es sein, der/m Behandler/in fundiertes Grundwissen bzgl. des Ölziehens zu vermitteln. Darüber hinaus wird die aktuelle Studienlage dargestellt, es werden Trends aufgezeigt und das Risiko der Lipidpneumonie erläutert. Die Autoren kommen zu dem Ergebnis, dass es derzeit geringe Evidenz für einen positiven Nutzen des Ölziehens gibt, sodass weiterführende Studien auf diesem Gebiet notwendig sind. Über das sehr geringe Risiko einer Lipidpneumonie bei nicht korrekter Anwendung sollten die Patientinnen und Patienten aufgeklärt werden. / This publication should provide the practitioner with sound basic knowledge about oil pulling. In addition, the authors present the current study situation, show trends and explain the risk of lipoid pneumonia. The limited evidence to date from clinical trials suggest that oil pulling may have beneficial effects, therefore more studies are necessary to prove beneficial effects on orodental hygiene. Furthermore, patients should be informed about the risk of lipoid pneumonia if used incorrectly.

Introducción: La neumonía es la principal causa de muerte en niños menores de 5 años a nivel global y el 90% de sus casos se registran en países en vías de desarrollo. Determinar los factores asociados (FA) a casos severos (CS) y casos fatales (CF) de neumonía adquirida en la comunidad (NAC) en niños menores de cinco años atendidos en el INSN entre los años 2013-2015 en lima Perú. Materiales y Métodos: Se realizó un estudio observacional, retrospectivo, analítico de casos y controles en pacientes atendidos en el INSN entre los años 2013 al 2015; el estudio se dividió en 2 sub-estudios, para determinar los factores asociados a casos fatales tenemos el denominado sub-estudio “A” y el denominado sub-estudio “B” para determinar los factores asociados a casos severos. Resultados: Los factores asociados a casos fatales en niños entre 1 a 59 meses con NAC atendidos en el INSN fueron: Tener una edad entre 1 a 5 meses (ORa=3.61, IC: 1.1-11.76), desnutrición aguda (ORa=3.74, IC: 1.1-12.63), tener consolidado multilobar (ORa=3.1, IC: 1.006-9.5) y tener consolidado en parche (ORa=0.17, IC: 0.057-0.5). Los factores asociados a casos severos fueron: Tener una edad entre 1 a 5 meses (ORa=0.28, IC: 0.18-0.55), ser pretérmino (ORa= 0.36, IC: 0.17-0.77), tener diarrea (ORa=0.36, IC: 0.15-0.87), que el cuidador tenga como grado de instrucción la secundaria (ORa= 2.43, IC: 1.36-4.35), negarse a comer (ORa= 3.84, IC: 1.14-12.84) y tener asma (ORa=10.66, IC: 1.11-102.3). Conclusiones: Los factores asociados a mortalidad identificados son: edad entre 1 a 5 meses, tener desnutrición aguda, tener consolidado multilobar. Los factores de riesgo para severidad son: grado de instrucción del cuidador secundaria, negarse a comer y tener asma. / Introduction: Pneumonia is the leading cause of death in children under 5 years of age globally and 90% of its cases are registered in developing countries. To determine the factors associated (AF) to severe cases (SC) and fatal cases (CF) of community-acquired pneumonia (CAP) in children under five years of age treated at the INSN between the years 2013-2015 in Lima, Peru. Materials and Methods: An observational, retrospective, analytical case-control study was carried out in patients treated at the INSN between 2013 and 2015; The study was divided into 2 sub-studies, to determine the factors associated with fatal cases we have the so-called “A” sub-study and the so-called “B” sub-study to determine the factors associated with severe cases. Results: The factors associated with fatal cases in children between 1 to 59 months with CAP treated at the INSN were: Being between 1 to 5 months old (ORa = 3.61, CI: 1.1-11.76), acute malnutrition (ORa = 3.74, CI: 1.1-12.63), have multilobar consolidated (ORa = 3.1, CI: 1.006-9.5) and have consolidated in patch (ORa = 0.17, CI: 0.057-0.5). The factors associated with severe cases were: Being between 1 and 5 months old (ORa = 0.28, CI: 0.18-0.55), being preterm (ORa = 0.36, CI: 0.17-0.77), having diarrhea (ORa = 0.36, CI : 0.15-0.87), that the caregiver has a secondary education grade (ORa = 2.43, IC: 1.36-4.35), refuse to eat (ORa = 3.84, IC: 1.14-12.84) and have asthma (ORa = 10.66, IC: 1.11-102.3). Conclusions: The factors associated with mortality identified are: age between 1 to 5 months, having acute malnutrition, having consolidated multilobar. Risk factors for severity are: secondary caregiver education level, refusal to eat, and asthma. / Tesis

ortalidad en niños menores de 5 años, a pesar de contar con medidas preventivas como la vacunación.  Objetivo: Evaluar el impacto de la vacuna antineumocócica conjugada sobre la incidencia de neumonía en niños menores de 5 años, a nivel nacional y departamental, así como las hospitalizaciones y mortalidad a nivel nacional, desde 2001-2019 en el Perú. Además, realizar un análisis entre departamentos con coberturas altas de vacunación y aquellos que alcanzan coberturas bajas.  Metodología: Diseño: Series de tiempo definidas por la introducción de la vacuna antineumocócica heptavalente (PCV7) en el periodo de tiempo entre 2009 y 2011 a nivel nacional y departamental. Posteriormente, se realizó un análisis multivariado contrastando la incidencia de casos entre los departamentos con alta y baja cobertura de vacunación. Procedimiento de obtención de datos: Los datos agrupados sobre la incidencia, hospitalización y mortalidad por neumonía fue obtenida de la CDC (Centro de Enfermedades Contagiosas); la cobertura de vacunación fue obtenida como base de datos del Ministerio de Salud (MINSA) Análisis específicos: se realizó un análisis multivariado contrastando la incidencia de casos de neumonía entre los departamentos con alta y baja cobertura de vacunación.  Resultados: Para las hospitalizaciones a nivel nacional, la tendencia de cambio post vacunación fue negativa y significativa (p <0.001). La incidencia y mortalidad tuvieron cambios no significativos. A nivel regional, Callao, Lima, Moquegua, Cusco, Huancavelica, Pasco, Loreto, San Martín y Ucayali tuvieron tendencia de cambio post vacunación negativa y significativa (p <0.001). Conclusiones: La vacunación ha demostrado ser efectiva para disminuir hospitalizaciones por neumonía en algunos departamentos y a nivel nacional. Sin embargo, existen factores individuales que pueden alterar la efectividad de la intervención, propias de la estrategia aplicada y del tipo de estudio utilizado. / Introduction: Pneumonia is an acute respiratory infection, the most common bacterial cause is Streptococcus pneumoniae and represents one of the major causes of mortality in children under 5 years of age, despite preventive measures. Objective: Assess the impact of the pneumococcal vaccine on the incidence of pneumonia in children under 5 years of age, at the national and departmental level, as well as hospitalizations and mortality at the national range, over 2001-2019 in Peru. In addition, perform an analysis between departments that achieve high vaccination coverage and those with low coverage.  Methodology: Study design: Time series interrupted by the inclusion of the heptavalent pneumococcal vaccine (PCV7) in the period between 2009 and 2011 at the national and departmental level. Multivariate analysis, contrasting the incidence of cases between departments with high and low vaccination coverage. Data collection procedure: Pooled data on pneumonia incidence, hospitalization, and mortality obtained from the CDC (Center for Communicable Diseases); vaccination coverage obtained as a database from the Ministry of Health (MINSA) Specific analyzes: multivariate contrasting the incidence of pneumonia cases between departments with high and low vaccination coverage. Results: Hospitalizations at the national level had a negative trend of change after vaccination (p <0.001). At regional level, Callao, Lima, Moquegua, Cusco, Huancavelica, Pasco, Loreto, San Martín and Ucayali had a negative and significant change trend post vaccination (p <0.001). Conclusions: Vaccination has proven to be effective in some departments and at the national level. However, there are individual factors and limitations of the study that may affect the outcome. / Tesis

Philosophiae Doctor - PhD / In the decade since first identified, the Acquired Immunodeficiency syndrome (AIDS) has become a serious global disease. The nature of the Human Immunodeficiency Virus (HIV) that causes AIDS, whereby a carrier may be asymptomatic yet remain infectious, has enabled its dramatic spread. The number of AIDS cases is increasing exponentially, averaging a doubling time of between 8-15 months in different countries. Of the millions of HIV carriers, it is now estimated that all will eventually go on to develop full-blown AIDS and probably die within 15 years. Unlike other infectiqus diseases, there is currently no known vaccine or cure. Further, HIV is now virtually completely dependent on volitional sexual behaviours for transmission to occur. It is therefore an entirely preventable disease. However, since the behaviours that contribute to HIV-transmission are influenced by biological, psychological, and social factors, their alteration in line with safer sexual practices has been shown to be considerably complex and difficult. Intervention strategies that have relied on imparting knowledge about the disease have achieved limited success in influencing behaviour change. Unsafe sexual practices, and the risk of HIV-infection, often continue even when knowledge regarding prevention is adequate. It has therefore become apparent that other variables intrude which may mediate between knowledge acquisition, attitude formation, and consequent sexual behaviours. There appear to be no models which adequately explain the complexities in this area, and which enable adequate intervention strategies to be developed. The present study was undertaken to redress this problem, and to explore those variables that mediate in the area. Various psychological and social factors appear to be implicated in influencing sexual attitudes and behaviours. In order to adequately test the impact of psychosocial variables that were found to have significant associations in an exploratory study, a measuring instrument was developed. The AIDS Psychosocial Scale was statistically validated using content, frequency, factor, and reliability analyses and included psychological factors of self concept, defenses of denial, repression, and rationalisation, perceived empowerment in the form of locus of control and selfefficacy, and the social factor of peer pressure susceptibility. The impact of these psychosocial variables on indices of knowledge, condom attitude, and sexual practices, and on other epidemiological variables was tested using a sample of students at the University of the Western Cape (n=308). Results indicated a number of correlational and causal links between variables, confirming the mediational role psychosocial factors have in influencing knowledge acquisition, attitude formation, and behaviour outcome. A profile of lower self concept, higher defenses, lower self-efficacy, more external locus of control, and higher peer pressure susceptibility emerged which was associated with poorer knowledge, more negative attitudes, and higher unsafe sex. Based on this study, a model of psychosocial mediation is developed and its implications for intervention strategies discussed.

Inflammaging is a hallmark of human aging. Defined as low-grade, chronic inflammation, it is characterized by heightened proinflammatory cytokines in the blood and tissues and predicts morbidity and mortality. Despite this, the etiology of inflammaging and its role in infection have remained elusive, an issue this thesis addressed. First, we provided a comprehensive overview of an intranasal Streptococcus pneumoniae colonization model (Chapter 2). We described in detail the colonization technique, and demonstrated how to isolate and phenotype recruited cells, quantify bacterial load and measure production of immune mediators in the nasopharynx. Since both myeloid cell recruitment and tumour necrosis factor (TNF) production were increased following S. pneumoniae colonization with age, we investigated whether TNF directly augmented monocyte frequency (Chapter 3). TNF increased CCR2 expression on monocytes in old mice, leading to their enhanced egress from the bone marrow, resulting in enrichment of this population in the circulation. Monocyte numbers directly influenced plasma IL-6 levels, and this negatively impacted anti-bacterial responses, as monocyte blockade improved pneumococcal clearance in old mice. Lastly, to better understand the fundamental source of inflammaging, we studied the impact of the host microbiome on its development. This work was rooted in Elie Metchnikoff’s early predictions that leakage of intestinal bacterial products could dysregulate macrophage function, resulting in inflammation that would progress aging (Chapter 4). We showed that old mice had increased intestinal permeability, aberrant expression of cellular junction genes and increased microbial translocation from the gut to the blood. Germ-free mice lived longer than their conventionally colonized counterparts, and were protected from the development of inflammaging and defective macrophage function. Together, these studies resolve a major disparity in the field by demonstrating that systemic TNF production is initiated by increased levels of circulating bacterial products, driving functional defects in myeloid cells, which ultimately impairs anti-bacterial immunity. / Thesis / Candidate in Philosophy