Dissertations / Theses on the topic 'Immunology'

More than a century after the identification of the tubercle bacillus and the first attempts at vaccination, tuberculosis (TB) still remains one of the world’s most serious infectious diseases. TB, caused by the bacterium Mycobacterium tuberculosis, is typically a disease of the lung, which serves both as port of entry and as the major site of disease manifestation. The currently used vaccine, BCG, is administered parenterally and induces a systemic immune response. However, it fails to protect against pulmonary TB, thereby raising the question whether vaccination targeting the mucosal immunity in the lungs could be favourable.

The respiratory mucosal surfaces represent the first line of defence against a multitude of pathogens. Secretory IgA, in mucosal secretions has an important function by blocking entrance of pathogenic organisms and preventing infections. Additionally, a role for IgA in modulation of immune responses is currently being revealed. In this work, we investigated the relevance of mucosal IgA in protection against mycobacterial infections using mice deficient for IgA and the polymeric Ig receptor, the receptor responsible for mucosal secretions of IgA. Gene-targeted mice were more susceptible to mycobacterial infections in the respiratory tract and displayed reduced production of proinflammatory, and protective, factors such as IFN-γ and TNF-α in the lungs. The mechanisms explaining the defective proinflammatory responses in the lungs of deficient mice might involve impaired signalling through Fcα receptors, or homologous receptors, which could lead to inadequate activation of pulmonary macrophages. This could subsequently result in suboptimal induction and production of cytokines and chemokines important for attraction and migration of immune cells to the site of infection.

Induction of optimal adaptive immune responses to combat mycobacterial infections requires prompt innate immune activation. Toll-like receptors (TLRs) are vital components of the innate branch of the immune system, ensuring early recognition of invading pathogens. Using TLR-deficient mice we demonstrated an important role for TLR2, and partly TLR4, in protection against mycobacterial infection in the respiratory tract. TLR2-deficient mice failed to induce proper proinflammatory responses at the site of infection, and macrophages derived from the knockout mice displayed impaired anti-mycobacterial activity.

Experimental evidence has concluded that the immune response upon an infection can influence the outcome of succeeding infections with other pathogens. Concurrent infections might additionally interfere with responses to vaccinations and have deleterious effects. We developed an in vitro model to study the effect of a malaria infection on a successive M. tuberculosis infection. Our results demonstrate that a malaria blood-stage infection enhances the innate immune response to a subsequent M. tuberculosis infection with a Th1 prone profile. Reduced infectivity of malaria-exposed dendritic cells implies that a malaria infection could impose relative resistance to ensuing M. tuberculosis infection. However, a prolonged Th1 response may interfere with malaria parasite control.

The outcome of this work emphasizes the importance of generating effective immune responses in the local mucosal environment upon respiratory mycobacterial infections. It furthermore puts new light on the immunological interaction between parasites and mycobacteria, which could have implications for future vaccine research.

Today, atopic allergy is the most common chronic disease among children in the developed world. The increase in allergy prevalence during the past decades in these countries might be associated with lower microbial exposure. The gut flora, consisting of approximately 800 different species of bacteria, has been postulated to be important for the development of a fully functional immune system. Essentially, these bacteria are in constant contact with the gut flora associated lymphoid tissue, the largest lymphoid tissue of the human body. Following birth, the sterile gut of the newborn is immediately colonised by various bacterial species. Actually, alterations in the infant gut flora have been associated with allergy development.

Human milk is the major food in infancy and could thus influence the composition of the infant gut flora. Immunomodulatory components in human milk might differ between mothers and could therefore explain the contradictory results seen regarding breastfeeding and allergy development. Oligosaccharides, the third most abundant solid component in human milk, survive the passage through the stomach and are utilised by the gut microbiota. We analysed nine abundant neutral oligosaccharides in colostrum samples from allergic and non-allergic women and related to subsequent allergy development in their children. We found a considerable variation in the concentration of neutral oligosaccharides in colostrum, which was not to be explained by the allergic status of the women. Neither was the consumption of neutral colostrum oligosaccharides related to the allergy development in children.

Relevant bacterial species in early faecal samples were analysed, with Real-time PCR, and related to allergy development in children followed up to five years of age. Infants who harboured Lactobacilli (L.) group I (L. rhamnosus, L. paracasei, L. casei) at 1 week of age and Bifidobacterium adolescentis at 1 month of age developed allergic disease less frequently during their first five years than infants who did not harbour these bacteria at the same time (p=0.004 and p=0.008 respectively).

In conclusion, the work presented in this thesis implies the importance of a diverse gut flora early in life for the development of a fully functional immune system. However, consumption of colostrum with high amounts of neutral oligosaccharides does not protect against early allergy development.

Onchocerciasis, or river blindness, is a parasitic disease that affects more than 20 million people globally. The induction of pathology is directly related to the presence and destruction of the microfilarial stages (mf) of this filarial nematode. The disease presents clinically with a wide spectrum of dermal and ocular manifestations, the basis of the variation is believed to involve the immune system. The clinical presentations of infected hosts relate to the intensity of the reactions against the parasite. Anti-microfilarial drugs are also thought to somehow involve the immune system in their pharmacological action. In this study we have investigated some of the factors that might contribute to the pathogenesis, with the aim of gaining a better understanding of the role of immune response in these host inflammatory reactions to Onchocerca volvulus parasite. In the first study we have highlighted the clinically most severe form of dermal onchocerciasis, known as reactive onchocercal dermatitis (ROD), one that is often ignored and has not been properly identified. This form has special characteristics and important biological information that could greatly assist the general understanding of the disease as a whole. Amongst the three major foci of the disease in the study country, Sudan, the prevalence of ROD was found to be associated with different environmental and epidemiological characteristics; strikingly higher in the hypo-endemic areas. Including ROD cases in the prevalence will upgrade the level of endemicity of a locality, and often bring patients much in need of treatment into mass treatment programs that currently only treat localities with medium to high levels of endemicity. In the following research studies, we tried to address the immunological characteristics of the clinically different onchocerciasis patients. Then we also investigated the role of genetic polymorphism in the gene encoding receptor that links innate and adaptive immunity, namely, FcγRIIa.

Patients with either of two major forms of the clinical spectrum-mild and severe dermatopathology were studied by assaying the antigen-driven proliferation of peripheral blood mononuclear cells and the ability of patients’ serum antibodies to promote cytoadherence activity to mf in vitro. Immune responses of those with severe skin disease were found to be stronger compared with the mild dermatopathology group. Mectizan® treatment was followed by an increase in immune responsiveness in those with initially poor responses. Thus the degree of dermatopathology is related to the host’s immune response against mf and immunocompetence may be necessary for Mectizan® to clear the infection efficiently.

The infection has also been associated with increased levels of circulating immune complexes (CIC) containing parasite antigens and a cytokine response that involves both pro-and anti-inflammatory cytokines. Our fourth paper investigated the effect of IC from the O. volvulus infected patients on the production of pro-and anti-inflammatory cytokines. CIC were increased in all patients studied. The precipitate from plasma treated with polyethylene glycol (PEG) were added to peripheral blood mononuclear cell (PBMC) cultures, and the levels of IL-10, tumor necrosis factor TNF-α, IL-1β and their endogenous antagonists soluble TNF-Rp75 and IL-1-receptor antagonist (IL-1ra) were measured. A significant induction of all cytokines measured occurred in the onchocerciasis patients compared to healthy controls. However, the IL-1ra level was suppressed. The suppression of the production of IL-1ra suggests that the IC containing antigens may have a selectively suppressive effect on the production of this anti-inflammatory cytokine; thus implicating its possible role in counteracting inflammatory responses associated with the disease, and suggesting a potential therapeutic significance.

FcgRIIa receptors are involved in many important biological responses, and considered as important mediators of inflammation. A polymorphism in the gene encoding this receptor, that is either arginine (R) or histidine (H) at position 131, affects the binding to the different IgG subclasses. We therefore hypothesized that this polymorphism might be one of the underlying mechanisms to the varied clinical presentations seen in this disease. FcgRIIa genotyping was carried out by gene specific polymerase chain reaction (PCR) and allele-specific restriction enzyme digestion of DNA from clinically characterized patients. The genotype R/R frequencies were found to be significantly higher among patients with the severe form of the disease (including ROD), and it was particularly associated with one tribe (Masaleet) compared to Fulani. Moreover, the H allele was found to be associated with lower risk of developing the severe form. As no significant difference was seen between onchocerciasis cases and controls, the study also implies that this polymorphism influences protection from developing the severe form rather than being related to protection from the infection.

Tuberculosis (TB) remains one of the world’s most serious infectious diseases. It is estimated that a third of the world’s population is latently infected and 8 million new cases are recorded each year. Although BCG vaccination triggers protective immune responses in the neonates, it confers protection against only certain forms of childhood TB. Protection mediated by BCG, against pulmonary TB, is controversial as reported with variable efficacy ranging from 0-80%. In addition to the problems associated with the BCG vaccine, diagnosis of TB cannot be performed readily with the available tools. At present, an effective control of TB is highly dependent on the development of a new TB-vaccine as well as proper identification and treatment of individuals with active disease. Therefore, we particularly focused on identification of biomarker (s) of infection and the development of better vaccines, with special emphasis on the immune responses in the respiratory tract.

In the first study, we aimed to identify immune biomarker (s) of infection for better diagnosis of TB. Mice were infected with BCG administered i.n. or i.v., and the bacterial burden in the lungs, spleen and liver was examined. We measured IL-12, IFN-γ, TNF, soluble TNF receptors (sTNFR) and mycobacteria-specific antibodies in the broncho-alveolar lavage (BAL) and in serum in order to find immune correlates of infection. Results showed that sTNFR and mycobacteria-specific antibodies in BAL, but not in serum, might be useful in distinguishing active from latent infection or exposure to mycobacterial antigens.

In the second study, we investigated whether we could improve the currently used BCG vaccine. For this purpose, we tested a combination of neonatal vaccination protocol using BCG and posterior boosting with the protein heparin-binding hemagglutinin adhesion (HBHA). It has been described that immunization with native (n) HBHA but not recombinant (r) HBHA conferred protection against M. tuberculosis challenge in mice.

This protection was comparable to that afforded by the BCG vaccine. In order to improve the protective efficacy of the nHBHA vaccine we followed heterologous prime-boost strategy, comprising BCG vaccination at the neonatal age, followed by nHBHA boosting at the infant and adult ages. We also examined whether the rHBHA protein could boost BCG-mediated protective immunity. Cellular immune responses and protection as measured by control of bacterial growth in the lungs of the treated animals were followed. Our results showed an improved effect of BCG-priming on HBHA-immunization. The BCG/HBHA immunization protocol was more effective in induction of HBHA-specific immune responses, as well as in protection than when the animals received only BCG or HBHA alone. Importantly, our study revealed that nHBHA does not require co-administration with adjuvant provided that mice were primed with live BCG before boosting.

Finally, we hypothesized that in utero sensitization of the fetal immune system with nHBHA may improve nHBHA-specific immune responses after birth. The pregnant mother was immunized with nHBHA 1 week before delivery. After birth, the offspring received two doses (week 1 and week 4) of nHBHA formulated with cholera toxin. We examined HBHA-specific recall responses and protection after challenge with a high dose of BCG. We found that immune responses were improved by priming the pregnant mother, and that this also provided better protection than when the offspring received only BCG or HBHA neonatal vaccinations.

More than a century after the identification of the tubercle bacillus and the first attempts at vaccination, tuberculosis (TB) still remains one of the world’s most serious infectious diseases. TB is typically a disease of the lung, which serves both as port of entry and as the major site of disease manifestation. The currently used vaccine, Mycobacterium bovis bacillus Calmette-Guérin (BCG), is administered parentally and induces a systemic immune response. However, it fails to protect against pulmonary TB, thereby raising the question whether vaccination targeting the mucosal immunity in the lungs could be favourable.

The respiratory mucosal surfaces represent the first line of defence against a multitude of pathogens. Secretory IgA (sIgA) in mucosal secretions has an important function by blocking entrance of pathogenic organisms and preventing infections. Yet, another role for IgA in protection against intracellular pathogens has lately been appreciated, when sIgA was demonstrated to neutralize viruses intracellulary. We aimed to investigate the relevance of sIgA in protection against mycobacterial infections using mice deficient for IgA and the polymeric Ig receptor. Mice were immunized intranasally with a mycobacterial antigen which elicited, in wild-type mice, a strong IgA response in mucosal secretions in the respiratory tract. Gene-targeted mice failed to induce the same response and more importantly, were more susceptible to mycobacterial infections in the respiratory tract, as demonstrated by higher bacterial loads in the lungs than wild-type mice. Analysis of immune responses after infection revealed reduced production of proinflammatory, and protective, factors such as IFN-γ and TNF-α in the lungs of deficient mice, which was in concordance with the higher bacterial burden seen in the lungs of these mice. The mechanisms explaining the defective proinflammatory responses in the lungs of deficient mice are not clear but might involve impaired signalling through Fcα receptors, or homologous receptors, which could lead to inadequate activation of pulmonary macrophages. This could subsequently result in suboptimal induction and production of cytokines and chemokines important for attraction and migration of cells to sites of infection in the lungs.

Our results demonstrate a role for IgA in protection against mycobacterial infection in the respiratory tract by blocking the entrance of the mycobacterium into the lungs, and/or by modulating the locally induced proinflammatory immune responses.