Development of the cariogenic oral biofilm coincident with the evolution of immune responses in very young children

Malcolm, Jennifer (2013) Development of the cariogenic oral biofilm coincident with the evolution of immune responses in very young children. PhD thesis, University of Glasgow.

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Abstract

Dental caries remains one of the most common chronic infectious childhood diseases and individuals remain susceptible to the disease throughout their lifetime. The disease continues to inflict a substantial economic burden. Moreover, dental caries demonstrates considerable socioeconomic disparities with the lowest socioeconomic groups suffering the greatest burden of disease. There is an unmet need to improve prevention and therapeutics and yet there remain fundamental gaps in the knowledge of the interrelationships between caries-associated risk factors, in particular how the immune system interacts with the evolving cariogenic biofilm in young children. This thesis sought to investigate the immune response to cariogenic biofilms. Three different approaches were used to achieve this. Firstly, the salivary immune response and development of the oral biofilm in very young children were investigated prior to the onset of caries, as part of a pilot longitudinal clinical study, using a dental public health program as a platform. Secondly, the initiation of adaptive immune responses to S. mutans exposure were investigated using a series of In vitro and In vivo studies. Thirdly, a novel S. mutans In vitro biofilm model was developed and optimised. Childsmile is a dental health improvement programme for children in Scotland and provides children with specific dental health interventions depending on need, from birth and up to 16-years of age. To achieve the first and primary aim of this thesis, plaque and saliva samples were collected from children aged one-year and again at age three-years. At follow-up, dental disease scores were also measured. Additionally, the biological mechanisms underlying the socioeconomic disparities in the dental health of young children were investigated, including the measurement of salivary cortisol as a surrogate measure of stress. Sixty-three Childsmile participants aged one-year were recruited to the study at baseline. Twenty-three children aged three-years were successfully recalled at follow-up. This work demonstrated that variables hypothesised to influence the development of carious disease can be collected and successfully quantified in children aged one- to three-years. Nonetheless, it was extremely challenging to recruit children of this age and the data were compromised by the small sample sizes. During the study period both the intensity and incidence of S. mutans colonisation increased in the dental plaque of children aged one- to three-years. Coincidentally, concentrations of salivary antimicrobial proteins increased, including lactoferrin, LL37, calprotectin, the HNPs 1-3 and sIgA antibody titres specific for oral streptococci. It could not be determined from these studies whether the increased colonisation with S. mutans or the concentrations of salivary antimicrobial proteins influenced the prevalence of dental caries. The major limitation of this study was the low recruitment rates which resulted in low power to detect statistically significant differences. As a consequence there was insufficient evidence to identify the potential biological pathways that may underlie the socioeconomic disparities of dental caries. From this pilot study a number of valuable lessons were learned regarding the recruitment of children of this age and recommendations for future clinical studies conducted within Childsmile are made. In children with high risk of developing dental caries effective salivary antibody responses are required to provide protection. The mechanisms leading to effective antibody responses remain unclear. Thus, the second aim of this thesis was to investigate the initiation of an adaptive immune response to S. mutans, in an attempt to elucidate the mechanisms that lead to effective antibody production. Using a novel system, In vitro evidence indicated that S. mutans does not elicit a robust inflammatory immune response upon colonisation of the host. Dendritic cells exposed to S. mutans were not functionally mature and failed to induce antigen-specific T cell proliferation. Furthermore, In vivo, dendritic cells failed to become activated in response to oral exposure to S. mutans. An In vitro S. mutans sucrose-dependent biofilm model was developed and optimised. Using this model an antibody fragment known as a minibody, denoted ‘SS2’ was demonstrated to inhibit S. mutans biofilm formation. This biofilm model represents an important first step for examining the potential of therapeutic molecules to inhibit S. mutans biofilm formation, prior to their application in In vivo models of dental caries and possible subsequent use in human clinical trials. Data described here indicate that S. mutans colonises the oral cavity at a time when children are immunologically immature. Increased colonisation by S. mutans coincides with the maturation of salivary immune responses. Moreover, In vitro and In vivo evidence suggest that S. mutans does not elicit a robust immune response upon colonisation of the host. Thus, early acquisition of S. mutans in a relatively immunologically immature host together with the absence of an inflammatory immune response likely aids the colonisation of S. mutans and its persistence within the oral biofilm and subsequent contribution to dental caries.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Streptococcus mutans, dental caries, oral biofilm, salivary immune responses
Subjects: Q Science > QR Microbiology
Q Science > QR Microbiology > QR180 Immunology
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing
Funder's Name: UNSPECIFIED
Supervisor's Name: Culshaw, Dr. Shauna E.
Date of Award: 2013
Depositing User: Miss Jennifer Malcolm
Unique ID: glathesis:2013-4082
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 13 Mar 2013 09:14
Last Modified: 15 Apr 2014 15:43
URI: http://theses.gla.ac.uk/id/eprint/4082

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