Microbial components in house dust : exposure assessment and immunologic characterization

Abstract

According to the “hygiene hypothesis” the rising numbers of people suffering from allergies and asthma may be associated with changes in modern lifestyle including the improvement of living and household standards as well as personal hygiene. This would have led to a substantial decrease in environmental exposures to microbial agents that are capable of interacting with the innate immune system. Frequently repeated or chronic stimulation of innate immunity by such microbial agents is in turn thought to have an immuno-modulatory effect on the developing immune system, such that atopic, thus IgE-mediated, sensitization to common airborne allergens is inhibited. As a result, airborne exposure to microbial agents in e.g. house dust, like the well known endotoxins from gram negative bacteria and ?-(1,3)-glucans from fungi, may result in an apparently protective effect against atopic diseases like allergic asthma and rhinitis. Investigations on a population level of these relations require valid and accurate exposure assessment for house dust-associated microbial agents. While the airborne exposures are supposed to give a better proxy of inhaled exposures, thus far in larger studies mainly analyses of floor or mattress dust samples have been applied. The aim of this thesis was therefore to improve exposure assessment of possibly immune-modulating microbial agents in the home environment. The applicability of passive airborne dust collection in large epidemiological studies was tested with respect to characterizing microbial exposure in home environments. To overcome the problem of the low sensitivity of the glucan assay in association with these airborne measurements a more sensitive assay for ?-(1,3)-glucan exposure assessment was developed and evaluated, and compared with measurements of bacterial endotoxins and ?-(1,3)-glucans in floor dust from the same sampling locations in farm or non-farm home environments. Finally the procedures of sampling and extracting samples collected with the new passive airborne dust sampling method were investigated in more detail to be able to proceed with optimal handling in future studies. The ?-(1,3)-glucans found in nature are not all of fungal origin. Many may also be produced by bacteria, or even plants, with differently structured glucan-chains, like mixed and/or branched ?-(1,3)- with ?-(1,4)- ?-(1,6)-glucan chains. Additionally, glucans from plants or fungi may only contain ?-(1,4)- or ?-(1,6)-linkages. Since most immunological research has focused on the ?-(1,3)-linked glucans, the aim of the second part of this thesis was to analyze immunological properties and differences of the various glucan structures. In the last chapter of this thesis, different fractions of cultures of typical indoor fungi were analyzed for ?-glucan or other substances and possible relation to their antigenic reactivity of the according fractions were investigated.