Background: Modern lifestyle and urbanization have been associated with a raised risk for atopic diseases whereas early and long-term exposure to a farm environment confers protection against atopic sensitization. Immunomodulatory potential and microbiological characteristics of settled airborne dust from an urban house and a barn were examined. Methods: Pulmonary inflammation was induced in mice by repeated intranasal administration of dusts. Monocyte-derived human dendritic cells (moDCs) were exposed to dusts followed by coculture with purified naïve T cells. Cytokine/chemokine mRNA and protein levels were analyzed by real-time polymerase chain reaction, enzyme-linked immunosorbent assay and flow cytometry. The dusts were analyzed by cloning and sequencing of 16S rRNA genes (290 sequences) for DNA, lipids, endotoxin and β-glucan, by live-dead staining, viable counting, isolation and identification of pure cultures (n = 76). Results: Repeated exposure to house dust elicited pulmonary eosinophilia in mice whereas exposure to barn dust elicited neutrophilic and lymphocytic airway inflammation. Stimulation of moDCs with urban house dust elicited expression of Th2-promoting OX40L and Jagged-1 costimulatory molecules. Dendritic cells (DCs) exposed to house dust directed naïve T cells towards Th2 responses. Exposure of DCs to barn dust elicited the development of Th1-dominated immune responses. Urban house dust contained bacterial debris almost exclusively of human commensal species (corynebacteria, streptococci) whereas barn dust comprised mainly intact, viable bacteria of high diversity and no commensal species. Conclusion: Contact to debris originating from human commensal bacteria in urban house dust elicited a Th2-type response whereas barn dust with high bacterial diversity directed the cells towards a Th1 response.

Listeria phage endolysin cell wall-binding domain (CBD) from the Listeria phage A500 was fused with flagellar subunit FliC in Escherichia coli, aiming at binding of E. coli cells to Listeria cells, followed by enhanced killing of Listeria by pediocin production. FliC::CBD chimeric flagella were expressed and detected by Western blot. However, only few chimeric flagella could be isolated from the recombinant cells compared with sufficient amount of wild-type flagella obtained from the host cells. Interestingly, wild-type flagella extract showed capacity of binding Listeria cells. Pediocin-secreting E. coli cells with Listeria-binding flagella killed approximately 40 % of the Listeria cells, whereas cell-free spent growth medium with the same pediocin concentration only inhibited Listeria growth. These results suggested that binding the Listeria to bacteriocin-secreting cells improves killing.

Cell surface display of target proteins has been widely used in biotechnology and industry. In this study, cell-wall binding domain (CBD) from Listeria phage endolysin A500 was fused with anchoring domains of YadA and OmpA, respectively, in Escherichia coli, aiming at binding of E. coli cells to Listeria cells. The fusion proteins were expressed after induction and their surface localizations were verified by Western blot. CBD-YadA fusion was displayed on the cell surface, however, was toxic to E. coli. OmpA-CBD fusion was translocated to the outer layer of the cell membrane but with compromised availability on the cell surface. Therefore, functional surface display of CBD in E. coli requires another anchor for fusion strategy.

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