Background: Bioaerosol-related airborne dermatitis was reported on e.g. in farmers and sewage workers. Bioaerosols consist of Gram-negative bacteria and so-called microvesicles (MV) emerging as a result of disruption of the bacteria. The present study was aimed at assessing the proinflammatory properties of microvesicles in vitro.
Methods: MV were produced through disruption of the bacterial wall of the Gram-negative bacterium Pantoea agglomerans (Erwinia herbicola). Peripheral blood mononuclear cells (PBMC) of five healthy volunteers were cultured for 6 h, 24 h, 3 days, and 5 days with dilution series of MV ranging from 0.48 - 1500 µg/ml. The following variables were observed: secretion of IFN-γ and TNF-α (ELISA and ELISPOT assays), intensity of cell proliferation (LPT), expression of surface markers CD8, CD14, CD16, CD25, CD69, CD80, CD83, HLA-DR, the apoptosis marker Annexin V, and PI permeability (flow cytometry).
Results: After 24 hours, a clear dose-dependent response to MV was seen for IFN-γ production starting already with the lowest MV concentration of 0.48 µg/ml (p=0.042). As for TNF-α, a significant (p=0.05) increase in the production of this cytokine was seen after 3 days at MV concentrations of 300 µg/ml or higher. On the LPT, there was a clear and significant dose-response to MV after 5 days (p=0.001). Regarding expression of cell surface markers, the only phenomenon seen in all donors was the decrease in the number of CD14(+)CD83(+) cells with increasing MV concentration (probably due to increased MoDC maturation).
Conclusion: We have shown that microvesicles are biologically active in PBMC cultures in a dose-dependent manner. IFN-γ production was increased already at lowest MV doses tested. These results explain clinical observations on the proinflammatory effect of bioaerosols on the skin.
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Document created: 29 August 2006, last updated: 1 September 2007.