Ex vivo cytokine release and pattern recognition receptor expression of subjects exposed to dampness: pilot study to assess the outcome of mould exposure to the innate immune system

Abstract

In rooms with moisture damage, the indoor air can be enriched with microorganisms causing a variety of symptoms. Due to the highly diverse composition of bioaerosols and the multiple effects on humans, an assessment of the health risk is not sufficiently possible. The aim of this study was to characterize the features of innate immunity using blood from subjects exposed to moisture damage compared to control subjects living in houses without visible moisture damage. We investigated the expression of TLR-2, TLR-4 and dectin-1 on the surface of monocytes from both fresh blood and after in vitro stimulation with the model substances E. coli endotoxin, zymosan A, Pam3Cys and Aspergillus versicolor in 25 exposed subjects and 25 control subjects. In vitro stimulation of whole blood with the same components was performed for 20 h and the release of inflammatory mediators IL-8 and IL-1β were quantified. In addition to an enhanced number of blood leucocytes, the expression of the receptors TLR-2, TLR-4 and dectin-1 on blood monocytes was significantly enhanced in exposed subjects. In contrast, no different alteration in expression was detected between exposed and control group after in vitro stimulation with the model substances. The release of IL-8 and IL-1β after stimulation of whole blood with A. versicolor was increased in subjects exposed to moisture damage. Furthermore, in the exposed subjects the IL-1β release was significantly enhanced after in vitro stimulation with E. coli endotoxin (1000 pg/mL). In conclusion, features of the innate immune system (receptor expression and mediator release of monocytes) are altered in subjects exposed to moisture damage which may be a potential explanation for the increased incidence of respiratory health diseases observed in these populations.

Figure 1. Leucocytes.

Number of leucocytes in subjects exposed to moisture damage (n=25) and subjects not exposed to moisture damage (controls; n=25). Statistically significant changes are indicated as **p<0.005 compared with control subjects. The box shows the median and interquartile range, whisker corresponds to 1.5 times the interquartile range.

Figure 2. E. coli endotoxin induced mediator release.

IL-8 (A) and IL-1β (B) response in fresh whole blood after 20 h stimulation with E. coli endotoxin in subjects exposed to moisture damage (n=25) and subjects not exposed to moisture damage (controls; n=25). Statistically significant changes are indicated as *p<0.05 compared with control subjects. Bold lines show median values.

Figure 3. A. versicolor induced mediator release.

IL-8 (A) and IL-1β (B) response after 20 h stimulation in fresh whole blood with A. versicolor in subjects exposed to moisture damage (n=25) and subjects not exposed to moisture damage (controls; n=25). Statistically significant changes are indicated as *p<0.05 compared with control subjects. Bold lines show median values.

Figure 4. TLR-2, TLR-4 and dectin-1 expression.

Expression of TLR-2 (A), TLR-4 (B) and dectin-1 (C) on monocytes of fresh and 22 h RPMI-incubated whole blood in subjects exposed to moisture damage (n=25) and subjects not exposed to moisture damage (controls; n=25). Mean relative fluorecence intensity (mRFI) is demonstrated. Statistically significant changes are indicated as *p<0.05, **p<0.005 and ***p<0.0005 compared with control subjects. Bold lines show median values.