2.4. Monocyte Activation Test (MAT)

The MAT was performed with human whole blood as described before [15]. Briefly, the cotton or synthetic swabs (untreated or pyrogen-impregnated) were placed in sterile 2 mL DNA LoBind Eppendorf reaction tubes, and 1.5 mL of 1:10 diluted pooled human whole blood was added and incubated for 18 h at 37 °C. Increasing 2-fold concentrations from 0.0125 to 0.5 EU/mL LPS (concentrations correspond to the volume in the incubation to enable a comparison to a solid swab material) were added to the diluted blood to detect the immune activation potential of the pooled blood to pyrogens (standard dilution row). A concentration of LPS in the middle of the used standard curve (0.1 EU/mL) served as liquid LPS spike and as the lower concentration for LPS impregnation of the swabs. Half of the sterile, non-impregnated swabs were spiked with liquid LPS directly at the time of incubation (yielding 0.1 EU/mL in the incubation) to detect potential interferences with the swabs. The LPS-impregnated samples (0.1 EU/mL and 1.0 EU/mL) were incubated with blood under the same conditions as the sterile swabs.

After the incubation, the samples were centrifuged at 300 g for 5 min, and the supernatant was analyzed for cytokine secretion by enzyme-linked immunosorbent assay (ELISA). Cytokine production triggered by the abdominal swabs was measured by ELISA (human IL1β Duo-Set; R&D Systems/BioTechne, Wiesbaden, Germany) according to the manufacturer’s instructions. The quantification of secreted IL1β was performed using Gen5 software (Biotek, Bad Friedrichshall, Germany).