Airway inflammation is reduced in workers exposed to protein from bacteria one year after cessation of exposure

Introduction
Bacterial single cell protein (BSCP), used as a protein enrichment in animal and fish feed, is extracted from dried bacterial mass. In the production of BSCP, workers are exposed to organic dust containing high levels of endotoxins. We have previously found that in the medium/low exposure group (geometric mean endotoxin exposure 230 EU/m3), FVC and FEV1 were significantly improved one year after exposure termination. Also the number of leukocytes, level of ECP and D-dimer decreased significantly. The aim of the present study was to investigate if the airway inflammation previously observed among the workers had declined one year after cessation of exposure.

Methods
Twenty four non-smoking production workers (age 31-42) were included. They had all worked at the factory for 2-6 years. Exhaled NO-analysis was performed along with collection of sputum samples from each worker in an exposed period and then one year after exposure cessation. Differential cell analysis and cell surface phenotypes were examined by flow-cytometry on cells recovered from sputum.

Results
Sputum neutrophil proportion and numbers were significantly decreased one year after cessation of exposure to BSCP (43% vs 71 %, 186 vs 598 cells/mg sputum; p<0.001) as were exhaled NO levels (16 ppb vs 20 ppb; p=0.02) and cytokines IL-b and IL-8. Neutrophils had enhanced expression of cell surface markers for innate immunity; CD11b/ CR3 (p = .03) and CD16/FcgRIII (p < .001) and macrophages had lower expression of CD86 (p = .02) one year after cessation of exposure.

Discussion
One year after closure of the plant airway neutrophils and exhaled NO levels resolved to lower levels and cell surface phenotypes recovered innate immune function indicating that these changes were partly reversible among workers exposed to endotoxins in a BSCP-plant.