Adaptation to organic dust exposure: a potential role of L-selectin shedding?

Swine confinement workers, exposed to high levels of organic dust, present a high prevalence of respiratory symptoms but show only mild lung inflammation. This contrasts with the intense inflammatory response observed when naive subjects are exposed to the same environment. Shedding of L-selectin may regulate the recruitment of inflammatory cells and explain this discrepancy. Soluble L-selectin (sL-selectin) levels were measured in sera of 36 workers, 35 control subjects and eight healthy volunteers briefly and repeatedly exposed to swine confinement buildings. White blood cell counts (WBC) and serum interleukin (IL)-6 levels were measured as markers of systemic inflammation. Higher concentrations of sL-selectin were found in the sera of workers than in controls (1452+/-62 ng x mL(-1) and 872+/-25 ng x mL(-1), respectively) whereas no differences were detected before and after acute repeated exposures of exposed volunteers. WBC were increased after exposure in exposed volunteers but not in workers. Both workers and exposed volunteers had increased IL-6 serum levels, although it was more pronounced for the exposed volunteers. These results support the hypothesis that shedding of L-selectin may downregulate the inflammatory response to organic dust-contaminated environments and constitute one mechanism of adaptation to the farm environment.