Occupational exposure alters innate and adaptive immune responses

Abstract

The farming environment is contaminated with high levels of organic dust. Especially pig barn facilities are highly polluted with airborne inhalable organic dust containing high amounts of molecular patterns from bacteria and fungi known to activate cells of the innate immunity through pattern recognition receptors (PRRs). Some hours of exposure in pig barn environment leads to an intensive upper and lower airway inflammation with systemic influences in previously unexposed healthy subjects. In farmers, daily exposed in the pig barn environment, the immune response becomes attenuated. The effect of the attenuated response is not apparent but respiratory symptoms are very common among farmers, a group with higher prevalence of respiratory chronic inflammatory disorders such as asthma-like syndrome, chronic bronchitis and chronic obstructive pulmonary disease (COPD) than the population in general.

Working with laboratory animals is associated with high exposure to allergens but involves also exposure to molecular patterns such as lipopolysaccaride (LPS). Respiratory symptoms, allergic sensitisation against laboratory animals and development of occupational asthma are common health problem among personnel in biomedical research and industry.

In paper I the aim was to study influence of regular exposure to organic dust on expression of pattern recognition receptors (PRRs) on blood neutrophils and monocytes and the cytokine profile interleukin (IL)-2, IL-4, IL-13 and interferon (IFN)-γ of blood T-cells before and after exposure in pig barn environment and a bronchial LPS challenge. The study included one group of pig farmers, one group of smokers, who are regularly exposed to organic material and like farmers have an increased prevalence of chronic respiratory diseases, and in one group of non-farming non-smoking healthy subjects. Blood from farmers and healthy controls were also stimulated ex vivo with pro-inflammatory stimuli. Before exposure farmers and smokers had increased concentration of blood neutrophils compared to controls. Farmers also showed decreased expression of TLR2 on blood monocytes compared to controls. After in vivo and ex vivo exposure, the expression of TLR2 and release of IL-6 were attenuated in farmers compared to controls. Further, farmers and smokers had increased proportion of IL-4 and IL-13 producing T-helper cells (Th) compared to controls before exposure. After in vivo exposures the proportion of IL-4 and IL-13 producing Th cells increased in controls but not in farmers and smokers. This attenuation in PRR expression in farmers is probably due to repeated exposure to microbial components and might be involved in the attenuated response to pig barn exposure previously observed in pig farmers. Increased proportion of Th2 cells is also probably due to regular exposure to microbial components and may be involved in development of respiratory symptoms and airway disorders (i.e. chronic bronchitis) that are frequently occurring in these groups.

In paper II the aim was to investigate expression of PRRs, lymphocyte activating markers, T-cell cytokine profile and serum levels of soluble CD14 (sCD14) and sST2 in laboratory animal (LA) workers who experience respiratory symptoms while working with laboratory animals (LAs), one group with and one group without allergic sensitization to LA. Two control groups not exposed in LA facilities were included, one group with birch pollen allergy (run during season) and one group of non-atopic subjects. Laboratory animal workers, especially those without LA atopy, showed increased expression of CD14 on blood monocytes compared to the control groups. Further was the level of sST2 in serum elevated in birch pollen atopics and in the group of LA workers who experienced respiratory symptoms but without LA atopy. Increased expression of CD14 may be a marker for LPS exposure which seems to be associated with respiratory symptoms. Increased levels of sST2 in serum might be due to LPS exposure and may prevent allergic sensitization to laboratory animals. However, it might also be caused by exposure to allergens and being an early marker for allergic sensitization.

In paper III the aim was to elucidate the influence of regular exposure in pig barn facilities on expression of PRR, adhesion proteins on blood and sputum neutrophils, levels of soluble PRRs in blood and sputum and serum levels of sST2 before and after exposure in a pig barn and a bronchial LPS challenge. A further aim was to study release of pro-inflammatory cytokines after ex vivo stimulations of blood with PRR ligands in presence or absence of anti-ST2. Farmers had decreased expression of adhesion moleculer (CD62L and CD162) on blood neutrophils and CD14 on sputum neutrophils compared to controls. Farmers also had lower levels of sTLR2 and sCD14 in sputum compared to controls. Before exposure there was no difference in sST2 levels in serum but after in vivo exposures sST2 levels in serum increased only in the controls. Attenuated release of sST2 in serum is probably due to development of tolerance among pig farmers. Decreased expression of adhesion molecules might be involved in the reduction in cell recruitment after exposure in pig barn environment previously observed in farmers.

In paper IV the aim was to further investigate the influence of regular exposure to organic material on the cytokine profile of Tcells. Proportion and concentration of blood Th cells and cytotoxic T-cells (Tc) producing IL-2, IL-4, IL-13, IFN-γ were investigated in pig farmers, smokers and non-farming, non-smoking healthy subjects. Farmers and smokers had increased proportion and concentration of Th cells producing IL-4 and IL-13 compared to controls. Smokers also had increased proportion and concentration of IL-4 and IL-13 producing Tc cells and concentration of Tc cells producing IL-2 compared to controls and farmers. Farming environment seems to favor a Th2 profile, however, not to the same extent as does smoking. This increase in IL-4/IL-13 producing cells likely stimulate goblet cell metaplasia and might therefore be involved in development of chronic bronchitis, a frequently occurring condition in these groups.

In conclusion, occupational exposure in pig barn and in laboratory animal facilities alters expression of receptors and cytokines important for the inflammatory response. This alteration may be of importance in the development of chronic inflammatory airway disorders that are known to be common both in smokers and in farmers.