The role of flame retardants in allergic responses to house dust mite

Over the past decades, the prevalence and severity of asthma and allergies has increased rapidly in parallel with rapid industrial development which has resulted in increasing exposure to diverse air pollutants introduced into our environment. HDM allergy and exposure to indoor air pollutants have both been associated with the development of allergic asthma. Over the last decades, additive flame retardants (FRs) have become a major indoor pollutant. They are likely to migrate from their products into indoor dust and inhalation of house dust is therefore one of the main human exposure routes to FRs. This implies that house dust mite (HDM) allergens are often inhaled in the presence of FRs. In HDM allergy, inhalation of harmless HDM allergens results in allergic sensitization in which dendritic cells (DCs) play a central role.
For the first time, we assessed the potential risk of exposure to FRs in the development of immune response to HDM allergens. Thus, we determined the possible immunomodulatory effects of FRs on HDM activated DCs in vitro and the outcome of this effect on the immune response to inhaled HDM in mice. We demonstrated that HBCD has a mild immunomodulating effect on sensitization to HDM in mice while it enhances HDM induced activation of human DCs towards an allergic phenotype. An in vitro study with DCs exposed to alternative PFRs TDCIPP or TPHP showed immunotoxic effects at cytotoxic concentrations. An epidemiologic study did not reveal an association between increased concentration of individual PFRs including TPHP and the development of childhood asthma.