Reactions of airway epithelial cells to birch pollen grains previously exposed to in situ atmospheric Pb concentrations: a preliminary assay of allergenicity.

A growing body of evidence suggests that interactions between pollen grains and environmental pollutants, especially air pollutants, could be of critical importance with regard to the increase in allergic responses observed in the past decades. Using birch pollen grains (BPG), a major allergy source in European countries, and lead (Pb), a highly toxic metal trace element (MTE) present in urban areas, the immune response of human epithelial cells exposed to BPG or to Pb-associated BPG was compared. The cellular response after exposure either to BPG, BPG exposed to 30 mg/L of Pb (BPG-30), or BPG exposed to 60 mg/L of Pb (BPG-60) was evaluated after two time lapses (2 and 6 h) by measuring mRNA levels of four mediators, including two inflammatory (interleukin-8 and interleukin-6) and two allergic (interleukin-5 [IL-5] and interleukin-13) cytokines. After 2 h of exposure, significant upregulation of the IL-5 gene was observed after exposure to BPG-60 in comparison with exposure to BPG and BPG-30 (N (IL-5) = 1.9, Mann-Whitney test, p = 0.003). After 6 h of exposure, significant upregulation of the IL-5 gene was observed after exposure to BPG-30 with N (IL-5) = 1.8 and to BPG-60 with N (IL-5) = 2.3 (Mann-Whitney test, p = 0.0029) in comparison with exposure to BPG. This first attempt to investigate the influence of pollution by MTE on pollen grain showed a dose-time-dependent increase in IL-5 gene expression after exposure to BPG combined to Pb.