Cobalt exposure via skin alters immune cells in lung and enhances pulmonary responses to cobalt in a mouse model

Background: Cobalt has been associated with allergic contact dermatitis and occupational asthma. However, the link between skin exposure and lung responses to cobalt is currently unknown. We investigated the effect of prior dermal sensitization to cobalt on pulmonary physiological and immunological responses after subsequent challenge with cobalt via the airways. Methods: BALB/c mice received epicutaneous applications (25 μl/ear) with 5% CoCl2*6H2O (Co) or the vehicle (Veh) dimethyl sulfoxide (DMSO) twice; they then received oropharyngeal challenges with 0.05% CoCl2*6H2O or saline five times, thereby obtaining four groups: Veh/Veh, Co/Veh, Veh/Co and Co/Co. To detect early respiratory responses non-invasively, we performed sequential in vivo micro-computed tomography (µCT). One day after the last challenge, we assessed airway hyper-reactivity (AHR) to methacholine, inflammation in bronchoalveolar lavage (BAL), innate lymphoid cells (ILCs) and dendritic cells (DCs) in lung, and serum IgE. Result: Compared with the Veh/Veh-group, the Co/Co-group showed increased µCT-derived lung response, increased AHR to methacholine, mixed neutrophilic and eosinophilic inflammation, elevated monocyte chemoattractant protein-1 (MCP-1) and elevated keratinocyte chemoattractant (KC) in BAL. Flow cytometry in the Co/Co-group demonstrated increased DC, type 1 and type 2 conventional DC (cDC1/cDC2), monocyte-derived DC, increased ILC group 2 and NCR-ILC group 3. The Veh/Co-group showed only increased AHR to methacholine and elevated MCP-1 in BAL, whereas the Co/Veh-group showed increased cDC1 and ILC2 in lung. Conclusion: We conclude that dermal sensitization to cobalt may increase the susceptibility of the lungs to inhaling cobalt. Mechanistically, this enhanced susceptibility involves changes in pulmonary DCs and ILCs.