Nitrogen dioxide promotes allergic sensitization to inhaled antigen

Area of Science:

• Immunology
• Environmental Health
• Pulmonology

Background:

• Allergen sensitization typically requires immunostimulatory molecules.
• Environmental pollutants like nitrogen dioxide (NO2) may alter immune responses to innocuous antigens.
• The role of NO2 in promoting adaptive immunity to non-immunostimulatory antigens is not fully understood.

Purpose of the Study:

• To investigate if exposure to NO2 followed by an innocuous antigen (OVA) induces allergen sensitization and allergic airway disease in mice.
• To elucidate the underlying mechanisms by which NO2 promotes allergic responses.

Main Methods:

• C57BL/6 mice were exposed to NO2 and aerosolized ovalbumin (OVA).
• Lung inflammation, mucus cell metaplasia, OVA-specific IgE and IgG1, and Th2 cytokine responses were assessed.
• Bronchoalveolar lavage fluid (BALF) analysis was performed to measure protein, LDH, and HSP70 levels.
• NF-kappaB activation in airway epithelial cells was evaluated.
• Experiments were repeated in Toll-like receptor 2 knockout (TLR2-/-) and MyD88 knockout (MyD88-/-) mice.

Main Results:

• Mice exposed to NO2 and OVA developed eosinophilic lung inflammation, mucus cell metaplasia, and OVA-specific IgE/IgG1 responses.
• NO2 exposure increased BALF protein, LDH, and HSP70 levels, and activated NF-kappaB in airway epithelial cells.
• Features of allergic airway disease were absent in TLR2-/- and MyD88-/- mice exposed to NO2 and OVA.
• These results suggest NO2 acts as an adjuvant, promoting sensitization to OVA.

Conclusions:

• Inhalation exposure to NO2 can induce allergen sensitization and allergic airway disease in the presence of an innocuous antigen.
• NO2 exposure promotes airway inflammation and Th2-type immune responses via NF-kappaB activation and potentially TLR signaling pathways.
• These findings provide a mechanism linking environmental NO2 exposure to the development of asthma.