Rationale: The role of endotoxin exposure in immune regulatory network of airway allergy is still largely unexplored. We hypothesize a significant alteration of immune regulatory cell populations [e.g., regulatory B cells (Breg), regulatory T cells (Treg)] and various subsets of dendritic cells (DC) in lungs and spleen of ovalbumin (OVA) sensitized mice upon endotoxin exposure.

Methods: Age-matched C57BL/6 female mice (6-8-week old) were immunized with intranasal delivery of 100 ng endotoxin (pure lipopolysaccharide in PBS) alone or with same amount of LPS plus 100 μg of OVA. After 24 h of the last immunization, both groups of mice were sacrificed and spleen, lung, and blood were collected. Single cell suspension from harvested tissue was prepared for flow cytometry analysis.

Results: We found slightly higher trend for the proportions of Tregs, eosinophil, and DCs (Gr-1+, CD11c+, CD4+ / CD11c+, CD205+, CD8+) in the lung homogenates of endotoxin plus OVA treated mice when compared with mice treated with endotoxin only. Bregs (CD19+,CD5+ foxp3+) population were relatively high in both groups (17.8 ± 1.4% in endotoxin plus OVA treated mice and 19.1 ± 3.8 % in mice treated with endotoxin only) than Tregs (corresponding proportions: 4.6 ± 1.4% and 6.05 ± 1.5%). Spleens from endotoxin plus OVA treated mice had significantly higher (p < 0.05) amount of DCs (Gr-1+, CD11c+, CD4+) than mice treated with endotoxin only.

Conclusions: Endotoxin exposure is associated with airway allergy and inflammation by alteration of immune regulatory network particularly with reference to regulatory T and B cells.