Objective: Bronchus-associated lymphoid tissue (BALT) plays an important role in the immunological defence of airways. However, the mechanisms of BALT development, antigen sampling, and subsequent cell kinetics remain unclear. To clarify these chronological processes, we used a Pseudomonas aeruginosa-exposed mouse model.
Methodology: In BALB/c and C57BL/6 mice, BALT development was induced by inhalation of heat-killed P. aeruginosa after sensitization with subcutaneous injection of P. aeruginosa in the presence of Freund's complete adjuvant. Subsequently, we chronologically killed these mice who had inhaled PKH26-labelled P. aeruginosa and examined bacterial transport using fluorescence microscopy. The distribution of interleukin-4-positive cells and interferon-gamma-positive cells was studied immunohistochemically.
Results: The degree of BALT hyperplasia was greater in sensitized mice than in non-sensitized mice and in BALB/c mice than in C57BL/6 mice. PKH26-labelled bacteria were found in BALT earlier in sensitized mice than in non-sensitized mice. Immunohistochemical studies revealed that interleukin-4-positive cells predominated over interferon-gamma-positive cells in the peripheral areas of lymphoid follicles.
Conclusion: These results indicate that administered antigens are actively transported into BALT and that sensitized Th2 lymphocytes play an important role in forming and maintaining BALT.