Oral administration of Bacillus subtilis promotes homing of CD3+ T cells and IgA-secreting cells to the respiratory tract in piglets.

Oral probiotics are used to induce immune responses in the intestines to protect against infection. However, oral probiotics may also affect immune responses in other mucosal tissues such as in the respiratory tract. To examine this possibility, we explored the potential of immunocytes to home to the respiratory system after oral administration of Bacillus subtilis. The results showed that B. subtilis could promote intestinal development and not cause pathological changes in the respiratory tract. Following the oral administration with B. subtilis, the number of IgA-secreting cells and CD3+ T cells not only significantly increased in the intestinal tracts but also in respiratory tracts (P < 0.01). Moreover, the levels of secretory IgA were significantly higher in the trachea, lungs, ileum, and jejunum after oral B. subtilis administration than in the control groups (P < 0.05). The mRNA expression of interleukin (IL)-1β, IL-5, IL-6, tumor necrosis factor-α, B cell activating factor, and IgA-inducing protein increased following B. subtilis administration (P < 0.01) in the trachea, lungs, ileum, and jejunum. These data suggest that B. subtilis administration regulates the immune response not only in the intestine but also in the respiratory tract of piglets. Our work highlights a potentially new strategy for promoting respiratory mucosal immunity and may contribute to the design of vaccines with B. subtilis as a mucosal adjuvant.