Vaccination by aerosols: modulation of clearance mechanisms in the lung.

Inhalation and deposition within the the airways are the initial steps before pathogens of the respiratory tract are able to adhere and colonize their host. Once the microorganisms are deposited in the lung lining fluids they do not remain at the location where they first came in contact with the mucous membranes. It is long known that lung clearance mechanisms translocate all deposited particles. At least, most of them are swallowed and cleared via the gastrointestinal tract. Aerosol vaccination with inactivated or (recombinant) live bacteria has been shown to be an efficient way to induce local protection against lung diseases. It can be assumed that the local concentration of the vaccine and the deposition pattern of the vaccine within the lung limit the strength of a local or systemic immune response. The local concentration of airborne bacterial antigen necessary to initiate a mucosal immunity in the respiratory tract is known for a very few microorganisms. Bacterial survival, infectivity, deposition, and persistence characteristics have to be defined when aerosols are included in vaccination experiments.