The nasal route for vaccination offers some important opportunities, especially for the prophylaxis of respiratory diseases. Vaccination via the respiratory tract is reviewed and the deposition and clearance of antigens in the deep lung and nose are described and contrasted. Lymphoid structures in the respiratory tract differ according to species; the rat and mouse have a well developed nose-associated lymphoid tissue, while in man, the structure known as Waldeyer's ring (that includes the tonsils), is important as an induction site. The immune response following intranasal administration can provide protection at the administration site and at various effector sites as part of the common mucosal immune system. A number of formulation considerations are important when designing novel systems for nasal administration as are physiological factors such as mucociliary clearance.

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The transport of 125I-radiolabelled latex nanoparticles across the nasal mucosa of rats was studied using a range of particle sizes and surface coatings. Translocation of the particles into the blood stream was examined by means of monitoring the radiolabel associated with the particles. Particles were detected in the blood after 5 minutes. The number of particles in the blood peaked at 60 minutes, and then remained constant for a further 2 hours. The smallest particles (20 nm) showed greater uptake than the largest particles investigated (1000 nm). The total maximum uptake seen for the smallest particles was in the order of 3.25% of administered dose. 100 nm particles coated with chitosan showed an increase in both the extent and rate of uptake, with the concentration in the blood peaking at 15 minutes rather than at 60 minutes. It is suggested that transport of the particles across the nasal membrane is due mainly to a transcellular transport mechanisms by the nasal associated lymphoid tissue (NALT), especially the M-cell like cells. However, some paracellular transport cannot totally be ruled out for the smallest particles, especially if coated with chitosan.