Mucosal application of vaccines with an appropriate adjuvant can induce immune responses at both systemic and mucosal sites, and therefore may prevent not only infectious disease, but also colonization at mucosal surfaces. Intranasal is more effective than intragastric immunization at generating earlier and stronger mucosal immune responses. Nasal lymphoid tissue (NALT) and its local draining lymph nodes may retain long-term immune memory. IgA isotype switching, and the differentiation and maturation of IgA antibody-secreting cells (ASC) may occur before these cells migrate out of NALT, whereas IgG ASC responses require passage of the cells through draining lymph nodes of the NALT. Knowledge of whether immune memory cells can recirculate to and reside in the inductive sites other than their origin after encountering antigen will be helpful for understanding the compartmentalization of the common mucosal immune system as well as for determining the best route for delivering a mucosal vaccine against a particular pathogen.