In general, the greater the dose of immunogen, the greater the immune response. However, there are limits to this rule. For unknown reasons, very high doses of immunogens tends to have the effect of tolerizing the animal. In other words, the immunogen is not effective when administered at very high doses, perhaps because instead of activating B and T cells, the immunogen is seen as a self antigen and the cells that bind this antigen undergo apoptosis rather than clonal expansion. The route of immunization affects the immune response in several ways.
Intranasal immunization induces more mucosal immunity than intravenous immunization.
Intramuscular injection tends to release immunogens more slowly and for a longer period of time to the immune system. This often leads to a stronger response. Booster immunization are very effective because they provide the opportunity for new rounds of clonal expansion of memory B and T cells. The mucosal immune system may have additional requirements for initiation of immune responses. Food antigens and normal environmental compounds do not induce an immune response when introduced to mucosal surfaces.