Final answer:
High and low doses of antigens may not be immunogenic because high doses can induce tolerance, and low doses might be insufficient to trigger a strong immune response. The optimal response is achieved with a balanced antigen dose that effectively stimulates the immune system, which is particularly important in the context of vaccination and the creation of immune memory.
Step-by-step explanation:
Relatively high and low doses of antigens are usually not immunogenic because the immune response to antigens depends on an optimal concentration. A very high dose can lead to the development of immunological tolerance, where the immune system learns to ignore the antigen. Conversely, a very low dose may not be sufficient to trigger the required immune response for memory cell formation. Multiple factors such as the antigen's molecular class, molecular complexity, size, and the presence of adjuvants that stimualte a general immune activation play a role in its immunogenicity.
Vaccination relies on administering antigenic materials to provoke the immune system without causing disease, which then leads to immune memory. The administration of booster shots mimics repeat exposures to pathogens, sustaining the pool of memory cells and ensuring continued protection. An antigen's molecular complexity and the presence of multiple epitopes can also influence the immune system's ability to detect and respond effectively to an antigen.