Here's why:

* Primary Immune Response: When you encounter a pathogen for the first time, your immune system mounts a primary response. This involves:

* Naive B cells: These cells differentiate into plasma cells, which produce antibodies against the pathogen.

* Naive T cells: These cells differentiate into effector T cells, such as cytotoxic T cells (kill infected cells) and helper T cells (support other immune cells).

* Secondary Immune Response: Upon re-exposure to the same pathogen, your immune system utilizes the memory cells generated during the primary response.

* Memory B cells: These cells rapidly differentiate into plasma cells, producing high levels of specific antibodies.

* Memory T cells: These cells quickly become effector T cells, eliminating the pathogen more effectively.

The presence of memory cells is the key to the faster and more robust nature of the secondary immune response, providing long-lasting protection against specific pathogens.