Immunological Memory

Immunological memory is the ability to react faster to the antigens that have previously activated the immune response.

This occurs due to long-lived antibodies and lymphocytes previously stimulated by such antigens.

When the body encounters an antigen for the first time, only a few lymphocytes exhibit the right specificity for the antigen, causing a delayed immune response.

However, subsequent encounters with the same antigen allow for quicker proliferation of helper and cytotoxic T cells, or plasma cells.

Immunological memory can be measured by the antibody titer — the amount of antibody in serum.

After the initial exposure, both IgM and IgG antibody titers slowly rise, and with time, they gradually decrease. This is known as the primary response.

Recovery from an infection without needing medication is usually due to this primary response.

Every subsequent encounter results in a higher IgG antibody titer, making the secondary response faster and more potent.

The secondary response is often so quick that the antigens are eliminated before any symptoms appear.

Vaccination-based immunization against diseases like polio is based on immunological memory.