Immunological memory

Immunological memory is the capacity of the immune system to respond differently after prior exposure to an antigen. It can produce faster or stronger responses on later encounters.

Memory B cell: A long-lived B lymphocyte formed during an immune response that can rapidly produce antibody-secreting cells after antigen re-exposure. These cells preserve antigen-specific B-cell responses between encounters.
Antigen: A molecule or molecular structure specifically recognized by antibodies or immune-cell receptors. An antigen provides the specific target that an immune response can remember.
Vaccination: The administration of a vaccine to induce protective immunity against a disease. Vaccines aim to establish immune memory without requiring the disease itself.
Innate immunity: The rapid, broadly acting immune defenses present before specific exposure to a pathogen. Unlike adaptive memory, innate defenses generally do not rely on antigen-specific recall.
Memory T cell: A long-lived T lymphocyte that responds rapidly to an antigen it encountered during an earlier immune response. These cells carry forward antigen-specific cellular immunity.
B cell: A lymphocyte that can recognize antigen and develop into antibody-secreting or memory cells. B cells form the antibody-producing branch of adaptive immune memory.
Booster dose: An additional vaccine dose given after an initial vaccination series to strengthen or restore protection. A booster re-exposes the immune system to antigen to reinforce memory responses.
Immunological tolerance: The failure of the immune system to mount a damaging response against particular antigens, especially self-antigens. Tolerance restrains responses to selected targets, whereas memory preserves readiness to respond.
Germinal center: A temporary structure in lymphoid tissue where activated B cells proliferate, mutate antibody genes, and undergo selection. Selection in germinal centers generates memory B cells with improved antigen recognition.
T cell: A lymphocyte that recognizes peptide antigens presented by other cells and coordinates or carries out immune responses. T cells provide memory for cellular responses and help B-cell responses develop.

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