Immune memory: The ability of the immune system to store information about prior infections or vaccinations so as to respond quickly if the infection is re-encountered.
Antibodies: Antibodies coat, mark for immune destruction, or render harmless foreign matter such as bacteria, viruses, or dangerous toxins. Antibodies also tag virus-infected cells, making them vulnerable to attack by other components of the immune system. Each antibody attaches itself to a single specific chemical sequence in an antigen.
T-helper cells: Also known as CD4 cells, T helpers are a type of T lymphocyte involved in protecting against viral, fungal, and protozoal infections. The CD4 cell modulates the immune response to an infection through a complex series of interactions with antigen presenting cells, and lymphocytes that directly attack foreign antigens, such as killer T-cells.
Killer T-cells: Immune system cells that kill cancerous and virus-infected cells. Also known as cytotoxic T-lymphocytes (CTL).
Antigen: A foreign substance, usually a protein that stimulates an immune response. An antigen contains several subunits called epitopes that are targets of specific antibodies and killer T-cells.
Naïve T-cell: A T-cell arising from the immune system's production of fresh cells in the bone marrow. Naïve T-cells respond to newly encountered pathogens containing antigens the immune system has not processed before. The naïve T-cells' activation and proliferation create an acquired immune response to the newly encountered pathogenic agent. After the disease is eradicated, a portion of the T-cell population engendered by the activated T-cells constitute a reservoir of memory cells, which proliferate and respond very quickly to any recurrence of the disease.
Primary immune response: The first encounter of a naive T-cell with antigen that results in activation, proliferation, and, finally, creation of memory T-cells.
Dendritic cells: Immune cells with long, tentacle-like branches called dendrites. Among the dendritic cells are the Langerhans cells of the skin and follicular dendritic cells in the lymph nodes. Most dendritic cells (other than the follicular type) function as antigen presentation cells.
Antigen presentation: The display of digested bits of foreign bodies on the surface of macrophages or dendritic cells in the lymph nodes for circulating T-cells to recognize. Upon recognition, the T-cells become activated.
Cytokines: Proteins produced by the white blood cells that act as chemical messengers between cells. Cytokines can stimulate or inhibit the growth and activity of various immune cells in response to the particular type of disease present.
Memory T-cells: A T-cell that bears receptors for a specific foreign antigen encountered during a prior infection or vaccination. After an infection or vaccination, some of the T-cells that participated in the response remain as memory T- cells, which can rapidly mobilize and clone themselves should the same antigen be re-encountered during a subsequent infection.