Immune system phenomena

Biological processes and effects produced by immune cells, molecules, and organs as they detect and respond to threats.

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Antigen presentation: The display of peptide fragments on cell-surface molecules for recognition by T cells. It connects detected threats to adaptive immune-cell responses.
Innate immune system: The rapid, broadly responsive defenses present before exposure to a specific pathogen. It provides the immediate defenses that shape later immune phenomena.
Vaccination: The administration of an antigen or its genetic instructions to induce protective immune responses. Vaccination uses immune memory to reduce the risk of future disease.
Autoimmunity: Immune reactivity directed against the body's own molecules or tissues. It contrasts defense against threats with attack on self.
Clonal selection: The activation and multiplication of lymphocytes whose receptors bind a particular antigen. It explains how a rare matching lymphocyte expands during a response.
Adaptive immune system: The antigen-specific arm of immunity, mediated chiefly by B and T lymphocytes. It produces highly specific responses and immunological memory.
Immunotherapy: Treatment that alters immune activity to fight disease or reduce harmful immune responses. Therapies can redirect immune phenomena against cancer or other disease.
Allergy: An immune response to a normally harmless substance that causes symptoms or tissue damage. It shows how a response to harmless exposures can become harmful.
Cytokine: A signaling protein that regulates communication and activity among cells, especially immune cells. Cytokines coordinate immune activity across tissues.
B cell: A lymphocyte that can produce antibodies and present antigens, with functions shaped by its activation state. B cells generate antibodies and contribute to lasting responses.