ofnæmisvarnir

Ofnæmisvarnir, or immune defenses, are the body's mechanisms for protecting against pathogens and abnormal cells. The system comprises two main components: innate (nonspecific) immunity and adaptive (specific) immunity. Innate defenses provide immediate, general protection through physical barriers such as skin and mucous membranes; chemical barriers such as acids and enzymes; and cellular defenses including phagocytes (neutrophils and macrophages) and dendritic cells, plus soluble factors like the complement system and interferons. Inflammation and fever are part of the innate response and help limit infection.

Adaptive immunity relies on B and T lymphocytes. B cells produce antibodies that recognize and neutralize pathogens. T cells include helper T cells, which support B cells and cytotoxic T cells, which destroy infected cells. Antigen presentation by dendritic cells and other antigen-presenting cells activates the adaptive response. Memory B and T cells provide long-lasting protection, enabling faster and stronger responses upon re-exposure, a principle exploited by vaccination.

Organs and tissues involved include primary lymphoid organs (bone marrow and thymus) where lymphocytes develop, and secondary lymphoid organs (lymph nodes, spleen, and mucosa-associated lymphoid tissue, MALT) where responses are coordinated. Regulation involves tolerance to self and regulation by regulatory T cells to prevent autoimmunity. Dysfunctions include immunodeficiencies, allergies, and autoimmune diseases, and immune function typically wanes with age (immunosenescence). Clinically, vaccines and immunotherapies harness these defenses to prevent disease and treat conditions.