Immunitat

Immunitat, or immunity, is the ability of an organism to resist infection and disease. It involves the immune system recognizing foreign substances, distinguishing self from non-self, and launching responses to eliminate pathogens and abnormal cells. Immunity can be broad and non-specific or precise and memory-based, producing long-term protection in some cases.

Innate immunity provides immediate, non-specific defense. It relies on physical barriers such as skin and mucous membranes, chemical barriers like stomach acid, and cellular responses from phagocytes (neutrophils, macrophages) and natural killer cells. The innate system also activates the complement cascade and inflammatory processes to contain and control invading organisms until adaptive immunity responds.

Adaptive immunity is specific and develops after exposure to a particular antigen. It involves lymphocytes: B cells produce antibodies that recognize pathogens and help neutralize them, while T cells can kill infected cells or help coordinate other immune responses. Adaptive immunity creates immunological memory, allowing a faster and stronger response upon subsequent encounters with the same pathogen.

Immunity can be categorized by its origin and by how it is acquired. Naturally acquired immunity occurs through infection or maternal transfer of antibodies. Artificially acquired immunity arises from vaccination or the administration of immune products. Active immunity develops after exposure to an antigen, resulting in memory, whereas passive immunity is conferred by antibodies from another individual and usually provides short-term protection.

Clinically, immunity is central to understanding infectious disease, vaccination strategies, immunodeficiencies, autoimmune conditions, and allergies. Immunotherapies seek to enhance or modulate immune responses for therapeutic benefit, including vaccines, monoclonal antibodies, and targeted cellular approaches.