imunit

Imunit, or immunity, is the capacity of an organism to resist infection and disease. It covers the body's ability to recognize and defend against pathogens such as bacteria, viruses, fungi, parasites, and malignant cells, and to limit tissue damage from infections.

The immune system operates through innate (nonspecific) defenses present from birth and adaptive (specific) defenses that develop after exposure. Innate immunity provides rapid, generic protection through barriers, cells, and proteins, while adaptive immunity targets particular pathogens and forms immunological memory.

Innate components include physical barriers such as skin and mucous membranes, chemical barriers like acidic pH and enzymes, and immune cells such as phagocytes and natural killer cells, together with the complement system and inflammatory responses. Adaptive immunity relies on lymphocytes (B cells and T cells) and produces antibodies and targeted cellular attacks.

The immune response typically starts when immune cells recognize foreign antigens. B cells may differentiate into antibody-producing plasma cells and memory B cells; T cells may become helper, cytotoxic, or memory T cells. Antibodies and effector T cells help eliminate pathogens, while memory cells provide faster responses upon re-exposure.

Immunity can be natural or artificial, and active or passive. Natural active immunity follows infection; natural passive immunity comes from mother to child. Artificial active immunity is vaccination; artificial passive immunity uses preformed antibodies. Vaccines aim to induce long-lasting protective memory.

Disorders of immunity include immunodeficiencies, allergies, and autoimmune diseases. Immune function is influenced by age, nutrition, stress, sleep, infections, genetics, and medications.