Overview

The immune system defends against pathogens and maintains tolerance to self through innate and adaptive mechanisms. Key components include lymphoid organs lymphocytes antigen presenting cells and soluble mediators. Balanced immune responses prevent infection and limit tissue damage.

Primary and Secondary Lymphoid Organs

Bone marrow and thymus generate lymphocytes while lymph nodes spleen and mucosal associated tissues coordinate immune responses. Lymphatic circulation transports antigens and immune cells for surveillance. Organ architecture supports antigen presentation and clonal expansion.

Cellular and Humoral Immunity

T cells mediate cellular immunity and B cells produce antibodies for humoral defense. Innate cells such as macrophages neutrophils and dendritic cells provide rapid nonspecific responses. Cytokines chemokines and complement orchestrate immune activity.

Clinical Relevance

Immune disorders include immunodeficiency autoimmunity and hypersensitivity reactions. Imaging identifies lymphadenopathy splenomegaly and organ involvement in systemic disease. Immunomodulatory therapies require monitoring for infection and malignancy risk.