Immunology

Immunology is the branch of biomedical science that studies the immune system, its structure, function, and disorders. The immune system defends against pathogens and foreign substances while distinguishing self from non-self. It comprises innate immunity, which provides immediate, non-specific defense, and adaptive immunity, which generates pathogen-specific responses and immunological memory.

Innate immunity includes physical barriers such as skin and mucous membranes, phagocytic cells like macrophages and neutrophils, natural killer cells, and soluble factors such as complement proteins and various cytokines. Adaptive immunity involves lymphocytes: B cells, which produce antibodies, and T cells, which can help B cells, destroy infected cells, or regulate the immune response. Antigen presentation by dendritic cells and macrophages activates adaptive responses. The humoral arm involves antibodies; the cellular arm involves T cell–mediated responses.

Key organs and tissues include primary lymphoid organs (bone marrow and thymus) where immune cells develop, and secondary lymphoid organs (spleen, lymph nodes, mucosa-associated lymphoid tissue) where immune responses are organized. Immunological memory enables more rapid and robust responses upon re-exposure to pathogens.

Clinical immunology covers immunodeficiency, autoimmunity, hypersensitivity, transplantation immunology, and cancer immunology, including immunotherapies such as monoclonal antibodies and checkpoint inhibitors. Immunology also explores vaccines, tolerance, and host-microbe interactions. Advances in immunology have implications for infectious disease, oncology, and regenerative medicine.