A cell of the immune system that produces antibodies and undergoes selection during immune responses.An immune cell is any cell that participates in the body's defense against pathogens, abnormal cells, or foreign substances. The immune system is not a single organ but a network of specialized cells that patrol the blood, lymph, and tissues. These cells include white blood cells such as lymphocytes (B cells and T cells), macrophages, dendritic cells, and neutrophils. Each type has a distinct role: some engulf and digest invaders, some release signaling molecules, and some produce antibodies — proteins that stick to a specific target and mark it for destruction. The seed definition mentions cells that produce antibodies and undergo selection, which points specifically to B cells and T cells, the key players in adaptive immunity.
Why do immune cells matter? They are the reason we survive infections and why vaccines work. When a pathogen enters the body, immune cells recognize molecular patterns on its surface. Some cells respond immediately, while others take days to mount a targeted attack. During that process, cells that recognize the pathogen are selected to multiply, while those that react to the body's own tissues are eliminated — a process called selection that prevents autoimmunity. This selection happens in organs like the thymus for T cells and the bone marrow for B cells.
Immune cells also explain immunological memory: after an infection, some B and T cells remain as memory cells, so a second encounter with the same pathogen triggers a faster, stronger response. That is the basis of vaccination. When immune cells malfunction, the result can be allergies, autoimmune diseases, or immunodeficiency.
The existence of white blood cells was described in the 19th century by Paul Ehrlich and others. The concept of antibodies was developed by Emil von Behring and Shibasaburo Kitasato in the 1890s. The selection process for lymphocytes was elucidated by Peter Medawar, Frank Macfarlane Burnet, and others in the 1950s and 1960s.
Immune cells work through recognition and response. Each B cell and T cell carries receptors on its surface that are generated randomly during development. When a receptor binds to a matching molecular shape (an antigen), the cell receives a signal to activate. B cells that bind can differentiate into plasma cells that secrete antibodies — soluble versions of their receptors. T cells can either help other immune cells (helper T cells) or kill infected cells (cytotoxic T cells).
Selection occurs in two stages: positive selection ensures that immune cells can recognize the body's own antigen-presenting molecules, and negative selection removes cells that react too strongly to the body's own tissues. This leaves a repertoire of cells that can fight foreign invaders without attacking the self. The process is continuous: new immune cells are produced throughout life, especially in response to new infections.
Immune cells are central to vaccine development, cancer immunotherapy (e.g., CAR-T cells), and treatments for autoimmune diseases.
The human body produces billions of new immune cells every day, and each B cell or T cell is unique in its receptor specificity — a diversity that can exceed the number of stars in the Milky Way.
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