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Phagocytes and lymphocytes both originate in the bone marrow as white blood cells and make up the body's natural immune system, but phagocytes include a larger group of cell types than lymphocytes. Phagocytic cells include granulocytes, macrophages, and dendritic cells while the lymphocyte population consists of B-cells, T-cells and natural killer cells. All may interact in the presence of infections caused by bacteria, fungi or viruses. These immune system defenses also respond in the presence of cancerous growths.
Monocytes are the white blood cells that matures into phagocytes and lymphocytes. Phagocytes generally defend the body by hunting, attacking, and consuming invading cells. When a perceived threat occurs, phagocytes arrive at the scene, encapsulate the invader and consume the antigen or cell. The phagocytes continue this process until they die. The pus produced by an infection typically contains large numbers of dead phagocytes.
Neutrophils are types of phagocytic granular lymphocytes. Under the microscope, neutrophils appear to have tiny spots or granules, which contain enzymes that are released as signals to other immune cells, and arrive in great numbers. They also contain a multi-lobular nucleus. These phagocytes often appear first at the infection site.
Macrophages respond to threats more slowly, are larger, and last longer. Besides having the ability to consume invaders, these cells may then carry the remains of the threat to lymphocytes, which perform varied tasks. Macrophages can also alert the immune system of trouble. Dendritic cells have phagocytic properties but largely remain in specific areas of the body, resembling guards.
After maturing in the bone marrow, lymphoctyes typically circulate in the organs and vascular structures of the lymph system. The spleen, thymus, and tonsils harbor these cells. The lymph vessels do as well.
B-cells are a type of lymphocyte that have the ability to consume invading threats. These agranular cells typically bind to antigens in a lock and key type formation.They also have the ability to remember specific antigens.
The T-cell, or T helper cell, is another type of lymphocyte. After leaving the bone marrow, these cells generally migrate to the thymus. CD8+ T-cells have cytotoxic properties. When viruses attack, they generally invade cells, hiding from an immune response and tricking cells into reproduction using viral deoxyribonucleic acid (DNA). The host cell responds to this attack by exhibiting proteins on its surface, which attracts CD8+ cells. The CD8+ cells then destroy the host cell and its contents before replication occurs.
The CD4+ cells are another type of T-cell. After consuming an invading cell, this lymphocyte presents the antigen to another immune cell. This cell releases chemicals calling for reinforcements, which surround the CD4+ cell, initiating the symptoms commonly associated with infection. CD4+ T-cells also perform antibody-mediated responses. Once B-cells emit chemical signals for T-cell response, this cell binds to the antigen, enabling B-cells to produce antibody-secreting clones.
Natural killer cells are variations of lymphocytes. When happening upon an infected cell, killer cells inject the host with toxic enzymes. They also signal the need for increased B-cell and T-cell production.
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