Overview
This lecture explains the main types of white blood cells (leukocytes), their functions, and how they help protect the body.
General Facts About White Blood Cells
- White blood cells (WBCs) are generally the largest cells circulating in the blood.
- WBCs are stored in the lymph system, circulate in blood, and are found in tissues.
- WBCs make up less than 1% of total blood volume.
- Some WBCs live just 18 hours, while others survive for years.
Five Major Types of White Blood Cells
- The five major groups are basophils, neutrophils, eosinophils, lymphocytes, and monocytes.
Basophils
- Basophils defend against parasites and bacteria by releasing histamine (causes allergy symptoms) and heparin (blood thinner).
- Basophils act immediately when any foreign substance is detected and are not antigen specific.
Neutrophils
- Neutrophils target bacteria and fungi and are the most plentiful WBCs in blood.
- They respond and multiply quickly, increasing total WBC counts during infection.
Eosinophils
- Eosinophils target larger parasites, such as worms.
- They also moderate allergic and inflammatory responses.
Lymphocytes
- Lymphocytes identify and destroy foreign invaders; main types are B cells, T cells, and natural killer (NK) cells.
- 75% of lymphocytes are T cells, 10% are B cells, 15% are NK cells.
- B cells identify invaders and are linked to antibodies.
- T cells mature in the thymus, attack invaders, and regulate immune response.
- NK cells help in destroying infected or abnormal cells (not detailed here).
Monocytes
- Monocytes are partially differentiated WBCs, maturing into macrophages or dendritic cells in tissues.
- Macrophages ingest microbes and infected cells.
- Dendritic cells present pieces of antigens to B cells to trigger an immune response.
- Monocytes produce cytokines, signaling molecules for cell communication, such as histamine.
Key Terms & Definitions
- Leukocytes (White blood cells) — immune cells that protect the body from infections.
- Basophils — WBCs releasing histamine and heparin to fight invaders.
- Neutrophils — most abundant WBCs, target bacteria and fungi.
- Eosinophils — WBCs targeting parasites and moderating allergies.
- Lymphocytes — WBCs including B cells, T cells, and NK cells that identify/destroy invaders.
- Monocytes — immature WBCs that become macrophages or dendritic cells.
- Macrophages — cells that ingest and destroy microbes and infected cells.
- Dendritic cells — cells that present antigens to other WBCs.
- Cytokines — signaling proteins produced by WBCs; histamine is an example.
Action Items / Next Steps
- Review antibody functions and interactions with white cells in upcoming videos.