White blood cells are essential components of the body's immune defense system. They circulate through the blood and tissues, helping detect and respond to bacteria, viruses, fungi, and other potentially harmful substances.Different WBC types have specialized functions. Neutrophils are among the first immune cells involved in responding to many infections. Lymphocytes help coordinate immune responses and include important B cells and T cells. Monocytes can develop into cells that help remove harmful organisms and damaged tissue, while eosinophils and basophils contribute to specific immune and inflammatory reactions.Doctors often check white blood cell levels through a complete blood count (CBC). A low WBC count, known as leukopenia, may increase susceptibility to certain infections depending on the cause and severity. A high WBC count, or leukocytosis, can occur in response to infection, inflammation, medications, or certain medical conditions.
