White Blood Cells Overview

Introduction

• White blood cells (leukocytes) are crucial components of the immune system, defending the body against infection and disease.
• They are produced in the bone marrow and circulate in the bloodstream.
• They are categorized into different types based on their morphology and function.

Types of White Blood Cells

• Granulocytes:
  • Neutrophils: The most abundant type, acting as phagocytes, engulfing and destroying pathogens. Characterized by multilobed nuclei and cytoplasmic granules.
  • Eosinophils: Involved in allergic reactions and parasitic infections. Identified by their reddish-orange cytoplasmic granules.
  • Basophils: Associated with allergic reactions and inflammation. Characterized by large, dark purple cytoplasmic granules.
• Agranulocytes:
  • Lymphocytes: A diverse group that includes B cells, T cells, and natural killer (NK) cells. Crucial for adaptive immunity, recognizing and responding to specific pathogens.
  • Monocytes: Large cells that mature into macrophages in tissues. Phagocytic cells that engulf cellular debris and pathogens.

Functions of White Blood Cells

• Defense Mechanisms (Phagocytosis):
  • Neutrophils and macrophages are phagocytes, engulfing and destroying bacteria and other foreign particles. This process is critical in innate immunity.
• Adaptive Immunity:
  • Lymphocytes (B cells and T cells) play a central role in adaptive immunity.
  • B cells produce antibodies that neutralize pathogens.
  • T cells directly attack infected cells. Helper T cells coordinate immune responses, cytotoxic T cells kill infected cells. Regulatory T cells control the immune response to prevent it from attacking the body's own tissues.
  • NK cells kill abnormal cells like cancer cells.
• Inflammation Response:
  • White blood cells release signaling molecules (cytokines) that initiate and regulate inflammatory responses. This localized response helps contain and eliminate the infection. Neutrophils, macrophages, and other cells release cytokines.

Regulation of White Blood Cell Production

• White blood cell production (hemopoiesis) is regulated by cytokines, growth factors, and hormones.
• The bone marrow is the primary site of white blood cell production.
• Feedback mechanisms maintain appropriate levels of different WBC types.

White Blood Cell Counts and Tests

• Complete blood count (CBC) is a routine blood test to measure the number of different types of white blood cells in the blood.
• Elevated white blood cell counts (leukocytosis) often indicate an infection or inflammation.
• Decreased white blood cell counts (leukopenia) may indicate a bone marrow disorder or certain medications.

Disorders Related to White Blood Cell Function

• Leukemias: Cancer affecting blood-forming cells in the bone marrow leading to an overproduction of immature white blood cells.
• Lymphoma: Cancer of the lymphatic system, characterized by abnormal lymphocytes.
• Immunodeficiencies: Conditions where the immune system is weakened, leading to recurring infections. These can be congenital or acquired.
• Autoimmune disorders: Conditions where the immune system attacks the body's own tissues.

Importance of White Blood Cells

• Essential for defending the body against infections.
• Maintain overall health and protection.
• Understanding their functions and regulation is critical for diagnostics, treatment, and preventative care.