Leukopoiesis and Leukocyte Types

Leukopoiesis Overview

• Definition: Process of producing white blood cells (leukocytes) that play a crucial role in the immune system.
• Related terms:
  • Leukopenia: A decrease in white blood cell production.
  • Leukocytosis: An increase in white blood cell production.

Leukocyte Characteristics

• Leukocytes are less numerous than red blood cells.
• Functions:
  • Defense against foreign invaders.
  • Involvement in phagocytosis (cellular ingestion of microbes).
  • Participation in inflammatory responses and immune defense.

Types of Leukocytes

• Divided into two main categories:
  • Granulocytes: Contain granules in their cytoplasm.
    • Types include:
      • Neutrophils
      • Eosinophils
      • Basophils
  • Agranulocytes: Lack visible granules.
    • Types include:
      • Monocytes
      • Macrophages (tissue-resident monocytes)
      • Lymphocytes
      • Plasma cells (activated lymphocytes)

Granulocyte Development

• Granulopoiesis: Production of granulocytes.
• Stages:
  • Myeloblast: Most immature form, large, rarely seen in peripheral blood.
  • Promyelocyte: Second stage, lighter blue cytoplasm with non-specific granules.
  • Myelocyte: Third stage, smaller, more specific granules begin to appear.
  • Metamyelocyte: Fourth stage, no further cell division occurs.

Neutrophils

• Most common type of white blood cell in dogs and cats, primarily involved in fighting infections.
• Neutrophilia: Increase in neutrophils; can be caused by factors like stress, inflammation, and infections.
• Neutropenia: Decrease in neutrophils; can result from long-term steroid use or viral infections.
• Banded Neutrophils: Immature form with a horseshoe-shaped nucleus.

Eosinophils

• Characterized by pink/orange granules; involved in allergic reactions and defense against parasites.
• Eosinophilia: Increase in eosinophils commonly associated with allergies or parasitic infections.
• Eosinopenia: Decrease in eosinophils due to increased corticosteroids.

Basophils

• Contain purple granules and are involved in allergic reactions.
• Rare in circulation; thought to be tied to mast cells in tissues.
• Basophilia: Increase in basophils often in relation to allergies.

Lymphocytes

• Major producers of antibodies and main type of white blood cell in ruminants.
• Types:
  • B-lymphocytes: Mature in bone marrow; develop specific receptors and can become plasma cells.
  • T-lymphocytes: Mature in thymus; important for cellular immunity and activating B-cells.
• Lymphocytosis: Increase in lymphocytes due to infections or excitement.
• Lymphopenia: Decrease often caused by steroid response or Cushing's disease.

Monocytes and Macrophages

• Monocytes are larger than granulocytes, with a kidney bean-shaped nucleus.
• Functions include phagocytosis and antigen processing.
• In tissues, they differentiate into macrophages.

Smudge Cells

• Result from excessive pressure during blood film preparation or fragile cells.
• Appear as pale nuclear remnants; few are benign, many indicate cell fragility.

White Blood Cell Response to Infections

• Bacterial Infections: Typically show leukocytosis with neutrophilia followed by potential left shift.
• Viral Infections: Initial leukocytosis transitioning to leukocytopenia.

Leukogram Evaluation

• Stress Leukogram: Characterized by neutrophilia and lymphopenia.
• Inflammatory Leukogram: Shows neutrophilia with left shift.
• Excitement Leukogram: Caused by epinephrine release, showing lymphocytosis and neutrophilia without left shift.

Platelets

• Function in clotting; classified as cellular fragments from megakaryocytes, aiding hemostasis.

Explore the intricacies of leukopoiesis, the process responsible for the production of white blood cells. This quiz covers the different types of leukocytes, their characteristics, and their essential roles in the immune system, including granulocyte development and classifications.