UNIT #3 - LEUKOCYTES


WHITE BLOOD CELLS (WBCs)

  • Definition: White blood cells, or leukocytes, are a crucial component of the immune system, playing a vital role in defending the body against infections and foreign substances.

  • Contrast with Red Blood Cells (RBCs): Unlike red blood cells that are primarily involved in oxygen transport, WBCs are key players in the immune response.

TYPES OF WHITE BLOOD CELLS

Overview

  • Five primary types of WBCs:

    1. Neutrophils

    2. Eosinophils

    3. Basophils

    4. Monocytes

    5. Lymphocytes

  • Each class has unique morphology and functional roles in the immune system.

Distinct Functions of Each WBC Type

Neutrophils

  • Predominantly found WBC in dogs, cats, and horses.

  • Functions:

    • Phagocytize foreign organisms, particularly bacteria, primarily in tissue and not in blood.

    • Comprise about 70% of total WBCs and are considered the first line of defense in acute infections.

  • Characteristics:

    • Neutral staining of granules, making them less visible compared to other leukocytes.

Eosinophils

  • Characteristics:

    • Distinct red/pink granules.

    • Short duration in circulation (1/2 to 1 hour in dogs).

  • Functions:

    • Recruit other cells to aid in inflammatory responses.

    • Key role in combating gastrointestinal parasites.

    • Associated with hypersensitivity reactions and allergies.

Basophils

  • Rarity:

    • The least common type of WBC in peripheral blood, particularly in dogs and cats.

  • Functions:

    • Involved in allergic responses and inflammation.

  • Characteristics:

    • Bilobed nucleus; granules are more visible in larger animals.

Monocytes

  • Characteristics:

    • Largest type of WBC with significant cytological variation.

    • Contain vacuoles and are short-lived in circulation but long-lived in tissues as macrophages.

  • Functions:

    • Engaged in phagocytosis and removal of foreign materials.

    • Process foreign antigens for recognition and response by lymphocytes, generating antibodies.

Lymphocytes

  • Functions:

    • Central role in the immune response.

    • Two main types:

    1. T cells

    2. B cells

  • Characteristics:

    • Small, with scant bluish cytoplasm and a round nucleus, typically twice the size of RBCs.

PRODUCTION OF WHITE BLOOD CELLS

Myelopoiesis

  • Definition: The process by which blood cells, specifically WBCs, are produced in the bone marrow.

  • Groups of WBCs:

    • Granulocytes:

    • Comprised of neutrophils, eosinophils, and basophils, which contain granules capable of phagocytosis.

    • Agranulocytes (Lymphocytes):

    • Lymphocytes lack granules and are pivotal in the immune response.

Granulopoiesis

  • Definition: The specific production and maturation of granulocytes (neutrophils, eosinophils, and basophils) in the bone marrow.

  • Timeline:

    • Normally takes 2-7 days for a WBC to mature.

  • Signals for production:

    • Triggered by body demands such as infections or inflammation, requiring leukopoietins.

Maturation Process of Granulocytes

  • Initiated when the body signals that additional granulocytes are needed.

  • Development stages:

    1. Myeloblast: First recognizable committed stem cell.

    2. Promyelocyte: The last stage capable of division, prior to differentiating into specific granulocytes.

    3. Band cell: Immature form of neutrophils present in healthy circulation (1-2%).

CIRCULATING AND MARGINALIZED POOLS OF WBCs

Circulation Pools

Marginated Pool

  • Cells adhered to the vessel walls and ready to be released into tissue during an acute response.

Circulating Pool

  • Granulocytes moving freely within the central part of blood vessels, not immediately positioned for quick mobilization.

DETERMINING WBC FUNCTIONALITY

Importance of WBC Differentiation

  • Analyzing WBCs in a Complete Blood Count (CBC) can signal:

    • Presence of infections or other abnormalities.

    • Acute vs. chronic conditions.

    • Degree of severity in pathologies.

Techniques for Differentiation

  1. Microscopic evaluation of blood smears.

  2. Automated machines applying algorithms for WBC classification.

  3. Factors considered for differentiation include:

    • Cell size

    • Nuclear characteristics

    • Cytoplasm characteristics

    • Presence of granules

    • Shape and size relationship to whole cell

CONCLUSION

Summary

  • Knowledge of each WBC's role enhances the understanding of the immune response and pathology.

  • Early detection and differentiation through blood work are crucial in diagnosing and treating infections effectively.

Practical Implications

  • Effective treatment can be strategized based on identified WBC counts and characteristics, making WBCs essential for clinical assessments in veterinary and medical practices.