Hematology Week 4-5: Leukocytes Overview

Leukocytes Overview

• Neutrophils are the most abundant type of white blood cells (WBCs) and are produced in the bone marrow.

Granulocytes

• Myeloblast Stages:
  • Type I Myeloblast: no visible granules.
  • Type II Myeloblast: developing azurophilic granules in the Golgi apparatus.
  • Type III Myeloblast: characterized by darker chromatin and purple cytoplasm, often associated with myeloid leukemia.
• Normal promyelocytes display a paranuclear halo, unlike abnormal promyelocytes.
• Promyelocytes contain 2-3 nucleoli, which form primary granules.
• Myelocytes are the last stage of granulocyte maturation capable of cell division and contain secondary granules.
• Metamyelocytes have a kidney-shaped nucleus and are the precursors of neutrophils; they contain tertiary granules.

Neutrophil Pools

• Marginated Neutrophil Pool: found in localized areas such as the liver, spleen, or lungs.
• Circulated Neutrophil Pool: a source of cytokines and assists in Vitamin B12 absorption.

Granules Composition

• Primary (Azurophilic) Granules: found in promyelocytes; contain myeloperoxidase and defensins.
• Secondary (Specific) Granules: found in myelocytes; include proteins like lactoferrin and gelatinase.
• Tertiary Granules: found in metamyelocytes and bands; contain b2-microglobulin and acetyltransferase.

Eosinophils and Basophils

• Charcot-Leyden crystals can be used to identify eosinophils through cytochemical staining.
• Basophils are the rarest WBCs (0-1%) and are involved in allergic reactions and inflammation.
• Mast cells, found in tissues, function similarly to basophils but are not classified as WBCs.

Agranulocytes

• Monocytes are the largest cells observed in peripheral blood smears and differentiate into macrophages in tissues.
• Macrophages play a crucial role in recognizing bacterial pathogens and participating in adaptive immunity through phagocytosis.

Immune Response

• Opsonization enhances the immune system's ability to identify and destroy pathogens or old cells.
• T-cells mature in the thymus gland; B lymphocytes are produced and mature in the bone marrow.
• Humoral immunity involves the production of antibodies.
  • T Lymphocytes:
    • CD4 cells help in antibody production.
    • CD8 cells are responsible for cytotoxic functions.

Lymphocyte Recirculation

• Lymphocytes circulate continuously through blood and tissues, aiding in immune surveillance.