Introduction to Hematology/White blood Cells Laboratory Procedures

Blood components All blood cells arise from the same stem cell. In response to various chemical messengers, called cytokines, the stem cells begin to differentiate into one of two types, myeloid or lymphoid. Further differentiation in response to additional cytokines results in forming cell types. The primary cytokine responsible for erythrocyte production is erythropoietin (EPO) The myeloid line differentiates into erythroblasts which become erythrocytes, megakaryoblasts, which become platelets, and the myeloblast, which become granulocytes and monocytes. The lymphoid line differentiates into lymphoblasts which become lymphocytes.

Terminology Erythrocyte= Red Blood Cell (RBC) Leukocyte=White Blood Cell (WBC) 5 main types of white blood cells which include three granulocytes.

Functions of Leukocytes Granulocytes: Characterized by the presence of cytoplasmic granules Function of these cells occurs in the tissues, not in the bloodstream. These cells do not recirculate

Granulocytes Neutrophils Basophils Eosinophils Produced predominately in the bone marrow. Capable of mitotic division up to the myelocyte stage. Responds to an increased demand infection Takes 3-5 days to influence peripheral numbers.

Neutrophil: front line in battle These are usually the most numerous leukocytes in the blood and are primarily responsible for fighting infections

Granulocytes: Neutrophils

Segmented neutrophil: Mature cells that have a segmented, irregular shaped nucleus.

lymphocyte Segmented neutrophil eosinophil

Band Neutrophil: An immature cell characterized by a horseshoe shaped nucleus

Neutrophil Hypersegmentation Neutrophils with five or more nuclear lobes. Normal aging change of neutrophils which normally occurs in the tissues, not bloodstream. May occur with excessive levels of corticosteroids from administration or hyperadrenocorticism. Chronic inflammation. Artifactual change in the blood that sits for a period of time.

Hyper-segmented neutrophil: A ‘senior’ cell that is characterized by having 5 or more ‘lobes’ in the nucleus.

Eosinophils Inhibit chemical mediators such as histamine and serotonin which are released during allergic (hypersensitivity reactions). Have phagocytic and bacteriocidal properties similar to neutrophils but not as effective. Have parasiticidal properties. Animals with heartworms may have high numbers of eosinophils.

Eosinophil: the allergy slayer Eosinophil : red granules compare the color to the erythrocytes

Under normal conditions, they do not return to circulation after reaching the tissue. There are 300 – 400 eosinophils in the bone marrow for every one circulating in the blood.

Basophils Secrete mediators of inflammation (histamine) associated with hypersensitivity reactions. This release occurs when antigens complex with IgE is located on the cellular surface.

Basophils: the unknown stranger Basophils have a poorly defined function and are relatively rare in canine and feline blood, however they are thought to have some function in inflammatory response

Normal morphology of Granulocytes Neutrophils: multiple nuclear lobules separated by constrictions. Band granulocytes: band (horseshoe) shaped nuclei. Eosinophil: Lobulated nucleus and cytoplasm containing reddish pink granules. Basophil: Lobulated nucleus and purple- blue (Basophilic) granules.

Lymphocytes Distributed in lymphoid tissue to include lymph nodes, spleen, thymus, tonsils, bone marrow, and blood. Capable of division. Recirculate in the blood. Functions: B cells: turn into plasma cells which secrete immunoglobulins. Usually stayin the lymphoid tissue. T cells: transform into effector cells that produce lymphokines which function in mediation of cellular immunity.

Lymphocyte: guard dog of the body These are the second most common leukocyte in the blood and their primary function is immune regulation.

In the mature cell, the nucleus is round and occupies most of the cell. These cells will be slightly smaller than neutrophils

B cell

T cell

Monocytes Differentiate into the cells of the mononuclear/phagocyte system present in most tissues. Become macrophages once they migrate into the tissues. Capable of multiplying within the tissues. Can survive for long periods of time

Monocyte Functions: Phagocytosis and digestion of particulate material, bacteria, and dead cells. Macrophages are less responsive to bacterial infections than neutrophils but are more effective against fungal infections. Synthesis and release of substances involved in inflammation and immune response. Expressions of immune response by presenting antigens to T-lymphocytes. Serve as a major source of colony stimulating factors and cytokines involved in hematopoiesis. Cause bone marrow to produce more granulocytes.

Monocyte: buzzard in the blood These are the third most common cell seen in the blood and they have diverse functions. The primary function is to seek out invaders and eat them.

Once they have been called to help fight an infection, the monocyte will move into the tissue and transform into a macrophage (big eater). They can complete this transformation in about 24 hours