Blood, part 2 Leukocytes, Immune System Basics, and Leukocyte Disorders

Leukocytes (WBCs)

• Only complete cells• < 1% total blood volume• Diapedesis: ability to leave blood vessels to

move independently through tissues– Ex. loose CT or lymphoid tissues– Use amoeboid motion, following chemical trail

released by damaged cells• Infections can increase WBC count to over

11,000 / mm3 – Normal WBC count ranges from 4800 – 10,800

Leukocyte Quantities(Most to least)

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Granulocytes

• Include:– Neutrophils, Eosinophils and Basophils

• Have membrane-bound granules: vesicles w/digestive enzymes and antimicrobial proteins

• Granules can be visualized using Wright stain• Lobed nuclei• Larger than RBC; shorter-lived• Phagocytic

Neutrophils• Most common WBC• Stain: – Granules stain w/ acidic (red) and basic

(purple/black) Wright stain dyes– lilac colored cytoplasm

• 2 Types of granules that lyse bacteria:– Lysosomes– Antimicrobial proteins: defensins

• 3-6 lobes in nuclei• Kills Bacteria and Fungus• Slays bacteria w/aid of “respiratory burst”

– O2 metabolized to create H2O2 and bleach

Eosinophils

• 2 – 4 % of WBCs• Red granules (acidic dye)– w/ lysosome-like digestive enzymes

• Bi-lobed Nuclei• Kills mostly parasitic worms• Lessens allergies by phagocytizing immune

complexes• Same size as Neutrophil

Basophil

• Rarest WBC (.5 – 1%)• Have U- or S- shaped nuclei• Purple/Black Granules (basic dye)– w/histamine that

• Function like mast cells in CT• Dilate vessels, increase inflammatory response• Attracts other WBCs

– w/heparin that• Promotes inflammation• Increases heparin• Acts as anticoagulant

• Same size as neutrophil

Agranulocytes

• Include:– lymphocytes (T- and B- ) and monocytes:

• Lack visible cytoplasmic granules– Have spherical or kidney-shaped nuclei

• Major players in specific immune response.– Recognize invaders– Produce antibodies– Attack viruses and tumors– Act as phagocytic macrophages

Lymphocytes

• 25% of WBC• Large, dark-purple, circular nuclei with thin rim of

blue cytoplasm• Found mostly in lymph nodes (some circulate in

blood)• Two types : – T cells:• Helper T: coordinates immune response• Killer T: directly kills invaders, tumors, viruses

– B cells: recognize invaders, make antibodies that bind, trap, and mark intruders for destruction

Monocytes

• 3-8 % of WBC• Largest leukocytes• Abundant pale-blue cytoplasm• Purple-staining, U- or kidney-shaped nuclei• Leave vessels, enter tissue, and become

macrophages where they – actively phagocytize invaders marked by antibodies

• Help activate lymphocytes by “presenting” the antigen of invaders they digest

Summary of Leukocyte Histology

Practice Identification

Agranulocyte Lymphocyte

AgranulocyteMonocyte

GranulocyteBasophil

GranulocyteEosinophil

GranulocyteNeutrophil

GranulocyteNeutrophil

More Practice

Neutrophil Eosinophil Basophil

Lymphocyte Monocyte

Leukopoiesis (WBC Differentiation)

(a) (b) (c) (d) (e)

Myeloid stem cell Lymphoid stem cell

Myeloblast MyeloblastMyeloblast Lymphoblast

Stem cells

Committedcells

Promyelocyte PromyelocytePromyelocyte Promonocyte Prolymphocyte

Eosinophilicmyelocyte

Neutrophilicmyelocyte

Basophilicmyelocyte

Eosinophilicband cells

Neutrophilicband cells

Basophilicband cells

Develop-mentalpathway

Eosinophils NeutrophilsBasophils

Granular leukocytes

Plasma cells

Some become

Monocytes Lymphocytes

Macrophages (tissues)

Agranular leukocytes

Some become

• Stem Cell Origin: Hematocytoblast

• Myeloid Stem Cells:− originate all WBCs− except Lymphocytes

• Myeloblasts and Lymphoblasts:− “committed”− lysosome formation begins

• Differentiation continues:− granule accumulation− lobing of nuclei

Hemocytoblast

What stimulates Leukopoiesis?• Interleukins (IL) and colony-

stimulating factors (CSFs)– act as chemical stimuli– Type and amount

determines the type of leukocyte formed

• Macrophages and T cells are most important sources of ILs and CSFs – released when a

pathogen (disease causing organism) is detected

Fun Fact:IL and CSFs often used to stimulate marrow of cancer patients

Leukocyte Disorders:Leukemia

• cancerous conditions of a “line” of WBCs• Acute leukemia:– blast-type cells– usually in children– progresses quickly

• Chronic leukemia: – later stages of cyte-type cells– usually adults– progresses slowly

• Named after cell type involved. Ex…– Myelocytic, Lymphocytic, Lymphoblastic

leukemia

Leukocyte Disorders:Leukemia

• Bone marrow crowded out with cancerous, immature leukocytes (no immune protection)

AnemiaBleeding (Internal)InfectionsFever, weight loss, painFatal

Leukocyte Disorders:Leukopenia

• Opposite of Leukemia• Abnormally LOW WBC count– Usually drug induced • ex. chemo-• Glucocorticoids (steroids that suppress IS)

– HIV infection