Hematology 8: Granulocytes and Monocytes

Introduction to Leukocytes and where they mature

•Differentiate, proliferate, and mature in the _bone marrow_

•Except for T lymphocytes - mature in thymus

granulocytes (Polymorphonuclear cells (PMNs)

neutrophils, eosinophils, basophils

Neutrophils

•Most abundant bacterial defense

•Eosinophils

•Allergy, parasitic infections

Basophils

Histamine release, inflammation

agranulocytes (mononuclear cells)

monocytes, lymphocytes

Myeloblast

Large nucleus, no granules - earliest recognizable precursor, scant light blue cytoplasm, Golgi apparatus, nucleus is round or oval and lacy and with evenly stained chromatin, nucleoli

Microscopic Features of myeloblast

•3-4x larger than a mature RBC

•High nuclear to cytoplasmic ratio

•Round Nucleus with immature chromatin (not clumped)

•Prominent nucleoli

•Cytoplasm is scant, gray to pale blue and lacks granules

promyelocyte

azurophilic granules appear - reddish purple primary granules (glitter) start to see, large N-C ratio, more cytoplasm, nucleus centrically located, chromatin coarser than blast, still open and lacy, several nucleoli

Microscopic Features of promyelocyte

2-3x larger than a mature RBC

High nuclear to cytoplasmic ratio (but more cytoplasm than Myeloblast)

Round Nucleus with immature chromatin (not clumped)

Nucleoli are present but less prominent than Myeloblasts

Cytoplasm with primary (azurophilic) granules

myelocyte

reduced size of nucleus, is oval or round or slightly flattened to one side, cytoplasm less blue, clear light area next to nucleus = golgi apparatus, has secondary granules

Microscopic Features of myelocyte

•2-3x larger than a mature RBC

•Intermediate N:C ratio (more cytoplasm than promyelocyte)

•Eccentrically placed oval Nucleus (No nucleus indentation) with more mature chromatin (clumped)

•Perinuclear clearing is common

•Nucleoli are absent (Note: absent nucleoli from this stage onward)

•More cytoplasm with only rare or absent primary (azurophilic) granules

metamyelocyte

nuclear chromatin coarse and climbed, no nucleoli visible, nuclear indentation kidney bean shape, tertiary granules synthesized, predominance of secondary granules

can start to differentiate between eosinphil, neutrophil or basophil?

Band neutrophil

Horseshoe shaped nucleus, indentation of nucleus of more than half the diameter, cytoplasm is pink to tan, granules all granules present, granules don’t stain as prominent

first stage normally found in peripheral blood vessels

segmented neutrophils

nucleus segmented with three to five lobes, condensed chromatin, cytoplasm is pink or tan to clear color, contains secondary granules, tertiary granules, smaller cytoplasm

positive for CD11b

leukocytosis

increase in leukocytes

leukopenia

decrease in leukocytes

neutrophil function and kinetics

first responders, most abundant WBC - 70%, migrate from peripheral blood into tissues in response to chemotactic stimulation induced by a foreign agent, where they engulf and destroy the invader.

first sign of underlying pathology

Alteration in concentration of PB leukocytes is often

Granulocytopenia

↓ in all types of granulocytes

Neutropenia:

•↓ only in neutrophils

Agranulocytosis:

•absence of granulocytes, high risk of developing infection

Granulocytosis:

•↑ in all granulocytes

Neutrophilia

↑ in neutrophils

Reactive response to bacterial infection, metabolic intoxication, drug intoxication, tissue necrosis

three roles of innate immune response neutrophil function

Adherence & Migration (chemotaxis)

Phagocytosis

Direct bacterial killing

Neutrophil Adherence and Migration

Neutrophil-endothelial cell adhesion facilitates diapedesis.

Once in tissues, neutrophils migrate towards infected site through chemotaxis.

phagocytosis

Neutrophil eats cell with psuedopodia pushing membrane out - actin mediated

steps of phagocytosis

recognition and attatchment: Neutrophils recognize and bind pathogens.

Engulfment:

Neutrophil extends pseudopods, enclosing the pathogen within a phagosome.

phagosome maturation: phagosome fuses with lysosome - forming phagolysosome

microbial killing mechanism - reactive o2 and n species and enzymes degrade

pathogen is broken down into fragments and expelled

Neutrophil extracellular traps (NETs)

Composed of DNA and proteins

Function to eradicate microbes independent of phagocytosis

Trap, neutralize, and kill bacteria, fungi, viruses, and parasites

prevent hte spread of microbes

Eosinophil Development & Maturation

Myeloblast → Large nucleus, no granules.

Promyelocyte → Azurophilic granules appear.

Myelocyte → Secondary granules form, no more mitosis. **here can tell it is eosinphil because stains red!!!

Metamyelocyte → Nucleus starts to indent.

Eosinophilic Band → Horseshoe-shaped nucleus.

Eosinophil → Mature, functional cell.

eosinophillic myelocyte

contains large, eosin staining crystalloid granules, granules larger than neutrophils and more of them

lots of cytoplasm, nucleus usually one lobe, maybe nucleoli, secondary granules

eosinphil

nucleus - no more than 2 or three lobes, no nucleoli

reddish cytoplasm completely filled with granules - crystaloid, uniform in size, evenly distributed, secondary granules

eosinophil defense function

Parasitic infections (helminths), too large to be phagocytosed so releases granules of major basic protein from granules on parasites

Allergic reactions and hypersensitivities (asthma, anaphylaxis

basophil maturation

Similar to neutrophil maturation

Gradual indentation and segmentation of the nucleus,

defining stage at basophilic myelocyte, stains purple

basophils function

Release histamine in granules & heparin → important in allergic responses

more involved in inflammatory responses

Releases enzymes that are vasoactive, bronchoconstrictive, and chemotactic

basophil morphology

segmented nucleus, no nucleolus, many dark purple granules, more cytoplasm - stained purple

monocytes

Primary role is host defense, which is fulfilled in tissues as macrophages

Produced in BM from progenitor cell (CFU-GM)

Monocytes and macrophages

Activated by

•T lymphocytes

•endotoxin

Monocyte Maturation

Monoblasts cannot be differentiated from the myeloblast in normal B M

Stages:

Monoblast

Promonocyte

Monocyte

Macrophage

monoblast

nucleus ovoid or round or slightly indented, pale purple blue, finely dispersed lacy chromatin, nucleoli, cytoplasm abundant blue and gray, sometimes see vacuoles

promonocyte

first morphologically recognizable cell, nucleus irregular and indented, fine chromatin network, coarser than monoblast, many nucleoli, cytoplasm blue gray

monocyte cell morphology

nucleus bean or horshoe shaped, numerous folds, chromatin loose and linear, cytoplasm blue gray, vacuoles frequently seen

macrophage

Monocyte leaves PB and enters tissues

Matures into macrophage

nucleus is round with reticular appearance, cytoplasm blue gray, irregular shape, many vacuoles

what tissues do macrophages live in?

are widely distributed in the body, specific name depending on their anatomic location

liver ?

lungs = alveolar macrophage

skin - langerhans cell

brain- microglia

Monocyte Function

Active in innate and adaptive immunity

Ingest and kill microorganisms

Inhibit the growth of intracellular microorganisms

Requires activation by T cells via cytokines

Killing is nonspecific

Can also be activated by endotoxins or opsonins

they are also important scavengers, remove toxic substances from blood,

what do macrophages phagocytize?

microorganisms

dead /dying cells

cells tagged with antigen - opsonized

particulate matter - foreign

cellular debris

denatured proteins

antigen-antibody complexes

clotting factors

what is the significance of macrophages being antigen presenting?

Initiate and regulate the adaptive immune response

Produce cytokines

Stimulate proliferation and differentiation of lymphocytes

granulocytes

Neutrophils

Most abundant bacterial defense

Eosinophils

Allergy, parasitic infections

Basophils

Histamine release, inflammation

agranulocytes

•Mononuclear cells

•Monocytes

•Differentiate into macrophages

•Lymphocytes

•B cells

•T cells

•NK cells