Leukocyte Development, Kinetics, and Functions Flashcards
Two categories
- Granulocytes
- Mononuclear cells
are a group of leukocytes whose cytoplasm is filled with granules with differing staining characteristics and whose nuclei are segmented or lobulated.
Granulocytes
categorized into MONOCYTES and LYMPHOCYTES. These cells have nuclei that are not segmented but are round, oval, indented, or folded.
Mononuclear cells
The number of circulating leukocytes vary depending on:
• Sexandage
• Activity andethnicity
• Timeofday
• Differs according to whether or not the leukocytes are reacting to stress, being consumed, orbeing destroyed, and whetheror not they are being produced by the bone marrowinsufficient numbers.
NormalValues:
Adult:
Children:
Newborn:
Adult: 3.6– 10.6 x 10³/µL or 3.6 x10.6x10⁹/L Children: 5.0– 17.0 x 10³/µL or 5.0–17.0x 10⁹/L Newborn:8.0–24.0x10³/µL or 8.0–24.0x10⁹/L
Overall function of leukocytes is in mediating immunity:
• Innate
• Adaptive
Neutrophils in two forms:
Segmented
Band shape
Major cytokine responsible for the stimulation:
Granulocyte Colony-Stimulating Factor (G-CSF)
also known as colony-forming units granulocyte, erythrocyte, monocyte and megakaryocyte(CFU-GEMMs)
CMP
consists of HSCs that are capable of self-renewal and differentiation.
Stem cell pool
consists of cells that are dividing
Proliferation pool
consists of cells undergoing nuclear maturation that form the marrow reserve and are available for release
Maturation pool
(Maturation pool)
Releases:
metamyelocytes, band neutrophils, and segmented neutrophils
Proliferation pool releases
Myeloblast
Promyelocytes
Myelocytes
is characterized by:
• A high N:C ratio of 8:1 to 4:1;
• Slightly basophilic cytoplasm;
• Fine nuclear chromatin; and
• Two to four visible nucleoli.
• It has no visible granules when observed under light microscopy with Romanowsky stain.
Type 1 myeloblasts
Shows the presence of dispersed primary (azurophilic) granules in the cytoplasm which does not exceed 20 per cell
Type II Myeloblast
• Have a darker chromatin and a more purple cytoplasm
• Rare in normal bone marrows, but they can be seen in certain types of acute myeloidleukemias
Type III myeloblasts
It has been proposed to combine Type II and Type III blasts into a single category of
granular blasts
• Comprise 1% to 5% of the nucleated cells in the bonemarrow.
• Relatively larger than the myeloblast cells and measure16 to25 µmindiameter.
Promyelocyte
• Nucleus: round to oval and is often eccentric.
• A paranuclear halo or “hof” is usually seen in normal promyelocytes but not in the malignant promyelocytes of acutepromyelocytic leukemia.
• Chromatin clumping may be visible, esp. around the edges of the nucleus.
• One to three nucleoli may be seen but may be obscured by thegranules
Promyelocyte
• The cytoplasm is evenly basophilic and full of primary (azurophilic) granules. These granules are the first in a series of granules to be produced during neutrophil maturation
Promyelocyte
• Make up 6% to 17% of the nucleated cells in the bone marrow
• Final stage to whichmitosis occurs
• Cell begins to manufacture secondary (specific) neutrophil granules.
Neutrophil myelocytes
may look very similar to the promyelocytes in size and nuclear characteristics except that patches of grainy pale pink cytoplasm representing secondary granules begin to be evident in the area of the Golgi apparatus, referred to as “dawn of neutrophilia”. The granules eventually turn more lavender-pink than blue.
Early myelocytes
measures 15– 18 µm, and the nucleus has considerably more heterochromatin. Nucleoli are difficult to see by light microscopy.
Late myelocytes
• Consists of 3% to 20% of nucleated marrow cells.
• The nucleus is indented (kidney bean shaped or peanut shaped), and the chromatin is increasingly clumped.
• Synthesis of tertiary (gelatinase) granules may begin during this stage.
• Cytoplasm contains very little residual RNA and therefore little or no basophilia
Neutrophil metamyelocytes
• Makes up 9% to 32% of nucleated marrow cells and 0% to 5% of the nucleated peripheral blood cells.
• Evidence of basophilia is absent
• Secretory granules, also known as secretory vesicles, may begin to be formed during this stage.
• Nucleus is highly clumped and nuclear indentation that began in the metamyelocyte stage now exceeds one half the diameter of thenucleus.
Neutrophil band
• Make up 7% to 30% of nucleated cells in the bone marrow.
• Secretory granules continue to be formed • The only morphologic difference between segmented neutrophils and bands is the presence of between two and five nuclear lobes connected by threadlike filaments. • Present in highest numbers among the leukocytes in adults.
Segmented neutrophils
• Formed during the promyelocyte stage
• Last to be released through exocytosis
PRIMARY (AZUROPHILIC) GRANULES
• Formed during the myelocyte and metamyelocyte stage
• Third to be released through exocytosis
SECONDARY (SPECIFIC) GRANULES
• Formed during metamyelocyte and band stages
• Second to be released
TERTIARY GRANULES
• Formed during band and segmented neutrophil stages
• First to be released (fuse toplasma membrane)
SECRETORY GRANULES (Secretory Vesicles)
Involves the movement of neutrophils and neutrophil precursors between the different pools in the bone marrow, the peripheral blood, and tissues.
Neutrophil kinetics
The transit time from myeloblast through myelocyte has been estimated to be roughly _____, and the transmit time through the maturation pool is approximately _____.
- 6 days
- 4-6 days
Half-life of neutrophils:
approximately 7 hours
Onceinthe peripheral blood, neutrophils are divided randomly into a
CNP and MNP
_____ ______are of significant importance in allowing neutrophils to marginate as well as exit the blood and enter the tissues by the process known as ______
- Integrins and selectins
- diapedesis
Major function of neutrophil
PHAGOCYTOSIS and DESTRUCTION of foreign material and microorganisms.
Neutrophil
Steps of phagocytosis
- Recognition and Attachment
- Attachment and Engulfment
- Killing and Digestion
- Formation of Neutrophil Extracellular Traps (NETs)
The term has been used to describe the unique form of neutrophil cell death
NETosis
These cells are “acid loving” that causes them to appear brick red after staining with eosin.
Eosinophils
Eosinophils arise from
CMP
Eosinophilic promyelocytes can be identified cytochemically due to the presence of _______ in their primary granules.
Charcot-Leyden crystal protein
The first maturation phase that can be identified as eosinophilic using light microscopy and Romanowsky staining is the
Early myelocyte
Characterizedby the presence of large, pale, reddish-orange secondary granules, along with azure granules in blue cytoplasm.
Eosinophil myelocyte
Eosinophil Metamyelocytes and Bands
Secondary granules increase in number, and a third type of granule is generated called
Secretory granule or secretory vesicle
Eosinophil Metamyelocytes and Bands
Electron microscopy indicates the presence of two other organelles:
lipid bodies and small lysosomal granules
• Usually display a bilobed nucleus.
• The cytoplasm contains characteristic refractile, orange-red secondary granules.
Mature eosinophils
Eosinophil primary granules
Charcot-leyden crystal protein
The time from the last myelocyte mitotic division to the emergence of mature eosinophils from the marrow is about
3.5 days
The mean turn over if eosinophils is approximately _____ cells/kg per day
2.2 x 10⁸
Eosinophil in the marrow:
9 and14 x10⁸ cells/kg
Once in the circulation, eosinophils have a circulating half-life of roughly ______ but it is prolonged wheneosinophilia occurs.
18 hours
Eosinophil survival time in human tissues ranges from
2-5 days
Ways of eosinophils to degranulate
- CLASSICAL EXOCYTOSIS
- COMPOUND EXOCYTOSIS
- PIECEMEAL DEGRANULATION
(Eosinophil degranulation)
granules move to the plasma membrane, fuse with the membrane, and empty their contents into the extracellular space.
CLASSICAL EXOCYTOSIS
(Eosinophil degranulation)
is a second mechanism in which granules fuse together within the eosinophil prior to fusing with the plasma membrane.
COMPOUND EXOCYTOSIS
Third method, in which secretory vesicles remove specific proteins from the secondary granules. These vesicles then migrate to the plasma membrane and fuse to empty the specific proteins into the extracellular space.
PIECEMEAL DEGRANULATION
Eosinophils also regulate mast cell function through the release of ______ that causes mast cell degranulation as well as cytokine production
major basic protein (MBP)
is a hallmark of allergic disorders
Eosinophilia
is capable of destroying tissue-invading helminths through the secretion of major basic protein and eosinophil cationic protein as well as the production of reactive species
Eosinophil
Are the least numerous WBCs that make up between 0% and 2% of circulating leukocytes and less than 1% of nucleated cells in the bone marrow.
Basophils
Lifespan of a mature basophil
60 hours
Functions as initiators of the allergic inflammation through the release of preformed cytokines.
Basophils
Also involved in helminth infections and also paly a nonredundant role in mediating acquired immunity against ticks.
Basophils
Mast cell progenitors (MCPs) originate from the
bone marrow and spleen
The major cytokine responsible for mast cell maturation and differentiation
KIT ligand (stem cell factor)
_____ is the major cytokine responsible for the growth and differentiation of monocytes.
Macrophage Colony Stimulating Factor (M-CSF)
Morphologic stages of monocyte development are
monoblasts, promonocytes, and monocytes
Monocytes are slightly immature cells whose ultimate goal is to enter the tissues and mature into
macrophages, osteoclasts, and dendritic cells
The nucleus may be round, oval, or kidney shaped, but more frequently is deeply indented (horseshoe shaped) or folded on itself.
Monocytes
Monocytes chromatin pattern is looser than other leukocytes and is sometimes described as
“lacelike or stringy”
Monocyte cytoplasm is blue-gray, with fine azure granules often referred to
azure dust or ground-glass appearance
• Liver –
• Lungs –
• Brain –
• Skin –
• Spleen –
• Intestines –
–Kupffer cells
–alveolar macrophages
–microglia
–Langerhans cells
–Splenic Macrophages
– intestinal macrophages
• Peritoneum –
• Bone –
• Synovial macrophages –
• Kidneys –
• Reproductive organ macrophages
• Lymph node –
–peritoneal macrophages
–osteoclasts
–type A cell
–renal macrophages
• Reproductive organ macrophages
–dendritic cells
Monocyte/Macrophage Functions
- Innate Immunity
- Adaptive Immunity
- Housekeeping functions
LYMPHOCYTES Divided into three major groups:
• T cells
• B cells
• Natural Killer (NK) Cells
play major role in the adaptive immunity
T cells and B cells
B and T cell development can be subdivided into:
Antigen-independent and Antigen-dependent phases
B lymphocytes develop initially in the bone marrow and go through three stages known as
pro-B, pre-B and immature B cells
Immature B cells, also known as
Hematogones
Effector B cells are antibody producing cells known as
- plasma cells (top)
- plasmacytoid lymphocytes (bottom)
responsible for immunological memory
Memory cells
are produced much faster, are more prolonged, and are more effective than the events of the primary response
Secondary humoral responses
T cells are subdivided into major categories:
CYTOTOXIC (KILLER) T CELLS
HELPER T CELLS
REGULATORY T CELLS–
- are CD8+ and specialize in killing virus-infected, cancer, or foreign graft cells. Releases toxic chemicals called PERFORINS and GRANZYMES from its granules.
CYTOTOXIC (KILLER) T CELLS
also called CD4+ T cells; produce cytokines that promote differentiation of B cells into plasma cells, activate macrophages to become phagocytic, activate cytotoxic T cells, and induce many parts of inflammatory reaction
HELPER T CELLS
–areCD4+CD25+and play a crucial roles in allowing immune tolerance, maintaining unresponsiveness to self-antigens and suppressing excessive immuneresponse; produce peripheral tolerance which backs up the central tolerance emerging from the thymus
REGULATORY T CELLS
- cells mediate immune response against intracellular pathogens
- cells mediate host defense against extracellular parasites, and also involved in induction of asthma and other allergic disease.
- cells are involved in the immune responses against extracellular bacteria and fungi.
- cells play a role in maintaining self-tolerance by regulating immune response.
• TH1
• TH2
• TH17
• Treg
are capable of killing target cells by secreting granules containing granzyme and perforin or by activating apoptotic pathways in the target cells
CD8+ effector lymphocytes
Also referred to as cytotoxic T lymphocytes.
CD8+ effector lymphocytes
are capable of killing certain tumor cells and virus-infected cells without prior sensitization
NK cells
