Exam 1: Leukocytes Flashcards
1
Q
Leukocyte
Types
A
-
Granulocytes
- Neutrophils
- Eosinophils
- Basophils
-
Agranulocytes (“Mononuclear leukocytes”)
- Lymphocytes
- Monocytes
2
Q
All leukocytes contain…
A
azurophilic granules
- “Primary granules”
- Produced first during differentiation
- Specialized lysosomes
3
Q
Only granulocytes contain…
A
specific granules
- “Secondary granules”
- Produced later during differentiation
- Non-lysosomal secretory vacuoles
4
Q
Granulocyte
Morphology
A
3 types of granulocytes
Distinguished by LM based on:
- Nuclear lobulation ⇒ neutrophil > eosinophil > basophil
- Size and staining affinity of specific granules
5
Q
Neutrophil
Morphology
A
-
Nucleus ⇒ 2-5 lobes connected by thin strands
- # and shape of lobes ∆ over time
- Inactivated X chromosome forms a drumstick appendage visible in some nuclei
- > 5 lobes ⇒ hypersegmented
-
Small, poorly staining specific granules
- Cytoplasm with “pebbly” appearance
6
Q
Neutrophil azurophilic granules contain…
A
myeloperoxidase
(Used for detection during automated flow cytometry)
7
Q
Neutrophil
Functions
A
-
Highly phagocytic
- Especially good at killing bacteria
- First leukocyte to arrive at site of acute infection or inflammation
8
Q
Neutrophil
Recognition
A
Membrane receptors bind to material to be phagocytized ⇒ enhances specificity and rate of phagocytosis
- Some receptors bind directly to target e.g. bacteria
-
Toll-like receptors (TLRs) or “Pattern recognition receptors (PRRs)
- Binds to highly conserved molecular sequences common to many pathogens and endotoxins ⇒ Pathogen-associated molecular patterns (PAMPs)
-
Toll-like receptors (TLRs) or “Pattern recognition receptors (PRRs)
- Some receptors bind indirectly to target via opsonins
- Only recognizes bound form of opsonin
- Ex: Neutrophil Fc receptors for IgG
9
Q
Neutrophil
Effector Mechanisms
A
Neutrophils kill via:
- Respiratory burst
- Mediators stored in azurophilic and specific granules
- Neutrophil extracellular traps (NETs)
10
Q
Respiratory Burst
A
A measurable increase in oxygen consumption triggered by phagocytosis.
- Enzyme cascades produce ROI/ROS that are antimicrobial
- Kill by oxidizing microbial macromolecules
- First step catalyzed by NADPH oxidase
- Inactive subunits found on plasma membrane and in cytosol
- Activation forms membrane-bound multimeric enzyme
- Also found on phagosome membranes
11
Q
Neutrophil
ROIs
A
- Superoxide anion radical (O2·-)
- Made by NADPH oxidase
- Hydroxyl radical (OH·)
- Hydrogen peroxide (H2O2)
- Hypochlorous acid (HOCl)
- Made from H2O2 by myeloperoxidase in azurophilic granules
- Dissociates to form hypochlorite (OCl-)
12
Q
Neutrophil
Azurophilic Granule Content
A
-
Myeloperoxidase
- H2O2 → Hypochlorous acid
-
Bactericidal permeability-increasing protein (BPI)
- Damages cell membrane of gram-negative bacteria
-
Lysozyme
- Attacks cell walls of bacteria, esp. gram-positive
-
Defensins
- Small cationic proteins that permeabilize bacterial membranes
- Neutrophil elastase
13
Q
Neutrophil
Specific Granule Content
A
-
Lysozyme
- Attack bacterial cell walls
-
Lactoferrin
- Competes for iron and copper ⇒ bacteriostatic
- Collagenase
14
Q
Neutrophil Extracellular Traps
(NETs)
A
Extracellular webs composed of nuclear/mitochondrial DNA bound by histones and granule proteins.
- Released from activated neutrophils
- Traps microbes ⇒ killed by high local concentration of granule contents
- Helps prevent microbial spread
- In sepsis, can form within blood vessels causing problems
15
Q
Neutrophil
Damage
A
- Mediator release into extracellular space can damage healthy tissue
- Ex. elastase and collagenase
- Release can occur during NET formation or phagocytosis
- With phagocytosis, due to premature fusion of granules with phagosome
16
Q
Activated neutrophils due by ___ forming the major component of ___ which is removed by ___.
A
apoptosis
pus
macrophages
17
Q
Acute Inflammation
Clinical Indicators
A
Largely due to neutrophils:
-
Leukocytosis
- ↑ number of leukocytes in the blood
- Due to increased number of neutrophils leaving bone marrow in response to inflammatory mediators
-
Left shift
- Neutrophil age distribution shifts towards less mature forms
- Occurs when reserve of mature neutrophils in bone marrow exhausted
18
Q
Acute Inflammation
Course
A
-
Edema
- Occurs within a few hours
- Due to increased vessel permeability by histamine and other mediators
-
Early phase
-
Neutrophils peak at ~ day 1 ⇒ “first wave”
- Secrete chemotactic factors that attract monocytes
-
Neutrophils peak at ~ day 1 ⇒ “first wave”
-
Late stage
- Monocytes peak within ~ 2 days ⇒ “second wave”
- Differentiate into macrophages
- Phagocytize dead neutrophils, damaged tissue, and debris
19
Q
Eosinophil
Morphology
A
- 2-3 lobed heterochromatic nucleus
- Large and eosinophilic specific granules
- 30+ mediators
- Cationic protins most abundant ⇒ important in parasitic infections
- Ex. Major basic protein
20
Q
Eosinophil
Functions
A
-
Kill larvae of certain parasitic worms (helminths)
- Binds to surface of larva and secrete damaging substances
- Major basic protein
- ROS from respiratory burst
- Binds to surface of larva and secrete damaging substances
- Phagocytize Ag-Ab complexes
- Modulate activity of basophils and mast cells
21
Q
Eosinophil
Damage
A
Activity can damage host tissues:
-
Asthma exacerbation
- Damages respiratory tract
- Stimulates excess mucus production
- Kills ciliated cells
- Induces lung remodeling
- ↑ CT and SM in airways
- Stiffens airways and makes them hypercontractible
- Damages respiratory tract
- Atopic dermatitis
22
Q
Basophil
Morphology
A
- Nucleus ⇒ usually 2 poorly defined lobes
-
Large basophilic specific granules
- Often obscures nucleus
- Appears homogenous or grainy
- Can look like membrane arranged in stacks or whorls ⇒ myelin figures
23
Q
Basophil
Activation
A
IgE cross-linking:
- IgE made following Ag exposure
- Binds to high affinity IgE receptors on basophils ⇒ “primed”
- Subsequent Ag exposure ⇒ Ag binds IgE on primed basophil ⇒ IgE molecules cross-linked by Ag ⇒ activation
24
Q
Basophil activation leads to…
A
-
Degranulation ⇒ mediators released from specific granules
- Histamine
- Heparan sulfate
- Eosinophil chemotactic factor (ECF)
- Neutrophil chemotactic factor (NCF)
-
Synthesis and secretion of cytokines
- IL-4
- IL-13
- Arachidonic acid pathway activation by phospholiases
25
Basophil
Functions
* Basophils & mast cells regulate blood vessels
* More common in extravascular CT than blood
* Important in defense against **ectoparasites** (e.g. ticks)
* Mediator functions:
1. **Vasodilation & ↑ vessel permeability**
* Post-capillary venules \> capillaries
* Promotes diapedesis and Ab/complement extravascularization
2. **↑ mucus secretion**
* Helps trap Ag
3. **Bronchoconstriction**
* **↑** airflow velocity easing transport of particles trapped in mucus
4. **Class switching** ⇒ ↑ IgE production
5. **Chemotaxis** of eosinophils, neutrophils, monocytes, and macrophages
6. **Pruritis**
26
Basophil
Damage
Excessive basophil/mast cell activation results in:
* **Edema**
* **Excessive mucus secretion**
* Clogs bronchiolar lumens
* Causes nasal congestion
* **Excessive bronchoconstriction**
27
Excessive basophil or mast cell activity can result in a...
**Type I hypersensitivity**
(Immediate hypersensitivity)
Which can manifest as:
* Hay fever
* Asthma
* Urticaria
* Anaphylaxis
28
Basophils arise from a ___ when stimulated by ___ and mature in the \_\_\_.
myeloid progenitor
IL-4
bone marrow
29
Monocyte
Morphology
Size and morphology highly variable:
* Irregularly shaped nucleus
* U or horsehoe shaped
* Folded on itself
* Flower petal pattern
* Not lobulated
* Lacy "moth-eaten" chromatin
* Sharp boundary between euchromatin & heterochromatin
* Nucleus and cytoplasm pale staining
* Few azurophilic granules
* No specific granules
* Well-developed golgi
* Can make azurophilic granules throughout lifespan
30
Monocyte
Differentiation
* Circulates in blood for up to several days before entering extravascular tissues
* In tissues, **differentiates into macrophages**
* Macrophages can be long-lived (several months)
31
Resident Macrophage
Classifications
Macrophages in certain tissues/organs have characteristic morphology, functions, and names:
* **Histiocytes** ("Ordinary" macrophages) ⇒ CT
* **Kupffer cells** ⇒ liver
* **Osteoclasts** ⇒ bone
* **Alveolar macrophages** ("dust cells") ⇒ lung
32
Macrophage
Morphology
* Larger and more irregularly shaped
* Pale with euchromatic nucleus by LM
* Evidence of phagocytic activity by EM
* More phagosomes
* More secondary lysosomes
* Highly active plasma membrane
* Many thin 'pseudopods' on cell surface
33
Macrophage
Activation
* **Interferon-gamma** is an important activator
* Activation enhances activity and changes morphology
34
Macrophage
Functions
1. **Phagocytosis**
* Has specialized applications that neutrophils are not good for
* Apoptotic bodies, tissue debris, nuclei from RBCs in bone marrow, old RBCs in spleen
2. **Antigen-presenting cells (APCs)**
* Activates T helper cells
3. **Secretes products involved in many processes**
4. **Walling off large particles or microorganisms**
35
Macrophage
Secretions
**Secretes products involved in:**
* **Inflammation** ⇒ IL-1 & IL-6
* **Fever** ⇒ IL-1 is a pyrogen
* **Hematopoiesis** ⇒ GM-CSF
* **Wound healing** ⇒ TGF-α (stimulates fibroblasts)
* **Normal turnover of ECM** ⇒ proteases like elastase & collagenase
36
Macrophage
Containment
**Walls off large particles or microorganisms:**
* Occurs in chronic inflammation if macrophages unable to eliminate foreign material
* Enlarge and congregate in groups to form **histiocyte** **epithelioid cells**
* Fuse to form multinucleated **giant cells**
37
Lymphocyte
Overview
* Major cell type of the immune system
* At least 3 functionally different types:
* B cells
* T cells
* NK cells
* All arise from pluripotent hematopoietic stem cells in bone marrow
* T & B cells indistinguishable by LM/EM
* NK cells w/ distinctive morphology
38
T-cell & B-cell
Overview
* Size varies based on activation state
* Inactive ⇒ **small lymphocyte**
* Active ⇒ **large lymphocyte**
* Activation ⇒ **blast transformation** ⇒ clonal expansion
* Daughter cells mature into either:
* **Effector cells** ⇒ participate in ongoing immune response
* **Memory cells** ⇒ reserved until a subsequent immune response
39
Small Lymphocyte
Morphology
* ~90% of lymphocytes in blood
* ~ 60-80% of blood lymphocytes are T-cells
* Nucleus ⇒ round/kidney bean shaped and heterochromatic
* Very thin rim of basophilic cytoplasm ⇒ 'sky-blue' color
* Few small azurophilic granules by LM
* No specific granules by LM or EM
* Few organelles
40
Large Lymphocyte
Morphology
"**Immunoblasts** or **Lymphoblasts**"
* Develop from small lymphocytes that undergo blast transformation
* Up to 30 microns
* Nucleus ⇒ euchromatic w/ 'smudged' chromatin pattern
* Amount of cytoplasm increases
* Few small azurophilic granules
41
Humoral Immunity
Immunity that can be transferred passively from an immune donor to a non-immune recipient **using serum alone**.
(Live cells are not required)
42
B-Cells
* Important in humoral immunity ⇒ Ab-mediated
* Specific for a particular Ag
* Ag binds BCR ⇒ activation ⇒ blast transformation ⇒ clonal expansion & affinity maturation
43
Plasma Cells
**Effector cells derived from activated B-cells.**
* Secrete Ab
* Short-lived ⇒ 10-30 days
* Old plasma cells may become **Russell body cells**
* Contain large, distended RER cisternae ⇒ Russel bodies
* Full of Ab and stain very eosinophilic
44
Cell-Mediated Immunity
Immunity that can only be transferred from an immune donor to a non-immune recipient **via live T-cells.**
* Live cells required because:
* Living T-cell has to directly carry out some function
* T-cell needed to produce constant supply of short-lived mediators
* Important in defense against **viral and fungal infections** and **tumor cells**
45
T-Cells
* Essential for cell-mediated immunity
* Specific for a particular Ag
* Ag binds TCR ⇒ activation
* Many different types including:
* Cytotoxic T-cells
* Helper T-cells
* Regulatory (suppressor) T cells
46
Cytotoxic T-cells
* **CD8+** surface marker
* **Kill target cells that express 'foreign' Ag**
* Virus infected cells
* Tumor cells
* Genetically different cells e.g. tissue grafts
* Killing requires binding of T-cell to target cell
* Kills via several mechanisms including secretion of:
* **Perforins**
* **Granzymes**
47
Perforins
Proteins that aggregate to form pores in target cell membranes.
48
Granzymes
"Fragmentins"
Proteases that enter target cells through pores and induce apoptosis.
49
Helper T-Cells
"TH cells"
* **CD4+** surface marker
* TCR recognizes Ag bound to MHC II of antigen-presenting cells
* **Main function to secrete cytokines**
* Helps activate cytotoxic T cells ⇒ stimulates cell-mediated immunity
* Helps active B cells ⇒ stimulates humoral immunity
50
Regulatory T-cells
"Suppressor T-cells"
* Diverse group
* **Downregulates immune responses**
* Maintains tolerance to self
* Helps prevent autoimmune diseases
51
NK Cells
* ~5-10% of lymphocytes in blood
* ~ 15 microns
* **Moderate number of large azurophilic granules** by LM
* **Able to kill some virus-infected cells and some tumor cells**
* Requires close contact to targets
* Several mechanisms
* Perforins
* Granzymes
