The Inflammatory Response: Neutrophils & Macrophages

Exam 1 - Lectures 2, 3, & 4

What are the 3 major way microbes can gain access to the body?

inhalation, ingestion, wounds

What is the general purpose of sentinel cells?

recognize invaders → signals generated → attract defensive cells to site of invasion

What are the sentinel cells?

dendritic cells, mast cells, eosinophils, neutrophils, macrophages, lymphocytes

What are the major 3 sentinel cells that possess the ability to recognize and phagocytize pathogens?

dendritic cells, mast cells, macrophages

What are the 2 possible stimuli that can result in an inflammatory response?

cellular damage

foreign antigenic substance (pathogen)

What does DAMP stand for?

damage associated molecular patterns

What are some of the possible causes of DAMP?

immunological rxn

nutritional imbalances

genetic defects

hypoxia

microorgansms

chemical agents

What does PAMP stand for?

pathogen associated molecular patterns

What are PAMPs?

unique components of microorgansms that are essential for their survival

T/F: PAMPs are found on normal host tissue.

FALSE - they are NOT found on host tissue

What are some examples of PAMPs?

unmethylated DNA, cell walls, bacterial flagella, etc

How does the host cell recognize the DAMP or PAMP?

toll-like receptors

What are toll-like receptors?

transmembrane proteins that mediate PAMP recognition

What happens when PAMPs bind to a toll-like receptor?

initiates intracellular signal transduction pathways that culminate in NF-kB

What is NF-kB?

major regulator of inflammatory gene transcription regulating the expression of chemokines, cytokines, etc

Chemokines and cytokines are examples of what?

proinflammatory genes

Toll-like receptors are found in high numbers on which cells?

dendritic cells, macrophages, & mast cells

T/F: Each TLR recognizes different components of PAMP.

TRUE - there are close to 13-15 TLR understood at this point

Sentinel cells mediate inflammation by way of what 3 things?

vasoactive molecules, cytokines, antibacterial molecules

What is considered the hallmark of acute inflammatory response?

vasodilation

What are sentinel cells?

circulating cell population that detects invaders or tissue damaged

What do sentinel cells do?

release cytokines and other substances that cause necessary vascular changes, and attract & activate phagocytic cells

Which cells are the first cells to arrive (primary effector) and deal with most if not all the invading organisms.

neutrophils

T/F: Sentinel cells are strategically located throughout the body to help mediate the inflammatory response.

TRUE

Hey this is important

What is the key to mediating the immune response?

cytokine production

What are the 4 major cytokines we discussed?

1. Tumor necrosis factor α (TNFα)

2. Interleukin-1 (IL-1)

3. Interleukin-6 (IL-6)

4. Chemokines

What are the 2 major sources for the 4 cytokines discussed?

macrophages & endothelial cells

In addition to macrophages and endothelial cells, what other cells can produce TNFα?

NK cells, T cells

What are the main actions of TNFα and IL-1?

activates endothelial cells → vasodilation

What is the main action of IL-6?

acute phase protein synthesis by the liver

What is the main action of chemokines?

regulate cell movement

T/F: Inflammatory cytokines only have local effects.

FALSE - systemic effects

What do inflammatory cytokines do?

• stimulate hypothalamus to produce prostaglandins → fever (pyrogen)

• stimulate liver to produce acute-phase proteins

A fever can be considered an _______ immune response.

innate

What do acute-phase proteins do?

cause “sickness behavior” → loss of appetite, lethargy, protein catabolism (muscle wasting)

Inflammatory cytokines are responsible for

clinical illness → septic shock, cachexia

What is the overall action of cytokines?

attract leukocytes to sites of infection

Cytokines trigger the formation of _________ on leukocytes.

lamellipodia → allows movement

Cytokines stimulate actin___________.

polymerization/ depolymerization

Cytokines increase expression of __________ on leukocytes.

adhesion molecules (β-integrins)

What are β-integrins?

receptor necessary for WBC to leave the vessels and enter the connective tissue

What are the 5 cardinal signs of inflammation?

1. Redness → increased blood flow to site of inflammation

2. Heat → increased blood flow to site of inflammation

3. Swelling → accumulation of fluid and cells

4. Pain → stimulation of sensory neurons by inflammatory mediators

5. Loss of function → tissue damage

Inflammation consists of how many changes in the small blood vessels in the area of infection?

3

What is the first change that occurs to the small blood vessels in the area of infection/ inflammation?

arterioles dilate → increased blood flow to affected area

What is the second change that occurs to the small blood vessels in the area of infection/ inflammation?

capillaries become more permeable → extra fluid + large serum proteins (antibody, complement) escape from blood

What is the term for the fluid containing large serum proteins that escapes from the blood during inflammation?

transudate → straw-colored yellow fluid, cloudy (protein rich)

What is the third change that occurs to the small blood vessels in the area of infection/ inflammation?

leukocytes migrate through venule walls into extravascular tissue

What is the term for WBCs when they migrate through venule walls into extravascular tissue during inflammation?

exudate

What is the hallmark of acute inflammation?

inflammation

T/F: There is a brief moment of transient vasoconstriction during the inital stages of inflammation.

TRUE → shock response of the nervous system that stimulates platelets

What does the leukocyte adhesion cascade (LAC) ensure?

that appropriate WBCs leave the appropriate vessel at the appropriate area of the body

ex: cut on finger → need WBCs to exit at the finger not a toe

What is the leukocyte adhesion cascade (LAC) mediated by?

cytokines

Explain the process of the LAC (vaguely)

macrophage releases cytokines → intravascuar WBC attracted to P & E-selectin on the endothelium membrane → binds in a “fast on - fast off” manor → acts as a speed bump to slow the WBC → WBC continues to roll down the endothelial membrane, binding and releasing from various receptors → as WBC rolls, it becomes more activated → WBC binds to integrins causing the it to stop → the binding changes cytoskeleton of WBC changing its shape (exit hole better) → more cytokines are activated → tell WBC that has just exited the vessel to travel to the recruiting WBC

Take a gander at this chart

What are the main effects of cytokines on the hypothalamus?

fever, anorexia, sleepiness, depression

What are the main effects of cytokines on the liver?

increased synthesis of acute-phase proteins, iron sequestration (keep from bacteria)

What is the main effect of cytokines on bone marrow?

increased WBC production (neutrophilia)

The liver produces increased amounts of _________ in response to proinflammatory cytokines.

acute phase proteins

What are the 5 main acute phase proteins that are produced by the liver in response to proinflammatory cytokines?

1. SAA (serum analoid A)

2. Fibrinogen

3. CRP (C reactive protein)

4. Ceruloplasmin

5. AGP (Alpha-1-glycoprotein)

What does SAA do?

role in WBC chemotaxis and induction of enzymes that degrade extracellular matrix

What does fibrinogen do?

plays a crucial role in hemostasis

What does CRP do?

assists in complement binding to antigenic or damaged cells

What does ceruloplasmin do?

oxidizes iron, facilitating for ferritin, inhibiting microbe iron uptake

What does AGP do?

increases with sepsis → exact function unclear

Increased serum electrophoresis of which protein fractions are features of inflammation?

α1, α2, β

Antibodies are found in which protein fraction?

γ (gamma)

In the context of innate immunity, acute phase proteins assist in the

recognition of microbial moieties (functional group/ subunit) and damaged cells or tissues

The major blood leukocyte is the

neutrophil

Which cell follows the neutrophil (primary effector cell) and deals with the remaining invaders while also cleaning up the mess?

macrophages

In order for the neutrophil to perform a specific action, the ________ must first be triggered.

correct receptor

ex: antibody receptor vs complement receptor, vs cell adhesion molecules

Once the correct neutrophil receptor is engaged, the activated neutrophil releases a ______.

net

What does the neutrophil net do?

directs neutrophil granules and contents toward the inflammatory stimulus

What are the 3 main steps of releasing the neutrophil net?

1. Nuclear envelope ruptures

2. Proteolytic breakup of chromatin

3. Plasma membrane ruptures and releases the net

What is the neutrophil net directed toward?

bacteria, PAMPs, and cytokines

In addition to casting the neutrophil net, the neutrophil undergoes

respiratory burst

What is respiratory burst?

a process by which numerous antimicrobial compounds and radicals are produced that can neutralize or eliminate pathogens

What are the key steps in respiratory burst in neutrophils?

1. NADPH oxidation & superoxide production

2. Superoxide conversion to hydrogen peroxide

3. Further conversion of hydrogen peroxide to other ROS (reactive O₂ species) like hypochlorous acid

4. Simultaneous neutralization of ROS

What are the contents of the primary granules of neutrophils?

• Defensins → bactericidal

• Myeloperoxidase → respiratory burst (provide Cl for hypochlorous acid)

• Neutral & acid hydrolases → degrade bacteria

• Lysozyme → destroys bacterial cell walls

What are the contents of the secondary granules of neutrophils?

• Lactoferrin → binds iron

• Collagenase → degrades connective tissue

• Lysozyme → destroys bacterial cell walls

Macrophages arise from a ________.

Myeloid stem cell

Macrophages mature into _______ in the blood.

monocytes

T/F: Once macrophages mature into monocytes in the blood, they remain only in circulation.

FALSE → they populate many organs in the body

Nomenclature of macrophages is based on what?

the organ in which they reside

Similar to neutrophils, in order for a macrophage to perform a specific action, the __________ must first be triggered.

correct receptor

T/F: Many macrophage cell surface receptors are grouped, meaning they have similar functions.

TRUE

What are the important cytokines produced by macrophages?

IL-1, IL-23, TNFα, IL-18, IL-12, IL-6

Macrophages are very efficient ________ cells.

phagocytic

What are the other phagocytic cell types?

neutrophils, monocytes, & dendritic cells

What are the 4 key steps of phagocytosis?

1. Chemotaxis → migration to the offending agent via chemotactic gradient

2. Adherence → mediated by cell surface receptors

3. Ingestion → the macrophage engulfs the particle

4. Digestion → breakdown of the particle effectively neutralized or kills the agent

How is phagocytosis triggered?

by the binding of a pathogen to receptors on the surface of the phagocyte (macrophage, neutrophil, etc)

Each step in phagocytosis is mediated by specific __________ interactions.

receptor-ligand

T/F: Only one receptor must be triggered in order to initiate and complete the phagocytic response.

FALSE → more than one

What is one of the main mechanisms by which macrophages recognize pathogens?

opsonization

What is opsonization?

process by which molecules (antibodies & complement) bind to the surface of a pathogen making that pathogen more susceptible to phagocytosis and destruction

The molecules that bind to the surface of a pathogen to induce phagocytosis are called ______.

opsonins

What is an essential function for cellular activation and deactivation?

crosstalk via cytokine network (i.e. macrophage & neutrophil crosstalk)

Different species clear particles from the blood in different areas of the body. Which sites are the most common among dogs, rabbits, guinea pigs, rats, and mice?

liver and spleen

Different species clear particles from the blood in different areas of the body. Which site is the most common among calf, sheep, and cats?

lungs