Pathology - Neutrophils, Granulomas, SIRS

Words that also mean: neutrophilic inflammation

- Suppurative
- Purulent
- Abscess
- Pus

Timeline of neutrophilic inflammation

- Hours: Neutrophils accumulation
- Days: Pus (bacterial infection)
- Weeks: Abscess (fibrosis of pus)

What triggers a neutrophilic inflammation?

- Bacterial infection
- Immune complexes (Type III rxn)
- Trauma
- Foreign material

How is pus formed?

Bacterial infection trying to escape from neutrophilic "traps" => Pus out

Outcomes of neutrophilic inflammation

- Resolution (apoptosis of neutrophils) (if treated!)

- Chronic inflammation (if stimulus persists)

- Fibrosis

- Contained into abscess

What happens to neutrophils when infection is resolved?

Undergo apoptosis => Phagocytosed by macrophages => Disappear!

Example of morphological diagnosis of neutrophilic inflammation

Chronic severe suppurative fibrinous multifocal inflammation

Gross appearance of neutrophilic inflammation

- Cloudy plaque
- Pus (if infected)
- Abscess (if long time fibrosis): White creamy filled nodules, tough fibrous tissues

5 steps of neutrophil response

0. Antigen recognition: Triggers cells to release mediators (PAMPs DAMPs - TLRs, Opsonization)

1. Inflammatory mediators: Stimulate vessel wall "leaks"

2. Rolling adhesion: Neutrophils roll and adhere to vessel walls via selectin

3. Firm adhesion: Integrins (neutrophil) attach to ICAM1 (vessel wall)

4. Diapedesis: Neutrophils migrate out of vessels

5. Chemotaxis: Inflammatory mediators/chemoattractants (IL8) attracts neutrophils towards injury site

What are the chemicals that help attract neutrophils? (3 names)

- Inflammatory mediators
- Chemoattractants
- Chemotaxic molecules

What would happen if an animal lacks chemical mediators (don't have CD18, IL8)?

=> Impaired neutrophil function/migration
=> Increased neutrophil levels in blood (as they can't migrate out of vessels)
=> PERSISTENT, RECURRENT INFECTIONS

Name some chemotaxic/inflammatory mediators

- Neutrophils: IL-8

- Eosinophils: Eotaxin

- Both: C5a

How do antibodies protect against infections? (4)

- Bind bacteria => Complement lysis

- Opsonisation

- Block bacteria's cell-adhesion proteins

- Neutralize toxin

3 ways for leukocytes to recognize antigens

- Opsonins coat pathogen -> attracts

- PAMPS/DAMPS - TLRs (innate) - on macrophages/leukocytes - recognize and bind to antigens => activate cells to produce inflammatory mediators

- Cytokines (mediators) trigger neutrophils action

Name some opsonins that enhance leukocytic recognition of pathogens

- IgG = Acquired (from Bcells)

- C3b = Acquired and Innate

- SP-A, MBL = Innate

How do neutrophils kill?

- Phagocytose, then kill with:

- Oxidative (ROS)

- Antimicrobials in granules

- Proteolytic enzymes in granules

- NETs = when neutrophils die -> net

Benefits and consequences of neutrophilic inflammation?

Benefits:

+ Killing bacteria (3 ways)

+ Phagocytosis -> eliminate bacteria

+ Contain infection in an area (abscess)

Consequences:

- Forming space-occupying lesion => Impair organs function/mobility, rupture organs

- ROS and proteases => Injure tissues, Pain

- Cytokines => Thrombosis, Ischemia/Infarction

- Fibrosis => toughen, stricture

- Fluid leakage (if in vessels) => Hemorrhage, Edema

Neutrophilic inflammation creating oxidative stress - how is it seen in histo?

= brown stains of malondialdehyde, that is mass produced when ROS is produced

Where are neutrophils found in healthy animals?

- Blood (vessels)
- Made from bone marrow

What trigger eosinophils?

- Parasites, worms, helminths, trematodes
- Allergy

Gross and microscopic appearance of eosinophil inflammation

- Gross: May be green

- Microscopic: Pink/eosinophilic

Explain the process of triggering eosinophils from pathogen to mediators

1. Recognition: Antigen-Ig; APC presents to lymphocytes

2. Mediators: Lymphocytes produce chemokines/mediators

3. Chemotaxis: Chemokines attract Eosinophils to site

3.2 Histamine effect: Mast cells -> histamine -> Vasodilation, hyperemia, permeability etc.

How are eosinophils different from neutrophils action?

- Similar: ROS, and proteins from granules to kill pathogen (but stronger?)

- Difference: NOT phagocytic

Generally, similar mechanisms of chemotaxis, but different mediators.

Explain type 3 hypersensitivity - how is it formed, and consequence if not resolved?

- Circulating immune complexes (of antigens + antibodies) deposit on vessel walls

- Whenever antigen meets antibody, a complex is always formed => mostly resolved (phagocytosis/complement)

-> If not resolved => cause infections via production of cytokines -> recruitment of neutrophils

=> Vasculitis: Neutrophil-induced damage

=> Platelet activation

=> Thrombosis

=> Ischemia, Infarction

=> Fluid leakage (fibrin, hemorrhage, edema)

What triggers Immune complex rxns?

- Antigens
- Neoplasia
- Drugs rxn
- Autoimmune

Sequelae of Immune complexes rxn, pathogenesis, and final consequence?

Immune complexes formed when meet antigens (ex. Strangles)

-> Trigger inflammatory mediators (cytokines, IL-8)

-> Activate complement + macrophages and neutrophils

-> Neutrophils recruitment and chemostaxis; Platelet activation

=> Vasculitis: Ischemia, infarction, leakage of fluid/edema/hemorrhage

Where do immune complexes dz usually happen and their corresponding names?

- Typically in well-vascularized tissues (glomerular, skin, synovium in joints)

- Vasculitis = skin

- Polyarthritis = joints

- Glomerular = glomerulonephritis

- Uveitis = eyes

- Systemic lupus = many tissues

Arthus reaction

Localized Type III immune complex reaction in the skin

Bastard strangles

= Strep. equi spreading from pharynx and lymph nodes to viscera

= Septicemia, NOT immune complexes

= Bacteremia

= Distant lesion = Abcess, septic

= INFECTIOUS VASCULITIS from Strep.

Purpura hemorrhagica

Strep. equi => Immune complexes => Vasculitis

- Wound fail to heal because damage to epithelium => No mitotic cells

= NON-INFECTIOUS VASCULITIS from Strep.

Purpura hemorrhagica vs Bastard strangles

- P. H. is non infectious, made from immune complexes
- B. S. is infectious, bacteremia
- BOTH cause vasculitis/abscess and neutrophilic inflammation

Define granulomatous inflammation

= Inflammation dominated by macrophages

Often include: fibrosis, giant & epithelioid macrophages

= Typically cell-mediated immune response (type IV)

NOT granulation tissue (this is new healing tissue!)

Define granuloma

= Nodular mass of activated macrophages (surrounded by lymphocytes rim)

= To localize pathogen to an area (similar to abscess)

Gross and microscopic appearance of granulomatous inflammation

GROSS:

- White, tan, red

- 2 types: Homogenous, diffuse thickening, OR Central necrosis nodules

- Neoplasm-like

Ex. adenocarcinoma liver, horses' colitis

MICROSCOPIC:

- Multinucleated & Giant macrophages

- Epithelioid macrophages

Appearance of mycobacterial infection

Nodules, necrotic centre
OR
Diffuse thickening

Pathogenesis of mycobacterial infetion inflammation (steps and pathological processes involved)

- Mycobacteria infect macrophages

-> Macrophages secrete chemokines -> Recruit more M and T-cells

-> T-cells -> IFN-y -> MORE Macrophages activation!

=> Granulomatous inflammation + Cell-mediated immunity (T-cells protection)

Define pyogranulomatous inflammation

= Inflammation involving BOTH macrophages (granulomatous) and neutrophils (pus/pyo)

Causes of granulomatous inflammation

- Foreign material
- Mycobacteria
- Fungi
- DTH type IV sensitivity reaction

Pathogenesis of granulomatous inflammation

- Response to foreign material
OR
- Immune response (type IV) w T-helpers, delayed

What's the typical time duration of granulomatous inflammation?

CHRONIC!

Sequelae of granulomatous inflammation

- Space-occupying lesion => Pressure on organs

- Cachexia: Chronic body wasting

Cachexia meaning

weakness and wasting of the body due to severe chronic illness

How are macrophages activated to kill pathogens and cause lesions?

Imagine a kid (macrophage) bringing a bag of candy (pathogen) to an adult (T-cell) to help open:

- Macrophage phagocytose antigen => Present antigen to T-helpers

- T-helpers produce IFN-y => Activate Macrophages

=> Now macrophages better kill!

- Macrophages also produce mediators (IL6, IL1) -> Permeabilty, hyperemia, vasodilation -> Edema, red, raised lesion

How do macrophages migrate to sites of injury?

SIMILAR TO NEUTROPHILS
1. Mediators
2. Rolling adhesion: Selectin
3. Firm adhesion: Integrin + ICAM1
4. Diapesis and Chemotaxis

Difference from macrophages rxn vs neutrophilic rxn?

Macrophages are present in BOTH blood and tissues!

- Blood: Monocytes

- Tissues: Macrophages

=> Rapid response!

Neutrophils MUST be recruited from blood

What do macrophages do in response to tissue injury?

- Remove necrotic debris => Repair tissues, fibrosis induced

- Kill pathogens => Defend host

- Cytokines secrete => Inflammation

- APC => Immune resp.

List some triggers of delayed-type hypersensitivity (type IV)? + a clinical example?

- Plants

- Topicals

- Textiles

- Rubber, latex

- Metal

Example: Tuberculin rxn

What's in poison ivy that triggers Type IV rxn?

Urushiol

Explain steps of type IV rxn (and relevance to granulomatous inflammation)?

- Sensitization phase (multiple exposures overtime): Allergen + Macrophages (APC) -> Present to naive T-cells (Th1) -> Form T-memory

- Elicitation phase (2-3 days after): Allergen + Macrophages (APC) -> Present to T-memory Th1 -> Secrete:

+ IFN-y: Activate macrophages => Granulomatous inflammation

+ Cytokines (IL6): Inflammation (hyperemia, permeability, vasodilation -> etc.)

+ Chemokines: Recruit MORE macrophages and lymphocytes

Explain cutaneous sterile pyogranuloma

- Dermatitis with sterile (non-infectious) granulomatous nodules

- Look like skin lumps

- Unknown cause!

= Type IV Immune-mediated WITHOUT CAUSE/pathogen

What clinical signs can a granulomatous infection in the lung cause, and how?

- Pathogen (ex. yeast) -> Macrophages and mediators

-> Histamine -> Bronchoconstriction

-> Fibrosis -> Decrease lung compliance

-> Vasodilation/Hyperemia -> Swelling, redness -> Decrease gas exchange

How to diagnose whether it is other types of rxn, or delayed (type IV)?

- Re-expose patient to allergen

=> Quick rnx = Other types (I, II, III)

=> Delayed after 2+ days = Delayed IV

What types of cells do you expect to see/react for each type of these pathogens?
Parasites
Mycobacteria
Bacteria
Virus, protozoa

Parasites = Eosinophils

Mycobacteria = Macrophages

Bacteria = Neutrophils

Virus, protozoa = Lymphocytes/T-cytotoxic

What can be the cause of lesions with each of these types of cells?
Eosinophils
Macrophages
Neutrophils
Lymphocytes/T-cytotoxic

Eosinophils = Parasites, Type I rxn

Macrophages = Mycobacteria, Fungi, Type IV rxn, foreign

Neutrophils = Bacteria, Type II rxn, foreign

Lymphocytes/T-cytotoxic = Virus, protozoa

Systemic Inflammatory Response Syndrome (SIRS) meaning

= Systemic consequences of either:

- LOCALIZED inflammation (ex. pneumonia, pancreatitis, leukocytosis, cytokinemia) + SYSTEMIC distribution of inflammatory mediators/cytokine storm

OR

- SYSTEMIC inflammation (anaphylaxis, liver injury, bacteremia)

SIRS vs Acute Phase Response

SAME THING!

Acute phase response = Systemic ADAPTIVE (Acute = Adaptive) response to severe inflammation

Sepsis meaning

= SIRS caused by infection

Bacteremia meaning

= Bacteria in systemic circulation (w or w/o dz)

Explain pathogenesis and steps of SIRS

- DAMPS and PAMPS + PRRS

-> Mediators (IL6, TNF-a, Complement cascade) causing:

- Acute response: Fever, depress, anorexia, leukocytosis, liver production of acute phase proteins

- Vasodilation: Systemic hypotension -> Ischemia! (ex. liver zone 3 necrosis and injury)

- Permeability: Edema

- Leuko activation: ROS, proteases

=> Tissue damage and systemic inflammation

- DAMPS and PAMPS + PRRS also activates endothelium: Increase tissue factors, decreases protein C and thrombomodulin

-> Coagulation -> Disseminated intravascular coagulation (DIC)

=> Consumptive Coagulopathy & Hemorrhage

Septicemia meaning

= Bacteremia WITH CLINICAL DZ

Explain some body changes/responses in Acute Phase Response and what organs it's caused by

Mostly physiologic:

- Fever - Hypothalamus

- Anorexia, depression - Brain

- Leukocytosis - BM

- Increase acute phase protein synthesis in liver and plasma levels (ex. C protein, fibrinogen) - Liver

- Cachexia

- Cortisol (stress)

Definition, benefits and consequence of of acute phase proteins

Definition: Proteins (serum) that increased in response to inflammation

Benefits:

- Control pathogens

- Stop inflammation

- Minimize damage in tissues

Consequence: Albumin secretion

Explain steps and pathogenesis of SIRS

- Inflammatory stimulus + macrophages

-> Mediators release (IL-6, IL-1, TNF-a) -> travel to other organs via blood (short half-lives; those with longer half-lives are inhibited at times)

-> Induce other factors (PGE2, CSFs)

-> Symptoms (fever, anorexic, leukocytose, acute phase proteins)

What are CSFs?

colony stimulating factors

What are acute phase proteins and what are they used for?

= Proteins made during acute phase response, which is a systemic cytokine effect

= Diagnose systemic inflammation

+ Ruminant: Fibrinogen, haptoglobins

+ Dogs/cats: Serum amyloid A

Autoimmune disease meaning

= Failure of self tolerance

= Ig or T-cell mediated

Explain steps to autoimmune rxn

- Igs or T-cells/T-cytotoxic react to self-antigens
-> Activate complement + opsonization
-> Inflammation and Cell lysis

Explain 3 mechanisms of autoimmune dz damages (which cell mediates?) + example dz (2 each)

- Ig-mediated complement and opsonization (Type 1 & 2): Hemolytic anemia, Thrombocytopenia,

- Immune complex + macrophage (Type 3): Vasculitis, uveitis

- T-cell mediated (Type 4): Lupus, hypothyroid

Examples of autoimmune dz

- Hemolytic anemia
- Thrombocytopenia
- Pemphigus
- Hypothyroidism
- Hypoadrenocortism
- Systemic lupus

General benefits of inflammation

- Contain injury to a site
- Remove necrotic tissues
- Initiate tissue repair(sometimes)

- Eliminate/kill pathogen

Gelatinous transformation of fat - meaning

- Bone marrow has gelatinous materials instead of fat

- Serous atrophy

= Chronic resorption of fat, only protein remains

How to diagnose SIRS or general inflammation?

- Fever
- Leukocytosis
- Acute phase protein levels high

Which organs are damaged in SIRS and consequences?

- Kidney
- Liver: Increased acute phase proteins
- Lung
- Heart
- Intestine
- Brain/hypothalamus: anorexia, depression, fever
- BM: leukocytosis

What's the major reason of death from SIRS?

- NOT from primary damage
- From secondary damages to organs