SEM 2 Lecture 9

Cytokines and Biomarker Testing for Inflammation

Inflammation

Cytokines and Biomarker Testing for Inflammation

1 recognition of the injurious agent

2 recruit-ment of leukocytes

3 removal of the agent

4 regulation (control) of the response

5 repair (resolution)

steps of the inflammatory response

1. HEAT (Calor)

2. REDNESS (Rubor)

3. SWELLING (Tumor)

4. PAIN (Dolor)

5. LOSS OF FUNCTION (Functio Laesa)

Cardinal Signs of Inflammation

Calor (Heat)

caused by increased blood dynamic flow (hyperemia) to the peripheral site

Tumor (Swelling)

Increased vascular permeability (caused by gaps forming between endothelial cells) allows protein-rich fluid, to move from the blood vessels into the interstitial space.

Rubor (Redness)

proinflammatory mediators (like Histamine and Nitric Oxide) cause vasodilation of the local arterioles.

Functio Laesa (Loss of Function)

refers to the functional impairment of the cells themselves due to toxic injury

CHRONIC INFLAMMATION

Characterized by infiltration of macrophages and lymphocytes.

PAMPs Molecular (Pathogen-Associated Patterns)

molecular signatures produced by microbial pathogens

DAMPs (Damage-Associated Molecular Patterns)

endogenous molecules released from damaged or dying host cells

Mast cells

initiate the immediate vascular response by releasing pre-formed granules of histamine, which triggers rapid vasodilation.

Neutrophils

serve as the hallmark of acute inflammation and are the first leukocytes recruited from the circulation to the site of injury.

Monocytes

recruited following the initial neutrophil wave and differentiate into macrophages to orchestrate the transition toward tissue repair.

Macrophages

primary cellular source for the potent pro-inflammatory cytokines tumor necrosis factor and interleukin-1.

Platelets

contribute to the inflammatory process by releasing serotonin and growth factors that link the coagulation process to immune activation.

complement system

provides a potent defense through a cascade of proteins that generate the anaphylatoxins c3a and c5a to increase vascular permeability.

opsonization

achieved through c3b, which coats microbial surfaces to enhance recognition and phagocytosis by immune cells.

cytokines

proteins produced by many cell types (principally activated lymphocytes, macrophages, and dendritic cells, but also endothelial, epithelial, and connective tissue cells) that mediate and regulate immune and inflammatory reactions.

Pleiotropy

One cytokine acts on multiple cell types

Redundancy

Multiple cytokines carry out the same function

synergy

two cytokines work together for a greater effect

Antagonism

One cytokine inhibits the action of another

Cascade induction

one cytokine triggers a sequence of others

Autocrine

Same cell secretes and recieves cytokine signal

IL-2 stimulating the same T cell that secreted it

Paracrine

Cytokine signal secreted to a nearby cell

IL-12 from a macrophage acting on a nearby t-cell

Endocrine

Cytokine signal secreted to circulatory system, travels to distant cells

IL-1 traveling through blood to the hypothalamus to induce fever

TNF (Tumor Necrosis Factor) and IL-1

produced by activated macrophages, dendritic cells, T-cells, and mast cells, triggered by microbial products, dead cells, immune complexes, and physical injury

Interleukin-6 (IL-6)

The main cytokine of the acute phase response.

Interferons (IFN)

Crucial for defense against intracellular pathogens like TB.

Type 1

Interferons for Antiviral activities

Type 2

Interferons that activate macrophages

Chemokines (IL-8/CXCL8)

Sub-family of cytokines that induce chemotaxis.

Acute Phase Response (APR)

Systemic reaction to local or systemic inflammation. This involves fever, increased sleep, and decreased appetite.

C-Reactive Protein (CRP) and High-Sensitivity CRP

pentameric protein that binds to phosphocholine on bacterial surfaces

Standard CRP (Conventional)

measures high levels of inflammation, typically in the range of 10 to 1,000 mg/L. used to detect acute infections (bacterial vs. viral), post-surgical complications, and flare-ups of autoimmune diseases.

High-Sensitivity CRP (hs-CRP)

uses advanced assays (like monoclonal antibody-enhanced nephelometry) to detect levels as low as 0.3 mg/L. Used to detect "micro-inflammation" in the walls of blood vessels.

Procalcitonin

precursor of calcitonin produced by extra-thyroidal tissues during stress. highly specific marker for bacterial infection over viral or non-infectious causes

Erythrocyte Sedimentation Rate

indirect measure of inflammation based on red blood cell aggregation

Calprotectin and Fecal Biomarkers

calcium-binding protein derived primarily from neutrophils. utilization in differentiating irritable bowel syndrome from inflammatory bowel disease

Ferritin

iron storage protein that doubles as a positive acute phase reactant. extreme elevations in macrophage activation syndrome and in monitoring disease activity in systemic-onset juvenile idiopathic arthritis

ELISA

primary method for quantifying soluble cytokines and inflammatory biomarkers in serum or plasma.

ELISA

utilizes a "sandwich" technique with capture and detection antibodies for high specificity.

Multiplex Bead-based Immunoassay (Luminex)

allows for the simultaneous detection of dozens of different cytokines in a single small sample volume.

Multiplex Bead-based Immunoassay (Luminex)

uses microscopic polystyrene beads internally dyed with specific ratios of two fluorescent dyes and detects complex "cytokine profiles" or "panels" (e.g., Th1/Th2/Th17 panels) in one run.

Nephelometry and Turbidimetry

standard laboratory methods for measuring high-abundance acute phase reactants like crp and complement.

Chemiluminescent Immunoassay (CLIA)

utilises chemical reactions that emit light to detect ultra-low concentrations of biomarkers.

Flow Cytometry

measures cytokine production at the single-cell level rather than soluble protein in fluid.