Inflammatory Response
Learning Objectives
Students will be able to:
- Explain the purpose and process of inflammation as an immune response
- Identify key cytokines involved in air pollution-induced inflammation
- Describe the role of different immune cells in the inflammatory cascade
- Distinguish between acute and chronic inflammation
- Analyze how chronic low-level exposure can lead to persistent inflammation
The Big Question
"Inflammation is meant to protect us, so why can it become harmful? How does particle exposure hijack this protective response?"
The Inflammatory Cascade
When cells detect particle damage, they initiate a coordinated inflammatory response:
Sequential Steps
- Recognition: Pattern recognition receptors (PRRs) detect damage-associated molecular patterns (DAMPs)
- Signal transduction: Activation of NF-kB and other transcription factors
- Cytokine release: Cells produce inflammatory mediators (IL-1beta, IL-6, TNF-alpha)
- Immune cell recruitment: Neutrophils and monocytes migrate to site
- Resolution or persistence: Either resolution occurs or chronic inflammation develops
Key Cytokines in PM-Induced Inflammation
| Cytokine | Source | Primary Effects | Systemic Impact |
|---|---|---|---|
| TNF-alpha | Macrophages, epithelium | Initiates inflammation, activates endothelium | Fever, acute phase response |
| IL-1beta | Macrophages, monocytes | Fever, activates T-cells | Systemic inflammation |
| IL-6 | Many cell types | Acute phase protein synthesis | CRP production in liver |
| IL-8 | Epithelium, macrophages | Neutrophil chemotaxis | Systemic neutrophilia |
Immune Cells in the Response
Alveolar Macrophages
- First-line defense in airways
- Phagocytose deposited particles
- Release cytokines when activated
- Can become overloaded with particles
- Impaired function leads to infection risk
Neutrophils
- Recruited from bloodstream
- Release reactive oxygen species
- Secrete proteases (elastase, MMPs)
- Short-lived but highly destructive
- Marker of acute inflammation
Dendritic Cells
- Bridge innate and adaptive immunity
- Sample antigens from airways
- Present to T-cells in lymph nodes
- Can trigger allergic responses
T-Lymphocytes
- Adaptive immune response
- Th1/Th2 balance important
- Th2 skewing promotes allergies
- Regulatory T-cells control inflammation
Acute vs. Chronic Inflammation
Acute Inflammation
- Rapid onset (minutes to hours)
- Neutrophil-dominated
- Cardinal signs: heat, redness, swelling, pain
- Normally self-limiting
- Purpose: eliminate threat and heal
Chronic Inflammation
- Prolonged (weeks to years)
- Macrophage/lymphocyte-dominated
- Low-grade, often "silent"
- Tissue remodeling and fibrosis
- Linked to chronic diseases
Key insight: Continuous low-level particle exposure can maintain chronic low-grade inflammation, even without obvious symptoms.
Biomarkers of Inflammation
Measurable Indicators
| Biomarker | Source | Clinical Use |
|---|---|---|
| C-reactive protein (CRP) | Liver (IL-6 stimulated) | General inflammation marker, cardiovascular risk |
| Fibrinogen | Liver | Clotting risk, cardiovascular marker |
| Exhaled NO | Airways | Airway inflammation (eosinophilic) |
| Blood neutrophil count | Bone marrow | Acute inflammation indicator |
Activity: Inflammatory Cascade Modeling
Build a Signaling Pathway Diagram
- Start with trigger: PM2.5 particle contacts alveolar epithelium
-
Map signal transduction:
- PRR activation (TLR4, etc.)
- NF-kB pathway activation
- Gene transcription
- Show cytokine effects: Which cytokines are released and what cells do they recruit?
- Include feedback: How might anti-inflammatory cytokines (IL-10) provide negative feedback?
Key Takeaway
Inflammation is a coordinated immune response designed to protect against threats and promote healing. However, continuous particle exposure can transform this protective response into a chronic, harmful condition. The cytokines and immune cells involved in lung inflammation can also trigger systemic effects throughout the body. Understanding this inflammatory cascade is crucial for comprehending how air pollution leads to diverse health outcomes.