Relating to or characterized by inflammation—the body's protective response to tissue damage, infection, or stress involving immune cell activation, cytokine production, vascular changes, and tissue repair processes. In cPNI, inflammatory responses exist on a spectrum from acute (adaptive and protective) to chronic low-grade (maladaptive and pathological), with the transition point representing a failure of resolution mechanisms rather than excessive activation.
Think of inflammation as a fire department responding to a building fire. When the alarm sounds (DAMPs or PAMPs detected), the fire trucks rush to the scene (immune cells recruited via vasodilation and increased vascular permeability). Firefighters spray water and foam (cytokines, prostaglandins, reactive oxygen species) to contain the blaze, and the building gets soaked and damaged in the process—but that's acceptable collateral damage to save the structure. The critical moment comes when the fire is out: a good fire department knows when to STOP spraying, pump out the water, and call in the reconstruction crew (specialized pro-resolving mediators).
Acute inflammation is a fire that's put out in 4-6 days, building repaired, department returns to base. Chronic low-grade inflammation is like leaving the hoses running at low pressure for months—no dramatic flames, but the building slowly rots from constant moisture damage. The problem isn't that the fire department responded; it's that they never got the signal to switch from "suppress fire" mode to "drain and rebuild" mode. This happens when the resolution machinery (resolvomics) fails—either the SPM production is insufficient, or the tissues have become deaf to their signals.
Inflammatory cascades are initiated when pattern recognition receptors detect danger signals:
Initiation Phase:
- PAMPs (pathogen molecules like LPS) or DAMPs (endogenous danger signals like HMGB1, extracellular ATP) bind to TLRs (Toll-like receptors 1-10), NLRs (NOD-like receptors), or RIG-I-like receptors on sentinel cells (macrophages, dendritic cells, epithelial cells)
- TLR4 (recognizes LPS) → recruits MyD88 adapter protein → activates IRAK kinases → activates TAK1 → phosphorylates IKK complex
- IKK complex phosphorylates IκB (inhibitor of NF-κB) → IκB degradation → NF-κB (p50/p65 heterodimer) translocates to nucleus
- NF-κB binds promoter regions → transcription of inflammatory genes: IL-1β, IL-6, TNF-α, COX-2, iNOS, IL-8, MCP-1
Amplification Phase:
5. Cytokines bind their respective receptors:
- IL-1β → IL-1R → further NF-κB activation (feedforward loop)
- TNF-α → TNFR1/TNFR2 → NF-κB + JNK + p38 MAPK activation
- IL-6 → IL-6R + gp130 → JAK-STAT3 signaling → acute phase protein production in liver (CRP, serum amyloid A, hepcidin)
- COX-2 converts arachidonic acid → prostaglandins (PGE2, PGD2, PGI2) → vasodilation, pain sensitization, fever
- 5-LOX converts arachidonic acid → leukotrienes (LTB4) → neutrophil chemotaxis
- iNOS produces NO → vasodilation + direct antimicrobial effects
Vascular and Cellular Response:
9. PGE2 + histamine + bradykinin → arteriolar dilation (rubor, calor) + increased endothelial permeability (tumor)
10. Endothelial cells upregulate adhesion molecules: E-selectin, P-selectin, ICAM-1, VCAM-1
11. Neutrophils roll → stick → transmigrate through endothelium (diapedesis) into tissue
12. Neutrophils phagocytose pathogens, release NETs (neutrophil extracellular traps), produce ROS via NADPH oxidase
13. Monocytes recruited → differentiate to M1 macrophages (produce more IL-1β, IL-6, TNF-α)
Resolution Phase (when functional):
14. Eicosanoid class switching: COX-2 becomes acetylated by aspirin or S-nitrosylated → produces 15-epi-lipoxins instead of prostaglandins
15. 15-LOX and 12-LOX convert EPA → E-series resolvins (RvE1-3); DHA → D-series resolvins (RvD1-6), protectins (PD1), maresins (MaR1-2)
16. SPMs bind ALX-FPR2, GPR32, GPR18 receptors → inhibit NF-κB, promote efferocytosis, stop neutrophil recruitment, induce M2 macrophage polarization
17. M2 macrophages produce IL-10, TGF-β → suppress inflammation, stimulate tissue repair
graph TD
A[PAMPs/DAMPs] --> B[TLR/NLR activation]
B --> C[MyD88/TRIF adapters]
C --> D[IKK complex activation]
D --> E["IκB phosphorylation & degradation"]
E --> F["NF-κB nuclear translocation"]
F --> G[Inflammatory gene transcription]
G --> H["IL-1β, IL-6, TNF-α, COX-2, iNOS"]
H --> I[Cytokine amplification loop]
I --> J[Vascular changes & immune cell recruitment]
J --> K{Resolution switch?}
K -->|SPMs produced| L[Resolvomics pathway]
K -->|SPMs deficient| M[Chronic low-grade inflammation]
L --> N[M2 polarization, efferocytosis]
L --> O["IL-10, TGF-β production"]
L --> P[Tissue repair & homeostasis]
M --> Q["Persistent NF-κB activation"]
M --> R[Metaflammation, insulin resistance]
M --> S[Chronic disease progression]
Chronic Inflammation Perpetuation:
When resolution fails, inflammatory mediators persist at subacute levels (CRP 3-10 mg/L vs. >10 mg/L in acute). Mechanisms include:
- Omega-6/omega-3 imbalance → insufficient EPA/DHA for SPM synthesis
- Obesity → adipocyte hypertrophy → constitutive NF-κB activation in adipose tissue macrophages
- Gut dysbiosis → chronic endotoxemia → continuous TLR4 stimulation at low level
- Psychological stress → HPA axis activation → cortisol resistance → loss of glucocorticoid anti-inflammatory brake
- Iron sequestration → hepcidin elevation → functional iron deficiency → impaired mitochondrial function → cellular stress
Distinguishing Acute from Chronic Inflammation:
The practitioner must identify whether inflammation is:
- Acute protective (pathogen clearance, wound healing): high CRP (>10 mg/L), IL-6 >100 pg/mL, neutrophil-dominant, resolves in 4-6 days
- Chronic pathological (metaflammation): CRP 3-10 mg/L, IL-6 5-15 pg/mL, monocyte-dominant, persists for months
cPNI Metamodel Integration:
- Metamodel 5 (Chronic Inflammation): The central driver of modern chronic disease—cardiovascular disease, type 2 diabetes, dementia, depression all share this common pathway. Intervention targets the root causes (gut barrier, metabolic stress, psychosocial stress) rather than suppressing inflammation with NSAIDs.
- Selfish Brain: Inflammatory cytokines (IL-1β, IL-6, TNF-α) directly signal the hypothalamus → HPA axis activation, sickness behavior, glucose shunting to brain. Chronic inflammation creates metabolic conflict between brain's energy demands and peripheral insulin resistance.
- Selfish Immune System: Iron sequestration during inflammation is ancient innate immunity (hepcidin blocks ferroportin → sequesters iron from pathogens), but chronic elevation causes anemia of chronic disease—the immune system "selfishly" prioritizes pathogen control over oxygen delivery.
Clinical Thresholds:
- CRP <1 mg/L: optimal cardiovascular risk
- CRP 1-3 mg/L: low-grade inflammation, investigate gut, metabolic, psychosocial sources
- CRP 3-10 mg/L: significant metaflammation, high chronic disease risk
- CRP >10 mg/L: acute inflammation, rule out infection/acute pathology
- IL-6 >5 pg/mL: associated with accelerated aging, frailty
- Ferritin >200 ng/mL with low transferrin saturation: suspect inflammatory sequestration
Intervention Implications:
- Acute inflammation: Support resolution with SPM precursors (EPA 2-3g/day, DHA 1-2g/day), avoid premature NSAID use (blocks both prostaglandins AND resolvins via COX-2 inhibition)
- Chronic low-grade inflammation:
- Restore gut barrier: glutamine, zinc carnosine, polyphenols, eliminate trigger foods
- Improve omega-6/omega-3 ratio: target <4:1, ideally 2:1
- Address psychosocial stressors: discrimination, loneliness, chronic stress activate inflammatory pathways equivalent to physical injury
- Restore insulin sensitivity: intermittent fasting, resistance training, metformin if indicated
- Ensure selenium (200 mcg/day) for glutathione peroxidase activity (limits oxidative amplification of inflammation)
Exam-Critical Concept:
Inflammation is NOT the enemy—it's a protective response. The pathology lies in failed resolution. NSAIDs suppress symptoms but prevent healing by blocking COX-2 (needed for both prostaglandin AND resolvin synthesis). The cPNI approach: enhance resolution machinery, remove chronic triggers, restore metabolic flexibility.
- Acute inflammation resolves within 4-6 days when resolvomics machinery is functional; failure of resolution (not excessive initiation) defines chronic inflammation
- Chronic low-grade inflammation (CRP 3-10 mg/L) increases all-cause mortality by 50-100% and is present in >60% of Western adults over age 50
- Inflammatory cytokines IL-1β, IL-6, TNF-α cross blood-brain barrier at circumventricular organs and activate HPA axis within 2-4 hours of peripheral immune challenge
- Psychosocial stress (discrimination, loneliness, chronic caregiving) activates identical NF-κB pathways as bacterial infection—CTRA (Conserved Transcriptional Response to Adversity) upregulates 50+ inflammatory genes
- Iron sequestration during inflammation is mediated by hepcidin (produced by IL-6 → STAT3 signaling in liver) blocking ferroportin; chronic inflammation causes anemia of chronic disease even with adequate iron stores
- COX-2 has dual function: in early inflammation produces prostaglandins (PGE2), but when acetylated by aspirin or S-nitrosylated produces 15-epi-lipoxins (resolution mediators)
- Omega-6/omega-3 ratio >10:1 (Western average 15-20:1) favors arachidonic acid → pro-inflammatory eicosanoids; ratio <4:1 supports EPA/DHA → SPM synthesis
- Adipocyte hypertrophy (cell diameter >100 μm) triggers macrophage infiltration → crown-like structures → constitutive TNF-α and IL-6 secretion from visceral adipose tissue (metaflammation)
- Inflammatory mediators (PGE2, bradykinin, NGF) sensitize TRPV1 and TRPA1 nociceptors, lowering activation threshold from 43°C to 37°C (explains inflammatory pain hypersensitivity)
- LPS translocation from gut (endotoxemia) occurs at concentrations as low as 50 pg/mL in portal blood, sufficient to activate hepatic Kupffer cells and initiate low-grade systemic inflammation
- Resolution phase requires eicosanoid class switching by 12:00-18:00 hours post-injury; if neutrophils persist beyond 48 hours, risk of chronic inflammation increases exponentially
- acute inflammation — is the time-limited, protective form of
- chronic inflammation — represents failed resolution of
- low-grade inflammation — is the subclinical metabolic form of
- metaflammation — describes metabolic tissue-specific
- inflammatory response — is the complete cascade of events in
- inflammatory phase — marks the initial stage of wound healing dominated by
- Inflammatory pain — results from nociceptor sensitization during
- cytokines — are the primary signaling molecules mediating
- NF-κB — is the master transcription factor activated during
- TNF-α — is a key amplifying cytokine produced during
- IL-6 — drives acute phase response and metabolic changes during
- IL-1beta — initiates and amplifies
- COX-2 — is upregulated during inflammation to produce prostaglandins and resolvins
- prostaglandins — are lipid mediators causing vascular changes in
- leukotrienes — recruit neutrophils during
- specialized pro-resolving mediators — are essential for resolving
- resolvomics — is the active process of transitioning from
- TLR4 — initiates inflammatory signaling upon detecting PAMPs/DAMPs
- PAMPs — are pathogen molecules triggering
- DAMPs — are endogenous danger signals initiating sterile
- leaky gut — permits microbial translocation causing systemic
- endotoxemia — drives chronic low-grade inflammation via persistent LPS exposure
- HPA axis — is activated by inflammatory cytokines, creating neuroendocrine-immune crosstalk
- cortisol resistance — develops during chronic inflammation, removing glucocorticoid brake
- insulin resistance — is both caused by and contributes to
- microglial activation — represents central nervous system
- sickness behaviour — is mediated by inflammatory cytokines signaling the brain
- CRP — is the biomarker for systemic
- hepcidin — sequesters iron during inflammation as innate immune strategy
- iron — becomes sequestered during inflammation causing anemia of chronic disease
- discrimination — activates inflammatory pathways comparable to physical injury
- chronic stress — perpetuates inflammation through cortisol resistance and sympathetic activation
- obesity — creates chronic inflammatory state through adipocyte-macrophage interaction
- gut dysbiosis — maintains low-grade inflammation through endotoxin production
- EPA — is the precursor for E-series resolvins that resolve
- DHA — is the precursor for D-series resolvins and protectins that resolve
- omega-3 fatty acids — provide substrate for resolution of
- M1 macrophages — amplify inflammation by producing pro-inflammatory cytokines
- M2 macrophages — resolve inflammation through efferocytosis and anti-inflammatory mediators
- neutrophils — are the first responders in acute
- adhesion molecules — enable leukocyte trafficking during
- vasodilation — is a cardinal sign (rubor, calor) of
- vascular permeability — increases during inflammation causing edema (tumor)
- oxidative stress — amplifies inflammatory signaling through ROS production
- atherosclerosis — is driven by chronic vascular inflammation
- neuroinflammation — represents inflammatory processes in CNS
- depression — shares inflammatory mechanisms with physical illness (cytokine theory)
- Alzheimer's Disease — involves chronic neuroinflammation and failed resolution
- type 2 diabetes — is characterized by chronic low-grade inflammation in metabolic tissues
- autoimmune disease — involves dysregulated inflammatory responses to self-antigens
- Module 1: Introduction to cPNI framework, discrimination as inflammatory stressor
- Module 2: Evolutionary medicine perspective on inflammation as defense mechanism, iron sequestration as innate immunity
- Module 3: Neuroendocrinology of inflammatory signaling, HPA axis activation, metabolic effects of inflammatory cytokines
- Module 4: Clinical assessment and intervention strategies for inflammatory conditions
- Module 5: Integration of inflammatory mechanisms across chronic disease states