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Inflammatory mediators are small proteins produced by immune and tissue cells that coordinate the inflammatory response. Cytokines (TNF-α, IL-1, IL-6, IL-10) regulate activation, differentiation, and survival of immune cells. Chemokines (CCL2, CXCL8) direct cell migration to inflamed sites. In acute inflammation, pro-inflammatory cytokines predominate; resolution requires anti-inflammatory signals. Dysregulated cytokine production leads to chronic inflammation, tissue damage, and systemic effects (fever, sickness behavior).
Map the cytokine networks in acute inflammation—how macrophages secrete TNF-α and IL-1, which activate endothelial cells and fibroblasts. Study the transition from pro- to anti-inflammatory signals during resolution. Consider therapeutic cytokine antagonism.
Cytokines are not produced only by immune cells—fibroblasts, endothelial cells, and stromal cells also produce them. Some cytokines are pro-inflammatory in some contexts and anti-inflammatory in others (IL-6 in acute vs. chronic inflammation).
From your prerequisite on cytokines and chemokines, you have a foundation: these are small signaling proteins that allow immune cells to communicate. Now we can focus on how they orchestrate the inflammatory response in a structured, sequential way — and what goes wrong when that orchestration breaks down. The inflammatory response is not a single alarm bell; it is a coordinated program with a beginning, a middle, and a resolution phase, each governed by specific mediators.
The acute inflammatory response begins within minutes of tissue damage or pathogen detection. Tissue-resident macrophages sense danger signals through pattern-recognition receptors and immediately release the primary pro-inflammatory cytokines: TNF-α (tumor necrosis factor-alpha) and IL-1β (interleukin-1 beta). These two cytokines act locally on endothelial cells in nearby blood vessels, upregulating adhesion molecules (ICAM-1, selectins) that slow circulating neutrophils and allow them to stick to the vessel wall. TNF-α and IL-1 also act systemically: they reach the hypothalamus and trigger the acute-phase response, including fever (via prostaglandin E2), and they stimulate the liver to produce acute-phase proteins (C-reactive protein, fibrinogen). IL-6 amplifies both local and systemic effects — it's the dominant driver of hepatic acute-phase protein production, which is why CRP rises dramatically in acute infection or inflammation.
Chemokines provide the directional signals that pull immune cells out of the bloodstream and toward the site of injury. CXCL8 (IL-8) is the primary neutrophil chemoattractant — it creates a concentration gradient from the injury site through the vessel wall, guiding neutrophils in the process called chemotaxis. CCL2 (monocyte chemoattractant protein-1) recruits monocytes and macrophages. Think of cytokines as the "raise the alarm" signals and chemokines as the "follow this trail" signals: cytokines amplify activation and systemic response; chemokines guide migration to the precise location.
Inflammation must resolve, or it transitions from protective to destructive. As pathogens are cleared, the milieu shifts toward anti-inflammatory mediators. IL-10 is a key resolution cytokine, produced by regulatory T cells and macrophages. It suppresses macrophage activation and inhibits pro-inflammatory cytokine production — acting as a feedback brake. When this resolution fails, cytokines that are pro-inflammatory in acute settings become chronically elevated, driving ongoing tissue damage. IL-6 illustrates the context-dependence captured in the Common Misconceptions: in acute inflammation it is adaptive and time-limited; in chronic low-grade inflammation (as in obesity or rheumatoid arthritis) its sustained elevation drives pathology including insulin resistance, cartilage degradation, and cardiovascular risk. This is why anti-cytokine biologics like anti-TNF antibodies (infliximab, adalimumab) or anti-IL-6 receptor antibodies (tocilizumab) are transformative therapies — they interrupt the chronic activation that the resolution program failed to stop.