Inflammation: Acute vs Chronic

Introduction to Inflammation

Inflammation is the body's natural defense mechanism against harmful stimuli such as pathogens, damaged cells, or irritants. The purpose of inflammation is threefold: to eliminate the initial cause of cell injury, clear out damaged cells and tissues, and initiate tissue repair.

Key Components:

Immune cells (neutrophils, macrophages)
Blood vessels (vasodilation, increased permeability)
Molecular mediators (cytokines, chemokines)
Plasma proteins (complement, clotting factors)

Cardinal Signs:

Rubor (redness)
Calor (heat)
Tumor (swelling)
Dolor (pain)
Functio laesa (loss of function)

Important Note:

While inflammation is essential for healing, it can become problematic when dysregulated, leading to chronic conditions and tissue damage.

Acute Inflammation

Acute inflammation is the initial, rapid response to harmful stimuli including pathogens, damaged cells, or irritants. It has a quick onset (minutes to hours) and short duration (hours to days), and is self-limiting with coordinated events to eliminate threats and begin healing.

Vascular Changes

Minutes to hours

Vasodilation, increased permeability, leukocyte recruitment

Cellular Response

Hours to days

Neutrophil infiltration, phagocytosis, cytokine release

Resolution

Days

Apoptosis of neutrophils, anti-inflammatory cytokines, tissue repair

Neutrophils

First responders arriving within minutes to hours, phagocytose pathogens, release NETs, short-lived.

Macrophages

Professional phagocytes that engulf pathogens and debris, release cytokines, derived from monocytes.

Mast Cells

Tissue-resident sentinels that degranulate to release histamine and inflammatory mediators.

Resolution Phase:

Involves specialized pro-resolving mediators (SPMs), neutrophil apoptosis, anti-inflammatory cytokines (IL-10, TGF-β), and tissue repair to restore homeostasis.

Chronic Inflammation

Chronic inflammation persists for months or years, featuring macrophages, lymphocytes, and fibroblasts. These cells interact in complex networks that sustain the inflammatory state, leading to persistent inflammation, tissue damage, and ultimately fibrosis.

Feature	Acute Inflammation	Chronic Inflammation
Duration	Hours to days	Months to years
Primary Cells	Neutrophils	Macrophages, lymphocytes, fibroblasts
Onset	Rapid (minutes)	Gradual
Outcome	Resolution	Fibrosis, tissue destruction
Systemic Effects	Fever, leukocytosis	Fatigue, anemia, cachexia

Cellular Players

Macrophages: Predominant cell type, secrete cytokines, form granulomas
T lymphocytes: CD4+ T helper cells coordinate response, CD8+ kill infected cells
B cells: Produce antibodies, form memory cells
Fibroblasts: Produce extracellular matrix, lead to fibrosis

Systemic Effects

Atherosclerosis and cardiovascular disease
Insulin resistance and type 2 diabetes
Anemia of chronic disease
Muscle wasting (cachexia)
Fatigue and depression

Metaflammation:

Chronic low-grade inflammation in metabolic disorders like obesity and diabetes, where adipose tissue becomes an endocrine organ driving inflammation and insulin resistance.

Prevention & Management

Dietary Approaches

Anti-inflammatory diet (Mediterranean style)
Rich in fruits, vegetables, whole grains
Omega-3 fatty acids (fish, flaxseeds, walnuts)
Polyphenols (berries, green tea, dark chocolate)
Limit processed foods and sugars

Lifestyle Factors

Regular physical activity (150+ min/week)
Adequate sleep (7-9 hours nightly)
Stress management (meditation, yoga)
Maintain healthy weight
Avoid smoking and excessive alcohol

Exercise Benefits:

Regular physical activity has powerful anti-inflammatory effects through multiple mechanisms including reduced adipose tissue inflammation, increased anti-inflammatory cytokines, and improved insulin sensitivity.