Necrosis and Cell Death

Necrosis is a form of cell death marked by loss of membrane integrity, leakage of cellular contents, and an accompanying inflammatory response. Classically regarded as the accidental, unregulated death that follows severe injury, necrosis is now recognized to include regulated variants such as necroptosis that share the same morphology but proceed through defined molecular pathways. Necrosis is distinguished from apoptosis by its inflammatory aftermath and its morphological patterns in tissue.

Definition

Necrosis is a type of cell death characterized by rupture of the plasma membrane, release of intracellular contents, and a consequent inflammatory reaction, encompassing both accidental (unregulated) death from overwhelming injury and regulated necrotic pathways such as necroptosis.

Scope

This topic covers the morphology of necrosis, its principal tissue patterns (coagulative, liquefactive, caseous, fat, fibrinoid, and gangrenous), the distinction between accidental and regulated necrosis, and necroptosis as the best-characterized regulated necrotic pathway. It contrasts necrosis with apoptosis but defers the detailed apoptotic machinery to the sibling topic.

Core questions

• How does necrosis differ morphologically and immunologically from apoptosis?
• What tissue patterns of necrosis exist and what do they signify?
• Is necrosis always unregulated, or can it be a programmed pathway?
• How does necrosis provoke inflammation through release of cellular contents?

Key concepts

• Loss of plasma-membrane integrity
• Coagulative necrosis
• Liquefactive necrosis
• Caseous necrosis
• Fat, fibrinoid, and gangrenous necrosis
• Necroptosis (regulated necrosis)
• Damage-associated molecular patterns and inflammation

Mechanisms

In accidental necrosis, severe injury depletes ATP and overwhelms membrane and organelle integrity, causing the cell to swell and rupture. Spillage of intracellular contents — including damage-associated molecular patterns — into the surroundings recruits inflammatory cells, which is the hallmark that distinguishes necrosis from the immunologically silent process of apoptosis. The morphological pattern depends on tissue and cause: coagulative necrosis preserves architecture in solid organs after ischemia, liquefactive necrosis dissolves tissue in the brain and in abscesses, caseous necrosis produces a cheese-like focus typical of tuberculosis, and fat, fibrinoid, and gangrenous patterns reflect particular settings. Necroptosis is a regulated form executed through receptor-interacting protein kinases (RIPK1 and RIPK3) and the pseudokinase MLKL, which permeabilizes the plasma membrane, producing necrotic morphology under genetic control.

Clinical relevance

Recognizing the pattern of necrosis in tissue helps localize and characterize disease processes — for instance, coagulative necrosis indicates infarction, caseous necrosis points to granulomatous infection, and liquefactive necrosis suggests an abscess or cerebral infarct. The entry describes these patterns for reference and does not provide diagnostic thresholds or management guidance.

Evidence & guidelines

The molecular classification of necrosis and its regulated variants is consolidated by the expert consensus of the Nomenclature Committee on Cell Death, while the classical tissue patterns are codified in standard pathology references.

History

Necrosis was long defined morphologically as the disordered breakdown of cells after lethal injury, and contrasted with apoptosis after the latter was characterized in 1972. The discovery in the 2000s and 2010s that some necrosis is genetically programmed — necroptosis, executed by RIPK3 and MLKL — overturned the assumption that all necrosis is accidental and prompted updated nomenclature distinguishing regulated from accidental cell death.

Debates

How much necrosis in vivo is regulated versus accidental?

The recognition of necroptosis and other regulated necrotic pathways raised the question of how often necrosis seen in disease reflects a programmed pathway amenable to modulation rather than passive collapse, a balance that varies by injury and tissue and remains under investigation.

Key figures

• Guido Kroemer
• Peter Vandenabeele
• Douglas Green

Seminal works

• galluzzi-2018-nomenclature
• pasparakis-vandenabeele-2015

Frequently asked questions

Why does necrosis cause inflammation but apoptosis usually does not?

Necrosis ruptures the plasma membrane and releases intracellular contents, including molecules that act as danger signals to the immune system, whereas apoptosis packages the cell into membrane-bound bodies that are cleared without spilling their contents.

Is necroptosis the same as necrosis?

Necroptosis produces necrotic morphology but is a regulated pathway driven by specific kinases (RIPK1, RIPK3) and the effector MLKL, so it is a programmed subtype rather than the accidental necrosis caused by overwhelming injury.