Extracellular histones, cell-free DNA, or nucleosomes: differences in immunostimulation

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Inflammation leads to cell death and release of extracellular chromatin.
• Extracellular histones and double-stranded DNA (dsDNA) have known immunostimulatory effects via toll-like receptors (TLRs) and intracellular sensing.
• Nucleosomes, the native form of chromatin, are also released during inflammation, but their effects are less understood.

Purpose of the Study:

• To review the current understanding of immunostimulation by extracellular chromatin components.
• To highlight the differences in immune activation by free histones, dsDNA, and nucleosomes.
• To emphasize the need for techniques differentiating these forms.

Main Methods:

• Literature review of studies on extracellular chromatin components and their immune effects.
• Analysis of mechanisms of immunostimulation by histones, dsDNA, and nucleosomes.
• Discussion of current technological limitations in differentiating histone forms.

Main Results:

• Histones activate TLR2 and TLR4, while dsDNA activates TLR9 and intracellular sensors.
• Nucleosomes exhibit distinct, less-studied cytotoxic and proinflammatory signaling.
• Existing methods often fail to distinguish between free and DNA-bound histones.

Conclusions:

• Extracellular histones, dsDNA, and nucleosomes differentially modulate immune responses.
• Understanding these distinctions is crucial for studying inflammatory diseases.
• Advanced detection techniques are needed to differentiate circulating chromatin forms.