Pentraxins

Pentraxins are a family of multifunctional, conserved proteins that play key roles in the immune system. They are characterized by a cyclic multimeric structure and are classified based on their primary structure into short and long pentraxins. Pentraxins act as pattern recognition molecules in the innate immune response, binding to pathogens and damaged cells, and initiating their removal through phagocytosis or complement activation.

Classification

Pentraxins are divided into two main classes: short and long pentraxins.

• Short Pentraxins: The prototypical members of this class are C-reactive protein (CRP) and serum amyloid P component (SAP). These proteins are produced primarily by the liver in response to inflammatory cytokines.
• Long Pentraxins: This class includes Pentraxin 3 (PTX3), which is produced by various cell types, including endothelial cells, fibroblasts, and immune cells, in response to pro-inflammatory signals.

Structure

Pentraxins are characterized by a pentameric structure, which is crucial for their ability to bind ligands. Each monomer in the pentamer is composed of a conserved pentraxin domain. Long pentraxins have an extended N-terminal domain in addition to the common pentraxin domain.

Function

Pentraxins play a crucial role in the innate immune response. They are involved in:

• Pathogen Recognition: Pentraxins can recognize and bind to microbial pathogens, facilitating their opsonization and removal.
• Complement Activation: By binding to pathogens, pentraxins can activate the complement system, leading to the lysis of the pathogen.
• Modulation of Inflammation: Pentraxins can influence the inflammatory response by interacting with immune cells and affecting their function.
• Tissue Repair: Long pentraxins, in particular, have been implicated in tissue remodeling and repair processes.

Clinical Significance

Pentraxins are biomarkers for various diseases due to their role in inflammation and immune response.

• Inflammatory Diseases: Elevated levels of CRP and PTX3 are associated with inflammatory conditions, such as rheumatoid arthritis and systemic lupus erythematosus.
• Cardiovascular Diseases: CRP levels are used as a marker for cardiovascular risk assessment, as they can indicate underlying inflammation in the vascular system.
• Infection: High levels of pentraxins can indicate an ongoing infection, as they are part of the acute phase response.

Research Directions

Research on pentraxins is focused on understanding their role in disease and their potential as therapeutic targets. For example, targeting pentraxins in diseases characterized by excessive inflammation or in cancer to modulate the immune response.

See Also

• Innate immune system
• C-reactive protein
• Complement system
• Inflammation