Pentraxin

Pentraxins are a family of evolutionarily conserved proteins characterized by their pentameric structure, resembling a star-shaped arrangement of five identical subunits. They play significant roles in innate immunity, inflammation, and tissue remodeling. The name "pentraxin" derives from the Greek word *penta*, meaning five, and *taxin*, referring to a toxin-neutralizing protein.

The most well-studied pentraxins include C-reactive protein (CRP), serum amyloid P component (SAP), and the long pentraxin PTX3. CRP and SAP are acute-phase reactants, meaning their levels rise rapidly in response to inflammation, infection, or tissue injury. CRP, discovered in 1930, binds to phosphorylcholine on bacterial cell walls and damaged host cells, facilitating opsonization and clearance by phagocytes. SAP, found in humans and other primates, has a broader role in immune regulation and tissue repair, potentially acting as a molecular scaffold in extracellular matrices.

PTX3, distinct from CRP and SAP, is secreted by various cell types, including monocytes, fibroblasts, and endothelial cells, in response to inflammatory stimuli. Unlike CRP and SAP, PTX3 is not an acute-phase protein but is induced locally at sites of inflammation. It participates in immune defense by promoting phagocytosis, complement activation, and angiogenesis, while also influencing tissue remodeling and fibrosis.

Structurally, pentraxins share a conserved core domain of approximately 200 amino acids, forming a cyclic pentamer. This structure allows them to bind multiple ligands simultaneously, enhancing their functional versatility. Mutations or dysregulation in pentraxin levels have been linked to autoimmune diseases, infections, and cancer, highlighting their importance in both health and disease.

Research continues to elucidate the precise mechanisms by which pentraxins mediate immune responses and tissue homeostasis, offering potential therapeutic targets for inflammatory and infectious disorders.