pentraxins

Pentraxins are a family of soluble, multimeric proteins that participate in the innate immune system as pattern recognition receptors. They are calcium-dependent and typically form pentameric assemblies in which five subunits create a disk-like structure. All pentraxins share a conserved C-terminal pentraxin domain, but differ in their N-terminal regions, which influences their multimeric state and functional interactions. The best characterized members are divided into short and long pentraxins, reflecting these structural differences.

Short pentraxins CRP (C-reactive protein) and serum amyloid P component (SAP) are mainly produced by the liver as acute-phase proteins. Their plasma concentrations rise rapidly during inflammation or infection. These proteins bind to certain ligands on microbes and dead or damaged cells, activate the classical complement pathway, and promote opsonization and clearance.

Long pentraxins include PTX3, produced by a broader range of cells such as dendritic cells, macrophages, and endothelial cells in response to pro-inflammatory signals. PTX3 recognizes microbial components and damaged-self ligands, activates complement, and participates in opsonization. It also has roles in tissue remodeling, angiogenesis, and regulation of inflammation, with effects that can be protective or detrimental depending on context.

In addition to CRP and SAP, other pentraxins (such as PTX4) are described, but less is known about their roles. Collectively, pentraxins contribute to host defense by recognizing pathogens and apoptotic cells, bridging innate recognition to effector mechanisms, and helping maintain tissue homeostasis.

Clinically, CRP is widely used as an inflammatory biomarker, with high-sensitivity assays informing cardiovascular risk and infection status. PTX3 is studied as an acute-phase marker in certain settings and as a potential mediator of inflammation and innate immunity. The pentraxin family is evolutionarily conserved across vertebrates, reflecting its fundamental role in immune surveillance.