CRP and SAP from different species have different membrane ligand specificities.

Human C-reactive protein (CRP) and serum amyloid component P (SAP) are well-characterised ligands for dying and dead cells, while facets of their physiological function still need to be unravelled. We partially characterised CRP and SAP from different species with similar acute-phase systems. Human, rabbit and porcine CRP bound phosphocholine (PC) and phosphoethanolamine (PEt). Human and porcine SAP bound PEt while rabbits seem to have very low levels of SAP or rabbit SAP does not bind PEt. Porcine serum additionally contained other ligands for PC and PEt. Some of them were immunoglobulins. Therefore, rabbits, pigs and humans cover the ability to bind PC and PEt with different extents.