Serum amyloid-P component of the Armenian hamster: gene structure and comparison with structure and expression of the SAP gene from Syrian hamster

A female-specific pentraxin, CrOctin, bridges pattern recognition receptors to bacterial phosphoethanolamine

Pathogen recognition and binding are crucial functions of innate immunity. It has been observed that the short pentraxin superfamily including C-reactive protein (CRP) and serum amyloid P component are pathogen pattern recognition receptors (PRR) in the plasma. We isolated and characterized a novel and distinctive pentraxin from the plasma of horseshoe crab, Carcinoscorpius rotundicauda, henceforth named CrOctin, which binds to bacteria via phosphoethanolamine (PE), a chemical component present on lipid A and core polysaccharide moieties of bacterial lipopolysaccharide (LPS). Infection enhances the formation of the PRR interactome constituting CrOctin, CRP and galactose-binding protein. In particular, infection increases the affinity of CRP to CrOctin by 1000-fold. Furthermore, we observed that by binding to PE, CrOctin acts as a linker that bridges the PRR interactome to the inner core of LPS. On the other hand, under normal physiological conditions, binding of CrOctin to PE appears to obscure other PRR from interacting directly with PE. Interestingly, the cluster of "CrOctin-interactive PRR" is sex specific. We report, for the first time, the change in PRR protein profiles with a distinctive gender difference during Pseudomonas infection.

Acute phase proteins and transformed cells

Acute phase proteins (APP) are plasma proteins whose concentration and glycosylation alters in response to tissue injury, inflammation, or tumor growth. Significant interspecies and sex differences in APP response exist. APP are produced mainly by hepatocytes, and their synthesis and glycosylation are controlled by a network consisting of cytokines, their soluble receptors, and glucocorticoids. The major cytokines involved in these processes belong to a group of interleukin-6-type cytokines that act through the hematopoietin receptor complex on hepatocytes and JAK-STAT signal transduction pathway. Transformed cells (hepatoma) display significant differences in synthesis of APP, cytokine responsiveness, expression of cytokine-receptor subunits and signal-transduction machinery. The most striking variability relates to the glycosylation alterations induced by cytokines. However, transformed cells (hepatoma) form a basic model for studying and understanding mechanisms controlling the synthesis and glycosylation of APP. Furthermore, APP may be secreted by transformed (tumor) cells of various origins and may display a growth factor-like function in certain cancer types.

Structure and function of the pentraxins

Over the past two years, the three-dimensional structure of the serum amyloid P component was defined by X-ray diffraction, the first such visualization of a pentraxin. Binding sites for calcium, ligands and complement were identified. New fusion proteins with amino acid sequence homology to the pentraxins were described, and new insights were gained into pentraxin phylogeny, biosynthesis, ligands, complement activation, leukocyte reactivity and biological functions in vivo.