Inflammatory interactions in fish exposed to pollutants and parasites: a role for apoptosis and C reactive protein.

Although previous studies have highlighted the inflammatory responses of fish infected with parasites and exposed to pollutants, very little is known about how these two stressors interact within the fish. In this review, which also contains original data, the effect of these two parameters on the fish inflammatory response is assessed and, in particular, the role of apoptosis and the acute phase protein, C reactive protein, is evaluated. In Cyprinus carpio exposed to 0.5 mg NH4+ l(-1) or 0.1 mg Cd2+ l(-1) and experimentally infected with the blood fluke, Sanguinicola inermis, the pollutant type and the order in which the fish experiences the parasite and toxicant, significantly affects the ultrastructural appearance and cellular content of the pronephros and thymus. This is reflected in the intensity of infection where the pollutant appears to have less effect on an established infection. Both stressors, pollutant and infection, may mediate their effects via the endocrine system. Studies have revealed that cortisol at 100 ng ml(-1) is able to induce apoptosis in pronephric cells of carp and that an increase in apoptosis is associated with an increase in phagocytosis in this immune organ. In addition, C reactive protein, which is used as a biomarker of the inflammatory response in humans and other mammals, is evaluated as a possible indicator of physiological states in fish exposed to pathogens and pollutants.

C-reactive protein and SAP-like pentraxin are both present in Limulus polyphemus haemolymph: crystal structure of Limulus SAP.

C-reactive protein and serum amyloid P component are members of the pentraxin family of oligomeric serum proteins which has been conserved through evolution. In humans both have pentameric structures and both play complex roles in the immune response, C-reactive protein being the classical acute-phase reactant produced in response to tissue damage and inflammation. An invertebrate SAP-like pentraxin has not previously been identified and it has been postulated that C-reactive protein and serum amyloid P component are products of a gene duplication event within vertebrate evolution. We have isolated serum amyloid P component from the haemolymph of the phylogenetically ancient "living fossil", the horseshoe crab Limulus polyphemus and determined the three-dimensional structure by X-ray crystallography. The structure of the previously undiscovered Limulus serum amyloid P component, the first invertebrate lectin structure to be determined, reveals the pentraxin fold and a novel doubly stacked octameric ring. The crystal structure and the discovery that both prototypic pentraxins are present in Limulus raises the possibility that both were present in the common ancestors of arthropods and chordates over 500 million years ago. The impact of the results on our understanding of the origins and evolution of pentraxins and innate immunity is discussed.