Phosphorylcholine substituents in nematodes: Structures, occurrence and biological implications

Phosphorylcholine (PC), a small haptenic molecule, is found in a wide varie ty of prokaryotic organisms, i.e. bacteria, and in eukaryotic parasites suc h as nematodes, as well as in fungi. Linked to parasite-specific glycoprote in glycans or glycolipids, it is assumed to be responsible for a variety of immunological effects, including invasion mechanisms and long-term persist ence of parasites within the host. Numerous reports have indicated various effects of PC-substituted molecules derived from parasitic nematodes on sig nal transduction pathways in B and T lymphocytes, displaying a highly adapt ed and profound modulation of the immune system by these parasites. The Nem atoda, comprising parasitic and free-living species, can be regarded as pro mising prototypic systems for structural analyses, immunological studies an d biosynthetic investigations. in this context, Ascaris suum, the pig paras itic nematode, is an ideal organism for immunological studies and an excell ent source for obtaining large amounts of PC-substituted (macro)molecules. Caenorhabditis elegans as a completely genome-sequenced species and express ing parasite analogous PC-substituted structures, together with the possibi lity for easy in vitro cultivation, represents a conceptual model for biosy nthetic studies, whereas filarial parasites represent important model syste ms for human pathogens, especially in developing countries. This review sum marises current knowledge on the tissue-specific expression of PC epitopes, structural data of glycoprotein glycans and glycosphingolipids bearing thi s substituent and biological implications for the immune systems of the res pective hosts.