The role of the envelope of Moniliformis moniliformis in immune evasion

[摘要] The biochemical composition of the envelope surrounding cystacanth larvae of Moniliformis moniliformis (Acanthocephala) was investigated in an attempt to understand how this structure protects developing larvae in the hostile environment of the haemocoele of the intermediate cockroach host Periplaneta americana. The results have shown that the envelope has a complex composition and contains six lipid species, at least 25 polypeptides and a glycosaminoglycan/proteoglycan-like molecule. The GAG-like molecule may be present at the outer surface of the envelope. The lipid composition is substantial and represents about 25% of the dry weight of the cystacanth envelope. At least six lipid species have been detected and three have been tentatively identified as phosphatidyl choline, phosphatidyl ethanolamine and cholesterol. Envelope proteins have been extracted and analysed by SDS-PAGE, and have been shown by lectin overlay to be glycoproteins. The molecular weights of those glycoproteins range from about 30 to > 300Kd. One of the envelope proteins has been identified as a collagen, and a similar molecule is also present in extracts of larval bodies. Thus the envelope collagen is apparently parasite derived. There is extensive cross-reactivity between epitopes present on envelope glycoproteins and glycoproteins from cell and plasma fractions of the blood (haemolymph) of the insect host. The cross-reactivity can, however, be attributed to carbohydrate epitopes present on the parasite and host molecules. Whether these shared epitopes are significant in the protective mechanism of the envelope or have some completely different function is not yet known. It has, however, been demonstrated that the host lipoprotein, lipophorin, is intimately associated with the cystacanth envelope. Two models have been proposed to explain the protective function of the envelope. One common theme of both models is that adsorption of lipophorin to the envelope surface in a native conformation is critical in the prevention of haemocyte recognition of the developing enveloped larvae.

[发布机构] University:University of Glasgow

[关键词] Biochemistry, Developmental biology, Entomology