Further evidence for the protective role of sub-parietal cell membranous secretory product on the cuticle of a pentastomid arthropod parasite developing in its rodent intermediate host.
The pentastomid parasite Porocephalus crotali, develops to an infective stage within a granulomatous lesion in the tissues of rodent intermediate hosts. A conspicuous layer of sub-parietal cell (SPC) secretory product, which coats the intermoult cuticle up to a depth of 12 microns, is described. Around the first five nymphal instars this material consists of an amorphous matrix with distinctive electron-lucid lacunae, but that around later instars (six and seven), while retaining much of the original morphology, possesses a significant membranous component. Host effector cells, most notably eosinophils and macrophage/epithelioid cells, are frequently completely enveloped by SPC secretion but invariably appear unreactive to it. Host cells may penetrate to the outermost layer of the epicuticle but again but again cytotoxic activity is absent. During ecdysis, effector cells are recruited to the intercuticular space where widespread degranulation is evident. Some of this is specifically directed against the underside of the cast cuticle, but not against the newly exposed cuticle. Protracted degranulation eventually reduces the cast cuticle to fragments which are endocytosed by giant cells. 1 cm long infective (seventh-stage) nymphs, which retain the sixth stage cuticle as a protective sheath, are largely devoid of membranous secretion and these were dissected from cysts, washed, and surgically transplanted into the body cavities of naive and infected mice. Pronounced differences in the onset and intensity of the subsequent inflammatory response in the two categories of host indicate some form of specific recognition. In both groups of mice though, the cuticle is an eventual target for attack by effector cells, and parasites are killed. The protective function of SPC secretion is discussed.
Ambrose
N C
NC
Department of Biological Sciences, University of Dundee, Scotland.
Riley
J
J
D000818:Animals; D001181:Arthropods / Q000254:growth & development / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D006790:Host-Parasite Interactions / Q000276:immunology / Q000502:physiology*; D007249:Inflammation / Q000209:etiology / Q000276:immunology; D007814:Larva / Q000276:immunology; D008566:Membranes; D051379:Mice / Q000469:parasitology*; D008854:Microscopy, Electron