Schistosoma mansoni: Ultrastructure of early transformation of skin- and shear-pressure-derived schistosomules

Against the background of cercarial fine structure, ultrastructural changes were compared in schistosomules of Schistosoma mansoni 30 min and 1 hr after their production in vivo by skin penetration and in vitro by shear pressure. The same developmental pattern was observed in schistosomules of both derivations. In vitro schistosomules, however, developed more slowly, resembled cercariae more closely, and varied less among organisms than did in vivo schistosomules. The greatest morphological changes were observed in the 1-hr in vivo schistosomules. These were as follows: (1) in tegument, formation of transient microvilli, a hepatalaminate outer membrane and accented surface invaginations, loss of glycocalyx, movement outward of cyton vesicles via bridges, accumulation of multilaminate bodies around bridge openings; (2) in the anterior organ (oral sucker), movement of head gland vesicles via the ducts into tegument followed by collapse of the gland fundus, disappearance of the circumfundal cells and two large support cells, and the appearance in these areas of membranes and parenchymal cells; (3) secretion of the acetabular gland contents, collapse of the glands and replacement by membranes and parenchymal cells; (4) peristaltic activity of the digestive tract as shown by alternate areas of lumen constriction and dilation; (5) loss of bladder and contraction of the small aboral collecting tubules; and (6) conversion of heterochromatic parenchymal cell nuclei to euchromatic. In contrast, the 1-hr in vitro shear schistosomules resembled 30-min in vivo schistosomules, retaining many cercarial features.     

Schistosoma mansoni: histological localization of gelatinase in the preacetabular glands of cercariae

Proteolytic activity was demonstrated in secretions from the preacetabular glands of cercariae of Schistosoma mansoni. Thin gelatin film substrates were lysed by living cercariae stimulated to penetrate by application on the films of skin surface lipid. Lysis was directly related to number of cercariae, time, and temperature of incubation and pH of the medium. Gelatinase activity in unfixed frozen sections of cercariae incubated on the gelatin films was in the preacetabular glands which are the source of the secretion emptied into skin during penetration. Protease activity, therefore, appears to be related to penetration. The schistosome larvae which made the penetration attempt satisfied the accepted criteria for schistosomules, and therefore appeared to have transformed into schistosomules even though they did not successfully penetrate anything.     

Schistosoma manonsi: cercarial penetration of host epidermis at the ultrastructural level

Invasion of the outer layers of the epidermis of mouse ear skin by cercariae of Schistosoma mansoni within 7 min of their application to it has been studied with the optical and the scanning and transmission electron microscopes.Entrance of cercariae was under the edges of the dead flattened keratinized cells of the horny layer (squames), and penetration through this layer was by disarticulation of the stacks of squames at their interdigitations. Mucus from the postacetabular glands was recognized with the light and electron microscopes on the skin surface, especially at squame edges and between layers of squames and along the keratogenous zone. The findings suggested that disarticulation of the squames was not effected solely by the muscular probing and pushing of the parasite, but that it might be aided by swelling of the mucus secretion deposited in the area from the postacetabular glands. Loosening of the interlocked edges of the squames by enzymatic action is also a possibility, but was not evaluated for this report.The migration path along the keratongenous zone was marked by extensive damage to the transitional cells of the granular layer subjacent to the squames. Packets of secretion from the cercarial preacetabular glands were identified below the horny layer in the cytoplasm of these cells. It was considered that the host tissue damage in this area was the result not only of tearing of the tissues by passage of the spiny schistosomules, but also of enzymatic activity, the enzyme source being the granules in the packets of preacetabular gland secretion.     

Schistosoma mansoni: cryopreservation of schistosomules.

Conditions were established for recovery of active schistosomules of Schistosoma mansoni after cryopreservation and storage in liquid nitrogen (?196 C). Schistosomules prepared from cercariae by a shear pressure technique were subjected to a two-step cooling process consisting of a slow cooling rate to an intermediate temperature, followed by rapid quenching of the sample in liquid nitrogen. Overall averages of 39 and 44% of the schistosomules, with a maximum of 88%, were recovered retaining normal activity with cooling rates of 0.4 C/min to ?32 C or 0.8 C/min to ?35 C, respectively. Methanol at 17.5% in Earle's lactalbumin hydrolysate was the freezing medium. As compared with 24 hr storage in liquid nitrogen, no loss in schistosomule motility was observed after 1 month. Following cryopreservation, attenuated schistosomules derived from ⁶⁰Co-irradiated cercariae (50 kR) exhibited structure and activity equivalent to that of unattenuated schistosomules. Infectivity for mice of unattenuated schistosomules derived from ⁶⁰Co-irradiated cercariae (50 Krad) exhibited structure and activity of unfrozen schistosomules ranged from 0.4 to 15.2%.