Immunocytochemical study on biologically active neurosubstances in daughter sporocysts and cercariae of Trichobilharzia ocellata and Schistosoma mansoni

SUMMARYImmunocytochemical techniques applied to sections and whole-mount preparations of cercariae from two species of trematodes, Trichobilharzia ocellata and Schistosoma mansoni, revealed the occurrence of immunoreactivity (IR) to several neurosubstances in the nervous system (NS). Immunostaining was localized in cerebral ganglia, in the main commissure, in anterior and posterior nerve trunks, as well as in a pair of nerve fibres running along the tail. In T. Ocellata, immunoreactivity (IR) was observed with antisera raised against: glutamate, FMRFamide, catch-relaxing peptide (CARP), small cardiac peptide B (SCPB), arg-vasotocin (AVT), arg-vasopressin (AVP), and substance P. In S. mansoni antisera raised against glutamate, FMRFamide, CARP, SCPB, α-caudodorsal cell peptides (α-CDCP), and cholecystokinin (CCK) showed neuronal IR. With the other 51 antisera tested no IR was observed. With anti-APGWamide, IR was observed outside the NS in cells of the wall of the daughter sporocyst and in flame cells of cercariae of T. ocellata. IR to FMRFamide was present in the escape glands of the intrasporocystic cercariae of T. ocellata and S. mansoni. IR to somatostatin was observed in subtegumental parenchymal cells of cercariae of S. mansoni. IR to met-enkephalin was present in cells of the cercarial embryos and in undifferentiated cells in developing cercariae. Trematodes are, together with cestodes, phylogenetically the oldest classes in which glutamate-like material and immunopositivity to a number of neuropeptides isolated from invertebrates has been demonstrated. The results are discussed in relation to immunocytochemical data obtained for other platyhelminths, to endogenous functions of the immunopositive materials, and to their possible role in parasite–host interactions.

Schistosoma mansoni: host cell adhesion to the different stages of the parasite, in vivo

The peritoneal cavity of laboratory mice was used to study the phenomenon of host cell adhesion to different evolutive stages of the Schistosoma mansoni (cercaria, adult worm, developing and mature eggs, miracidium, young and mature daughter sporocysts). Material recovered from the peritoneal cavity 30 and 180 min after the inoculation of each evolutive form was examined with the help of a stereomicroscope. The free swimming larvae (cercaria and miracidium), and the evolutive forms producing such larvae (mature egg and mature daughter sporocyst) elicited the host cell adhesion phenomenon. In all forms but cercariae the adherent cells remained as so till 180 minutes after inoculation

Lecithochirium furcolabiatum (Jones, 1933), Dawes 1947: the miracidium and mother sporocyst

ABSTRACTExperimental infections of the marine topshell Gibbula umbilicalis with Lecithochirium furcolabiatum (Digenea: Hemiuroidea) have allowed the development of a model system which will enable further studies of the molluscan host response. The long-lived intertidal prosobranch host is easily maintained in the laboratory, and experimental infection rates of 98% were consistently achieved. The miracidium and mother sporocyst have been studied at both light and ultrastructural levels, providing the first account of the morphology of these stages in Hemiuridae. The ingested egg hatches within the host intestine, treatment with L-cysteine and alkaline pH stimulating miracidial emergence in vitro. The general body surface of the miracidium is devoid of spines or cilia, the latter being restricted to four plates near the anterior extremity. The miracidium swims actively prior to penetration of the gut wall, the sporocyst being released from the miracidial epidermal Coat within the haemocoel. Within 5 weeks of infection, the filamentous mother sporocyst Contains 1 to 3 oval germ balls, daughter sporocysts being recorded free within the digestive gland haemocoel 7 weeks later. Twenty three weeks after ingestion of eggs, the daughter sporocyst extends into the host gill filaments, containing cystophorous cercariae ready for emergence.

Influence of larval schistosomes on polysaccharide synthesis in albumin glands of Biomphalaria glabrata

SUMMARYAn in vitro bioassay was used to examine [14C]glucose incorporation into polysaccharides in albumen glands (AGs) of susceptible M-line Biomphalaria glabrata infected with the NMRI strain of Schistosoma mansoni. Polysaccharide and galactogen synthesis were unaffected by larval trematode infection in AGs of snails at days 14, 21, and 28 post-infection (p.i.) when compared to uninfected controls. Further experiments were conducted to determine if daughter sporocysts, hypothesized to be primary mediators of parasitic castration in this system, were able to exert direct effects on synthetic activity of uninfected AGs via haemolymph-borne molecules or in vitro culture-generated larval excretory–secretory (ES) products. When AGs were incubated in the presence of infected snail haemolymph, significant differences in quantities of polysaccharides and galactogen were detected only in test organs incubated in day 28 p.i. haemolymph. Daughter sporocyst ES products generated during the first 48 h of culture caused a significant reduction in polysaccharide and galactogen synthesis in test organs. When ES products from days 3 to 6 of in vitro culture were tested similarly, no significant differences in either polysaccharide or galactogen synthesis were observed between control and test organs. These data demonstrate that daughter sporocysts are able to modulate a specific aspect of the reproductive activity of the snail host through haemolymph-borne molecules of host or parasite origin, or directly through in vitro culture-generated ES products.