Antibodies to Tyvelose Exhibit Multiple Modes of Interference with the Epithelial Niche ofTrichinella spiralis

Abstract

Infection with the parasitic nematode Trichinella spiralis is initiated when the L1 larva invades host intestinal epithelial cells. Monoclonal antibodies specific for glycans on the larval surface and secreted glycoproteins protect the intestine against infection. Protective antibodies recognize tyvelose which caps the target glycan. In this study, we used an in vitro model of invasion to further examine the mechanism(s) by which tyvelosespecific antibodies protect epithelial cells against T. spiralis. Using cell lines that vary in susceptibility to invasion, we confirmed and clarified the results of our in vivo studies by documenting three modes of interference: exclusion of larvae from cells, encumbrance of larvae as they migrated within epithelial monolayers, and inhibition of parasite development. Excluded larvae bear cephalic caps (C. S. McVay et al., Infect. Immun. 66:1941-1945, 1998) of immune complexes that may physically block invasion or may interfere with sensory reception. Monovalent Fab fragments prepared from a tyvelose-specific antibody also excluded larvae from cells, demonstrating that antibody binding can inhibit the parasite in the absence of antigen aggregation and cap formation. In contrast, encumbered larvae caused extensive damage to the monolayer yet were not successful in establishing a niche, as reflected by their failure to molt. These results show that antibodies to tyvelose exhibit multiple modes of inhibitory activity, further implicating tyvelose-bearing glycoproteins as mediators of invasion and niche establishment by T. spiralis.The parasitic nematode Trichinella spiralis has a wide host range which includes humans and over 100 other vertebrate species (10). T. spiralis infection is acquired by ingestion of muscle tissue containing L1 larvae. Enzymes in the acidic environment of the stomach free larvae from tissue, allowing them to initiate infection by invading columnar epithelial cells in the small intestine. Here, they rapidly undergo four molts, grow, and reproduce (10). Larval and adult stages localize to the crypt-villus junction, where they migrate in what appear to be epithelial syncytia (21,22). Establishment of T. spiralis in this intestinal habitat is crucial for successful completion of the life cycle.Although it has been known for many years that T. spiralis invades gut epithelium, the host-parasite relationship at this site is poorly understood. Our approach in investigating this relationship is based on the premise that the study of an effective host immune defense against a pathogen can reveal insights into the mechanisms of parasitism deployed by the agent. We have shown that niche establishment by T. spiralis is prevented in the rat by antibodies which are specific for L1 larval glycoproteins (1, 3). So-called rapid expulsion eliminates up to 100% of an oral dose of L1 larvae within hours of challenge (4, 9, 13, 15). Protective antibodies are specific for tyvelose (3,6-dideoxy-D-arabinohexose) which caps the antennae of tri-and tetra-antennary glycans shared by ...

Expulsion of Secondary Trichinella spiralis Infection in Rats Occurs Independently of Mucosal Mast Cell Release of Mast Cell Protease II

“…Rapid expulsion displayed by neonatal rat pups born to infected dams can be reproduced in pups born to naive dams by passive immunization with tyvelose-specific IgG (21). The protective mechanisms of the Abs have been documented in vivo (21,24) and confirmed in an in vitro model (23). Direct effects of Abs on T. spiralis larvae include entrapment of larvae in mucus as well as exclusion from and encumbrance in the epithelium (23,24).…”

“…The protective mechanisms of the Abs have been documented in vivo (21,24) and confirmed in an in vitro model (23). Direct effects of Abs on T. spiralis larvae include entrapment of larvae in mucus as well as exclusion from and encumbrance in the epithelium (23,24). The potential for mast cells to contribute to Ab-mediated protection has not been investigated previously in neonatal rats.…”

“…Protective Abs are specific for tyvelose-bearing glycans that are unique to L 1 (22). In the presence of tyvelose-specific Abs, L 1 are excluded from the epithelium, entrapped in mucus, or encumbered in epithelial cells (23,24). Abs are protective when delivered to pups orally or by i.p.…”

Molting, Ecdysis, and Reproduction of Trichinella spiralis Are Supported In Vitro by Intestinal Epithelial Cells

“…Rat monoclonal antibody (MAb) 18H (3) protects epithelial cells in vitro from infection with T. spiralis L1 larvae (28). The antibody binds to tyvelose-bearing N-glycans on L1 stage glycoproteins (15).…”

“…This mimics the location and activity of larvae in the intestinal epithelium of the animal host (36,37). Recently, we reported that L1 larvae molt and ecdyse when they are inoculated into cultures of human colonic epithelial cell line Caco-2 (28). The aims of the present study were to extend these initial findings in order to further define the requirements for ecdysis and to establish culture conditions that support development, growth, and reproduction of T. spiralis.…”