Immunocytolocalization study of the external covering of Trichinella spiralis muscle larva.

The antibody-binding sites of the muscle larva of Trichinella spiralis were investigated by immunogold staining on the ultrathin sections of LR white resin. The antibodies, which were produced in the course of T. spiralis infection in rats, specifically bound to the inner layers of the body cuticle and the cuticle of the hindgut, but not to the cuticle of the esophagus. This is the first report that reveals the antigenic nature of the inner layers of the external coverings of T. spiralis larva. The body cuticle of Trichinella spiralis is an extracellular material that covers the entire surface of the worm, and is the most obvious point of contact between the worm and the host. Because T. spiralis stimulates complex, stage-specific immunologic responses in the host (Philipp et al., 1980, 1981), antigenic presentation by the cuticle in a natural infection has attracted a great deal of attention (Silberstein, 1983). There is no doubt about the antigenicity of the cuticle surface judging from a number of the studies including those of Despommier et al. (1967), Gadea et al. (1967), Stankiewicz and Jeska (1973), Vernes et al. (1974), McLaren et al. (1977), Mackenzie et al. (1980), Philipp et al. (1980, 1981), Kim and Ledbetter (1981), and Silberstein and Despommier (1984). However, there are no immunocytochemical data available regarding the antigen in the cuticle inner layer. This lack of information may be due to technical limitations in immunocytochemical staining. Because the cuticle is considered to be impermeable to large molecules, antibodies for immunostaining may not penetrate deep inside the cuticle, i.e., the cuticle inner layer. The only way to expose the cuticle inner-layer antigen to the antibody is by thin-sectioning of the cuticle followed by immunostaining. This method allows the antibody access to the cuticle inner-layer antigen. However, because the antigen is found only in small amounts on the cut surface of the cuticle, immunofluorescence and immunoperoxidase light microscopic techniques are not sensitive enough to detect such a small amount of antigen. This investigation deals with the localization of antigen in the cuticle of the muscle larva of T. spiralis taking advantage of recent methodological advances of postembedding immunoReceived 23 March 1987; revised 29 June 1987; accepted 26 October 1987. staining using a colloidal gold marker (Beesley, 1985). MATERIALS AND METHODS