Prospects for new vaccines against helminth parasites

Invertebrate Muscles: Muscle Specific Genes and Proteins

This is the first of a projected series of canonic reviews covering all invertebrate muscle literature prior to 2005 and covers muscle genes and proteins except those involved in excitation-contraction coupling (e.g., the ryanodine receptor) and those forming ligand- and voltage-dependent channels. Two themes are of primary importance. The first is the evolutionary antiquity of muscle proteins. Actin, myosin, and tropomyosin (at least, the presence of other muscle proteins in these organisms has not been examined) exist in muscle-like cells in Radiata, and almost all muscle proteins are present across Bilateria, implying that the first Bilaterian had a complete, or near-complete, complement of present-day muscle proteins. The second is the extraordinary diversity of protein isoforms and genetic mechanisms for producing them. This rich diversity suggests that studying invertebrate muscle proteins and genes can be usefully applied to resolve phylogenetic relationships and to understand protein assembly coevolution. Fully achieving these goals, however, will require examination of a much broader range of species than has been heretofore performed.

Toxocara canis: a labile antigenic surface coat overlying the epicuticle of infective larvae

An electron-dense coat covering the surface of Toxocara canis infective-stage larvae is described. This coat readily binds to cationized ferritin and ruthenium red, indicating a net negative charge and mucopolysaccharide content, and can be visualized by immuno-electron microscopy only if cryosectioning is employed. Monoclonal antibodies reactive to the surface of live larvae bind the surface coat but not the underlying cuticle in ultrathin cryosections. The surface coat is dissipated on exposure to ethanol, explaining the lack of surface reactivity of conventionally prepared immunoelectron microscopy sections of T. canis. Differential ethanol extraction of surface-iodinated larvae demonstrates that the major component associated with the coat is TES-120, a 120-kDa glycoprotein previously identified by surface iodination, which is also a dominant secreted product. The surface-labeled TES-70 glycoprotein is linked with a more hydrophobic stratum at the surface, while a prominent 32-kDa glycoprotein, TES-32, is more strongly represented within the cuticle itself. Antibody binding to the coat under physiological conditions results in the loss of the surface coat, but this process is arrested at 4 degrees C. This result gives a physical basis to earlier observations on the shedding of surface-bound antibodies by this parasite. An extracuticular surface coat has been demonstrated on Toxocara larvae prior to hatching from the egg and during all stages of in vitro culture, suggesting that it may play a role both in protecting the parasite on hatching in the gastrointestinal tract and on subsequent tissue invasion in evading host immune responses directed at surface antigens.

Surface associated glycoproteins from Toxocara canis larval parasites

The surface of infective larvae of Toxocara canis, the dog ascarid nematode, reveals relatively few exposed surface proteins which can be recovered in soluble form. The major components identified by surface labelling have molecular weights of 32, 55, 70 and 120 kilodaltons (kDa), and are all significantly glycosylated. All are recognised by the immune response in definitive (canine) and paratenic (murine or human) hosts. Expression of these antigens on the parasite surface begins after the larvae hatch from infective ova in vitro, and presumably in vivo. Each of these molecules may also be found in the set of secreted (ES) glycoconjugates released by larval parasites cultivated in vitro, and currently available biochemical and functional data on the surface/secreted ES glycoproteins are presented. Analysis with monoclonal antibodies (MAbs) confirms the identity of surface and ES molecules, and these MAbs show differing patterns of binding to the epicuticle, the cuticular matrix and to the oral orifice. Alternative mechanisms for antigen synthesis, insertion into the cuticle and export from the parasite are discussed.