Immunochemical and Biochemical Analysis of Larval Secreted Antigens from the Parasitic Nematodes Ascaris suum and Ascaris lumbricoides

There is a relatively small amount of experimental data regarding the in vitro - released secretory products (IVRS) of the parasitic roundworm nematodes of man and swine, Ascaris lumbricoides and Ascaris suum respectively. The importance of detailed biological examination of the IVRS from these nematodes is justified by the relative inadequacy, for serodiagnosis or prophylaxis, of alternative sources of nematode-derived material: for instance, cuticular surface molecules, or worm homogenates. Here the IVRS from L2 and L3/4 stages of Ascaris lumbricoides and Ascaris suum were examined for the first time both immunochemically and biochemically to evaluate their usefulness for specific detection of ascariasis and for possible use in vaccination of animals or humans against Ascaris infection. The main techniques used involved the extrinsic (125I) or intrinsic (35[S]-methionine) labelling of parasite secretions followed by precipitations with either lectins or immune sera and final analysis of the precipitated nematode products by SDS-PAGE. Alternatively, radio-iodinated IVRS from A. suum were incubated with various proteinases and the products of the reactions also analysed by SDS-PAGE. The first studies of radio-iodinated A. suum IVRS showed that the range and number of worm products were different as the parasites developed from the L2 stage to lung stages (L3/4) and that there was considerable, but incomplete stage-specificity of the repertoire of secretions produced. S. aureus-mediated radio-immunnoprecipitations (SRIP's) of A. suum-immunised rabbit antisera and A. suum IVRS showed that, except for one product from A. suum L3/4 IVRS, all the secretions of A. suum L2 and L3/4 worms are antigenic. The non-antigenic component of L3/4 products was identified as rabbit serum albumin. Antisera from A. suum-immunised mice and rats also precipitated components of larval IVRS in SRIP's but different distinct sets of antigens from those recognized by infected rabbits. One possible reason for these differences could be attributed to the separate genetic composition of each species. Mouse anti-A. suum antisera failed to immunoprecipitate an Mr 14000 component of A. suum larval secretions, which was also found to be the major antigen of adult A. suum body fluid (ABF). As ABF is a commonly used source of material for immunological analysis of Ascaris infection, it could be advisable to look for alternative sources of target antigens that avoid an undue bias towards the Mr 14000 product. Immunological crossreactions have been a major stumbling block for specific detection of nematode parasite infection of humans and animals. One of the ways in which crossreactions could lead to false positive results in serodiagnostic immunoassays is the possible occurence of similar antigens among the products of different species of parasites. The secreted products of A. suum and A. lumbricoides were examined by radio-iodination followed by SDS-PAGE. The results showed that the secretions of larval stages of both species were very similar in SDS-PAGE profile except that IVRS from the larvae of the human roundworm apparently contained a secretion of Mr 17000 that was unique to these. SRIP's with sera from rabbits infected either by A. suum or A. lumbricoides and 125I-labelled IVRS of the larval stages of these parasites followed by examination of the immunoprecipitates by SDS-PAGE, showed that there was complete crossreactivity of a given antiserum of one species and the antigens of the other, including the Mr 17000 antigen of A. lumbricoides. Additionally there was also extensive crossreactivity of antiserum from rabbits infected with the ascaridoidean parasite Toxocara canis and the secreted antigens of both A. suum and A. lumbricoides. These findings advised against the use of IVRS from Ascaris species in possible serodiagnostic assays or in serological tests to differentiate between A. suum and A. lumbricoides as separate species. However it might be possible, by raising monoclonal antibodies (McAb) against Ascaris IVRS to find McAb's that differentiate between the Ascaris species and/or provide specificity in serodiagnostic assays. Radio-iodination of IVRS from Ascaris species involved material collected from the supernatants of worm cultures in vitro, not necessarily representative of the products of living worms, but could have consisted of worm somatic components. One biochemical method that aid in confirming that, for the most part, living worms synthesised the IVRS is the technique of intrinsic (or metabolic) labelling of Ascaris larval products. (Abstract shortened by ProQuest.)