Characterization of excretory-secretory antigens of Fasciola hepatica.

Twenty-one day old Fasciola hepatica were recovered from the livers of infected mice and cultured for 5-7 days in a serum-free medium containing either [14C]leucine, [14C]isoleucine or [35S]methionine, or in a medium containing [14C]leucine and serum from sheep vaccinated with excretory-- secretory (ES) antigens of juvenile F. hepatica. All three labelled amino acids were incorporated into fluke proteins. Labelled proteins also appeared in the culture medium. Three major polypeptides detected in the culture media had apparent molecular weights of 26,000, 24,000 and 23,000. All were immunoprecipitated from [14C]leucine-labelled culture medium using antisera against fluke somatic antigens raised in rabbits or from sheep vaccinated with ES antigens of juvenile F. hepatica. A polypeptide of molecular weight 27,000 was also prominent in the culture medium when [14C]isoleucine was used. This polypeptide was present was a minor component when [14C]leucine and [35S]methionine were included in the culture media; it did not appear to be immunoprecipitated by the above antisera from [14C]leucine-labelled culture medium. In the presence of serum from vaccinated sheep, the ES antigens formed immune complexes which contained the polypeptides mentioned above, together with several higher molecular weight polypeptides. Additionally, a number of minor bands of varying molecular weight were present. After micro-Ouchterlony gel immunodiffusion, 2 precipitin lines formed between the labelled ES antigens and antisera. Electrophoresis of these indicated that the 23,000, 24,000 and 26,000 Dalton labelled polypeptides were present in each. The higher molecular weight and the 27,000 Dalton labelled polypeptides were also present in one of the lines.