Use of a 203 alphaalpha fragment of Tc-PDI to detect IgA activity during infection by Teladorsagia circumcincta in sheep.

The objectives of this study are to find an appropriate ELISA technique to monitor IgA activity during infection by Teladorsagia circumcincta in sheep as well as to identify the degree of resistance to the infection. Previous studies have shown the relationship between IgA in infected sheep and the resistance to the infection. In this study, the titre of IgA in resistant and susceptible infected ewes was tested in blood, nasal secretions and saliva. ELISAs were carried out against somatic antigen from L4 and against a 203 amino acid fragment of a recombinant protein disulphide isomerase of T. circumcincta (Tc-PDI). The results showed that, in general, the titres of IgA against a fragment of a Tc-PDI were lower than against the somatic antigen. These lower levels are clearly shown in blood samples and nasal secretions in contrast to saliva samples where the titre reached higher values testing the IgA against Tc-PDI. This could be due to the fact that, in the detection of IgA against Tc-PDI, the antibody-antigen reaction is more specific than against the whole somatic antigen. To differentiate between resistant and susceptible animals, the significant differences were more present with the somatic antigen. Nevertheless, the ELISA technique using the somatic antigen cannot be standardized, and the antigen-antibody reactions are more unspecific; therefore, the recombinant Tc-PDI could be a better option.