Identification of immunodominant antigens for the laboratory diagnosis of toxocariasis.

OBJECTIVES

To identify immunodominant antigens of Toxocara canis recognised by Toxocara-infected sera as recombinant reagents for immunodiagnosis of toxocariasis.

METHODS

Pooled sera from human cases of toxocariasis were used to identify immunodominant antigens by immunoscreening a T. canis larval expression cDNA library. The positive clones were sequenced to reveal the identity of the antigens. The recombinant proteins were expressed in E. coli and then used to confirm their immunoreaction with sera of humans with toxocariasis. Two chosen antigens were also used to differentiate Toxocara infection from other helminth infections in mice.

RESULTS

Eleven antigens with immunodiagnostic potential were identified, including two C-type lectins (CTLs) that reacted strongly with the Toxocara-positive serum pool. The first CTL (Tc-CTL-1) is the same as TES-32, previously identified as a major immunodominant component of TES; the second CTL (Tc-CTL-2) is a novel C-type lectin sharing 83% amino acid sequence identity within the functional domain of Tc-CTL-1. The E. coli-expressed recombinant Tc-CTL-1 was strongly recognised by the Toxocara-positive serum pool or sera from animals experimentally infected with T. canis. Reactivity with recombinant Tc-CTL-1 was higher when the unreduced protein was used in an enzyme-linked immunosorbent assay (ELISA), dot-blot assay or Western blot test compared to the protein under reduced condition. Both recombinant Tc-CTL-1- and Tc-CTL-2-based ELISAs were able to differentiate T. canis infection from other helminth infections in experimentally infected mice.

CONCLUSIONS

Both Tc-CTL-1 and Tc-CTL-2 were able to differentiate Toxocara infection from other helminth infections and could potentially be used as sensitive and specific immunodiagnostic antigens.