In this invention, the inventors report the characterization of BCLA (brain
cyst-loaded
antigen), a
protein uniquely expressed in the merozoite stage of a parasite. In cysts directly purified from mouse brain, the
protein is distributed both internally and on the surface of the
cyst. ELISA
antibody capture using a combination of serologically reactive BCLA
peptide and recombinantly expressed C-terminal domain (rBCLA) constitutes an effective serological marker of latent infection with high sensitivity, definitively and uniquely correlated with the presence of cysts in mouse brain. Antibodies against the BCLA
antigen have been detected in human patients. Enrichment titers were detected in patients identified as seropositive for Sag1 or tachyzoite-associated
antigen. Further correlation between anti-BCLA IgG synthesis and cysts in humans was demonstrated by significantly stronger recorded titers in the
pathology group strongly correlated with the presence of cysts. Furthermore, newborns with confirmed congenital
toxoplasmosis showed significantly higher levels of anti-BCLA IgG at birth compared to their mothers, indicating specific intrauterine synthesis of this IgG. Therefore, this invention relates to a novel
Toxoplasma gondii protein, hereinafter referred to as BCLA, which is a novel serological marker whose expression is limited to latent
toxoplasmosis (schizonts / cysts). This
specific protein and its antigenic fragments can be used to detect autoantibodies
in patient serum for the diagnosis of latent
toxoplasmosis. This invention also relates to derived antibodies that specifically bind to this
novel protein, generated through immunization with BCLA.