The relationship between nucleoside triphosphate hydrolase (NTPase) isoform and Toxoplasma strain virulence in rat and human toxoplasmosis.

ABSTRACT

Avirulent strains of Toxoplasma gondii possess only the nucleoside triphosphate hydrolase II (NTPaseII) isoform, whilst virulent strains possess both NTPaseI and NTPaseII. To determine if it is possible to identify the infective strain type (virulent or avirulent) in T. gondii infections by serological methods, we developed isoform-specific peptide ELISAs from the NTPaseI and NTPaseII antigens of T. gondii. When rats were immunized with either recombinant NTPaseI or NTPaseII, the ELISA could differentially identify antibody reactivity to each NTPase isoform. This ELISA was then used to test six groups of rats that were infected with either one of three virulent (RH, P or Ent) or three avirulent (Me49, C or TPR) strains of T. gondii. No differential antibody reactivity was detected by either whole recNTPase ELISA or peptide ELISA in the sera of rats, whether infected by virulent or avirulent strains of T. gondii. We also studied a panel of human sera from patients infected with known laboratory strains of T. gondii or naturally infected patients where the parasite was isolated and its virulence determined in mice. Differential reactivity to whole recNTPase isoforms was detected in some human sera, but this reactivity was not detected by the isoform-specific peptide ELISAs. Although the NTPase peptides do exhibit differential antibody reactivity, this is not correlated with the virulence status of the infecting strain.