Proteomic host response to Toxoplasma gondii strains of distinct viruence phenotypes
Toxoplasma gondii is an obligate intracellular protozoan parasite that can infect all warm-blood animals. In humans, it is estimated that one-third of world's population is infected with T. gondii. Most T. gondii strains can be classified into three genotypes; type I, II and III. Type I strains (e.g. RH) are virulent strains with features of rapid growth. Type II (e.g. Me49) and type III strains (e.g. CTG) are avirulent, with slower growth and more readily form cysts in the brain in the chronic infection. In infected host cells, the parasite modulates the host immune system for their successful replication and dissemination. To investigate the host response to three different virulence phenotypes, we proposed to use a two dimensional-differential gel electrophoresis (2D-DIGE) based proteomic approach. Though preliminary studies, it was concluded that Me49 was not appropriate for this study due to their significantly slower growth rate within 24 hours p.i.. Subsequent studies were then done comparing the type I RH strain vs. the type III CTG strain. Using the RH strain, kinetic analysis of the host cell response to infection was done, analyzing samples at 2, 12 and 24 hours p.i.. Few protein changes were observed at 2 and 12 h p.i., and thus only 24 hours p.i. was analyzed via 2D-DIGE analysis. For 2D-DIGE analysis, quadruplicates of protein extracts were separated in 2DDIGE based on pH and molecular weight. For RH strain, we found a total of 439 protein spots were found to be significantly affected by infection, with 247 spots with increased expression and 187 spots with decreased expression and fold-changes ranging from 0.16 to 13.1. For CTG straina total of 175 protein spots were found with significant expression changes. Among them, 48 spots were increased and 127 were decreased with expression changes ranging between 0.66 and 2.41. Interestingly, many decreased spots were seen in trains of spots indicating these may be due to a post-translational modification such as phosphorylation. For the further studies, the identification of protein spots is necessary to elucidate the interactions between host cell and T. gondii strains of distinct virulence phenotypes.