Caracterização molecular dos mimetopos H2 (SAG2A) e B12 (SRS6) de moléculas de superfície de Toxoplasma gondii

Abstract

Toxoplasma gondii is a protozoan parasite that infects the majority of warm-blooded vertebrates. It actively penetrates in any nucleated cell using a surface antigen superfamily, including the typical evolutionary and developmental products expressed by SRS (SAG1-re!ated sequences) genes, as SAG1 and SAG2A molecules, which mediate host cell attachment and invasion. Considering that little is known about SRS epitopes, the main purpose of the present study was to characterize the epitopes recognized by A3A4 and A4D12 monoclonal antibodies (mAbs) by using phage display libraries. When evaluated by 1D and 2D electrophoresis, the A3A4 mAb recognized a conformational epitope shared by five isoforms of the SRS6, BSR4, SAG5A, SAG5C and SAG5D members of SRS superfamily from a monomeric (p30) or dimeric (p60) molecule. In contrast, a linear SAG2A epitope (p22) shared by two isoforms was recognized by A4D12 mAb and the epitope mapping showed a peptide core consensus at the DGSSA sequence that resulted in a considerable alignment with SAG2A located at its C-terminal domain (137-141 amino acids). Secretion and gliding assays revealed that both A3A4 and A4D12 epitopes are present in enriched excreted/secreted antigens (ESA). Also, they are shed in trials left by T. gondii during gliding motility. In addition, A3A4 and A4D12 epitopes are present in both type I and II genotypes of T. gondii, but no reactivity was detected in N. caninum or E. acervulina lysates, indicating these epitopes are species- but no strain-specific. Pretreatment of RH strain tachyzoites with A3A4 or A4D12 mAb did not show significant protection in C57BL6 mice against T. gondii infection, suggesting that the blockage of the epitopes seems that they do not interfere with infectivity of virulent RH strain in vivo.