Development of a Lateral Flow Immunoassay Using Recombinant Dense Granular Antigen (GRA) 7 to Detect AntiToxoplasma gondii IgG Antibodies

Toxoplasma gondii is an intracellular protozoan parasite that causes toxoplasmosis and is of medical importance in pregnant women and immunosuppressed patients. In recent years, many methods have been developed for the detection of infection caused by this parasite; however, most of the developed methods are not adequately sensitive. The dense granular antigen (GRA) 7 is a highly immunogenic protein that is used as a specific antigen for the diagnosis of toxoplasmosis. This study was designed to produce recombinant GRA7 (rGRA7) antigen in bacterial system in order to be applied as an antigen for developing a simple and rapid lateral flow immunoassay test strip using a gold nanoparticlepAb conjugate probe to detect Toxoplasma IgGspecific antibodies in human sera. After the extraction of genomic DNA from RH strain tachyzoites, polymerase chain reaction (PCR) was performed using specific primers considering restriction sites and BglII and XhoI enzymes. Subsequently, the GRA7 gene was cloned in pET32a (+) expression vector, and then pET32a(+)GRA7 was transformed into E. coli Rosetta (DE3). The induction of protein production was accomplished by IPTG, and the product was finally purified by NiNTA affinity chromatography. In order to make the strip test, the antihuman gold nanoparticle conjugate was applied on conjugate pad, rGRA7 antigen was immobilized to a nitrocellulose membrane as the capture agent, and sample and absorbance pads were assembled on a backing card. For the analysis of the sensitivity and specificity of the assay, the selected patients’ sera samples were tested by standard chemiluminescence immunoassay (CLIA) method, and then compared with TOXOIgG strip results. The findings showed that the use of rGRA7 is an accurate, sensitive, and inexpensive technique for the rapid detection of antiToxo­plasma IgG in human sera. Therefore, rGRA7 can be applied as a diagnostic agent in laboratories.