Toxoplasma gondii (T. gondii) IgG is a type of antibody that the immune system produces in response to an infection with the parasite Toxoplasma gondii. Toxoplasma gondii is a protozoan parasite that can infect humans and many other warm-blooded animals. It is commonly found in the environment and can be transmitted through various routes, including the ingestion of contaminated food or water, handling cat litter, or through organ transplantation and blood transfusion.