Early Kinetics of Intestinal Infection and Immune Responses to Two Toxoplasma gondii Strains in Pigs

Abstract

Toxoplasma gondii is an obligate intracellular parasite, able to infect all homeothermic animals mostly through ingestion of (oo)cysts contaminated food or water. Recently, we observed a T. gondii strain-specific clearance from tissues upon infection in pigs: while the swine-adapted LR strain persisted in porcine tissues, a subsequent infection with the human-isolated Gangji strain cleared parasites from several tissues. We hypothesized that intestinal immune responses shortly after infection might play a role in this strain-specific clearance. To assess this possibility, the parasite load in small intestinal lymph node cells and blood immune cells as well as the IFNγ secretion by these cells were evaluated at 2, 4, 8, 14, and 28 days post oral inoculation of pigs with tissue cysts of both strains. Interestingly, at day 4 post inoculation with the LR strain the parasite was detected by qPCR only in the duodenal lymph node cells, while in the jejunal and ileal lymph node cells and PBMCs the parasite was detected from day 8 post inoculation onwards. Although we observed a similar profile upon inoculation with the Gangji strain, the parasite load in the examined cells was much lower. This was reflected in a significantly higher T. gondii-specific serum IgG response in LR compared to Gangji infected pigs at day 28 post inoculation. Unexpectedly, this was not reflected in the IFNγ secretion upon re-stimulation of the cells where almost equal IFNγ secretion was observed in both groups. In conclusion, our results show that T. gondii first enters the host at the duodenum and then probably disseminates from this site to the other tissues. How the early immune response influences the clearance of parasite from tissues needs further study.

Archetypal type II and III Toxoplasma gondii oocysts induce different immune responses and clinical outcomes in experimentally infected piglets

“…A trend towards higher parasite burdens was also observed in another report where pigs were infected with a type II strain ( T. gondii IPB-LR) compared to those infected with a hybrid type I/II strain ( T. gondii IPB-Gangji) ( 8 ). As previously reported in the literature, a wide distribution of the parasite has been observed in tissues such as the brain and heart, as well as in other muscles of commercial interest ( 40 – 43 ). Similar tropism was observed for both TgShSp1 and TgShSp24 isolates in this study.…”

Early Immune Initiation by Porcine Cells following Toxoplasma gondii Infection versus TLR Ligation

“…In mice and humans, interferon gamma (IFNγ) is the primary driver of resistance to acute T. gondii infection [ 5 , 6 ]. Similarly, Rahman et al (2020) [ 7 ] demonstrated that peripheral blood mononuclear cells (PBMCs) isolated from T. gondii -infected pigs produce IFNγ upon antigen-specific restimulation, beginning 8 days post-infection, and peaking 14 days post-infection. This confirms the presence of an antigen-specific T-cell response in pigs to T. gondii .…”

Key Limitations and New Insights Into the Toxoplasma gondii Parasite Stage Switching for Future Vaccine Development in Human, Livestock, and Cats

“…gondii oral infection with oocyst or cysts promotes mucosal and systemic humoral responses. The presence of anti-T gondii IgG antibodies in sera of pig infected orally with T. gondii oocysts or cysts was detected within 2 weeks post infection (Verhelst et al, 2011;Burrells et al, 2015;Basso et al, 2017;Campero et al, 2020;Rahman et al, 2020). Anti-T. gondii IgM antibodies were detected 2 weeks post-infection and disappeared by week 6 post-infection with T. gondii cysts (Verhelst et al, 2011).…”

“…Following oral infection of pig with T. gondii cysts, IFN-g secretion by mediastinal and duodenal lymph node cells stimulated with T. gondii antigens was observed from day 8 post-infection onwards while jejunal and ileal lymph node cells did not secrete IFN-g (Rahman et al, 2020). Restimulated PBMC cells secreted IFN-g from day 14 post-infection onwards (Rahman et al, 2020).…”