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Mechanism of recognition and immune processing of antigens enhanced by radiation gamma in toxoplasmosis

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Andréa da Costa
Total Authors: 1
Document type: Doctoral Thesis
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Instituto de Medicina Tropical de São Paulo (IMT)
Defense date:
Examining board members:
Heitor Franco de Andrade Junior; Roberto Mitsuyoshi Hiramoto; Patrick Jack Spencer
Advisor: Heitor Franco de Andrade Junior

Toxoplasmosis, caused by the protozoan Apicomplexa, Toxoplasma gondii, is widely disseminated and little symptomatic. Chronic infection maintains residual cysts throughout life, but protects from reinfection. In this complex scenario, vaccines with residual cysts are not feasible and vaccines of subcomponents result in low protection. Ionizing radiation was used for enhancement of either live or subcomponent immunogens. The use of gamma radiation in soluble extracts of T. gondii tachyzoites was efficient in protecting mice against infection using different strains, without adjuvants and easy management. The irradiated antigen undergoes physical changes without addition of new molecules, with protein aggregation, chain breaks and oxidative reactions, which can improve its targeting to cellular receptors in antigen-presenting cells (APCs). The irradiated extracts showed minimal structural alterations affecting 60% of the proteins, but with maintenance of the antigenic and immunogenic characteristics. The extracts irradiated at 1500Gy (STag 1500Gy) induced greater protection and higher humoral response than the native extract (p <0.05), more evident at a dose of 10?g/animal, with high specific IgG antibody levels and increased maturation of specific IgG affinity, with similar or lower efficiency at higher doses. Animals immunized with STag 1500Gy presented higher proportions of memory lymphocytes B and CD4+ while immunization with irradiated intact tachyzoites showed an increase in CD8+ lymphocytes, both much larger than that induced by native STag. We construct STag labeled by biosynthetic pathway or by coupling to different non-oxidative markers. STag3H 1500Gy showed greater and longer uptake by macrophages, with no degradation as STag3H native. The use of fluorescent STags showed that the greater binding of the STag 1500Gy is not related to the loss of protease susceptibility, given the same sensitivity of the extracts for peptidases, besides remaining in the cell for much longer time by fluorescence. In the presence of Scavengers receptor blockers Dextran sulfate (SRA) and Probucol (CD36), binding and uptake of STag 1500Gy in macrophages was more affected by oxidized radical (CD36) inhibitors than by negative radical inhibitors (SRA). In peritoneal macrophages of Scavenger receptor CD36 deficient mice (KOCD36-/-), we observed an inverse kinetics, with less incorporation of STag 1500Gy, as evidenced by both quantitative assays and individual cells by cytometry flow, compared to wild type macrophages. KOCD36-/- animals did not show significant production of specific IgG in all immunogens used, and were highly susceptible to challenge with viable strains of aggressive or cistogenic T. gondii strains. Transplantation of normal peritoneal macrophages \"primed\" with STag 1500Gy induced increase of specific IgG in sera from CD36-/-recipient animals. The best immunogenicity of the irradiated antigens should be related to the uptake of oxidized proteins via CD36 in APCs, which directs these antigens to the intracellular route favorable to their presentation for adaptive immune response. Our results show that ionizing radiation was able to modify STag proteins, making its processing by immune cells more efficient without the addition of adjuvants to the process. (AU)

FAPESP's process: 14/17029-4 - Mechanism of immune recognition and antigen enhanced by gamma radiation processing in toxoplasmosis
Grantee:Andrea da Costa
Support Opportunities: Scholarships in Brazil - Doctorate