Scavenger receptors mediate increased uptake of irradiated T.gondii extracts by J774 macrophages

Abstract

Purpose

Protein extracts developed increased immunogenicity without the aid of adjuvants after gamma irradiation. Gamma irradiation of snake venom increased antivenin production by detoxification and enhanced immunity, probably due preferential uptake of irradiated venoms by macrophage scavenger receptors. We studied this uptake of irradiated soluble Toxoplasma gondii extract (STag) by the J774 macrophage cell line similar to antigen presenting cells.

Material And Methods

We labeled STag by biosynthesis in living tachyzoites with radioactive amino acids before purification and irradiation or by adding labels as biotin or fluorescein in stored STag, for quantitative studies or subcellular distribution visualization.

Results

There was enhanced binding and uptake of irradiated STag into the cells compared to non-irradiated STag. Using fluorescein labeled antigens and morphological assays, we confirmed that cells avidly ingested both native and irradiated proteins but native STag were digested after ingestion while irradiated proteins remained in the cell, suggesting diverse intracytoplasmic pathways. Native or irradiated STag present the same in vitro sensitivity to three types of peptidases. Inhibitors of scavenger receptors (SRs) such as Dextran sulfate (SR-A1 blocker) or Probucol (SR-B blocker) affect the specific uptake of irradiated antigens, suggesting its association with enhanced immunity.

Conclusions

Our data suggests that cell SRs recognize irradiated proteins, mainly SRs for oxidized proteins, leading to antigen uptake by an intracytoplasmic pathway with fewer peptidases that prolongs presentation to nascent major histocompatibility complex I or II and enhances immunity by better antigen presentation.

Keywords:

• Adaptive response
• immune responses
• macrophages

Acknowledgement

We gratefully thank the staff of the Laboratório de Protozoologia for the support of this work. J.P. Rodrigues provides helpful discussions during the evolution of the research. Andrea da Costa was a Ph.D. fellow of FAPESP (Proc no. 14/17029-4) and this work was a part of her Ph.D. in Tropical Medicine. HF Andrade Jr. was a fellow of CNPq and FFM. C.A. Carvalho was a post-doctoral fellow from FAPESP (Proc. No. 14/17029-4).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The research was partially supported by grants from FAPESP (Proc.no. 13/04676-9), CAPES (88881.5702232/2020-01) and LIMHCFMUSP.

Notes on contributors

Andrea da Costa

Andrea da Costa, BSc, MSc, PhD, fellow of the Lab. of Protozoology of the Instituto de Medicina Tropical de São Paulo, Universidade de São Paulo, dealing with in vitro immunology assays and animals models for vaccines for toxoplasmosis that could be used in animals, specially devoted to antigen presentation. Now she maintains a in vitro toxicology assays lab in a private company.

Camila Aparecida de Carvalho

Camila Aparecida de Carvalho, BSc, MSc, is a postdoctoral fellow of the Lab. of Protozoology of the Instituto de Medicina Tropical de São Paulo, Universidade de São Paulo, dealing with interference of small antigen molecules or monovalent immune complexes in Leishmania infantum disease evolution or serology diagnostic assays in human, dog or mouse disease.

Nanci do Nascimento

Nanci do Nascimento, BSc, MSc, PhD, deceased in 2017, was the former chief of the Division of Radiobiology of the Instituto de Pesquisas Energéticas e Nucleares, and a leadership of vaccine production using gamma radiation using both intact parasites, parasites extracts or purified proteins.

Heitor Franco de Andrade

Heitor Franco de Andrade Jr., MD, PhD, since 1986 is an associated professor at the Department of Pathology of the Faculdade de Medicina, Universidade de São Paulo, working in the Lab. Protozoology of the Instituto de Medicina Tropical de São Paulo, Universidade de São Paulo. His research interests were pathology, diagnostic assays and immunology of tropical diseases, mainly those caused by protozoa and viruses.