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Abstract
Despite the great interest in the development of a vaccine against African swine fever (ASF) in wild boar, the immunological mechanisms that induce animal protection are still unknown. For this purpose, tertiary lymphoid organs (TLOs) of wild boar were characterised and compared with mucosa-associated lymphoid tissues (MALTs) by histopathology, histomorphometry and immunohistochemistry (CD3, CD79, PAX5, LYVE1, fibronectin). In addition, real-time polymerase chain reaction (qPCR) and immunohistochemistry (p72) were used to evaluate the presence of ASF virus (ASFV) in blood and tissues samples, respectively. TLOs were observed in animals infected with a low-virulent ASFV isolate (LVI), animals co-infected with low and high-virulent ASFV isolates (LVI-HVI) and animals infected only with the high virulence isolate (HVI). TLOs in LVI and LVI-HVI groups were located adjacent to the mucosa and presented a similar structure to MALT. Immunoexpresion of p72 observed in the inflammatory cells adjacent to TLOs/MALTs confirmed its development and reactivity generated by ASF attenuated isolates. Immunohistochemical evaluation, based on cellular composition (T and B lymphocytes), and histomorphometrical study revealed a more pronounced maturation of TLOs/MALTs in the LVI-HVI group. It is currently unclear whether these formations play a protective role by contributing to local immunity in chronic inflammatory diseases. However, the structural similarities between TLOs and MALTs and the location of TLOs close to the mucosa suggest that they may perform a similar function, facilitating a local protective response. Nevertheless, further investigations are warranted to assess the cellular and humoral dynamics of these lymphoid organs induced by attenuated isolates.
Acknowledgments
We would like to thank all those who participated in the development of this study by obtaining samples and collecting data, particularly the SUAT and VISAVET teams. We would also like to thank Pedro Sánchez-Cordón from the Centre for Animal Health Research (CISA-INIA) and his team of technicians for their technical support and contributions. We appreciate the work of the technicians of the Pathology and Forensic Veterinary Unit of the VISAVET Health Surveillance Centre, G. Torre and M.C. Jiménez. We would also like to thank Lidia Sánchez for her valuable contribution. Finally, we are grateful for the statistical analysis performed by A. Gómez-Buendía, and the language revision of the manuscript by Sally Newton and Blanca Chinchilla.
Authors’ contributions
NPG, ARB, JMSV and JAB designed the study. NPG, ARB, AK and JAB performed the sampling and veterinary inspection. NPG and AK performed laboratory analysis. ARB and JMSV acquired the funds. NPG wrote the initial manuscript. JMSV, ARB, AK, and JAB reviewed the manuscript. All the authors have read and approved the final version of the manuscript.
Ethical statement
The authors confirm that the ethical policies of the journal have, as noted on the journal’s author guidelines page, been adhered to, and that the appropriate ethical review committee approval has been received. The US National Research Council’s guidelines for the Care and Use of Laboratory Animals were followed. All experiments were carried out following European, national and regional regulations and were approved by the Ethics Committee of the Comunidad de Madrid (reference PROEX 124/18).
Disclosure statement
The authors declare that there is no conflict of interest with regard to the present research.
Data availability statement
The original contributions presented in the study are included in the paper/supplementary material; further inquiries can be directed to the corresponding author.