This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.
It today’s Science Page Kassandra Durazo-Martínez, Fernando A. Osorio, Gustavo Delhon, Jesús Hernández, and Hiep L. X. Vu share the results of their study looking at testicular tissue cell types and their susceptibility to PRRSV infection.
Key Findings:
- Spermatogonia Stem Cells (SSC) cultured in vitro are highly susceptible to PRRSV infection.
- PRRSV does not infect cells in the germinal epithelia of prepuberal pigs.
Introduction: PRRSV is known to primarily infect macrophages residing in the lung alveolar space and lymph nodes (2). However, virus-infected cells have also been found in the germinal epithelium of sexually mature boars, leading to significantly reduced semen quality (3, 4). Notably, the virus has been detected in the semen of infected boars, and the use of contaminated semen in artificial insemination has contributed to its global spread. This study aimed to identify the specific cell types within testicular tissue that are susceptible to PRRSV infection.
Materials & Methods: Two major testicular cell types: Spermatogonia stem cells (SSCs), the progenitor cells of sperm, and Sertoli cells were isolated from the testes of newborn pigs and cultured in vitro (5). The susceptibility of these cells to PRRSV was subsequently assessed.
To identify the putative susceptible cell types within the testes, 12 uncastrated 4-week-old pigs were infected with a virulent PRRSV strain. At various time points post-infection, three infected pigs were randomly selected, and their testicular tissues were collected for histological analysis. Dual in situ hybridization (ISH) and immunohistochemistry (IHC) staining were used to identify virus-infected cells and cell-specific markers.
Results: SSCs isolated from newborn piglets and cultured in vitro were fully susceptible to PRRSV infection, with viral replication kinetics resembling those observed in porcine alveolar macrophages, the primary cellular target for PRRSV infection in pigs. In contrast, Sertoli cells, another testicular cell type, were not susceptible to PRRSV.
In infected pigs, PRRSV-infected cells were primarily localized to the interstitial tissue and at the base of the seminiferous tubules but were not found inside the tubules containing SSCs. IHC/ISH staining identified macrophages and myoid cells as the main PRRSV-infected cell types.
Discussion and Conclusion: We demonstrate that SSCs are highly susceptible to PRRSV infection and provide direct evidence that non-macrophage cells in pigs can be infected with PRRSV. Previous studies have detected virus-infected cells inside the seminiferous tubules of sexually mature boars by day 7 post-infection (6). Interestingly, in this study, virus-infected cells were not detected in the seminiferous tubules of prepubertal pigs. Together, these results highlight a difference in the testicular tropism of PRRSV between prepubertal and sexually mature boars. We believe that this difference is attributed to anatomical differences in testicular tissue between sexually mature and prepubertal boars.
References
1. Durazo-Martinez K, Chaudhari J, Kumari S, Vu HL. 2024. Porcine peritoneal macrophages are susceptible to porcine reproductive and respiratory syndrome virus infection. Frontiers in Microbiology 15:1505900.
2. Duan X, Nauwynck H, Pensaert M. 1997. Virus quantification and identification of cellular targets in the lungs and lymphoid tissues of pigs at different time intervals after inoculation with porcine reproductive and respiratory syndrome virus (PRRSV). Veterinary microbiology 56:9-19.
3. Christopher-Hennings J, Nelson EA, Nelson JK, Hines RJ, Swenson SL, Hill HT, Zimmerman JJ, Katz JB, Yaeger MJ, Chase C. 1995. Detection of porcine reproductive and respiratory syndrome virus in boar semen by PCR. Journal of Clinical Microbiology 33:1730-1734.
4. Sur J-H, Doster AR, Christian JS, Galeota JA, Wills RW, Zimmerman JJ, Osorio FA. 1997. Porcine reproductive and respiratory syndrome virus replicates in testicular germ cells, alters spermatogenesis, and induces germ cell death by apoptosis. Journal of virology 71:9170-9179.
5. Park MH, Park JE, Kim MS, Lee KY, Park HJ, Yun JI, Choi JH, song Lee E, Lee ST. 2014. Development of a high-yield technique to isolate spermatogonial stem cells from porcine testes. Journal of assisted reproduction and genetics 31:983-991.
6. Sur JH, Doster AR, Christian JS, Galeota JA, Wills RW, Zimmerman JJ, Osorio FA. 1997. Porcine reproductive and respiratory syndrome virus replicates in testicular germ cells, alters spermatogenesis, and induces germ cell death by apoptosis. J Virol 71:9170-9.
Full paper link: https://journals.asm.org/doi/10.1128/spectrum.02964-24