The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused over 9.263 million cases and taken more than 477,000 lives as of June 24, 2020 – just six months after the initial outbreak in Wuhan, China, was reported. The illness, called COVID-19 disease, caused by SARS-CoV-2 is a severe pneumonic illness, caused by the entry of the virus into the type II alveolar cells.
While a majority of the infections result in asymptomatic cases, mild or moderate infection, a significant minority develops severe and even critical infection. About 10% to 15% will eventually need mechanical ventilation, and about 5% may die rather than recover from lung injury and accompanying multi-organ dysfunction.
Novel Coronavirus SARS-CoV-2 Transmission electron micrograph of a SARS-CoV-2 virus particle, isolated from a patient. Image captured and color-enhanced at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Credit: NIAID
ACE2 and Tissue Injury in COVID-19
The pulmonary impact of the virus is thought to be related to the expression of the angiotensin-converting enzyme 2 (ACE2) molecule on lung cells. The ACE2 molecule acts as the receptor to which the virus binds and activates before it enters and infects the host cell.
However, ACE2 expression is not limited to lung cells. It is also found on vascular endothelium and in the heart. A recent single-cell RNA sequencing study shows that this receptor is also found in germ cells, Leydig cells, and Sertoli cells – different testicular tissues. Thus, the testes could be another target of the virus.
Another single-patient postmortem study failed to show any abnormality in the testes, and several other studies show conflicting evidence of the presence of the virus in semen. The current study is, therefore, aimed at examining the testicular tissue in detail so as to detect the virus and identify any cytopathic effects on the virus. This is important to help decide if the virus can be spread via semen and if there is any potential for infertility in younger patients.
The Study: Mapping ACE2 Expression to Testicular Injury
The study included 12 patients, with an average age of 65 years, with a mean duration of disease of 42 days from the earliest symptom to death. The examination of 11 patients showed various changes in the testicular tissue, mostly affecting the Sertoli cells. These are the cells that support the germ cells.
These were swollen, with vacuole formation and thinning of the cytoplasm, while the cells were detached from the underlying basement membrane of the seminiferous tubules. Some cells were dead and shed into the lumina of the tubules. Among the patients, five patients had signs of injury to 10% to 50%, while four patients had injury to more than 50% of tubules.
As controls, and to make sure that these changes were not due to the prolonged duration of severe illness since all these patients died of COVID-19, the investigators also looked at five other patients who died of other causes after being sick for at least 7 days. They found that either no or only mild injury was found in the testes of these patients.
The number of Leydig cells, which produce testosterone, was significantly lower in the severe COVID-19 cells compared to the controls. The testicular interstitial tissue showed edema and inflammatory cells, mostly CD3 T cells and histiocytes, but no B cells or plasma cells. The seminiferous tubules were not observed to have any inflammatory infiltrate.
In three patients, normal sperm generation was observed to be proceeding, but in the others, it was less in an age-dependent manner. The ACE2 expression was diffuse in Sertoli cells but strongly present in Leydig cells, and zero in spermatogonia.
No viral particles were seen in the tissue. Even though the viral RNA was found in lung tissue from 10 of the patients, it was seen in only one of the cohort, in a patient who had a high viral load, with positive RT-PCR results for lung, kidney, spleen, and testis. This patient’s testes showed mostly fibrous tissue and blood vessels.
Is Sperm Donation Safe in COVID-19 Patients?
The complaint of scrotal pain in a fifth of cases at the time of diagnosis has led to suspicions that the testes could also be affected by the virus, prompting the American Society for Reproductive Medicine and the Society for Assisted Reproductive Technology to issue a caution against sperm donation from these patients.
In contrast, the current study failed to find signs of viral infection in testicular tissue, and only one case was positive by RT-PCR. The single positive case had a mostly fibrovascular testis, and the result may reflect the presence of the virus in the blood rather than in the testicular tissue. This supports earlier studies that showed no evidence of the live virus in semen or testicular tissue even at 30-40 days from the first symptom. This indicates the safety of sperm donation or impregnation in the convalescent period.
The tissue damage observed in the testis, mainly to the Sertoli cells, together with the robust ACE2 expression on Sertoli and Leydig cells, may mean that viral membrane proteins, including the spike protein, contribute to testicular damage. Of course, it could be merely the result of increased temperatures, hypoxia, the use o steroids, or secondary bacterial infection.
Implications and Future Directions
Despite the lack of direct viral injury to the sperm-containing cells, the damage to the Sertoli cells and androgen-producing Leydig cells can cause the seminiferous tubules to atrophy, and eventually, cause reduced or no sperm formation in recovered COVID-19 patients.
The researchers comment: ”Our findings suggest that studies should be undertaken to find ways to mitigate the risk of testicular injury during the COVID-19 disease course. These findings can provide evidence-based guidance for sperm donation and inform management strategies to mitigate the risk of testicular injury during the COVID-19 disease course.”