The development and function of immune responses against the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) are still unclear. We need methods to improve them and limit tissue damage inflicted by chronic inflammation that may lead to lung fibrosis in COVID-19 patients.
One starting point are Tertiary Lymphoid Structures (TLS), which are ectopic immune cell infiltrates formed at sites of peripheral tissue stimulated by antigens due to inflammation, auto-immunity, cancer or infections. TLS promote the encounter of antigens with lymphocytes for antigen-specific adaptive immune responses.
In vivo manipulation of potentially existing TLS in SARS-CoV-2 infections could be an important step in enhancing immunity against the virus.
The aim of this study is to document the prevalence of TLS in the lungs of COVID- 19 patients and to describe their association to clinico-pathological features.
This single centre retrospective study evaluated the lungs of 22 patients deceased from SARS- CoV-2 infection and autopsied at the Institute of Pathology, CHUV. All available 697 haematoxylin and eosin (H&E) stained slides were assessed for the number of TLS per slide and presence of TLS-associated germinal centres. Autopsy reports and clinical files on the
software Soarian were then studied for the analysis of the clinico-pathological features.
The results showed that 21 out of 22 patients had TLS in their lungs. The average number of TLS per slide was 0.86, equivalating to around 0.0032 TLS per mm2. The median number was 0.36 (range: 0 – 4.20). The patient with the most TLS per slide had 42 TLS per 10 slides and the patient with the most TLS in total had 134 TLS per 73 slides. No germinal centres were histomorphologically detected. Positive correlations with the increase in TLS prevalence were an increase in number of days with symptoms of COVID-19 and overlying bacterial infections, speaking in favour of a longer, noisier battle with the virus before death.
No correlations were found regarding the age and sex of the patient, COVID-19 wave, Diffuse Alveolar Damage (DAD) stage, medications or COVID-19 vaccine received, pre-existing pulmonary comorbidities and triggers such as smoking.
In conclusion, this study found a non-negligible number of TLS in patients deceased with a SARS-CoV-2 infection, setting the stage for future studies aiming at a comprehensive