Alveolar Neutrophilic Recruitment in COVID-19 May Not be Mediated by Th17 Response

<p>Introduction: The COVID-19 current pandemic disease differs from the H1N1pdm09 caused by Influenza A virus H1N1 subtype, by how it induces a pro-inflammatory response in infected lungs. </p><p>Objective: Investigate the role of Th17 response in the pathogenesis of COVID-19 injury by analyzing the tissue expression of interleukins 8 and 17A and the neutrophils in lung samples of patients who die of COVID-19, comparing to H1N1pdm09. Study design and post-mortem results: Six lung samples from patients SARS-CoV-2 infected (COVID-19 group), and ten lung samples from adults who died from H1N1pdm09 (H1N1 group), were tested. A control group was also added to the study. H&E slides were used for neutrophils scoring. The tissue expression of IL-8 and IL-17A was identified by immunohistochemistry. Tissue expression increasing of IL-17A and IL-8 and a higher number of neutrophils were identified in samples from the H1N1 group when compared to the COVID-19 group. </p><p>Discussion: It is suggested that the SARS-CoV-2 virus evokes an exacerbated response of the host's immune system but differs from that observed in the H1N1pdm09 disease because it may not be trigger by Th17 response. With the low expression of IL-8, IL-17A, neutrophil recruitment to the site of infection becomes impaired, resulting in viral persistence. On the other hand, in the COVID-19 disease, the immune response by Th2 cells seems to be exacerbated, observed by the extent of the lung injury. This uncontrolled response and, mainly, the lack of a therapeutic target, culminates in disease progression and, consequently, in shorter survival time.</p>