Journal
FRONTIERS IN IMMUNOLOGY
Volume 12, Issue -, Pages -Publisher
FRONTIERS MEDIA SA
DOI: 10.3389/fimmu.2021.661052
Keywords
SARS-CoV-2; COVID-19; macrophages; dendritic cells; lymphocytopenia; spleen; lymph nodes
Categories
Funding
- National Key Research and Development Program of China [2016YFA0502204]
- National Natural Science Foundation of China (NSFC) [81701562, 81701551, 81971478, 81771691]
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The study retrospectively reviewed clinical and immunological data from fatal COVID-19 cases and found severe lymphocytopenia with high levels of inflammatory cytokines. Post-mortem examinations of additional cases showed severe tissue damage and lymphocyte apoptosis in spleens and lymph nodes, where SARS-CoV-2 viral RNA accumulates, leading to lymphocytopenia. Overall, the results suggest that SARS-CoV-2 induces lymphocytopenia by promoting systemic inflammation and direct damage to human spleen and lymph nodes.
While lymphocytopenia is a common characteristic of coronavirus disease 2019 (COVID-19), the mechanisms responsible for this lymphocyte depletion are unclear. Here, we retrospectively reviewed the clinical and immunological data from 18 fatal COVID-19 cases, results showed that these patients had severe lymphocytopenia, together with high serum levels of inflammatory cytokines (IL-6, IL-8 and IL-10), and elevation of many other mediators in routine laboratory tests, including C-reactive protein, lactate dehydrogenase, alpha-hydroxybutyrate dehydrogenase and natriuretic peptide type B. The spleens and hilar lymph nodes (LNs) from six additional COVID-19 patients with post-mortem examinations were also collected, histopathologic detection showed that both organs manifested severe tissue damage and lymphocyte apoptosis in these six cases. In situ hybridization assays illustrated that SARS-CoV-2 viral RNA accumulates in these tissues, and transmission electronic microscopy confirmed that coronavirus-like particles were visible in the LNs. SARS-CoV-2 Spike and Nucleocapsid protein (NP) accumulated in the spleens and LNs, and the NP antigen restricted in angiotensin-converting enzyme 2 (ACE2) positive macrophages and dendritic cells (DCs). Furthermore, SARS-CoV-2 triggered the transcription of Il6, Il8 and Il1b genes in infected primary macrophages and DCs in vitro, and SARS-CoV-2-NP+ macrophages and DCs also manifested high levels of IL-6 and IL-1 beta, which might directly decimate human spleens and LNs and subsequently lead to lymphocytopenia in vivo. Collectively, these results demonstrated that SARS-CoV-2 induced lymphocytopenia by promoting systemic inflammation and direct neutralization in human spleen and LNs.
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