In patients with the new coronavirus (COVID-19), excessive infiltration of CD4+/CD8+ cells, plasma cells, and macrophages into lung tissues is common, which is believed to lead to severe damages to lung tissues and pulmonary fibrosis.
A group of the National Defense Medical Center, Taipei has reported that excessive infiltration of naïve B cells triggers observed pathophysiology of COVID-19.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0242900
Possible mechanisms include:
COVID-19 causes the accumulation and activation of naïve B-cells in the mediastinal lymph nodes through activation of β2-integrin and α4β1 integrin. Excessive infiltration of naïve B-cells activated by SARS-CoV-2 S-proteins secretes large amounts of IgM and activates the humoral immune
response. This recruits a large amount of monocytes into lung tissues, and the monocytes differentiate to macrophages. The secreted IgM simultaneously activates the complement system, Fc receptors on dendritic cells, and macrophages, increasing the antigen presentation of SARS-CoV-2 and enhancing phagocytosis. In addition, an increase in antigen presentation of SARS-CoV-2 accelerates the extrafollicular response through stimulation of IL-12-dependent plasma cell differentiation in naïve B cell to produce more IgM , suppressing formation of germinal centers and B-cell proliferation.
In conclusion, the importance of therapies targeting naïve B-cells has been proposed.