4- Adaptive immune responses
Adaptive immune responses are the key players against viral infections. CD4+ T cells facilitate virus-specific antibody production through the T-dependent activation of B cells. However, CD8+ T cells are cytotoxic and kill virus-infected cells (X. Xu & Gao, 2004). The immune system cannot effectively control the virus in the acute phase (pneumonia phase), the patient will become severe or critical type. It seems that T cells and B cells are further reduced while inflammatory cytokines and D-Dimer continued to increase in severe type patients (Lin, Lu, Cao, & Li, 2020).