Fig. 1.

Host immune defense towards coronavirus infections. The figure illustrates the major pathways host organism recognizes coronaviruses (CoV) and responds. (1) Macrophage recognition and presentation to T cells, (3) activation of toll-like receptor 3 (TLR-3) signaling via TRIF, and (4) induction of type I interferon and downstream interferon response genes and cytokine secretion. Negative effect on CD4+ T and CD8+ T cells-purple line block. (5) Activation of SAMHD1 gene (upregulated during viral infections) triggering TLR-4 and MyD88-independent signaling activation leading to type I interferon and cytokine release. (6) Additionally, infected cells respond with the secretion of cytokines and chemokines for lymphocyte and leukocyte recruitment. SAMHD1; SAM and HD domain containing deoxynucleoside triphosphate triphosphohydrolase 1