Fig. 1.

The entry of the virus leads to activation of the innate immune system which comprises of macrophages and dendritic cells. Coronavirus antigens are presented by the dendritic cells (DC) which serve as antigen presenting cells (APC) which load viral antigens on MHC-1 and 2 to the T cells leading to the activation of the adaptive immune system. Activation of cytotoxic T cells leads to the proliferation of Th1 cells, Th2 cells and Th17 cells. This leads to the elaboration of several cytokines and chemokines producing the cytokine storm. Also, the activated macrophages could stimulate the MyD88 pathway leading to the activation of downstream signaling pathways such as MAPK and NFκB resulting in the expression of cytokines. MHC: major histocompatibility complex; IL: Interleukins; TNF: tumor necrosis factor; IFNγ: Interferons; MyD88: Myeloid differentiation primary response 88; MAPK: Mitogen activated protein kinase; NFκB: Nuclear factor kappa B.