Table 1.

Cytokine storm and its effect on bone health

S. no	Inflammatory cytokines	Source	Levels in COVID-19 disease patients	Effect on bone health	Reference
1	IL-1β	Monocytes, macrophages, neutrophils, CD4+ T cells	High	Stimulates osteoclastogenesis and inhibits bone formation by directly activating a RANK mediated signaling pathway	[66] [67]
2	IL-6	Monocytes, macrophages, neutrophils, CD4+ T cells	High	Promotes bone resorption by enhancing the interaction of OCs and OBs/osteocytes via the RANK-RANKL axis	[68, 69]
3	IL-8	Monocytes, macrophages, fibroblasts, endothelial cells	High	Stimulates osteoclastogenesis and promotes osteolysis	[27, 70]
4	IL-17	Th17 cells	High	Stimulates osteoclastogenesis by augmenting the levels of M-CSF and RANKL and by promoting autophagy in bone marrow cells	[71, 72]
5	IL-18	Monocytes, macrophages, neutrophils, dendritic cells	High	Enhance OCs differentiation via upregulating RANKL on T cells	[73, 74]
6	TNF-α	Monocytes, macrophages, Th17 cells	High	Promotes OCs differentiation via upregulating RANKL on OBs via NFκB signaling pathway	[75, 76]