Fig. 4. The inflammatory activation and osteoclastic differentiation of monocyte-macrophage lineage after SARS-CoV-2 infection.

a The expression of osteoclastogenesis-related genes in the bone tissue of the hamsters at day 4 after treatment with PBS (Mock, n = 4) or SARS-CoV-2 infection (4 dpi, n = 5). b Representative immunofluorescence staining images showing the increase in the number of CD68⁺ and TRAP⁺ osteoclasts (indicated by arrowhead) after SARS-CoV-2 infection (n = 4). Tile scans (scale bars = 200 µm) and high-magnification of the boxed regions (scale bars = 50 µm), as well as corresponding quantification for the fluorescence intensity of CD68, are shown. c Representative immunofluorescence staining images and the corresponding quantification showing the upregulation of RANK-expressing cells at the trabecular bone surface after SARS-CoV-2 infection. Tile scans (scale bars = 200 µm) and high-magnification of the boxed regions (scale bars = 50 µm) are shown. d Representative multicolor immunohistochemical staining for TRAP, CD68, RANK, and IL-1β was performed at the distal metaphysis of the femur on day 4 after treatment with PBS (Mock) or SARS-CoV-2 infection (4 dpi). DAPI was used for nuclear counterstaining. Tile scans (scale bars = 200 µm) and high-magnification of the boxed regions (scale bars = 50 µm) are shown. Arrowheads indicate osteoclasts on the bone surface (n = 3). e The expression of IL-1β signaling-related genes in bone tissue at day 4 after treatment with PBS (Mock, n = 4) or SARS-CoV-2 infection (4 dpi, n = 5). Data were mean ± SD. ns: P > 0.05, *P < 0.05, **P < 0.01 by two-sided Student’s t-test.