It is tempting to speculate that the increased amount of collagen in granulomas (Figure 4H) and the presence of abundant collagen fibers between epithelioid cells in areas without well-formed granulomas (Figure 3F, G) in Ctsk-/- mice is due to the lack of the collagenase activity of cathepsin K. This accumulation of collagen fibers might also be responsible for the smaller number and size of granulomas. This evidence concerns the gene CTSK and Granuloma.