Fig. (2) SPARC-null Periodontal Ligament (PDL) is More Susceptible to Collagen Loss Following Lipopolysaccharide Induction of Inflammation. Mice were injected 3 times weekly for four weeks with lipopolysaccharide (LPS, C and D) or vehicle control: phosphate buffered saline (PBS, A and B). SPARC-null PDL (D) exhibited significant loss of collagen as compared to WT (C), white arrows (see ref. [28]). Furthermore, given one week to recover (no LPS injections), WT PDL (E) re-established baseline levels of collagen characterized by the presence of thick collagen fibers (orange/red-white arrows), whereas SPARC-null PDL (F) did not exhibit a return to base-line conditions as indicated by the abundance of thin collagen fibers in SPARC-null mice after one week of recovery (green- white arrows). B: bone, T: Tooth, PDL: Periodontal Ligament.