BQ-788 sodium salt Our tissue localization studies Figs

Our tissue localization studies (Figs. 1, 2 and 7) confirmed the restricted expression of αvβ5 within the limbus, and the fact that αvβ5-enriched BQ-788 sodium salt support higher CFE (Fig. 6) suggests that this integrin could be useful and an alternative LESC marker. We cannot accurately comment on whether αvβ5 is better than currently used markers, as comprehensive comparisons were not performed. Certainly, it is co-expressed by CK-15 and N-cadherin positive cells (Figs. 2, 7, and 8), and its cell-surface location renders it advantageous for isolating and sorting cells. Notably, when αvβ5+ were plated on VN-coated surfaces, although more colonies formed, a level of significance was not reached (Fig. 6). We suspect that the anti-αvβ5-coated magnetic beads remain cell-bound, as shown by others (Coxon et al., 2012), thereby preventing receptor/ligand (αvβ5/VN) interactions, potentially forcing cells to undergo apoptosis, a process recently identified in human breast cancer cells expressing αvβ3 (Staflin et al., 2010). Little is known about the immune-regulatory factors that support and protect LESC. However, these cells lack HLA-DR and were unable to induce allogeneic T-cell proliferation, and when treated with interferon-γ, they over-expressed B7-H1, indoleamine 2, 3-dioxygenase and HLA-G (Vasani et al., 2011). These factors suppress T-cell activation and are likely to contribute to the immune privileged status of LESC. Bian et al. (2010a) demonstrated that limbal epithelial progenitors produce glial cell-derived neurotrophic factor, which suppressed Th17-induced inflammatory stress via the NF-κB signaling pathway. In addition, LESC express anti-apoptotic factors which safeguard against cell-mediated cytotoxicity and apoptotic enhancing factors (Holan et al., 2010). Furthermore, when limbal epithelial cells were co-cultured with limbal stromal fibroblasts, expression of LESC markers and holoclones were preserved through the production of IL-6 (Notara et al., 2010). Using a similar in vitro model, others reported sphere formation when LESC and their adjacent mesenchymal niche cells were combined and that this union was dependent on the expression of CXCL12/stromal cell-derived factor-1 by epithelial progenitor cells and its receptor CXCR4 by stromal niche cells (Xie et al., 2011). Over the past few years, a multitude of investigations have attempted to identify markers and signaling pathways associated of LESC through the use of global transcriptional profiling (Nieto-Miguel et al., 2011; Takacs et al., 2011; Akinci et al., 2009; Bian et al., 2010b; Albert et al., 2012). We performed a similar assay to profile the genes differentially modulated between two phenotypically and functionally diverse epithelial populations (αvβ5+/−) that were derived from the same region on the ocular surface. Amongst the highest expressed genes were four interferon-dependent proteins, including CXCL11/ITAC, CXCL10/IP-10, IFI44, and IFI44L (Supplementary Table 2). The reasons why limbal epithelial progenitors express these factors are unknown. Although it is known that chemokines are chemotactic not only for leukocytes, but also for non-hematopoietic cells including epithelial cells, fibroblasts and endothelial cells (Zlotnik and Yoshie, 2000). Thus, it is tempting to speculate that chemokines and their receptors may be involved in the deployment and centripetal migration of SC from the limbal perimeter under physiological and wound-healing conditions. Secondly, we suspect chemokines contribute to the immune-protective and immune-privilege status of limbal niche (Holan et al., 2010). For example, IP-10 elicits strong anti-tumor, anti-metastatic (Keyser et al., 2004), anti-angiogenic (Bodnar et al., 2009; Yang et al., 2009), and anti-viral (Yang et al., 2009) activities, and in addition to ITAC, is capable of recruiting mesenchymal SC (Kalwitz et al., 2010) which have been identified and isolated from the limbal stroma (Branch et al., 2012; Garfias et al., 2012) and are themselves immunosuppressive (Garfias et al., 2012).