The avascular cornea is a protective barrier with intact innate immune, but restricted adaptive immune response for optimal vision. Surgery, injury and infection of the cornea can disrupt this balance between innate and adaptive immune response leading to intense inflammation and loss of vision. We found lumican, an abundant extracellular matrix (ECM) stromal proteoglycan, to regulate corneal immune functions. Lumican itself binds LPS that can be removed competitively by CD14, the cell surface protein that transfers LPS to toll-like receptor 4, the trans-membrane IPS receptor. Mice, deficient in lumican (Lum-/-), are hypo-responsive to bacterial lipopolysacharide endotoxin (LPS), and produce lower amounts of proinflammatory cytokines. More importantly, in LPS-induced corneal keratitis, the Lum-/- mice show reduced neutrophil influx early, but overall delayed healing. Thus, innate immune response is impaired in our Lum-/- mice. Lumican also binds FasL and TGFbeta, and in the Lum-/- mice these pathways are disrupted. The Fas-FasL mediated apoptosis and TGFbeta signaling in the cornea help to maintain an immunosuppressive environment for immune privilege. Our overarching hypothesis is that in the cornea lumican promotes early innate immune response, but provides an immunosuppressive microenvironment to restrict adaptive immunogenic mechanisms to maintain immune privilege. The following aims will test this hypothesis. 1) Test if lumican regulates corneal inflammation and immune privilege such that Lum-/-corneal allografts have decreased survival. Test if lumican regulates bone marrow cell (BMC) functions directly by evaluating allograft success in Lum+/+ and Lum-/- BMC chimera hosts. 2) Test if lumican promotes corneal innate immune response via the LPS-specific CD14-TLR4 pathway, a) in cell culture by assessing the ability of recombinant lumican to rescue LPS-induction of TNFa in Lum-/- macrophages also lacking CD14, and b) by comparing LPS-induced keratitis in Lum+/+ and Lum-/- BMC CD14-null chimeras and parental strains. 3) Investigate connections between lumican and the TLR4-signaling pathway and its therapeutic implications. Test binding of lumican-derived synthetic peptides to LPS and their ability to regulate innate immune response in macrophage culture and their effects on LPS-induced keratitis. This study will elucidate a novel link between the ECM and corneal immune functions and lead to the development of therapeutic lumican-products to alleviate detrimental inflammatory responses in the cornea, a major focus of the National Eye Institute.
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