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| Ocular immune system ： ウィキペディア英語版 |
Ocular immune system
The Ocular immune system protects the eye from infection and regulates healing processes following injuries. The interior of the eye lacks lymph vessels but is highly vascularized, and many immune cells reside in the uvea, including mostly macrophages, dendritic cells, and mast cells.〔P.G. McMenamin, The distribution of immune cells in the uveal tract of the normal eye. Eye, 1997. 11(Pt 2): p. 183-93.〕 These cells fight off intraocular infections, and intraocular inflammation can manifest as uveitis (including iritis) or retinitis. The cornea of the eye is immunologically a very special tissue. Its constant exposure to the exterior world means that it is vulnerable to a wide range of microorganisms while its moist mucosal surface makes the cornea particularly susceptible to attack. At the same time, its lack of vasculature and relative immune separation from the rest of the body makes immune defense difficult. Lastly, the cornea is a multifunctional tissue. It provides a large part of the eye’s refractive power, meaning it has to maintain remarkable transparency, but must also serve as a barrier to keep pathogens from reaching the rest of the eye, similar to function of the dermis and epidermis in keeping underlying tissues protected. Immune reactions within the cornea come from surrounding vascularized tissues as well as innate immune responsive cells that reside within the cornea.
== Immune difficulties for the cornea ==
The most important function of the cornea is to transmit and refract light so as to allow high-resolution images to be produced on the back of the retina. To do this, collagen within the cornea is highly ordered to be 30 nanometers in diameter and placed 60 nanometers apart so as to reduce light scatter.〔Quantock, A.J. and R.D. Young, Development of the corneal stroma, and the collagen-proteoglycan associations that help define its structure and function. Dev Dyn, 2008. 237(10): p. 2607-21.〕 Furthermore, the tissue is not vascularized, and does not contain lymphoid cells or other defense mechanisms, apart from some dendritic cells (DC).〔Hamrah, P., et al., The corneal stroma is endowed with a significant number of resident dendritic cells. Invest Ophthalmol Vis Sci, 2003. 44(2): p. 581-9.〕 Both of these factors necessitate the small number of cells within the cornea. However, this necessitates keeping immune cells at a relative distance, effectively creating a time delay between exposures to a pathogen and mounting of an immune response.〔Akpek, E.K. and J.D. Gottsch, Immune defense at the ocular surface. Eye, 2003. 17(8): p. 949-56.〕 Therefore, many immune and protective responses within the cornea, such as moistening and nutrition, come from non-local sources, such as the conjunctiva.
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