Aqueous humour (AH) which fills the anterior chamber (AC) of the eye provides nutrients to the cornea and the lens. Clearance of cellular and particular matter from AH is necessary for good visual acuity. In part this is achieved by high turnover of AH production by the ciliary body and removal via the trabecular meshwork. Moreover, the tissues surrounding the AC, corneal epithelium, ciliary body epithelium and trabecular meshwork all have phagocytic activity. An enzyme lysosomal phospholipase A2 (LPLA2) is ubiquitously present in tissues, and particularly in phagocytic cells such as macrophages. LPLA2 is a secreted protein and is found in many extracellular fluids. In this paper, Hiraoka et al. established endotoxin-induced uveitis (EIU) by subcutaneous injection of lipopolysaccharide in rats. This leads to AC inflammation with cellular and protein infiltrate. LPLA2 activity was significantly increased in AH from rats with EIU and correlated with the extent of inflammation. There was no increase in activity in the serum or cerebrospinal fluid (CSF) of these animals. Immunohistochemistry showed that it was tissue macrophages that expressed LPLA2, and increased migration of these cells may explain the increased enzymatic activity. AH from individuals undergoing cataract surgery including some with uveitis. LPLA2 activity was greater in those patients with uveitis compared to those without. Controlling inflammation in the eye is a complex process particularly in response to infection. While the immune system is required to eliminate pathogens it can also do damage. Increased LPLA2 activity during inflammation gives another mechanism by which the processes of protection and resolution can be mediated.

Increase of lysosomal phospholipase A2 in aqueous humor by uveitis.
Hiraoka M, Abe A, Lennikov A, et al.
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Graham Wallace

Birmingham and Midland Eye Centre, Birmingham, UK.

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