Anomalous effects of anti-inflammatory corticosteroids in endotoxin-induced ocular inflammation

The effect of anti-inflammatory corticosteroids upon leukocyte infiltration was investigated in vivo, using the eye as an experimental model. The inflammatory response was induced by injecting bacterial endotoxin into the vitreous body of the albino rabbit eye. Polymorphonuclear leukocyte (PMN) infiltration into the aqueous humor was quantified by counting cells directly, whereas accumulation of leukocytes in the ocular tissues was determined by measuring myeloperoxidase (MPO) activity. Systemically administered corticosteroids inhibited plasma protein leakage and PMN infiltration into the aqueous humor, but, anomalously, increased MPO activity and hence the number of PMNs in the ciliary body. These findings were confirmed qualitatively by histology. However, the clinical manifestations of the inflammatory responses were almost totally suppressed by the corticosteroids. We suggest that the inhibitory effect of corticosteroids on PMN infiltration into the aqueous humor, and possibly inflammatory exudates in general, represents the suppression of inflammatory cell activity in a manner which is unrelated to a direct effect on leukocyte movement.