The reduction of inflammatory responses in lipopolysaccharide-tolerant eyes

The development of tolerance induced by subcutaneous or intraocular injections of lipopolysaccharide (LPS, Escherichia coli) in rat eyes has been studied. In addition, the ocular inflammatory responses to the reversed passive Arthus (RPA) reaction in the tolerant eyes were investigated. The tolerance in the eye after a single injection of LPS persisted for at least 42 days. Up to 42 days, vasodilatation, disruption of the blood-aqueous barrier, and leukocyte accumulation in the anterior chamber after a second injection of LPS were inhibited. Unilateral intraocular injection of LPS produced local tolerance, which was not observed in the contralateral eyes. The inflammatory reactions in response to RPA in the LPS-tolerant eyes were also significantly attenuated. It was also found that inflammatory reactions induced by RPA or 16,16-dimethyl prostaglandin E2 had no inhibitory effect on the responses to subsequent RPA or LPS administration, which indicated that initial inflammatory reactions do not render the tissues refractory to the response to a second stimuli. The results of this study suggest that some, as yet unknown, local changes in the ocular tissues caused by LPS may be involved in the development of tolerance.