Lipopolysaccharide tolerance inhibits eye inflammation. I. Reduced immune complex or lipopolysaccharide effects

Age as a Determinant Factor for Endotoxin Induced Uveitis

PURPOSE

To determine if susceptibility to systemic endotoxin-induced uveitis is an age-related phenomenon in the rabbit.

METHODS

Young and adult rabbits were injected intravenously with 2.5 microg/kg of E. coli endotoxin or saline. Thereafter, the number of exudating cells at 2, 6, 12, 24 and 48 hours were determined. The levels of lipopolysaccharide-binding protein, total protein, prostaglandin-E2, nitric oxide and interleukin-6 in aqueous humor were also determined 24 hours after the injections.

RESULTS

A significant increase in the number of exudating cells and the levels of lipopolysaccharide-binding protein, total protein, prostaglandin-E2 and nitric oxide in aqueous humor was observed only in adult rabbits 24 hours after endotoxin injection. No differences were observed in the increased IL-6 levels.

CONCLUSIONS

Life stage seems to be a critical factor in developing an eye-inflammatory response induced by systemic endotoxin. This could be a consequence of a differential specific activation of the ocular immune response.

Comparative study of the endotoxemia and endotoxin tolerance on the production of Th cytokines and macrophage interleukin-6: differential regulation of indomethacin

Endotoxin tolerance reduces the capacity of monocytes to produce proinflammatory cytokines, results in cellular immune paralysis, and down-regulates the production of helper T (Th)1 type cytokines with a shift toward a Th2 cytokine response. Prostaglandin (PG)E2 in the immune system also results in macrophage inactivation and the suppression of Th1 activation and the enhancement of Th2 activation. However, the inhibitory effects of PGE2 on the altered polarization of the Th cell and macrophage interleukin (IL)-6 production characterized in part by cellular immune paralysis in a state of endotoxin tolerance is unclear. This study was undertaken, using indomethacin, to investigate the role of endogenous PGE2 on the Th cytokines and macrophage IL-6 production in a state of endotoxin tolerance compared to those with endotoxemia mice, wherein, in this latter case, the increased production of proinflammatory cytokines and PGE2 is exhibited. Endotoxemia was induced by injection of lipopolysaccharide (LPS; 10 mg/kg in saline) ip. once in BALB/c mice, and endotoxin tolerance was induced by pretreatment with LPS (1 mg/kg in saline) injected i.p. daily for two consecutive days and then with LPS 10 mg/kg on day 4. Splenocytes or macrophages were obtained from endotoxemia and endotoxin tolerance models pretreated with indomethacin, and then cytokine production was induced by Con A-stimulated splenocytes for the Th cytokine assays and LPS-stimulated macrophages for the IL-6 assay. Our results showed that endotoxemia led to significantly reduced IL-2 and IL-4 production, to significantly increased IL-6 production, whereas interferon (IFN)-gamma production was not affected. Indomethacin in the case of endotoxemia markedly attenuated IFN-gamma and IL-6 production and didnt reverse IL-2 and IL-4 production. Endotoxin tolerance resulted in the significantly reduced production of IL-2 and IFN-gamma and the significantly increased production of IL-4 and IL-6. Indomethacin in endotoxin tolerance greatly augmented IL-2 production, significantly decreased IL-4 production, and slightly attenuated IL-6 production. These findings indicate that endogenous PGE2 may mediate the suppressed Th1 type immune response, with a shift toward a Th2 cytokine response in a state of endotoxin tolerance, whereas endotoxemia may be regulated differentially. Also, endogenous PGE2 may mediate macrophage IL-6 production in the case of endotoxemia to a greater extent than in the case of endotoxin tolerance.

Enzymatic activities in the iris-ciliary body of the rabbit eye during experimentally induced acute ocular inflammation

Intravitreal injection of 5 micrograms of Shigella endotoxin, in the rabbit eye, induced an acute inflammatory response which was characterised by conjunctival hyperaemia, limbal and ciliary vascular injection, iritis, aqueous flare, miosis and reduction in intraocular pressure. Iris-ciliary body tissues, from normal and inflamed eyes, were fractionated into subcellular enriched fractions and the activities and distribution of selected enzymes were estimated. Alkaline phosphatase, a plasma membrane-bound enzyme, showed an increase in activity, whereas succinate dehydrogenase and Mn-Superoxide dismutase, both mitochondrial-bound enzymes, exhibited decreased activities. Lysosomal acid phosphatase displayed an increase in free activity and retention of latent activity inside the organelle. No alteration in free activity was shown by acid cathepsin. The cholinesterases did not exhibit any changes in activities nor did the cytosolic enzymes Cu/Zn-superoxide dismutase and lactate dehydrogenase. The decrease activity of the respiratory mitochondrial enzyme succinate dehydrogenase may contribute to the reduction in intraocular pressure, and the ability of the lysosomal organelles to retain their hydrolytic enzymes, ensures recovery of the cell from acute inflammatory attack.

Uveitis induction in the rabbit by muramyl dipeptides

Intraocular inflammation (uveitis) was produced in rabbits by intravenous or subcutaneous treatment with N-acetylmuramyl-L-alanyl-D-isoglutamine and several of its synthetic analogs at doses of greater than or equal to 0.2 mg/kg in saline. A dose-dependent increase in permeability of the ocular blood-aqueous barrier as measured by leakage of protein or fluoresceinated dextran from the serum into the eye was observed from 2 to 14 h after glycopeptide treatment. Peak response occurred at approximately 3 h postdose. The lowest dose found to produce maximal vascular leakage for the most active glycopeptide analogs was 1 mg/kg. The adjuvant-inactive L-L stereoisomer of N-acetylmuramyl-L-alanyl-D-isoglutamine was inactive, even at doses as high as 10 mg/kg. Analogs of N-acetylmuramyl-L-alanyl-D-isoglutamine which were homologous in the lactyl side chain were found to cause less uveitis. Chronic biweekly intravenous treatment of rabbits for 1 month with either N-acetyl-L-alpha-aminobutyryl-D-isoglutamine or its lipophilic 6-O-stearoyl derivative at 1 mg/kg, but not with murabutide, resulted in leukocytic inflammatory lesions unique to the uveal tract of the eye. The uveitis was potentially reversible and occurred with decreased severity as long as 2 months after cessation of chronic treatment. Vascular leakage but not cellular infiltrate in the choroid could be modulated by pharmacologic means. Pyrogenicity but not adjuvanticity correlated with ability of glycopeptides to induce vascular leakage. Several adjuvant-active muramyl dipeptide analogs with minimal ability to cause acute vascular leakage or chronic inflammation in the rabbit eye have been identified.

Endotoxin tolerance diminishes certain antiinflammatory effects of endotoxin

Endotoxin (bacterial lipopolysaccharide, LPS) is paradoxically both inflammatory and antiinflammatory. A single intravenous injection of 100 micrograms Escherichia coli LPS markedly inhibits the inflammatory changes associated with cutaneous reversed passive Arthus (RPA) reactions in New Zealand white rabbits. Polymorphonuclear (PMN) leukocytes from LPS-treated rabbits exhibit diminished responsiveness in vitro to complement (C5) -derived peptides. Repeated injections of LPS render animals "tolerant", that is, refractory to the toxic and inflammatory effects of LPS. We examined whether tolerance would enhance the ability of LPS to inhibit inflammation not attributable to LPS. Surprisingly, as compared with rabbits receiving a single dose of LPS, tolerant rabbits demonstrated greater inflammatory changes (i.e., PMN exudation, vascular permeability) associated with RPA reactions. PMNs from LPS-tolerant rabbits responded in vitro to C5-derived peptides significantly more than PMNs from rabbits that received a single dose of LPS. We speculate that some antiinflammatory effects of LPS require the toxic or inflammatory effects of LPS itself. These observations might relate to the limited efficacy of fever therapy and the variable effects of gram-negative sepsis on functions of human PMNs.