Monocyte chemotactic activity induced by intravitreal endotoxin

In order to clarify the factors responsible for the cellular infiltrate characteristic of anterior uveitis, the authors have induced inflammation in rabbits by the intravitreal injection of 100 ng of Escherichia coli or Salmonella endotoxin (ET). A 2% concentration of aqueous humor 18 to 24 hr after ET consistently induced monocyte migration as measured in modified Boyden chambers. Activity was significantly greater in these samples than in aqueous after saline injection or 3 hr after endotoxin injection (prior to cellular infiltrate). Using either sephadex G-75 molecular sieve chromatography or a cibacron blue column, the vast majority of migratory activity co-eluted with albumin. Serum albumin, however, at a comparable concentration did not induce migration. Activity was largely heat- and acid-stable and was maximal in the presence of a concentration gradient, indicating that it was chemotactic rather than chemokinetic. A second peak of activity eluted from the G-75 column just prior to a marker with molecular weight of 427 and was also present in eluates from normal aqueous humor. Chloroform:methanol extraction, radioimmunoassay, and high performance liquid chromatography indicated that a small portion of the chemotactic activity could be ascribed to lipid including leukotriene B₄. In contrast to the prominence of complement (C5a) derived chemotactic activity resulting from intravenous ET, C5a was not a major contributor to aqueous chemotactic activity subsequent to local ET. These observations demonstrate that leukocyte migration factors in aqueous humor can be characterized and compared. This approach can be used to test the hypothesis that subsets of anterior uveal inflammation might be distinguished on the basis of associated chemotactic factors.