Background: To study the role of macrophages in experimental melanin-induced uveitis (EMIU), we used the method of intravital microscopy to analyse changes in leukocyte adhesion to iris venules of live rats with EMIU after pretreatment with liposomal clodronate.
Materials and methods: EMIU was induced in Lewis rats (n = 48) by intraperitoneal immunisation with bovine crude melanosomes emulsified in complete Freund's adjuvant (CFA) and pertussis toxin (PTX). Control animals received CFA and PTX only (n = 12) or no injection (n = 6). Animals were treated with liposomal clodronate (DMDP-lip) or empty liposomes on days -2, +1, 4, 6 and 8. Using IVM, postcapillary iris venules of rats were examined to quantify leukocyte rolling and firm adhesion to the vascular endothelium.
Results: Depletion of macrophages caused a decreased percentage of rolling leukocytes on day 8 (2 +/- 1.1% vs 15.2 +/- 1.6%, DMDP-lip vs EMIU, mean +/- SEM, ANOVA, p < 0.05) and day 10 (2.6 +/- 0.3% vs 14.2 +/- 1.6%). A significant decline in the number of firmly adherent leukocytes was detected on days 8 and 10 (88 +/- 13/mm2 vs 175 +/- 18/mm2 and 129 +/- 13/mm2 vs 372 +/- 31/mm2, DMDP-lip vs EMIU). Treatment with empty liposomes showed no changes in leukocyte firm adhesion.
Conclusions: Elimination of macrophages prevents the induction of EMIU. In autoimmune-mediated uveitis, macrophages play a crucial role in the initiation of leukocyte-endothelium interaction.