Human CMV (HCMV) retinitis frequently leads to blindness in iatrogenically immunosuppressed patients and in the end stage of AIDS. Despite the general proinflammatory potential of HCMV, virus infection is associated with a rather mild cellular inflammatory response in the retina. To investigate this phenomenon, the influence of HCMV (strains AD169 or Hi91) infection on C-X-C chemokine secretion, ICAM-1 expression, and neutrophil recruitment in cultured human retinal pigment epithelial (RPE) cells was studied. Supernatants from infected cultures contained enhanced levels of IL-8 and melanoma growth-stimulating activity/Gro α and induced neutrophil chemotaxis compared with supernatants from uninfected RPE cells. Despite HCMV-induced ICAM-1 expression on RPE cells, binding of activated neutrophils to HCMV-infected RPE cells and subsequent transepithelial penetration were significantly reduced. Reduced neutrophil adhesion to infected RPE cells correlated with HCMV-induced up-regulation of constitutive Fas ligand (FasL) expression. Functional blocking of FasL on RPE cells with the neutralizing mAbs NOK-1 and NOK-2 or of the Fas receptor on neutrophils with mAbB-D29 prevented the HCMV-induced impairment of neutrophil/RPE interactions. Fas-FasL-dependent impairment of neutrophil binding had occurred by 10 min after neutrophil/RPE coculture without apoptotic signs. Neutrophil apoptosis was first detected after 4 h. Treatment of neutrophils with a specific inhibitor of caspase-8 suppressed apoptosis, whereas it did not prevent impaired neutrophil binding to infected RPE. The current results suggest a novel role for FasL in the RPE regulation of neutrophil binding. This may be an important feature of virus escape mechanisms and for sustaining the immune-privileged character of the retina during HCMV ocular infection.

In fibroblasts, infection with human cytomegalovirus (HCMV) inhibits expression of the extracellular matrix proteins thrombospondin-1 and -2 (TSP-1 and TSP-2). These effects may depend on expression of HCMV immediate-early (IE) genes, which are activated by cellular transcription factor NF-kappaB. The influence of HCMV infection on TSP-1 and TSP-2 expression and the ability of different antiviral drugs to prevent these cellular changes in permissive cultures of human retinal glial cells were observed. Ganciclovir inhibited only HCMV late antigen (LA) expression, whereas antisense oligonucleotide ISIS 2922 and peptide SN50, inhibitors of HCMV IE expression and NF-kappaB activity, respectively, inhibited both IE and LA expression. ISIS 2922 and SN50, but not ganciclovir, prevented down-modulation of TSP-1 and TSP-2. The results showed that HCMV-induced down-modulation of TSP-1 and TSP-2 in retinal glial cells is prevented by inhibition of HCMV IE expression. These findings may be relevant to pathogenesis and treatment of HCMV retinitis.

ISIS 2922, but not ganciclovir (GCV), inhibits HCMV immediate early protein (IE) expression in different infected cell lines and prevents down-modulation of extracellular matrix proteins thrombospondin-1 and -2 induced by IE proteins. While action of ISIS 2922 is mainly due to specific inhibition of IE 2 mRNA, there is also evidence for unspecific effects in terms of inhibition of virus adhesion and penetration.

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