Neutralizing tumor necrosis factor-alpha activity suppresses activation of infiltrating macrophages in experimental autoimmune uveoretinitis

Abstract

Purpose: During experimental autoimmune uveoretinitis (EAU), infiltrating macrophages become activated to express nitric oxide synthase (NOS)-2 and generate nitric oxide (NO). The current study was designed to determine whether neutralizing TNF activity with a soluble fusion protein of TNFp55 receptor (sTNFr-IgG) inhibits macrophage activation, thereby contributing to reduced tissue damage observed with such treatment.

Methods: EAU was induced in Lewis rats by active immunization with soluble retinal extract (RE) and pertussis toxin (intraperitoneally), and animals were treated on days 6 and 8 after immunization with either sTNFr-IgG or human (hu)IgG. Disease course and severity were noted clinically, and eyes were enucleated for histologic scoring, including TUNEL immunofluorescence, at various stages of disease. Infiltrating retinal macrophages were isolated through a density gradient and subsequently phenotyped by flow cytometry, analyzed for ability to produce nitrite, either spontaneously or after cytokine stimulation, and assayed by PCR for cytokine gene expression.

Results: Neutralizing TNF activity suppressed tissue damage without impeding myeloid cell infiltrate. Moreover, with sTNFr-IgG treatment, infiltrating macrophages demonstrated reduced nitrite production at the height of disease, and the level of apoptosis within the retina of both ED1(+) cells and resident cells was reduced. PCR analysis demonstrated a significant increase in TGF beta signal and absent or low TNF signal throughout the disease course after treatment with sTNFr-IgG.

Conclusions: sTNFr-IgG successfully suppresses retinal damage and impairs macrophage activation but not trafficking during EAU. sTNFr-IgG-mediated suppression of NO production results in reduced levels of apoptosis of inflammatory cells and reduction in photoreceptor damage.