Abstract
Purpose: :
The immune system has emerged recently as a critical factor in the pathogenesis of age-related macular degeneration (AMD), although precise cellular and molecular mechanisms remain to be defined. Carboxyethylpyrrole (CEP) is an oxidation fragment associated with AMD. Mice immunized with CEP-adducted mouse serum albumin (CEP-MSA) develop autoantibodies and AMD-like lesions, providing an ideal setting to study immune responses that may be linked to AMD development. We have previously shown autoreactive T cell activation and a tissue-specific role for macrophages in our model at the earliest stages of disease onset, prior to overt retinal damage. In this study we aimed to elucidate in more detail the potential cooperation of innate and adaptive immunity in AMD development.
Methods: :
CEP-specific T cells from wild type C57BL/6 or BALB/c immunized with CEP-MSA were stimulated and expanded ex vivo for 4 days. Bone marrow-derived primary macrophages were generated from naïve or immunized mice. T cells and macrophages were co-cultured at different ratios and different time points (6, 12, 24 and 48 hr), the supernatants were collected to measure cytokine production by ELISA and RNA was isolated from each cell type to analyze gene expression of relevant genes by quantitative real-time PCR. Macrophages were also polarized toward either M1 or M2 phenotypes and injected subretinally, followed by eye harvest and gene expression analysis 7 days later.
Results: :
Macrophages become activated and polarized toward the M1 pathway (as measured by upregulation of TNF, IL-12, KC, IL-1b, and iNOS) when cultured in the presence of CEP-specific T cells, but only when the cognate antigen (CEP-MSA) is included. Furthermore, there was also a downregulation of M2 markers, such as IL-10 and Arginase. Direct effects of local injection of macrophages within the retina in the context of CEP activation are currently under investigation.
Conclusions: :
Our previous data provided strong evidence linking immune responses against oxidative damage with early presence of macrophages at sites of future AMD and may help to clarify the role of these cells in AMD pathology. We now show a more direct effect of antigen-specific T cells on the polarization of M1 macrophages, which are associated with tissue damage. The exact nature of this interaction in vivo is still unknown but is one of the main questions to be addressed in future studies. We propose a two-step model for the onset of AMD: first, T cell activation leads to pro-inflammatory cytokine production (IFN-g and IL-17) that primes macrophages for M1 polarization once they get recruited to the retina through chemokine signaling.
Keywords: age-related macular degeneration • inflammation • oxidation/oxidative or free radical damage