title: Retinal pigment epithelium and microglia express the CD5 antigen-like protein, a novel autoantigen in age-related macular degeneration.
abstract: We report on a novel autoantigen expressed in human macular tissues, identified following an initial Western blot (WB)-based screening of sera from subjects with age-related macular degeneration (AMD) for circulating auto-antibodies (AAbs) recognizing macular antigens. Immunoprecipitation, 2D-gel electrophoresis (2D-GE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS), direct enzyme-linked immunosorbent assays (ELISA), WBs, immunohistochemistry (IHC), human primary and ARPE-19 immortalized cell cultures were used to characterize this novel antigen. An approximately 40-kDa autoantigen in AMD was identified as the scavenger receptor CD5 antigen-like protein (CD5L), also known as apoptosis inhibitor of macrophage (AIM). CD5L/AIM was localized to human RPE by IHC and WB methods and to retinal microglial cells by IHC. ELISAs with recombinant CD5L/AIM on a subset of AMD sera showed a nearly 2-fold higher anti-CD5L/AIM reactivity in AMD vs. Control sera (p = 0.000007). Reactivity ≥0.4 was associated with 18-fold higher odds of having AMD (χ2= 21.42, p = 0.00063). Circulating CD5L/AIM levels were also nearly 2-fold higher in AMD sera compared to controls (p = 0.0052). The discovery of CD5L/AIM expression in the RPE and in retinal microglial cells adds to the known immunomodulatory roles of these cells in the retina. The discovery of AAbs recognizing CD5L/AIM identifies a possible novel disease biomarker and suggest a potential role for CD5L/AIM in the pathogenesis of AMD in situ. The possible mechanisms via which anti-CD5L/AIM AAbs may contribute to AMD pathogenesis are discussed. In particular, since CD5L is known to stimulate autophagy and to participate in oxidized LDL uptake in macrophages, we propose that anti-CD5L/AIM auto-antibodies may play a role in drusen biogenesis and inflammatory RPE damage in AMD.
authors.affiliation: University of Tennessee Health Science Center, Department of Ophthalmology, Hamilton Eye Institute, Memphis, TN, USA; Department of Ophthalmology, Duke Eye Center, Duke University School of Medicine, Durham, NC, USA. Electronic address: alessandro.iannaccone@duke.edu.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Iannaccone
authors.affiliation: University of Tennessee Health Science Center, Department of Ophthalmology, Hamilton Eye Institute, Memphis, TN, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Hollingsworth
authors.affiliation: University of Tennessee Health Science Center, Department of Ophthalmology, Hamilton Eye Institute, Memphis, TN, USA; University of Tennessee Health Science Center, Department of Pharmaceutical Sciences, Memphis, TN, USA.
authors.forename: Diwa
authors.initials: D
authors.lastname: Koirala
authors.affiliation: University of Tennessee Health Science Center, Department of Ophthalmology, Hamilton Eye Institute, Memphis, TN, USA.
authors.forename: David D
authors.initials: DD
authors.lastname: New
authors.affiliation: University of Tennessee Health Science Center, Department of Ophthalmology, Hamilton Eye Institute, Memphis, TN, USA; University of Tennessee Health Science Center, Department of Medicine, Division of Endocrinology, Memphis, TN, USA.
authors.forename: Nataliya I
authors.initials: NI
authors.lastname: Lenchik
authors.affiliation: University of Tennessee Health Science Center, Department of Pharmaceutical Sciences, Memphis, TN, USA.
authors.forename: Sarka
authors.initials: S
authors.lastname: Beranova-Giorgianni
authors.affiliation: University of Tennessee Health Science Center, Department of Medicine, Division of Endocrinology, Memphis, TN, USA.
authors.forename: Ivan C
authors.initials: IC
authors.lastname: Gerling
authors.affiliation: University of Tennessee Health Science Center, Department of Microbiology, Immunology and Biochemistry, Memphis, TN, USA.
authors.forename: Marko Z
authors.initials: MZ
authors.lastname: Radic
authors.affiliation: University of Tennessee Health Science Center, Department of Pharmaceutical Sciences, Memphis, TN, USA.
authors.forename: Francesco
authors.initials: F
authors.lastname: Giorgianni
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001324:Autoantigens; D015551:Autoimmunity; D015153:Blotting, Western; D018956:CD5 Antigens / Q000096:biosynthesis*; D002460:Cell Line; D015180:Electrophoresis, Gel, Two-Dimensional; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008264:Macrophages / Q000276:immunology / Q000378:metabolism; D008268:Macular Degeneration / Q000378:metabolism* / Q000473:pathology; D008297:Male; D017628:Microglia / Q000378:metabolism* / Q000473:pathology; D018613:Microscopy, Confocal; D008875:Middle Aged; D012160:Retina / Q000378:metabolism* / Q000473:pathology; D055213:Retinal Pigment Epithelium / Q000378:metabolism* / Q000473:pathology; D053719:Tandem Mass Spectrometry
chemical_list: D001324:Autoantigens; D018956:CD5 Antigens
keywords: Age-related macular degeneration; Auto-antibody; Autoimmunity; CD5L; Microglia; Retinal pigment epithelium; Scavenger receptor