Photoreceptor retinoid-transport protein
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About Interphotoreceptor retinoid-binding protein (IRBP / RBP3)
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About Interphotoreceptor retinoid-binding protein (IRBP / RBP3)
Overview and History
Interphotoreceptor retinoid-binding protein (IRBP, also called RBP3) is a high–molecular-weight, secreted glycoprotein produced primarily by retinal photoreceptor cells. It is a major component of the interphotoreceptor matrix and is classified biochemically as a retinoid-binding transport protein.
Functionally, IRBP binds and transports retinoid molecules — including 11-cis and all-trans retinoids — between photoreceptors and the retinal pigment epithelium, a key step in the visual cycle. Because it is abundant and extracellular, IRBP can be a target of immune recognition; laboratory studies and clinical reports have identified immune responses directed against IRBP in contexts of retinal stress and immune activity.
Interpreting Highs and Lows
Elevated immune reactivity to IRBP (measured as increased autoantibody signal) may indicate that the immune system is recognizing retinal components, a pattern that can be associated with visual symptoms, retinal inflammation, or prior tissue stress. Low or absent reactivity does not rule out retinal problems; it simply indicates no detectable antibodies to IRBP on this assay. Interpretation should focus on patterns across the Immune Zoomer panel and clinical findings, since single-marker results are most informative when combined with other immune and sensory markers.
Featured Test
IRBP is included in the Immune Zoomer to assess immune targeting of retinal tissue within the Neurological and Sensory domain. Testing for IRBP reactivity helps map whether immune activity is focused on photoreceptor-associated antigens, contributing to pattern recognition and more precise, tissue-aware clinical interpretation.
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Mary Beth Augustine
DCN, RDN, FAND- Lead Clinical Educator
Suzanne Barker
MS, RDN, LD, CTTS, CGP- Clinical Educator
Suzette Garcia
MSc- MHNE- Clinical Educator
Brooke Mader Ganev
MS, CNS, LDN, FDN- Clinical Educator
Adair Anderson
MS, RDN, LDN- Clinical Educator
Lillie Luu Nguyen
DCN, CNS, LDN- Clinical Educator
Jason Barker
ND- Clinical Educator
Emaline Brown
ND- Clinical Educator
Dana Filatova
DCN, CNS, LDN- Clinical Educator
Jessy Dhanjal
ND- Clinical Educator
Nour Amri
MS, LDN, CNS, CKNS- Clinical Educator
