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Microglia in human retina: a heterogeneous population with distinct ontogenies
J M Provis1, C M Diaz, P L Penfold
1Department of Clinical Ophthalmology, University of Sydney, N.S.W., Australia.
Abstract:
Microglia of the adult human retina are a heterogeneous population of cells, some having characteristics of dendritic antigen presenting cells (DC) and others resembling macrophages, or MPS cells. Studies of the development of microglial distributions in human retina suggest that cells bearing macrophage markers are ontogenetically distinct from microglia that do not. Quantitative studies indicate that macrophage antigen immunoreactive microglia are a subpopulation CD45- and MHC-immunoreactive microglia. While CD45 and MHC-I and -II immunoreactive microglia are seen in the retina prior to the arrival of the vasculature, significant numbers of macrophage-positive microglia only arrive along with the vascular precursors, at about 14 to 15 weeks of gestation. Microglia appear to enter the retina from the ciliary margin prior to vascularization but from both the optic disc and ciliary margin, postvascularization. Macrophage antigen positive microglia enter the retina mainly via the optic nerve head. It is argued that macrophage-antigen positive microglia become established in the retina as vessel associated (perivascular and paravascular) microglia and that the MHC-positive, but macrophage-antigen negative microglia (representing DC), become established as the parenchymal, ramified microglia of adult retina.
Insights
Human retinal microglia are diverse, with distinct populations resembling macrophages and dendritic cells (DCs). Macrophage-like cells arrive later with blood vessels, suggesting different origins and roles in retinal development.
Area of Science:
- Ophthalmology
- Immunology
- Developmental Biology
Background:
- Adult human retinal microglia exhibit heterogeneity, with some cells displaying characteristics of dendritic antigen-presenting cells (DCs) and others resembling macrophages.
- Studies suggest that microglia expressing macrophage markers are ontogenetically distinct from those lacking these markers.
- Macrophage antigen-immunoreactive microglia represent a subpopulation of CD45- and MHC-immunoreactive microglia.
Purpose of the Study:
- To investigate the developmental origins and distribution patterns of distinct microglial subpopulations in the human retina.
- To differentiate between macrophage-like microglia and dendritic cell-like microglia based on their developmental timing and entry routes into the retina.
Main Methods:
- Quantitative analysis of microglial populations in developing human retina.
- Immunohistochemical staining for macrophage and MHC antigens (MHC-I and -II) and CD45.
- Correlation of microglial distribution with vascular development and gestational timing.
Main Results:
- MHC-I and -II immunoreactive microglia are present in the retina before vascularization.
- Significant numbers of macrophage-positive microglia appear with vascular precursors around 14-15 weeks gestation.
- Microglia enter the retina from the ciliary margin before vascularization, and from both the optic disc and ciliary margin post-vascularization.
- Macrophage-positive microglia primarily enter via the optic nerve head, associating with vasculature.
Conclusions:
- Macrophage-antigen positive microglia are likely vessel-associated (perivascular/paravascular) in the adult retina.
- MHC-positive, macrophage-antigen negative microglia (representing DCs) likely form the parenchymal, ramified microglia of the adult retina.
- Distinct ontogenetic pathways exist for different microglial subsets in the human retina.