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Evidence for lymphatics in the developing and adult human choroid
Mark E Koina1, Louise Baxter2, Samuel J Adamson2
1Discipline of Anatomy, School of Medical Sciences, Bosch Institute, The University of Sydney, Sydney, New South Wales, Australia Department of Anatomical Pathology, ACT Pathology, The Canberra Hospital, Garran, Australian Capital Territory, Australia.
Insights
Researchers found lymphatic-like structures in the human choroid, crucial for fluid balance and immune surveillance. These findings reveal a new anatomical basis for antigen presentation in the posterior eye.
Area of Science:
- Ophthalmology
- Anatomy
- Immunology
Background:
- Lymphatic vessels are vital for fluid homeostasis, immune surveillance, and tumor metastasis.
- Understanding ocular lymphatic structures is essential for comprehending posterior eye immunity and disease.
Purpose of the Study:
- To identify and characterize lymphatic-like structures in the human choroid.
- To investigate the development and structural features of these choroidal lymphatics.
Main Methods:
- Utilized multiple-marker immunohistochemistry (IHC) on human fetal and adult choroids.
- Employed transmission electron microscopy (TEM) for ultrastructural analysis.
- Examined lymphatic and vascular-specific markers including PROX-1, LYVE-1, podoplanin, and VEGFR-3.
Main Results:
- Identified a central-to-peripheral topography of lymphatic formation in the choroid.
- Observed blind-ended lymph sacs external to the choriocapillaris and infrequent lymphatic channels.
- Characterized ultrastructural features of adult choroidal lymphatics, such as anchoring filaments and fragmented basal lamina.
Conclusions:
- The identified lymphatic system in the human choroid is well-positioned for fluid recirculation and immune surveillance.
- These lymphatic-like channels provide an anatomical basis for antigen presentation in the posterior eye.
- Suggests a potential pathway for antigen transport from the eye to sentinel lymph nodes.
Purpose:
Lymphatics subserve many important functions in the human body including maintenance of fluid homeostasis, immune surveillance, and tumor metastasis. Our aim was to provide structural and phenotypic evidence of lymphatic-like structures in the human choroid, including details of its development.
Methods:
Using multiple-marker immunohistochemistry (IHC), choroids from human fetal eyes (8-26 weeks gestation) and adults (17-74 years) were examined with lymphatic- and vascular-specific markers: prospero homeobox-1 (PROX-1), lymphatic vascular endothelium receptor-1 (LYVE-1), podoplanin, D2-40, endomucin, VEGF-C, vascular endothelial growth factor receptor-3 (VEGFR-3 or Flt4), UEA lectin, platelet endothelial cell adhesion molecule-1 (PECAM-1), CD34, and CD39. Transmission electron microscopy (TEM) was used to establish evidence for choroidal lymphatics, and to provide details of stratification and relative frequency of lymphatics compared to choroidal blood vessels.
Results:
Immunohistochemistry and TEM indicated a central-to-peripheral topography of lymphatic formation, with numerous blind-ended lymph sacs just external to the choriocapillaris, as well as the presence of infrequent precollector and collector lymphatic channels. Characteristic ultrastructural features of lymphatics in adult human choroid included anchoring filaments, luminal flocculent protein but absence of erythrocytes, fragmented and/or absent basal lamina, absence of intracellular Weibel-Palade bodies, infrequent pericyte ensheathment, and lack of fenestrae.
Conclusions:
The system of blind-ended initial lymphatic segments seen just external to the fenestrated vessels of the choriocapillaris is ideally placed for recirculating extracellular fluid and strategically placed for immune surveillance. The presence of a system of lymphatic-like channels in the human choroid provides an anatomical basis for antigen presentation in the posterior eye, with a possible route from the eye to the sentinel lymph nodes, similar to that already described for anterior eye lymphatics.
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