Histological and immunohistochemical characterization of the porcine ocular surface

PLoS One. 2020 Jan 13;15(1):e0227732. doi: 10.1371/journal.pone.0227732. eCollection 2020.

Abstract

The ocular surface of the white domestic pig (Sus scrofa domestica) is used as a helpful model of the human ocular surface; however, a complete histological description has yet to be published. In this work, we studied porcine eyeballs with intact eyelids to describe and characterize the different structures that form the ocular surface, including the cornea and conjunctiva that covers the bulbar sclera, tarsi, and the nictitating membrane. We determined the distribution of goblet cells of different types over the conjunctiva and analyzed the conjunctival-associated lymphoid tissue (CALT). Porcine eyeballs were obtained from a local slaughterhouse, fixed, processed, and embedded in paraffin blocks. Tissue sections (4 μm) were stained with hematoxylin/eosin, Alcian blue/Periodic Acid Schiff, and Giemsa. Slides were also stained with lectins from Arachis hypogaea (PNA) and Helix pomatia (HPA) agglutinins and immunostained with rabbit anti-CD3. We found that the porcine cornea was composed of 6-8 epithelial cell layers, stroma, Descemet's membrane, and an endothelial monolayer. The total corneal thickness was 1131.0±87.5 μm (mean±standard error of the mean) in the center and increased to 1496.9±138.2 μm at the limbus. The goblet cell density was 71.25±12.29 cells/mm, ranging from the highest density (113.04±37.21 cells/mm) in the lower palpebral conjunctiva to the lowest density (12.69±4.29 cells/mm) in the bulbar conjunctiva. The CALT was distributed in the form of intraepithelial lymphocytes and subepithelial diffuse lymphoid tissue. Lenticular-shaped lymphoid follicles, about 8 per histological section, were also present within the conjunctival areas. In conclusion, we demonstrated that the analyzed porcine ocular structures are similar to those of humans, confirming the potential usefulness of pig eyes to study ocular surface physiology and pathophysiology.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Conjunctiva / cytology
  • Conjunctiva / ultrastructure
  • Cornea / ultrastructure
  • Eye / ultrastructure*
  • Goblet Cells / ultrastructure
  • Limbus Corneae / ultrastructure
  • Lymphoid Tissue / ultrastructure
  • Meibomian Glands / ultrastructure
  • Staining and Labeling / methods
  • Sus scrofa* / anatomy & histology

Grants and funding

YD, MAT2013-47501-C2-1-R (Spanish Ministry of Economy and Competitiveness and European Regional Development Fund) http://www.mineco.gob.es/ and https://ec.europa.eu/regional_policy/en/funding/erdf/ YD and LGP, RTI2018-094071-B-C21 (Spanish Ministry of Science, Innovation and Universities and European Regional Development Fund) http://www.ciencia.gob.es/portal/site/MICINN/ and https://ec.europa.eu/regional_policy/en/funding/erdf/ LGP, Postdoctoral contrats 2017 call (University of Valladolid) http://www.uva.es/export/sites/uva/ MCM, Regional JCyL Scholarship/European Social Fund Program ORDEN EDU/128/2015 (Regional JCyL and European Social Fund) https://www.jcyl.es/ and https://ec.europa.eu/esf/home.jsp The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.