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Retinal pigment epithelial cells phagocytosis of T lymphocytes: possible implication in the immune privilege of the eye

¹ Interdisciplinary Research Institute (IRIBHN), Université Libre de Bruxelles, Brussels, Belgium
² Department of Ophthalmology, CHU Saint-Pierre and Brugman, Université Libre de Bruxelles, Brussels, Belgium
³ Department of Immunology, Erasme Hospital, Université Libre de Bruxelles, Brussels, Belgium
⁴ Department of Anatomopathology, Université Libre de Bruxelles, Brussels, Belgium

Correspondence to:
Correspondence to:
François Willermain, IRIBHN, ULB-Erasme, Bat C, 808 Route de Lennik, 1070 Bruxelles, Belgium;
fwillermain{at}hotmail.com

Aim: To investigate the capability of retinal pigment epithelium (RPE) cells to phagocytose T lymphocytes and to further analyse the immunobiological consequences of this phagocytosis.

Methods: Human RPE cells pretreated or not by cytochalasin, a phagocytosis inhibitor, were co-cultured with T lymphocytes for different time points. Phagocytosis was investigated by optic microscopy, electron microscopy, and flow cytometry. T cell proliferation was measured by ³H thymidine incorporation. RPE interleukin 1ß mRNA expression was quantified by real time PCR.

Results: RPE cells phagocytose apoptotic and non-apoptotic T lymphocytes, in a time dependent manner. This is an active process mediated through actin polymerisation, blocked by cytochalasin E treatment. Inhibition of RPE cell phagocytosis capabilities within RPE-T cell co-cultures led to an increase of lectin induced T cell proliferation and an upregulation of interleukin 1ß mRNA expression in RPE cells.

Conclusions: It is postulated that T lymphocyte phagocytosis by RPE cells might, by decreasing the total number of T lymphocytes, removing apoptotic lymphocytes, and downregulating the expression of IL-1ß, participate in vivo in the induction and maintenance of the immune privilege of the eye, preventing the development of intraocular inflammation.

Keywords: retinal pigment epithelium; T lymphocytes; phagocytosis; immune privilege; interleukin 1

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