Role and expression of CD40 on human retinal pigment epithelial cells.
OBJECTIVE
To examine the CD40 costimulatory molecule expression on normal resting or activated adult human retinal pigment epithelium (hRPE) cells and to evaluate its role as an activation molecule considering the potential antigen presentation functions of hRPE cells.


METHODS
Expression of HLA-DR and costimulatory (CD40, B7.1, B7.2, CD54, and CD58) molecules on hRPE cells was analyzed by flow cytometry. CD40 triggering was performed using soluble CD40L or cocultures with CD40L transfected fibroblasts. Interleukin (IL)-6, -8, -10, and -12 secretions were measured by enzyme-linked immunosorbent assay. Antigen presentation function of hRPE cells was assessed by coculturing hRPE cells with allogeneic T cells. T-cell proliferation was measured by [(3)H]-thymidine incorporation, and T-cell apoptosis by measurement of caspase-3 activity.


RESULTS
Interferon (IFN)gamma-activated hRPE cells expressed CD40, but not B7.1 or B7.2. Although interferongamma enhanced IL-6 and IL-8 production, CD40 triggering of IFNgamma-activated hRPE cells did not induce IL-12 secretion. hRPE cells did not stimulate allogeneic resting T cells and downregulated phytohemagglutinin-activated allogeneic T cells via a cell-to-cell contact-dependent mechanism. Some induction of apoptosis was detected.


CONCLUSIONS
CD40 is expressed on IFNgamma-activated hRPE cells. Its ligation leads to an increased production of IL-6 and IL-8 but fails to induce B7.1 or B7. 2 expression, or to induce IL-12 secretion. Accordingly, hRPE cells do not activate allogenic T cells but inhibit T-cell proliferation, partly through induction of apoptosis. These results suggest that hRPE cells could be implicated more in a deviant antigen presentation. If the exact molecular mechanisms are unclear, it is likely that CD40-CD40L interaction could play a role in this process.
Willermain
F
F
I.R.I.B.H.N., Campus Erasme, Université Libre de Bruxelles, Faculty of Medicine, Brussels, Belgium. fwillermain@hotmail.com
Caspers-Velu
L
L
Baudson
N
N
Dubois
C
C
Hamdane
M
M
Willems
F
F
Velu
T
T
Bruyns
C
C
D000818:Animals; D017951:Antigen Presentation / Q000502:physiology; D000938:Antigen-Presenting Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015703:Antigens, CD / Q000096:biosynthesis; D017209:Apoptosis; D019013:CD40 Antigens / Q000096:biosynthesis*; D023201:CD40 Ligand; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002478:Cells, Cultured; D018920:Coculture Techniques; D016207:Cytokines / Q000096:biosynthesis; D005347:Fibroblasts; D005434:Flow Cytometry; D006684:HLA-DR Antigens / Q000096:biosynthesis; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000502:physiology; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013601:T-Lymphocytes / Q000502:physiology; D015854:Up-Regulation
D015703:Antigens, CD; D019013:CD40 Antigens; D015815:Cell Adhesion Molecules; D016207:Cytokines; D006684:HLA-DR Antigens; D008562:Membrane Glycoproteins; D023201:CD40 Ligand; D007371:Interferon-gamma; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases