Impaired killing of HCMV-infected retinal pigment epithelial cells by anti-pp65 CD8(+) cytotoxic T cells.
OBJECTIVE
Host defense against infection by human cytomegalovirus (HCMV) is ensured in great part by cytotoxic CD8(+) T lymphocytes (CTLs) directed against the tegument protein pp65. The hyperimmediate release of incoming pp65 into the major histocompatibility complex (MHC) class I pathway after fusion of the virus with the cell membrane provides a very early mechanism of defense. In retinal pigment epithelial (RPE) cells HCMV is known to enter through endocytosis. This study was conducted to determine whether this means of penetration into the cells would allow the virus to elude immune surveillance.


METHODS
Infection of RPE cells with HCMV AD169 was performed for 6 hours, 48 hours, and 8 days. Expression of intracellular pp65 in RPE cells and in the astrocytoma reference cell line U373MG was evaluated by flow cytometry, fluorescence microscopy, and Western blot analysis. Killing of both HCMV-infected cell lines by HLA-A2-restricted CD8(+) CTLs directed against pp65 was monitored by (51)Cr-release assays.


RESULTS
RPE cells were not lysed by CTLs directed against incoming pp65, contrary to U373MG. Moreover, both cell lines were not killed by anti-pp65 CTLs later after infection, because of the MHC class-I-downregulating effect of HCMV unique short (US2-11) proteins.


CONCLUSIONS
In RPE cells, both HCMV entry through endocytosis and the immunosuppressive effect of US proteins could allow the virus to evade immune surveillance at any stage of infection, which could promote viral spreading within the retina.
Allart
Sophie
S
National Institute of Health and Medical Research (INSERM), Toulouse, France.
Lulé
Jacqueline
J
Serres
Brigitte
B
Jones
Thomas
T
Davignon
Jean-Luc
JL
Malecaze
François
F
Davrinche
Christian
C
D015153:Blotting, Western; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002460:Cell Line; D003587:Cytomegalovirus / Q000502:physiology*; D003602:Cytotoxicity, Immunologic / Q000502:physiology*; D005434:Flow Cytometry; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D008856:Microscopy, Fluorescence; D010750:Phosphoproteins / Q000276:immunology*; D010857:Pigment Epithelium of Eye / Q000378:metabolism / Q000821:virology*; D011233:Precipitin Tests; D013602:T-Lymphocytes, Cytotoxic / Q000502:physiology*; D014763:Viral Matrix Proteins / Q000276:immunology*
D010750:Phosphoproteins; D014763:Viral Matrix Proteins; C065418:cytomegalovirus matrix protein 65kDa