Mechanisms of immune suppression for CD8+ T cells by human corneal endothelial cells via membrane-bound TGFbeta.
OBJECTIVE
To determine whether CD8(+) T cells in vitro are suppressed or converted into regulators (Treg cells) by human corneal endothelial (HCE) cells.


METHODS
HCE cell lines were established from primary HCE cells, and allogeneic CD8(+) T cells were isolated from peripheral blood mononuclear cells of healthy donors. T-cell activation was assessed for proliferation by [(3)H]-thymidine incorporation. Expression of TGFbeta on HCE cells was evaluated by flow cytometry, RT-PCR, and immunohistochemistry. Anti-TGFbeta-neutralizing antibodies or TGFbeta siRNA was used to abolish the HCE-mediated inhibitory function. CD8(+) T cells exposed to HCE cells were used as Treg cells, to induce Treg cells in vitro by exposure to HCE cells. Expression of CD25 or Foxp3 on Treg cells was evaluated by flow cytometry.


RESULTS
Cultured HCE cells produced the membrane-bound active TGFbeta isoform 2. HCE surface TGFbeta2 was necessary, to inhibit CD8(+) T-cell activation via direct cell contact. In addition, although HCE cells were found to constitutively express costimulatory molecules, such as programmed death-ligand 1 (PD-L1) and PD-L2, and secreted thrombosponsin-1, only membrane-bound TGFbeta2 was actually delivered to the CD8(+) T cells. HCE cells were also found to convert some CD8(+) T-cell populations into Treg cells via their membrane-bound TGFbeta. These HCE-induced Treg cells produced soluble forms of TGFbeta1, but not of TGFbeta2, and they also acquired a regulatory phenotype that expressed CD25(high) and Foxp3.


CONCLUSIONS
Ocular resident tissue-exposed T cells can be suppressed or induced to become regulators within the human peripheral microenvironment.
Yamada
Yukiko
Y
Department of Ophthalmology and Visual Science, Tokyo Medical and Dental University Graduate School of Medicine, Tokyo, Japan.
Sugita
Sunao
S
Horie
Shintaro
S
Yamagami
Satoru
S
Mochizuki
Manabu
M
D019138:Antibodies, Blocking; D015703:Antigens, CD / Q000378:metabolism; D060890:B7-H1 Antigen; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002460:Cell Line; D018920:Coculture Techniques; D016207:Cytokines / Q000378:metabolism; D004728:Endothelium, Corneal / Q000502:physiology*; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D051858:Forkhead Transcription Factors / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D007165:Immunosuppression Therapy; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D053645:Interleukin-2 Receptor alpha Subunit / Q000378:metabolism; D008213:Lymphocyte Activation / Q000502:physiology; D061027:Programmed Cell Death 1 Ligand 2 Protein; D034741:RNA, Small Interfering / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050378:T-Lymphocytes, Regulatory / Q000276:immunology*; D053781:Transforming Growth Factor beta2 / Q000235:genetics / Q000378:metabolism*
D019138:Antibodies, Blocking; D015703:Antigens, CD; D060890:B7-H1 Antigen; C423236:CD274 protein, human; D016207:Cytokines; C418974:FOXP3 protein, human; D051858:Forkhead Transcription Factors; C508017:IL2RA protein, human; D036341:Intercellular Signaling Peptides and Proteins; D053645:Interleukin-2 Receptor alpha Subunit; C556977:PDCD1LG2 protein, human; D061027:Programmed Cell Death 1 Ligand 2 Protein; D034741:RNA, Small Interfering; D053781:Transforming Growth Factor beta2