Liver transplant recipient sera derived soluble HLA mediates allele specific CTL apoptosis.
BACKGROUND
Significant levels of donor soluble human leukocyte antigen (HLA) class I (sHLA) are present in patients after transplants. We investigated the possibility that sHLA may inhibit cytolytic T lymphocyte (CTL) activity by inducing apoptosis of the CTL, thereby serving as a mechanism for specific tolerance.


METHODS
sHLA-A2 and A3 were isolated from the sera of liver transplant recipients by affinity chromatography. T cell bulk lines directed against HLA-A2 and HLA-A3 were generated by stimulation with HLA-A2, A3+ peripheral blood leukocytes and B-lymphoblastoid cells. Induction of T cell apoptosis by sHLA was analyzed by adding sHLA to allospecific CTL 4 or for 24 hr before flow cytometric analysis of propidium iodide and fluorescein isothiocyanate-conjugated annexin V stained cells. T cell receptor (TCR) engagement by sHLA was demonstrated using a monoclonal antibody specific for the TCR.


RESULTS
sHLA-A3 inhibited CTL activity of a HLA-A3 T cell line by 53%, whereas sHLA-A2 had no effect. sHLA-A3 also increased T cell death by 77% over the control, whereas sHLA-A2 had no significant effect. However, sHLA-A2 induced 21% apoptosis of an anti-HLA-A2 T cell line, whereas sHLA-A3 caused only 3% apoptosis. The antibody complexed form of sHLA was ineffective in the induction of apoptosis. Preincubation of the T cells with anti-T cell receptor monoclonal antibody protected the T cells from sHLA-induced apoptosis, indicating that sHLA-TCR engagement is necessary for this process to occur.


CONCLUSIONS
TCR-mediated apoptosis of alloreactive CTL may serve as a mechanism by which sHLA can modulate the immune response.
Smith
M A
MA
Department of Surgery, Washington University School of Medicine, St. Louis, MO 63110, USA.
Naziruddin
B
B
Poindexter
N J
NJ
Haynes
A E
AE
Howard
T
T
Mohanakumar
T
T
D000483:Alleles; D017209:Apoptosis / Q000502:physiology*; D002460:Cell Line; D015789:HLA-A2 Antigen / Q000097:blood / Q000502:physiology*; D015791:HLA-A3 Antigen / Q000097:blood / Q000502:physiology*; D006801:Humans; D016031:Liver Transplantation / Q000276:immunology*; D011948:Receptors, Antigen, T-Cell / Q000502:physiology; D012995:Solubility; D013602:T-Lymphocytes, Cytotoxic / Q000502:physiology*
D015789:HLA-A2 Antigen; D015791:HLA-A3 Antigen; D011948:Receptors, Antigen, T-Cell