Tuesday July 03, 2018 from 09:45 to 11:15
False-Positive Flow-Cytometric T Cell Crossmatch caused by Blood Type Antigen Expressed on Lymphocytes in ABO Incompatible Kidney Transplantation
Daiki Iwami1, Makoto Ito2, Kiyohiko Hotta1, Haruka Higuchi1, Nobuo Shinohara1.
1Department of Renal and Genitourinary Surgery, Hokkaido University, Graduate School of Medicine, Sapporo, Japan; 2Division of Laboratory and Transfusion Medicine, Hokkaido University Hospital, Sapporo, Japan
Background: Flow-cytometric T cell crossmatch (FTXM) uses live donor lymphocytes to detect anti-donor-human leukocyte antigen (HLA) IgG antibodies. Therefore, the results can be affected by individual cell surface molecular expression. Herein we report three cases with FTXM false-positive living-related kidney transplants whose positivity was influenced by the expression of incompatible ABO blood-type antigens.
Patients and Methods: The kidney recipients were three men with blood type O who received from their wives with blood type B. Their anti-B IgG titers were 1:32, 1:128, and 1:256. Lymphocyte cytotoxic assays were negative in all cases. Median of mean channel shift (MCS) in FTXM was 78.7% (range, 52.8%–85.7%). There were no anti-HLA (either donor-specific or not) class I IgG antibodies in all 3 cases detected by a solid-phase bead assay. We hypothesized that non-HLA antigens expressed on T lymphocytes affect false-positive FTXM results. To examine this, we incubated the patients’ sera with donor-type red blood cells (RBCs) to adsorb anti-ABO antibodies prior to FTXM.
Results: When the incubated sera were tested in FTXM with donor T lymphocytes, the results were negative in all cases with median MCS 3.75% (0.0%–7.5%). To clarify the expression of ABO antigens on the donor T lymphocytes, we incubated donor T lymphocytes with recipients’ sera and then incubated the cells with acid solution to detach the bound antibodies from the T lymphocytes. The eluates showed agglutination in indirect Coombs test with blood type B RBCs but no agglutination with O blood type RBCs. This indicates that the donor T lymphocytes expressed blood type B antigen and anti-blood type IgG antibodies reacted with the B antigen. These results show that anti-blood type IgG antibodies can bind to ABO-blood type antigens on the surface of T lymphocytes, resulting in positive FTXM. The false-positive FTXM can be excluded by short-term incubation of recipients’ sera with donor-type RBCs.
Conclusion: In ABO-incompatible kidney transplantation, anti-blood type IgG antibodies can be detected as anti-donor IgG antibodies in FTXM.