Background: Donor-specific antibodies (DSA) are recognized as important factors in determining outcome in renal transplantation.Typically DSAs of the IgG isotype are measured, but little is known about the role, if any, of other isotypes. IgE is an antibody isotype that is structurally different from other isotpyes and that has unique functional properties and effector mechanisms. Here, we studied if MHC/HLA-specific IgE occurs during an alloresponse.

Methods: Skin or hearts of Balb/c (H-2^d) or C3H (H-2^k) mice were grafted onto untreated B6 (H-2^b), C3H or Balb/c mice, respectively. At several time-points H-2D^{d or k} -, H-2K^{d or k}-, and I-E^{d or k}-specific IgE levels were measured in serum with an ELISA using recombinant MHC provided by the NIH tetramer facility. In addition, HLA-specific IgE was measured in a pilot cohort of IgG-DSA positive kidney transplant recipients via a modified Luminex method employing class I and II Labscreen Singlebeads (OneLambda). In functional in vitro degranulation assays, rat basophil leukemia (RBL) cells (binding murine IgE via FcεRI) or RBL cells transfected with human FcεRI, respectively, were loaded with mouse or patient sera, respectively. Subsequently recombinant H-2K^k/H-2D^k monomers or beads loaded with a single HLA antigen, respectively, were added and mediator release was measured.

Results: Donor MHC-I-specific IgE consistently developed upon rejection of MHC-mismatched skin and heart grafts in all strain combinations tested (n=6 skin and n=4 hearts; for all strain combinations) and persisted for more than 12 months. Anti-I-E^d (but not anti-I-E^k) was also detectable after skin and heart transplantation. Further, 4/5 tested patients were positive for anti-HLA IgE, including donor HLA class I and II specificities. Recombinant MHC/HLA triggered specific mediator release in RBL degranulation assays in vitro.

Conclusion: These data demonstrate, for what we believe to be the first time, that MHC/HLA-specific IgE develops upon allograft rejection and is functional at the effector cell level in vitro.

CITATION INFORMATION: Farkas A, Baranyi U, Unger L, Mahr B, Hock K, Pilat N, Regele H, Wahrmann M, Böhmig G, Valenta R, Wekerle T. MHC/HLA-Specific IgE in Allotransplantation. Am J Transplant. 2016;16 (suppl 3).

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