Immunoglobulin isotype-specific characterization of anti-human leukocyte antigen antibodies eluted from explanted renal allografts.

To evaluate the immunoglobulin isotypes of anti-human leukocyte antigen (HLA) antibodies harbored in rejected renal allografts, we isolated proteins by acid elution accumulated in 94 rejected and explanted kidneys and characterized their antibody specificities by complement-dependent cytotoxicity, enzyme-linked immunosorbent assay, and flow cytometry (Luminex) techniques. In addition, we differentially analyzed non-complement-binding immunolglobulin (Ig) G2/4 and IgA1/2 antibodies in the eluates using two modified solid phase assays. We found non-complement-binding IgG2 and IgG4 antibodies in 16/58 (28%) of the IgGall-positive eluates, 15 eluates with anti-HLA class I and 4 with anti-HLA class II specificities, respectively. Anti-HLA class I IgG2/4 antibodies directed against the donor were found in 7 eluates (54% of the IgG2/4-pos. eluates), whereas 2 eluates (50%) had class II IgG2/4 antibodies directed against the donor. IgA1/2 antibodies could be detected in 9 eluates (16%); 5 of them had anti-HLA class I and 5 anti-HLA class II antibodies. We could clearly exhibit that explanted kidney allografts harbor anti-HLA antibodies. Moreover, our study demonstrates that non-complement-binding anti-HLA antibodies accumulate in rejected renal allografts.