Efficacy of IgM anti-blood type antibody monitoring by enzyme-linked immunosorbent assay after renal transplantation across the blood barrier: high-dose immunoglobulin administration blocks IgM rather than IgG anti-blood type antibodies.

We used an enzyme linked immunosorbent assay (ELISA) to investigate the presence of subtypes of anti-blood-type antibodies in patients with biopsy-proven humoral rejection after ABO-incompatible renal transplantation. High agglutinin IgG and IgM anti-blood type antibodies from 12 ABO-incompatible recipients with vascular rejection were separately assessed using an ELISA. Patients who exhibited excellent renal function despite high agglutinin titers of anti-blood-type antibodies(n = 8) were also examined. All 12 rejection patients exhibited highly elevated titers of IgG and IgM, while the eight stable patients exhibited only slightly elevated IgG titers, but not IgM. IgG and IgM titers did not change after plasmapheresis and steroid pulse therapy, whereas IVIg treatment significantly blocked both IgG and IgM, with IgM being blocked to a larger extent than IgG. Blocking of IgM seems to play an important role in improving ABO-incompatible grafts.