Edamura K, Nasu K, Iwami Y, Nishimura R, Ogawa H, et al.
Xenotransplantation •
Changes in the expression of galactose (Gal) alpha1-3Gal, swine lymphocyte antigen (SLA) class II and intracellular adhesion molecule (ICAM)-1 of single porcine pancreatic endocrine (PE) cells during the culture period were investigated. Cultured porcine PE-cells were fixed in 10% buffered formalin for histological evaluation. At 1, 3, 6, 9 and 12 weeks of culture, mRNA was obtained from porcine PE-cells so that the expression of SLA class II and ICAM-1 genes could be examined by reverse transcriptase-polymerase chain reaction. The rates of Galalpha1-3Gal and SLA class II-positive cells did not decrease during the culture period, but the rates of Galalpha1-3Gal and SLA class II strongly positive cells significantly decreased. ICAM-1-positive cells were scarcely observed during the culture period. SLA class II and ICAM-1 mRNAs were detected at 1 and 3 weeks of culture, but were not detected after 6 weeks of culture. These results suggest that partial reduction in the expression of these antigens could be obtained by a long-term culture.
The most prevalent anticarbohydrate antibodies in human serum are anti-Gal interacting specifically with the alpha-gal epitope (Galalpha1-3Galbeta1-4GlcNAc-R) and anti-blood group antibodies interacting with blood group A and B antigens. The alpha-gal epitope, although absent in humans, comprises part of the core of carbohydrate chain in A and B antigens. Therefore, it was of interest to determine whether immunoglobulin (Ig) G antibodies, elicited in patients rejecting ABO-incompatible kidney allografts, can interact with the alpha-gal epitope. Anti-A and anti-B antibodies were determined by enzyme-linked immunosorbent assay (ELISA) with blood group A or B human red cell membranes, as solid phase antigens. Anti-Gal was determined by ELISA with alpha-gal-bovine serum albumin as solid-phase antigen. Specific removal of anti-Gal was performed by adsorption on fixed rabbit red cells. Blood group O patients who underwent transplantation with either A or B kidney produced an antibody that bound to all three carbohydrate antigens. This multispecific antibody, designated anti-Gal A/B, is specific to the core alpha-gal epitope within A and B antigens. Recipients of allograft expressing incompatible blood group B also produce anti-Gal B antibody, which binds to the core alpha-gal epitope only in the B antigen. Anti-Gal A/B and anti-Gal B constitute most of the elicited anti-blood group antibody response. Allograft recipients also produced pure anti-A, or pure anti-B, which require the complete blood group structure for binding. The findings in this study imply that much of the immune response elicited by incompatible A or B antigens on kidney allografts results in activation of anti-Gal B-cell clones producing antibodies to the core alpha-gal epitope in these blood group antigens. Only less than 25% of the elicited antibodies interact with the complete A or B antigens (i.e., pure anti-A or pure anti-B). These findings suggest that prevention of the anti-Gal response may decrease the immune rejection of ABO-incompatible allografts.