NATURAL HUMAN ANTIBODY-MEDIATED DESTRUCTION OF PORCINE NEONATAL ISLET-CELL GRAFTS

Porcine pancreata may be considered a potential source of islets for t ransplantation into diabetic recipients; however, whether porcine isle t grafts will be susceptible to damage by natural antibody-mediated hy peracute rejection remains unknown. In this study, we performed Wester n blots to determine whether membrane proteins present on porcine neon atal islet cells (NIC) are recognized by xenoreactive antibodies prese nt in human sera. Western blots of freshly isolated porcine NICs with AB sera detected the presence of 14 antigens (MW 24-164 kDa) and 4 ant igens (MW 101-150 kDa) to which antiserum against human IgM and IgG bo und, respectively, The most prominent antigens with IgM reactivity had MWs of 36, 63, and 120 kDa, whereas for IgG, the most intensely react ive antigen had a MW of 120 kDa. When membrane fractions prepared from purified porcine aortic endothelial cells and LLC-PK1 cells were anal yzed, the major antigens had molecular weights comparable to those see n for NICs. After culturing the NICs for 5 days, the number of detecte d xenoreactive antigens binding IgM or IgG decreased and the antigens present at 36, 63, and 120 kDa with IgM reactivity were shown to have a decreased intensity of binding, Incubation of cultured porcine NICs for 18 hr in the presence of human AB serum containing complement resu lted in a 55% loss of cellular insulin content (P < 0.0001), a 45% red uction in recoverable DNA (P < 0.0001), and a marked reduction in insu lin secretory response to an in vitro glucose challenge. Recovery and viability of porcine NICs was not affected when incubated with AB seru m depleted of anti-Gal antibodies with Synsorb 90. These results demon strate that natural human antibodies of both IgM and Ige subtypes bind to antigens present on porcine NICs and that exposure of the NICs to human AB sera and complement reduces islet cell survival and functiona l viability. Adsorbing serum with the alpha Gal(1-3)beta Gal(1-4)beta Glc carbohydrate removes natural human antibody-mediated destruction o f porcine neonatal islet cell grafts.