SELECTIVE PROTECTION AGAINST IGG BINDING TO RED-CELLS TREATED WITH PHTHALOCYANINES AND RED-LIGHT FOR VIRUS INACTIVATION

Background: Irradiation with red light of red cells (RBCs) containing the photodynamically active phthalocyanine (Pc) dyes is being studied for inactivation of lipid-enveloped viruses. One of the outstanding pr oblems with this treatment is the binding of IgG to RBCs. The effects of oxygen and type I or type II quenchers on this IgG uptake were eval uated. Study Design and Methods: The Pc compounds used were aluminum p hthalocyanine tetrasulfonate (AlPcS(4)), HOSiPcOSi(CH3)(2)(CH2)(3)N(CH 3)(2) (Pc 4); HOSiPcOSi(CH3)(2)(CH2N+(CH3)(3)l(-) (Pc 5); and SiPcOSi[ (CH3)(2)(CH2N+(CH3)(3)](2)2l(-) (Pc-6). RBCs were analyzed by flow cyt ometry for the presence of IgG. Results: Irradiation with red light fo r 30 minutes of RBCs containing either 2 mu M Pc 4, 2 mu M Pc 5, 2 mu M Pc 6, or 6.5 mu M AlPcS(4) resulted In an uptake of IgG. These condi tions completely inactivated the lipid-enveloped vesicular stomatitis virus (VSV) (25 log,, kill). IgG uptake was reduced when oxygen was de pleted. The addition of reduced glutathione (GSH) or mercaptoethanol p revented the binding of IgG with RBCs treated with AlPcS(4), Pc 4, Pc 5, and Pc 6. Specific binding of IgG2 but not of C3d was observed upon Irradiation of RBCs with Pc 5 and Pc 6 in the absence of GSH. No gros s changes were observed in RBC antigen strength after irradiation with the dyes in the presence of GSH. Inactivation of VSV by Pc plus light was not affected by GSH. Conclusion: Sulfhydryl compounds are useful in preventing IgG binding to RBCs following Pc photosensitization. Sin ce virus inactivation proceeds at the same rate in the presence and th e absence of sulfhydryl compounds their addition to treated RBCs shoul d allow crossmatching for transfusion after treatment. The binding of IgG depends to a large extent on the generation of reactive oxygen spe cies.