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 lipidenveloped viruses. One of the outstanding problems 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 evaluated. Study Design and Methods: The Pc compounds used were aluminum phthalocyanine tetrasulfonate (AlPcS 3 ) 2 HOSiPcOSi(CH 3 ) 2 (CH 2 ) 3 N(CH 3 ) 2 (Pc 4); HOSiPcOSi(CH 3 ) 2 (CH 2 ) 3 N + (CH) 3 I - (Pc 5); and SiPcOSi[(CH 3 ) 2 (CH 2 ) 3 N + (CH 3 ) 3 ] 2 2I - (Pc 6). RBCs were analyzed by flow cytometry for the presence of IgG. Results: Irradiation with red light for 30 minutes of RBCs containing either 2 μM Pc 4, 2 μM Pc 5, 2 μM Pc 6, or 6.5 μM AlPcS 4 resulted in an uptake of IgG. These conditions completely inactivated the lipid-enveloped vesicular stomatitis virus (VSV) (>5 log 10 kill). IgG uptake was reduced when oxygen was depleted. The addition of reduced glutathione (GSH) or mercaptoethanol prevented 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 gross 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. Since virus inactivation proceeds at the same rate in the presence and the absence of sulfhydryl compounds, their addition to treated RBCs should allow crossmatching for transfusion after treatment. The binding of IgG depends to a large extent on the generation of reactive oxygen species