EXPRESSION OF FUNCTIONAL DECAY-ACCELERATING FACTOR (CD55) IN TRANSGENIC MICE PROTECTS AGAINST HUMAN COMPLEMENT-MEDIATED ATTACK

Transgenic mice expressing human CD55 were generated by microinjection of a CD55-minigene under the control of the mouse H2K(b) (MHC class I ) promoter, Offspring were tested for transgene integration by PCR ana lysis, and for CD55 expression on peripheral blood leukocytes (PBLs) b y flow cytometry. Expression levels of 15 founders ranged from 30 to 8 0% of that on human neutrophils. Immunohistochemical analysis of kidne y, heart, liver, and lung tissue demonstrated staining for CD55 on end othelial surfaces as well as general diffuse staining throughout the t issues. The capacity of the transgenically expressed CD55 to prevent h uman C3 deposition on the surface of mouse splenocytes was assessed by flow cytometry, Cells from hemizygous mice incubated with 10% fresh h uman serum as a source of natural antibody and complement bound approx imately 65% less C3 than control littermates, No further protection wa s seen using cells from homozygous littermates, and the protective eff ect was abrogated by prior incubation with an anti-CD55 monoclonal ant ibody. Similarly, transgenic mice were afforded significant protection from human serum-mediated lysis, determined using an LDH release assa y, Hearts perfused with human plasma showed no increase in survival ti me in a modified Langendorff perfusion system, however deposition of h uman C3c was greatly reduced in transgenic hearts.