Protection of Chinese Hamster Ovary Cells from Complement-Mediated Lysis by Human CD35
Full-length recombinant human complement receptor type 1 (CR1) was expressed in Chinese hamster ovary (CHO) cells, and shown to inhibit complement-mediated lysis of the host cells. The efficiency of inhibition was directly proportional to the number of receptors per cell. Purified polyclonal anti-s CR1 antibody was capable of abrogating the complement inhibitory activity of CR1 in a dose dependent manner. The complement lysis of untransfected CHO cells loaded with entrapped fluorescent dye was not inhibited by the addition of transfected CHO cells expressing CR1 but lacking dye. CR1 has long been recognized to regulate extrinsic complement activation, that is, to bind to and promote the degradation of fluid phase C3b and of C3b attached to immune complex. These results demonstrate that CR1 inhibits complement-mediated lysis of the cell on which it is expressed, but does not protect neighboring cells.