Membrane Attack Complex (MAC)

This image depicts the MAC. Complement-dependent cytotoxicity activates the MAC, which causes a malignant or infected cell to leak or explode. The C1Q (C1q) complex, consisting of C1Q (blue and green) with serine proteases consisting of dimers of C1r (purple) and C1s (orange), attaches to immunoglobin antibodies that have bound to numerous copies of an antigen on the surface of the affected cell (in this example a CD19-positive B cell tumor). This sequence activates the MAC, which forms pores in the cell membrane.