IgGMedCompAct - Determinants of IgG-mediated complement activation

Antibodies (immunoglobulins; IgG) are some of the most important molecules of our immune defense against pathogens and tumor cells. These Y-shaped proteins recognize and tightly bind specific structures on the surface of viruses, bacteria and tumor cells via their two "arms", the so-called Fab regions, and thus mark them for destruction by the immune system. This is possible because the stem of the Y-shaped antibody, the so-called Fc region, then protrudes from the surface of the target cell, and other molecules of the immune system, in particular components of the classical complement pathway, can recognize it. If everything goes right, these molecules bind to the Fc region and to each other, ultimately causing the perforation of the cell membrane thus the elimination of the antibody-tagged target cell.
There are four different subclasses of IgG antibodies (IgG1 - IgG4) in our blood that differ mainly in the length and flexibility of the so-called