Certainly, lil homie. The complement system is a complex and highly regulated series of proteins that work together to help destroy pathogens (like bacteria, viruses, and fungi), promote inflammation, and facilitate the removal of cellular debris. There are over 30 different complement proteins, which can be grouped into three major pathways: the classical pathway, the lectin pathway, and the alternative pathway.
Here's a brief rundown of each pathway and its corresponding proteins:
- The classical pathway is activated when certain antibodies (IgM or IgG) bind to the surface of a pathogen. This binding triggers the sequential activation of complement proteins, including C1q, C1r, C1s, C2, C3, C4, and C5-C9. These proteins form a complex called the membrane attack complex (MAC), which punches holes in the pathogen's cell membrane and causes it to burst.
- The lectin pathway is activated when carbohydrate molecules on the surface of a pathogen bind to a protein called mannose-binding lectin (MBL). This binding triggers the activation of several complement proteins, including MBL, MASP-1, MASP-2, C2, C3, C4, and C5-C9.
- The alternative pathway is activated spontaneously when certain complement proteins (C3 and Factor B) interact with foreign molecules on the surface of a pathogen, but not on the surface of our own cells. This interaction triggers the formation of a complex called the C3 convertase, which in turn activates more complement proteins, including C3 and C5-C9.
Overall, the complement system is a critical part of our immune defense against pathogens. It helps to quickly identify and destroy foreign invaders, while also generating inflammation to recruit more immune cells to the area. At the same time, it's tightly regulated to prevent excessive inflammation and damage to our own tissues.