C4 protein

C4 protein

C4 protein is one of the complement components that helps start and shape the immune response when certain triggers are present. When it is activated, C4 is split into fragments that help assemble the machinery needed to activate the central components of the system and to tag microbes or damaged cells for removal. One fragment can attach to a surface and act as a platform for further steps in the cascade, while the other can promote inflammation and recruitment of immune cells. C4 mainly participates in the classical and lectin pathways, which respond to antibodies or certain sugar patterns on microbes, respectively. Because it helps form the enzyme complexes that drive the rest of the response, C4 is important for efficient clearance of pathogens and immune complexes. Variations in C4 levels or function are linked to differences in susceptibility to infections and to autoimmune conditions where the immune system attacks the body’s own tissues. Doctors sometimes measure C4 as part of immune testing to help diagnose or monitor these conditions. Understanding how C4 works also helps researchers design therapies that can reduce harmful inflammation without shutting down needed defense functions.