Illustration of the main components of blood plasma, the liquid component of blood. At top left is a C1 complex (1) from the complement system. The complement system is a part of the innate immune system that complements the action of antibodies and phagocytic cells. Immunoglobulin G (IgG, 6, Y-shaped) and immunoglobulin M (IgM, 7, bottom left) antibodies are proteins produced by B-lymphocyte white blood cells as part of an immune response. Also seen are fibrinogen (2) and von Willebrand factor (3), which are proteins that facilitate blood clotting. Ferritin (4), a protein that acts as an iron store, is at top right. High and low density lipoproteins (HDL, 5, and LDL, 9) carry cholesterol around the body. The most abundant protein in the blood plasma is albumin (dark blue, 8), which transports hormones, fatty acids (orange) and many drugs.