Immunoglobulin G (IgG) is part of the family of glycoprotein immunoglobulins, which stage immune responses against pathogenic organisms. IgG antibody subtype is the most abundant of serum immunoglobulins of the immune system. It is secreted by B cells and is found in blood and extracellular fluids and provides protection from infections caused by bacteria, fungi and viruses. IgG contributes to the immune response by mobilizing innate immune effector cells and inducing and pro-inflammatory responses. Such proinflammatory responses are mediated by Fc gamma receptors which interact with sialylated Fc fragments on IgG molecules. The coupling of Cy5 to Anti-Human IgG antibody allows for the visualization of proteins by fluorescent microscopy.