Immunoglobulin G (IgG) is a type of antibody found in the blood and extracellular fluid. It plays a crucial role in the immune system by identifying and neutralizing pathogens like bacteria and viruses. IgG is the most abundant antibody, making up about 75% of the total immunoglobulin in the body. IgG is produced by B cells, a type of white blood cell, in response to infections or vaccinations. It can also cross the placenta, providing passive immunity to the fetus during pregnancy. This ability makes IgG essential for long-term protection against diseases.