Immunoglobulin, abbreviated as Ig, is a group of globulins that have antibody (Ab) activity or a chemical structure similar to antibody molecules. Immunoglobulins are composed of two identical light chains and two identical heavy chains connected by interchain disulfide bonds, forming a tetrapeptide chain structure. Immunoglobulins can be divided into five types, namely immunoglobulin G (IgG), immunoglobulin A (IgA), immunoglobulin M (IgM), immunoglobulin D (IgD), and immunoglobulin E (IgE).