There are four IgG subclasses (abbreviated simply as IgG1, 2, 3 and 4) in humans, named in order of their abundance in serum ( being the most abundant). A cleavage reaction using papain can result in Fc and Fab fragments and a Fc fragment. Proteolytic enzyme pepsin cleaves below the hinge region, forming a F(ab')2- and a pFc' fragment. The F(ab')2 fragment can be split further into two Fab' fragments by reduction.
Functions of IgG
antibodies are involved in the secondary immune response (IgM is the main antibody involved in primary response). IgG can bind pathogens, like for example viruses, bacteria, and fungi, and thereby protects the body against infection and toxins. Comprising up to 80% of the antibodies found in the human body, IgG is the smallest, yet most abundant human antibody, and that of other mammals. can be found in all bodily fluids, and is the only antibody that can protect a foetus by passing through the mother's placenta.