_____ is the most abundant class of antibodies in serum
Immunoglobulin G (IgG) is the most abundant circulating antibody, making up 80% of the total antibodies and 75% of that found in serum. It contains a single antibody protein complex, with two heavy chains and two light chains.
There are four IgG subclasses (IgG1, 2, 3, and 4) in humans, named in order of their abundance in serum (IgG1 being the most abundant). Note: IgG affinity to Fc receptors on phagocytic cells is specific to individual species from which the antibody comes as well as the class.