which antibody class is most prevalent in the bloodstream?
1 IgM. 2  IgM antibodies are the largest antibody. 3  They are found in blood and lymph fluid and are the first type of antibody made in response to an infection. 4  They also cause other immune system cells to destroy foreign substances. 5  IgM antibodies are about 5% to 10% of all the antibodies in the body. 6  IgE.