on becomes bound to mast cells and basophils, and when its receptors ends are triggered by an antigen, it causes the cells to release histamine and other chemicals that mediate inflammation, and an allergic reaction. ??? ??? ??? IgG is the most abundant abundant and diverse antibody in plasma, 75% - 85% of circulating anitbodies. protects aganist bacteria, viruses, and toxins circulating in blood