-most abundant

  -found in blood and lymph and intestines

  -fights bacteria and viruses and their toxins

  -only Ab that crosses the placenta

  -found in sweat, tears, mucus, saliva, breast milk, GI secretions, blood and lymph.

  -fight bacteria and viruses on mucous membranes (*prevents pathogens from adhering to epithelia and penetrating other tissues)

  -provides passive immunity to newborn

  -found in blood and lymph

  -1st Ab secreted

  -anti-A and anti-B antibodies  of ABO blood group that bind to antigens A and B during incompatible blood transfusions are IgM Abs

  -found in blood and lymph and on surface of B cells as antigen receptors

  -activate B cells

  -found on surface of mast cells and basophils where they stimulate release of histamine.

  -involved in allergic and hypersensitivity reactions

  -attracts eosinophils to site of parasitic infections