Immunoglobulin A has the following characteristics:

b) exists in serum and secretory forms;

c) does not pass through the placental barrier;

d) exists in the form of a monomer, with 2 antigen-binding centers and in polymeric form in the form of a di- or trimer;

e) prevents the adhesion of microbes on epithelial cells and the generalization of infection within the mucous membranes;