Background
Defensins are small positively charged peptides (29–47 amino acids) that are highly conserved among species and play a role in host defense against bacteria and viruses. There are two categories of defensins: A-defensins are secreted from human neutrophils, and B-defensins are produced from the epithelial cells. Each peptide contains six cystein amino acid residues, connected with disulfide bonds. The physicochemical properties of defensins are similar with the properties of another molecule, B2-glycoprotein I (B2-GPI), the major target of the autoantibodies found in the sera of patients with antiphospholipid syndrome (APS).