With the intention of providing an antibody which does not bind to fibrinogen and which has a high affinity for and a high specificity to insoluble fibrin, it is found that a site comprising the amino acids at positions 231 to 246 of the fibrinogen Bβ chain and a site comprising the amino acids at positions 232 to 246 of the fibrinogen γ chain are bound to each other in a fibrinogen molecule. Further, it is shown that when fibrinogen is converted to insoluble fibrin, the binding is released, and these sites are exposed. It is also found that antibodies obtained by immunization with these sites do not bind to fibrinogen and have high affinity for and high specificity to insoluble fibrin.
