A2AP

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α2-Antiplasmin (α2-AP) is a glycoprotein body synthesized by the liver. α2-Antiplasmin combines with plasmin and inactivates it. Plasma α2-antiplasmin detection includes the determination of its activity and antigen, and can be used as an auxiliary diagnostic method for arterial and venous thrombosis, malignant tumors and α2-AP deficiency diseases.

Figure 1. Structure of α2-AP.

Inspection Method

1. α2-AP activity detection

After adding plasmin and chromogenic substrate to test plasma and normal control plasma diluted with different concentrations for a certain period of time, colorimetry is performed at 405nm wavelength, and the standard curve is checked to obtain the activity of test plasma α2-AP.

2. α2-AP content detection

Add the known standard and the specimen to be tested into the microwells of an enzyme-linked reaction plate coated with anti-α2-AP antibody, and incubate at 37°C to make α2-AP and its antibody fully bind. After washing several times, add the same antibody labeled with enzyme and incubate at 37°C to form an antibody-α2-AP-enzyme-labeled antibody complex. Wash off the unbound enzyme-labeled antibody and then add the enzyme substrate. The substrate is hydrolyzed by the enzyme to develop color. The stop solution is added to terminate the reaction. The absorbance is measured at 450nm wavelength, and the standard curve is checked to obtain the antigen content of the tested plasma α2-AP.

Clinical significance

1. Reduce

It is seen in severe liver disease, post-surgery, diffuse intravascular coagulation (DIC) and hereditary α2-AP deficiency. Plasma α2-antiplasmin antigen and activity are reduced in type I patients, and α2-antiplasmin antigen in type II patients Normal, but its activity is reduced. There are very few cases of A2AP deficiency (<20). As plasmin degrades blood clots, the weakening of the inhibition of plasmin leads to a bleeding tendency, which is more severe in the reported cases. In liver cirrhosis, the production of α2-antiplasmin is reduced, resulting in reduced inactivation of plasmin and increased fibrinolysis. This is related to an increased risk of bleeding from liver disease.

2. Increase

Seen in physiological changes, such as pregnancy, childbirth and menstruation. Pathological changes include arterial and venous thrombosis and malignant tumors.

Interactions

Alpha 2-antiplasmin has been shown to interact with neutrophil elastase and plasmin.

Neutrophil elastase

Neutrophil elastase is a serine protease of the same family as chymotrypsin and has broad substrate specificity. Secreted by neutrophils and macrophages during inflammation, it destroys bacteria and host tissues. It also locates in neutrophil extracellular traps (NETs) by its high affinity for DNA, which has unusual properties for serine proteases.

Figure 2. Structure of neutrophil elastase.

Plasmin

Plasmin is a serine protease that can dissolve fibrin. In addition to fibrinolysis, plasmin also proteolyzes proteins through many other systems: it activates collagenase (some mediator of the complement system) and weakens the walls of Graafian follicles, leading to ovulation. Fibrinolytic enzyme is also involved in inflammation. It cleaves fibrin, fibronectin, thrombospondin, laminin and von Willebrand factor. Plasma proteins, like trypsin, belong to the serine protease family.

Figure 3. Structure of plasmin.