11.2 - Actions of Antibodies

There are five main mechanisms that the antibodies use to remove foreign antigens. For instance, agglutination , neutralization , opsonization , precipitation and lysis.

1. Agglutination

• Antibodies bind to surface antigens and a clump is formed. The bigger molecule then becomes an easy target for macrophage to phagocytose.

Figure 12 - This happens when incompatible blood types are mixed. For example, blood type A is incompatible with blood type B. Therefore, the wrong blood transfusion can be fatal.

2. Neutralization

• Antibodies bind and neutralize the toxins produced bacteria and render it ineffective.

Figure 13 - A neutralizing antibody is capable of blocking the entry of pathogens by binding to them.

3. Opsonization

• A process where antigens were marked by binding antibodies. The marker facilitates phagocytosis.

Figure 14 - Antibodies such as IgG and IgE are opsonins. Opsonized foreign antigens will be targeted by phagocytes to be eliminated.

4. Precipitation

• Antibodies bind to soluble antigens to form an insoluble product which can be easily removed by phagocytes.

Figure 15 - This reaction is more commonly seen in tests/assays to determine the presence of pathogens in patients' serums.

5. Lysis

• Antibodies bind to antigens such as bacteria. It activates the complement system which forms pores in the bacterial cell wall. Eventually, the cell wall breaks down and the bacteria lyse.

Figure 16 - Pathogens like bacteria have cell walls which can be easily targeted. The complement system is activated to lyse their cell walls (basically it is creating holes at the cell wall).