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The Five Antibody Classes in Placental Mammals

Antibodies are special antibody proteins produced by the immune system. They protect the body from being invaded by infections and diseases by "recognizing" viruses, bacteria, and infected cells. In placental mammals, there exist five different types of antibodies, or antibody classes or isotypes, which define what role the antibody plays in the body. This article will walk you through these antibody classes.

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The Five Antibody Classes in Placental Mammals

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  1. The Five Antibody Classes in Placental Mammals Creative Biolabs

  2. Introduction Antibodies are special antibody proteins produced by the immune system. They protect the body from being invaded by infections and diseases by "recognizing" viruses, bacteria, and infected cells. In placental mammals, there exist five different types of antibodies, or antibody classes or isotypes, which define what role the antibody plays in the body. This article will walk you through these antibody classes.

  3. II. IgG The five antibody classes are named using the convention Ig*, where Ig stands for immunoglobulin and * for the specific isotype. IgG ( including the idiotype and camel antibodies) accounts for approximately 70 ~ 80% of the immunoglobulin content, half of which exists in plasma. When stimulated by an antigen for the first time, the body can immediately produce IgG, at a rate only slower than producing IgM. Besides, IgG plays a major role in anti-infective immunity mediated by antibodies. IgG, whose molecular weight ranges from 160,000 to 180,000, can resist the invasion of bacteria, viruses and other microorganisms. In in vitro serological reactions, it also engages in the precipitation reaction, agglutination reaction, complement binding reaction and neutralization reaction.

  4. III. IgM In serum, the content of IgM is second only to IgG. As the largest globulin in the body, IgM has a molecular weight of about 900,000. This immunogloblin mainly distributed in the blood vessels can lyse cells, bacteria and neutralize viruses by activating complements. It has a immune function 100 times stronger than that of IgG. Since the content of IgM occupies only 1/10 of IgG and this antibody functions for a very short time, it cannot play a major role in anti-infection immunity. In in vitro serological reactions, it’s involved in agglutination reaction and complement binding reaction.

  5. IV. IgA IgA comes in monomer and dimer forms. The former exists in the serum, with a molecular weight of about 170,000. The monomer, also known as serotype IgA, can fight against bacteria and viruses. The dimer is mainly found in external secretions, such as saliva, colostrum, tears and tracheal secretions, of which colostrum has the highest content. IgA in the dimer form, also known as secretory IgA, is produced by plasma cells present in the mucosa and tissues. Having a molecular weight of 400,000 and a content 6-8 times higher than that of monomer, the dimer serves as an important defense factor of mucosa that can prevent bacteria or viruses from adsorption on the mucosal surface.

  6. V. IgE IgE is a special glycoprotein with an antibody molecular weight of 190,000. It’s produced by plasma cells in the mucosa propria of the digestive tract and respiratory tract, and local lymph nodes. It occupies a tiny proportion in serum. As a kind of sensitizing antibody, it can easily adsorb on the surface of bacteria and cause allergic reactions when binding to certain antigens. It hardly helps fight against bacterial and viral infections. IgD, present on the naïve B cell membrane, can activate basophils and mast cells to produce antimicrobial factors. Currently, the research about this type appears quite limited in comparison to the other ones.

  7. VI. Conclusions Each of the five antibody classes differs from each other whether in terms of locations or roles they play in the immune system. To some extent, this way to categorize antibodies gives us a keen insight into the natural antibodies in placental mammals. However, this is simply one of the many ways to classify antibodies. As the research about antibodies goes deeper and deeper, there may be more precise perspectives to help us understand the different classes of antibodies in a better manner.

  8. About Creative Biolabs Creative Biolabs is a leading custom service provider, boasting rich experience in antibody production and engineering. Its service portfolio includes mouse and rat monoclonal antibody production using hybridoma technology, human, monkey, rabbit, chicken, dog, llama and camel monoclonal antibody production using various antibody library technologies. In addition, the company also conducts in-depth antibody humanization and affinity maturation.

  9. Thanks for your attention!

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