Li Dan, Department of Clinical Laboratory, Strategic Support Force Characteristic Medical Center (formerly 306 Hospital).
Edited by Liu Yan/Cui Yan, Medical Science Popularization Center
Immunoglobulins (Ig) are globulins that have antibody functions or are chemically similar to antibodies. The immune function of the human body can generally be divided into cellular immunity (immune cells directly participate) and humoral immunity (immune cells are indirectly involved by secreting molecules such as immunoglobulins), and immunoglobulins are mainly involved in the humoral immune response of the human body.
In layman's terms, immunoglobulin is like a high-precision sniper rifle, consisting of a scope (antigen recognition zone) and a rifle (constant zone). According to the different amino acid composition and characteristics of the constant region, immunoglobulins can be divided into the following five categories: IgG, IgM, IgA, IgE, and IgD.
(1) IgG: It has the highest content in the five kinds of immunoglobulins in the blood, accounting for 75%~80%, and is the main antibody of humoral immune response, with high affinity for antigens such as invading pathogens, and plays an important role in the body's immune defense against infection and neutralization of toxins. IgG is also the only immunoglobulin that can cross the placenta, which is an important means of anti-infection immunity in neonates. Most antibacterial antibodies, antiviral antibodies, and most autoantibodies fall into this category.
(2) IgM: The body is often composed of five monomeric IgM pentamers (everyone must be impressed by the firepower of "double launchers" and "triple shooters" in "Plants vs. Zombies"), IgM is the earliest immunoglobulin in the initial humoral immune response, which plays an important role in the body's early immune defense. The presence of IgM in the blood usually indicates a recent infection and is often used by doctors to diagnose infectious diseases early.
(3) IgA: divided into serotype and secretory type. The latter is often composed of two molecules composed of dimers, which are secreted into the mucosa of the respiratory tract and digestive tract through epithelial cells, and are mainly involved in local mucosal immunity. One of the advantages of nasal spray vaccines developed during the pandemic is that they can induce the production of IgA, which provides additional protection for the mucous membranes of the respiratory tract, the site of invasion of the coronavirus.
(4) IgE: Although it is the least abundant immunoglobulin in human blood, IgE is closely related to human allergic diseases, causing symptoms such as skin itching, redness and swelling, shortness of breath, and runny nose. IgE levels of specific allergens are often measured to determine whether a person is allergic to an allergen. In addition, most people are infected with parasites and have elevated IgE levels.
(5) IgD: Compared with the first four immunoglobulins, the biological function of IgD is still unclear. Only one of the rarer forms of multiple myeloma is known to be significantly elevated.
In short, immunoglobulin determination is an important means to reflect the immune function of the human body, and the five immunoglobulins perform their respective functions and construct the basic line of defense of humoral immunity.
(The picture comes from the Internet)