Antigens are substances that trigger an immune response in the body. They can be found all around us, from the bacteria and viruses that cause infections to the food and pollen that we encounter on a daily basis. In biology, antigens can be broadly classified into two main types: self and non-self.
Self antigens are molecules that are produced by an organism’s own cells. They are critical for the proper functioning of the immune system as they help the body to recognize its own healthy cells and tissues, and therefore, avoid attacking them. Self antigens are unique to each individual and are determined by their genetic makeup.
One type of self antigen is major histocompatibility complex (MHC) molecules. These molecules are found on the surface of cells and act as markers that identify the cells as “self.” There are two main types of MHC molecules: class I and class II. Class I MHC molecules are found on almost all cells and present antigens from inside the cell, while class II MHC molecules are mainly found on immune cells and present antigens from outside the cell.
Another type of self antigen is the ABO blood group antigens. These are found on the surface of red blood cells and determine a person’s blood type. The body’s immune system is able to recognize and tolerate these antigens, which is why blood transfusions can only be successful if the donor and recipient have compatible blood types.
Non-self antigens, on the other hand, are substances that are recognized as foreign to the body. These can include bacteria, viruses, fungi, and other foreign particles. When the immune system encounters a non-self antigen, it triggers an immune response to destroy it and protect the body from harm.
One type of non-self antigen is pathogen-associated molecular patterns (PAMPs). These are structural components found on the surface of bacteria, viruses, and other microorganisms that are not present in the host’s cells. These patterns act as “flags” for the immune system to recognize and respond to, leading to the destruction of the invader.
Another type of non-self antigen is alloantigens. These are antigens that are produced by other members of the same species but are different from the individual’s own antigens. They are often involved in transplant rejections, where the recipient’s immune system attacks the transplanted organ or tissue as it contains foreign alloantigens.
In addition to self and non-self antigens, there are also autoantigens. These are self antigens that are recognized as foreign by the immune system and mistakenly attacked. This can result in autoimmune disorders, where the body’s immune system attacks healthy cells and tissues, leading to various diseases.
In conclusion, antigens play a crucial role in the body’s immune response. They can be classified into two main types in biology: self and non-self antigens. Self antigens are produced by the body’s own cells and are essential for distinguishing between self and non-self. Non-self antigens, on the other hand, are foreign substances that trigger an immune response to protect the body from harm. Understanding the different types of antigens is key in understanding how the immune system works and how it protects us from various diseases.