Human antigens include blood factors and those that help the body distinguish between foreign and healthy cells. Blood type is determined by the presence or absence of A and B antigens, and transfusions should not contain unknown antigens. Antigens are identified by the human leukocyte antigen system encoded on DNA. Exogenous antigens enter the body and are considered hostile, while endogenous antigens are foreign invaders within healthy cells.
The most common human antigens are blood factors, which determine a person’s blood type. Human antigens also include those antigens that help antibodies attach to and destroy foreign proteins that can cause harm to a person’s body. These antigens help the body distinguish cells that belong in a person’s system from foreign cells or proteins that need to be removed.
Human blood cells can contain one or both of the two human antigens. These human antigens are called A and B, and their presence or absence determines a person’s blood type. People with blood type A have human A antigen and those with blood type B have human B antigen. An individual with blood type AB has both, and people with blood type O have neither of these antigens on their Red blood cells . There is also a human blood antigen that determines whether a person has a positive or negative blood type.
The presence of a blood group antigen means that the corresponding antibody is absent from a person’s system. Conversely, the absence of certain antigens means that the person creates antibodies for those particular antigens, which is why blood transfusions should not be given if they contain a human antigen not normally present in the patient’s body. For example, a person with blood type A should not receive a transfusion of blood type B. Unknown blood antigens cause an immune response, which can lead to serious complications or even death of the patient.
A human antigen is created by the human leukocyte antigen system, which helps identify antigens that belong to foreign proteins. The human leukocyte antigen system is encoded on human deoxyribonucleic acid (DNA) on the sixth chromosome. This section of DNA is used to make proteins that recognize antigens. The process of identifying an antigen is called antigen presentation.
Most of the antigens in the human body are those that have entered the body through the air, bloodstream or digestive tract. These are called exogenous antigens and are considered hostile by the human immune system. The other types of antigens that exist within a person’s body are called endogenous antigens. They are often foreign invaders that have taken over a healthy human cell and replicated within it. The presentation of the antigen allows these invaders to be identified and destroyed by antibodies in the immune system.
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