Antigen is a harmful substance which enters the body which causes the body to make antibodies as a response to fight off disease. An example of an antigen is a common cold virus which causes the body to make antibodies which help prevent the person from getting sick. Antigens are usually proteins, peptides (amino acid chains) and polysaccharides (chains of monosaccharide’s/simple sugars) but lipids and nucleic acids become antigens only when combined with proteins and polysaccharides.

A blood protein produced in response to counteracting a specific antigen. Antibodies combine chemically with substances which the body recognizes as alien, such as bacteria, viruses, and foreign substances in the blood.

Your immune system makes antibodies to fight things it sees as "not you." Most of the time, that's great because antibodies usually target germs. And when you're pregnant, your immune system takes care of your baby, too. But if your red blood cells are different from your baby's, that may cause problems.

During pregnancy, the RBC antibody screen is used to screen for antibodies in the blood of the mother that might cross the placenta and attack the baby's red cells, causing hemolytic disease of the newborn. An Rh-negative mother may develop an antibody when she is exposed to blood cells from an Rh-positive fetus.

Both Kell antigens and Rh incompatibility may cause a mother to make antibodies against her baby's blood. The antibodies can destroy the baby's red blood cells, causing a severe form of anemia. But you can get a treatment that will prevent you from making antibodies that could harm your baby.

There are many types if antibodies:-

  • Immunoglobulin G (IgG): is a type of antibody. Representing approximately 75% of serum antibodies in humans, IgG is the most common type of antibody found in blood circulation. IgG molecules are created and released by plasma B cells. IgG protects against bacterial and viral infections. IgG can take time to form after an infection
  • Immunoglobulin M (IgM): Found mainly in blood and lymph fluid, this is the first antibody the body makes when it fights a new infection.
  • Immunoglobulin D (IgD): This is the least understood antibody, with only small amounts in the blood.
  • Immunoglobulin E (IgE): Normally found in small amounts in the blood. There may be higher amounts when the body overreacts to allergens or is fighting an infection from a parasite.
  • Immunoglobulin A (IgA): It's found in the linings of the respiratory tract and digestive system, as well as in saliva (spit), tears, and breast milk.

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