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The Rh factor and hemolytic disease

The Rh factor or rhesus factor is an antigen on the surface of red blood cells named after the monkeys in which it was first discovered. Rh incompatibility or Rh disease occurs when a woman that is Rh- (no Rh antigens in her RBC’s) is exposed to Rh+ red blood cells leading to the production of Rh antibodies.

Rh incompatibility can occur through two main mechanisms:

1) An Rh- mother and an Rh+ father produce a baby that is Rh+. This is not usually a problem during the pregnancy because the fetal blood cells do not cross the placenta and cause the production of antibodies. However, upon delivery, fetal blood may mix with maternal blood causing the production of Rh antibodies. These antibodies remain in the maternal bloodstream. If the mother gets pregnant with another Rh+ baby, the antibodies will cross the placenta and attack the Rh+ baby’s blood causing a condition called erythroblastosis fetalis.

2) An Rh- woman may receive an Rh+ blood transfusion and develop antibodies to the Rh antigen. If she has an Rh+ baby afterwards, the antibodies will cross the placenta and attack the Rh+ blood (as in example # 1).

Some immune disorders/diseases

1) Allergies – hypersensitive responses to molecules that are not normally antigens called allergens such as pollen grains, dust, food, or drugs. The common symptoms of watery eyes, sneezing, develop of hives are caused by the release of histamines by sensitized mast cells or basophils. In extreme cases, anaphylactic shock or death could ensue.

2) Autoimmune diseases – occurs when an organism fails to recognize its own “self” molecules leading to the body mounting an immune response against its own cells. Prominent autoimmune diseases include insulin-dependent diabetes (damage of pancreatic cells), systematic lupus erythematosus or SLE (immune system may attack any cell or organ in the body), rheumatoid arthritis (damage in the joints), and multiple sclerosis (damage in the nerve cells).

3) Immunodeficient diseases – occur when the immune system’s ability to fight infectious disease is compromised or absent. Usually, the second and third lines of defense are weakened. Patients often suffer from prolonged and repeated infections.

a. Primary immunodeficiency – hereditary, congenital (from birth) – examples include a lack of B- and/or T-cells, phagocytes, antimicrobial proteins, etc.

b. Secondary or acquired immune deficiency – may be caused by drugs (such as those given when an organ transplant is accepted or those given when a patient undergoes chemotherapy) or a virus such as the human immunodeficiency virus (HIV) that destroys the helper cells that play a critical role in immune response. HIV infection leads to a series of conditions that together are called AIDS (Acquired Immune Deficiency Syndrome).

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