Based on the five immunoglobulin classes, what is the difference between Anti-B antibodies of a...


Based on the five immunoglobulin classes, what is the difference between Anti-B antibodies of a mother rarely affect the RBCs of a type B fetus? Yet anti-D antibodies of an Rh- woman sometimes cross the placenta and hemolyze the RBCs of an Rh+ fetus.


Antibodies, also known as immunoglobulins, are large proteins secreted by activated B cells (called plasma cells) after antigenic stimulation. There are five major classes of immunoglobulins - IgM, IgG, IgE, IgA and IgD, which differ from each other by the type of the heavy chain in their structure. They also have different functions and are produced selectively based on the antigen that has to be eliminated. Two of them, IgM and IgD, act as B cell receptors (BCRs) on the surface of naive B cells. Each monomeric antibody is composed of 2 identical light and 2 identical heavy chains, linked together by disulfide bridges. Some immunoglobulins, however, exist in the form of polymers, namely IgA can be dimeric or trimeric, whereas IgM, when secreted by plasma cells, has a pentameric structure. IgG is the most abundant antibody in serum and is the major antibody in the late primary and in the secondary immune response. An important feature of this antibody is that it can cross the placenta.

Answer and Explanation: 1

There is a huge variety of blood-group antigen systems, the most important of them being the ABO(H) system and the Rhesus system. An interesting feature of the ABO(H) system is that a person of a certain blood group has naturally existing IgM antibodies in his/her serum against the missing antigens. For example, if someone is blood group A and hence possesses antigen A on the surface of their erythrocytes, then they have anti-B antibodies in their serum. The presence of natural antibodies, i.e. antibodies that are not produced upon antigenic stimulus, has important implications for blood transfusion. The most important antigen of the Rhesus system is the D antigen. Importantly, anti-D antibodies in D-negative individuals are produced only in case of incompatible blood transfusions and do not naturally exist in serum. Anti-D antibodies can be produced by a Rh- woman in case the erythrocytes of a Rh+ fetus enter the woman's body, which usually happens during childbirth, but can also occur in case of abortion or ectopic pregnancy. If the woman gets pregnant with a second child that is Rh+, the anti-D antibodies produced after the first pregnancy can "attack" the fetal erythrocytes and cause hemolysis. This condition is called "hemolytic disease of the newborn" and is due to the fact that anti-D antibodies belong to the the immunoglobulin G class - the only immunoglobulin that can cross the placenta. To prevent this disease, the Rh- woman is immunized with anti-D antibodies after the first childbirth - this prevents the activation of her immune response and the development of long-lasting immunity against the D antigen. If the mother is B- and the fetus is B+, nothing is going to happen because the naturally existing anti-B antibodies in the mother's serum are IgM antibodies and they cannot cross the placenta.

Learn more about this topic:

Rh Blood Group, Rh Factor & Erythroblastosis Fetalis


Chapter 13 / Lesson 6

The Rh blood group system is a classification system for blood based on the presence or absence of Rh antigen. Individuals who possess the Rh antigen are considered Rh positive, whereas individuals who do not carry the antigen are considered Rh negative. Learn about blood groups, the Rh blood group system, Rh negative blood, and the effect of Rh factor in erythroblastosis fetalis.

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