What class of antibodies is responsible for causing hemolytic disease of the newborn?

Hemolytic disease of the newborn (HDN) primarily occurs due to the transfer of maternal antibodies across the placenta, leading to the destruction of fetal red blood cells. The specific class of antibodies responsible for this condition is IgG.

IgG antibodies are known for their ability to cross the placenta, which allows them to enter the fetal circulation. This is particularly significant in cases where the mother has developed antibodies against Rh(D) antigens present on the red blood cells of the fetus. When an Rh-negative mother carries an Rh-positive fetus, her immune system may recognize the fetal blood cells as foreign and produce IgG antibodies that can attack and destroy those cells, resulting in hemolysis.

IgA, IgE, and IgM do not play a significant role in HDN. IgA is mainly found in mucosal areas and provides protection in secretions; IgE is involved in allergic responses and defense against parasitic infections; and while IgM is the first antibody produced in response to an infection, it does not effectively cross the placenta like IgG. Thus, the detailed understanding of these different immunoglobulin classes highlights why IgG is specifically implicated in hemolytic disease of the newborn.