A 34-year-old female has recently been diagnosed with an autoimmune disease. She has also recently discovered that she is pregnant. Which of the following is the only immunoglobulin that will provide protection to the fetus in the womb?
A. IgA
B. IgD
C. IgE
D. IgG
Correct Answer: D. IgG
IgG is the only immunoglobulin that can cross the placental barrier. About 70-80% of the immunoglobulins in the blood are IgG. Specific IgG antibodies are produced during an initial infection or other antigen exposure, rising a few weeks after it begins, then decreasing and stabilizing. The body retains a catalog of IgG antibodies that can be rapidly reproduced whenever exposed to the same antigen. IgG antibodies form the basis of long-term protection against microorganisms.
Option A: IgA antibodies protect body surfaces that are exposed to outside foreign substances. Immunoglobulin A (IgA) is the first line of defence in the resistance against infection, via inhibiting bacterial and viral adhesion to epithelial cells and by neutralisation of bacterial toxins and virus, both extra- and intracellularly. IgA also eliminates pathogens or antigens via an IgA-mediated excretory pathway where binding to IgA is followed by poly immunoglobulin receptor-mediated transport of immune complexes.
Option B: IgD antibodies are found in small amounts in the tissues that line the belly or chest. Secreted IgD appears to enhance mucosal homeostasis and immune surveillance by “arming” myeloid effector cells such as basophils and mast cells with IgD antibodies reactive against mucosal antigens, including commensal and pathogenic microbes.
Option C: IgE antibodies cause the body to react against foreign substances such as pollen, spores, animal dander. IgE antibodies are found in the lungs, skin, and mucous membranes. They are involved in allergic reactions to milk, some medicines, and some poisons.