(C) Type II hypersensitivity.
This clinician is concerned that the fetus may have erythroblastosis fetalis (hemolytic disease of the newborn). This disease is mediated by maternally derived IgG anti-Rh antibodies developed in Rh-negative mothers that are directed at the Rh antigen present on the fetal RBCs of a Rh-positive fetus in a previous pregnancy. If the mother possesses the antibodies developed from a previous exposure to an Rh-positive fetus, they may cross the placenta (antibodies of the IgG isotype readily cross the placenta) and coat the fetal RBCs of a Rh-positive fetus if the mother is now pregnant with another Rh-positive child. Antibody coating of the RBCs leads to phagocytosis of RBCs (via Fc receptors) and/or destruction of the RBCs by the complement system and potentially fatal anemia. This antibody-mediated cytotoxic reaction is an ex- ample of a type II hypersensitivity reaction.
Answer A is incorrect. GVHD is a potentially lethal side effect of bone marrow transplantation.
Answer B is incorrect. Type I hypersensitivity reactions are antibody-mediated but require antigen binding to IgE, which is prebound to the surface of mast cells. Mast cell degranulation then ensues. Examples include anaphylaxis, asthma, hives, and local wheal and flare.
Answer D is incorrect. Type III hypersensitivity reactions are immune complex-mediated. Examples include polyarteritis nodosa, glomerulonephritis, rheumatoid arthritis, and systemic lupus erythematosus.
Answer E is incorrect. Type IV hypersensitivity reactions are a group of T-cell-mediated pathologies. Examples include the tuberculin skin test, transplant rejection, and contact dermatitis.