Erythroblastosis-foetalis is a example of which type of hypersensitivity reaction:
**Core Concept**
Erythroblastosis-fetalis is a condition characterized by the hemolysis of fetal red blood cells, leading to anemia and potential fetal distress. This condition is primarily caused by the maternal immune system reacting to antigens present on the fetal red blood cells, resulting in the production of antibodies that target the fetus.
**Why the Correct Answer is Right**
The correct answer is an example of a Type II hypersensitivity reaction, also known as cytotoxic hypersensitivity. In this reaction, antibodies produced by the maternal immune system bind to antigens on the surface of the fetal red blood cells, marking them for destruction by complement or phagocytosis. The primary antibody responsible for this reaction is IgG, which is able to cross the placenta and reach the fetus.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Type I hypersensitivity reactions are mediated by IgE antibodies and are typically associated with allergic responses, such as anaphylaxis.
**Option B:** This option is incorrect because Type III hypersensitivity reactions involve the formation of immune complexes, which deposit in tissues and cause damage, but are not directly responsible for the hemolysis seen in erythroblastosis-fetalis.
**Option C:** This option is incorrect because Type IV hypersensitivity reactions are cell-mediated and involve T lymphocytes, but are not directly responsible for the hemolysis seen in erythroblastosis-fetalis.
**Clinical Pearl / High-Yield Fact**
Erythroblastosis-fetalis is a classic example of a Type II hypersensitivity reaction, and is often caused by Rh incompatibility between the mother and fetus. This condition highlights the importance of Rh typing and screening in pregnant women to prevent hemolytic disease of the newborn.
**Correct Answer: C. Type II hypersensitivity reaction.**