A 20 year old college student working pa-time in a pediatric AIDS clinic develops a viral exanthem with a rash. Her blood is drawn and tested for specific antibodies to varicella-zoster (chickenpox). Anti-varicella immunoglobulin belonging to which of the following antibody classes would indicate that she is immune to chickenpox?

**Core Concept**
The question tests the student's understanding of the immune response to varicella-zoster virus (VZV) and the role of specific antibody classes in providing immunity against chickenpox. Varicella-zoster virus is a herpesvirus that causes chickenpox in children and shingles in adults. The immune system produces antibodies to fight off VZV infection.

**Why the Correct Answer is Right**
The correct answer is IgG, which indicates that the individual has developed a long-term immune response to VZV. IgG antibodies provide humoral immunity, protecting against future infections by neutralizing the virus and preventing its replication. In this case, the presence of anti-varicella IgG antibodies suggests that the student has been exposed to VZV in the past and has developed immunity to chickenpox.

**Why Each Wrong Option is Incorrect**
* **Option A:** IgM is the first antibody to be produced in response to an infection and indicates recent or acute exposure to the virus. It is not indicative of long-term immunity.
* **Option B:** IgA is primarily found in mucosal secretions and provides protection against infections of the respiratory and gastrointestinal tracts. It is not directly related to immunity against VZV.
* **Option D:** IgE is involved in allergic reactions and is not relevant to the immune response against VZV.

**Clinical Pearl / High-Yield Fact**
It's essential to note that IgG antibodies against VZV can persist for many years, providing long-term immunity against chickenpox. However, immunity can wane over time, making individuals susceptible to shingles later in life.

**Correct Answer:** C. IgG.

✓ Correct Answer: D. IgG