**Core Concept**
Celiac disease is a chronic autoimmune disorder characterized by an immune-mediated reaction to gluten, leading to small intestine mucosal damage and malabsorption of nutrients. The condition is triggered by the consumption of gluten, a protein found in wheat, barley, and rye.

**Why the Correct Answer is Right**
The immune response in celiac disease is mediated by T cells that recognize gluten peptides presented by HLA-DQ2 and HLA-DQ8 molecules. This triggers an inflammatory response in the small intestine, leading to the destruction of villi and the release of pro-inflammatory cytokines. The damage to the small intestine results in malabsorption of nutrients, including iron, calcium, and vitamin D.

**Why Each Wrong Option is Incorrect**
**Option A:** Celiac disease is caused by an allergic reaction to gluten. **Incorrect** because it is an autoimmune reaction, not an allergic response. Allergies involve the release of histamine and other mediators from mast cells, whereas celiac disease involves a complex immune response involving T cells and cytokines.

**Option B:** The only treatment for celiac disease is a gluten-free diet. **Incorrect** because, although a gluten-free diet is the primary treatment, a small percentage of patients may experience persistent symptoms or complications despite adherence to the diet.

**Option C:** Celiac disease is more common in children than adults. **Incorrect** because it is actually more common in adults, although it can present at any age. The diagnosis of celiac disease in children is often made incidentally during testing for other conditions.

**Clinical Pearl / High-Yield Fact**
Celiac disease is often associated with other autoimmune disorders, such as type 1 diabetes, autoimmune thyroid disease, and rheumatoid arthritis. Patients with celiac disease are also at increased risk of developing other conditions, including osteoporosis, anemia, and neurological disorders.

**Correct Answer:** B