**Core Concept:** Contact dermatitis is an inflammatory skin condition caused by an allergic or irritant reaction to external stimuli. It involves the activation of immune cells and the release of inflammatory mediators.

**Why the Correct Answer is Right:** In contact dermatitis, the major cells that play a significant role include:

1. **Option C: Langerhans cells:** These are dendritic cells located in the epidermis that act as antigen-presenting cells, playing a crucial role in the initiation of adaptive immune responses. In contact dermatitis, they present the foreign antigen to T cells, leading to their activation and migration to the dermal-epidermal junction.

2. **Option D: Mast cells:** These cells are involved in the early phase of contact dermatitis. They release histamine and other inflammatory mediators, leading to vasodilation, increased vascular permeability, and pruritus (itching).

3. **Option A: Eosinophils:** Although eosinophils are involved in the later phase of contact dermatitis, they are not the major cells involved in the initial stages.

**Why Each Wrong Option is Incorrect:**

1. **Option B: Neutrophils:** Neutrophils are involved in the later phase of contact dermatitis, particularly in resolving the inflammation. They play a secondary role compared to mast cells and eosinophils.

2. **Option A: Eosinophils:** While eosinophils are involved in the later phase of contact dermatitis, they are not the primary cells responsible for the initial stages of inflammation. The primary cells are Langerhans cells, mast cells, and neutrophils.

**Clinical Pearl:** An understanding of the cell types involved in contact dermatitis is crucial for understanding the pathogenesis and treatment approaches in this condition. Knowledge of the role of these cells helps dermatologists in formulating an appropriate diagnosis and treatment plan.

In summary, the correct answer is options C, D, and A. Langerhans cells, mast cells, and eosinophils contribute to the early phase of contact dermatitis. Mast cells and eosinophils are also involved in the later phase, but the primary cells are Langerhans cells, mast cells, and neutrophils.