**Core Concept:** HLA (Human Leukocyte Antigen) is a group of proteins on the surface of cells that play a crucial role in immune system functioning. HLA-I is a subset of HLA proteins that are involved in presenting intracellular proteins to CD8+ T cells, thereby activating cytotoxic T cells and regulating immune responses.

**Why the Correct Answer is Right:** HLA-I is found on the surface of nucleated cells, including epithelial cells, endothelial cells, macrophages, and dendritic cells. It presents endogenous antigens (proteins generated within the cell) to cytotoxic T cells, which are responsible for identifying and eliminating infected or damaged cells. This helps maintain immune surveillance and prevents autoimmunity.

**Why Each Wrong Option is Incorrect:**

A. Epithelial cells and endothelial cells express HLA-I, so this option is partially correct but lacks specificity.
B. HLA-II is another subset of HLA proteins involved in presenting exogenous antigens (antigens from extracellular sources). Since HLA-I presents endogenous antigens, this option is incorrect.
C. Dendritic cells are a type of antigen-presenting cell (APC) and do express HLA-I, but the question asks about the cells that express HLA-I generally, not specifically.
D. Macrophages are another type of APC that express HLA-I, but the question asks about cells that express HLA-I generally.

**Clinical Pearl:** The correct answer highlights the importance of the HLA system in immune surveillance and maintaining immune homeostasis, while the wrong options emphasize the roles of specific cell types and subsets within the HLA system.

**Correct Answer:** C. Dendritic cells express HLA-I, making this the correct option.