What layer of skin contains the majority of the immune response cells, including macrophages?

The dermis is the layer of skin that contains a significant concentration of immune response cells, including macrophages. This is crucial for the immune function of the skin, as the dermis is the thicker layer beneath the epidermis that provides mechanical support and contains blood vessels, nerves, and various cell types involved in immune responses.

Macrophages in the dermis play a vital role in detecting pathogens and orchestrating immune responses. They can engulf and digest foreign material, which helps to protect the body against infections. Additionally, the dermis houses other immune cells, such as mast cells and lymphocytes, contributing to a robust immune surveillance system.

In contrast, the epidermis is primarily composed of keratinocytes and lacks significant immune cells like macrophages. The hypodermis, or subcutaneous layer, serves mainly as a fat storage area and insulation, while the stratum corneum is the outermost layer of the epidermis, consisting of dead keratinized cells that provide a barrier to the external environment but lacks immune cells. Hence, the dermis is the correct answer, as it is the layer where the majority of immune response cells are found.