Which cells in the epidermis are the first line of defense against infections or invading microorganisms?

The first line of defense against infections or invading microorganisms within the epidermis is provided by Langerhans cells. These specialized dendritic cells are strategically located in the skin's outermost layer and play a crucial role in the immune response. Langerhans cells help detect pathogens by capturing foreign substances, processing them, and presenting them to T cells in the lymph nodes. This initiates an adaptive immune response, thereby providing protection against potential infections.

In contrast, melanocytes are primarily involved in producing melanin, which helps protect skin from UV radiation but does not play a direct role in defense against infections. Keratinocytes, while serving as a physical barrier and involved in the skin's structural integrity, do not have the specific immune functions that Langerhans cells possess. Fibroblasts are found in the dermis and are responsible for producing collagen and other extracellular matrix components but are not involved in the immune defense mechanism of the epidermis.