What are the first cells in the epidermis that fight infection or invading microorganisms?

Langerhans cells are specialized immune cells located in the epidermis that play a critical role in the body's defense against infection and invading microorganisms. They originate from bone marrow and migrate to the skin, where they reside primarily in the stratum spinosum layer of the epidermis. Langerhans cells are equipped to identify and capture pathogens through processes such as phagocytosis. Once they encounter an invading organism, these cells can present processed antigens to T cells in the lymph nodes, thus activating the immune system to respond effectively. This capability marks them as key players in the skin's immune response.

Other cell types mentioned do not directly engage in fighting infections. Keratinocytes are the primary cells in the epidermis that produce keratin, forming a protective barrier. Melanocytes are responsible for producing melanin, which provides pigmentation to the skin and protects against UV damage but does not combat infections. Fibroblasts, found in the dermis, are involved in the formation of connective tissue and healing but do not have a direct role in immune defense within the epidermal layer.