The Epidermis as an Outpost of the Immune System

The principle task of the immune system is to protect the host by eliminating or neutralizing foreign molecules. The epidermis is a site of antigen entry and destruction. It also contains cells which participate in the initiation and regulation of immune response. Many of the most common skin disorders involve immune response. These include psoriasis, cancer and eczema.

Specialized cells called Langerhans cells, present in the epidermis, process and present antigens to T lymphocytes and can initiate antigen specific immune responses.

Keratinocytes, the hard, scaly cells of the outer epidermis, are capable of secreting a wide variety of immuno-modulating cytokines that can regulate (up or down) many immune responses. T cells are not usually present in the epidermis, arriving when mediated by Langerhans cells and cytokines.

The epidermis is a formidable barrier, both physically and chemically. It's pH controls the presence and balance of microbes on its surface to further inhibit dangerous inhabitation.