L

With their dendrites, LCs form a close network inside the upper epidermis, which may be regarded as the first barrier of the

immune system

toward the environment. All

antigens

that penetrate into the human body through the

epidermal barrier

have to pass this first immunological wall of defense. Routine light microscopic examination (formaline fixation, paraffin embedding, HE staining) shows the LC as a clear cell, which can be separated from surrounding

keratinocytes

due to a fixation artifact. These clear nonkeratinocytes include melanocytes (mostly basal), Merkel cells (very rare), but mostly LCs. LCs can also be directly identified by immunohistological staining of their

surface molecules

HLA

-

DR

and

CD1

a.