Expression of Ia antigen on epidermal keratinocytes is a consequence of cellular immunity

Ia antigen is seen in the normal epidermis only in Langerhans cells. However, when there is damage to the epidermis induced by cellular immunity Ia is expressed in the keratinocytes. This phenomenon is not seen in trauma or chemical inflammation. It is suggested that the expression of Ia in keratinocytes is due to cellular immunity possibly due to a lymphokine.