[Malpighian epithelia infected by DNA viruses and Langerhans cells]

Malpighian epithelia exhibit an immune surveillance through Langerhans cells (LC) against the DNA viruses, which induce various epithelial lesions, mainly on the skin, conjunctiva, mouth, uterine cervix. These viral infections are usual during childhood. The most common DNA viruses are: adenoviruses (more than 40 types), human papillomaviruses (HPV, more than 50 types) and Herpes viruses (herpes simplex type 1 and 2, varicella and Zooster, Epstein-Barr virus). Different clinical aspects are observed (exanthema, erythema, eruption, papillomas, vesicle, bullous) are well as histological signs. All of these viruses are replicating in the nuclei of epithelial cells which show eosinophilic inclusions and finally cell degeneresence with a typical aspect for each virus such as koilocyte for HPV infection. These lesions are commonly infiltrated with T lymphocytes; the intensity of the local cellular immune response varies with the lesion. LC are reduced in infected epithelia; they are sometimes found in conjunctive tissues and their morphology can be altered; their role in antigen presentation to T lymphocytes has only been demonstrated in herpes simplex virus infections. Profound modifications of membrane antigens of epithelial cells (loss of HLA class 1 antigen) might contribute to the disappearance of LC or to their functional inability. Most of the DNA virus infections are inapparent, benign and transient. However some lesions can evolve towards malignancy; this progression depends on the oncogenic potential of the viruses (such as HPV types 16 and 18 or herpes simplex virus type 2) associated to a local or a general immune deficiency of the patient as well as to other exogenous factors (UV for example).