Intracellular Transport Of Human Class I Antigens And An Adenoviral Glycoprotein

Virally infected cells can only be recognized by cytolytic T lymphocytes provided viral products are expressed in the context of class I antigens of the major histocompatibility complex. To evade immune surveillance viruses may have acquired the ability to modulate the expression of such antigens. Recent reports have suggested that at least three types of viruses may interfere with the cell surface expression of class I antigens. While data for two of the viruses, cytomegalovirus and herpes simplex virus, are scant the information for the adenovirus family is substantial. Thus, it has been shown that the oncogenic adenoviruses of subgenus A selectively repress the transcription of class I antigens in infected cells. Adenoviruses of the other subgenera also reduce the cell surface ex-pression of class I antigens but by another mechanism. These viruses encode a membrane bound glycoprotein which is produced early during the infection. This protein, called E19, is a resident protein of the endoplasmic reticulum (ER) and forms complexes with class I antigens. The complex formation prevents the intracellular transport of the class I molecules. Class I antigens that already exist in the plasma membrane of the infected cell are gradually eliminated by normal turnover. This results in the infected cell becoming more resistant to the attack of cytolytic T lymphocytes.