BIOLOGICAL IMPLICATIONS OF HLA-DR EXPRESSION IN TUMORS

HLA-DR antigens show restricted tissue distribution in comparison with the more extensive expression of HLA class I molecules. This constitu tive expression is genetically controlled by well-defined mechanisms. In addition, DR antigen expression can be induced by a variety of cyto kines through different molecular genetic events that convert DR-negat ive epithelia into positive cells. In this review we analyse the two m ajor pathological situations in which abnormal DR expression occurs: a utoimmune diseases and tumour development. We hypothesize that convers ion to DR-positivity may produce two opposite effects in both clinical situations: (1) a useful one in tumours associated with a good progno sis; and (2) a harmful one in autoimmune diseases with increased tissu e damage.