Induction of erythrocyte HLA expression during interferon treatment and HIV infection.

Although HLA antigens are present on the surface membrane of most cells, erythrocytes express little or no HLA. Occasionally red cells from normal individuals or patients with certain diseases express elevated levels of these molecules. The reasons for such variations are currently not understood. We report here that the expression of very high levels of HLA on erythrocytes occurs in response to interferon alpha given as a therapeutic agent for viral hepatitis. Increased expression became apparent after the second or third week of treatment, peaked at 3-4 months, and decreased at the end of the treatment period. This chronology suggests that elevated HLA expression is originated during erythropoiesis and persists throughout the lifetime of the erythrocyte. Furthermore, erythrocyte HLA expression did not correlate with changes of plasma HLA or beta 2-microglobulin concentrations and was not affected by in vitro chloroquine treatment, ruling out the possibility that HLA was adsorbed from plasma. Increased expression of HLA on erythrocytes was also demonstrated in patients infected with the human immunodeficiency virus, a disease in which increased production of endogenous interferon has been previously documented. We conclude that high HLA expression in red cells occurs in response to persistent interferon stimulation. Further studies will determine if this effect can also be produced by interferon tau or other factors.