Differential down-regulation of CD95 or CD95L in chronically HIV-infected cells of monocytic or lymphocytic origin: cellular studies and molecular analysis by quantitative competitive RT-PCR

We analysed the expression of CD95/CD95L in two widely used models for stud ying the cellular effects of chronic infection with human immunodeficiency virus type 1 (HIV-1), i.e. ACH-2 cells, derived from the lymphocytic cell l ine A301, and U1, derived from monocytic U937 cells. A301 and ACH-2 mounted the same amount of plasma membrane CD95, while U1 had a consistent decreas e in CD95 expression. Using different antibodies, we failed to detect the p lasma membrane form of its ligand, CD95L, but we could see the intracellula r presence of that molecule in A301 cells and, to a lesser extent, in ACH-2 cells, but not in U937 or U1 cells. To confirm the cytofluorimetric data a nd quantify the expression of CD95L at the RNA level, we developed a quanti tative competitive RT-PCR assay. The HUT78 cell line had about 50 000 copie s mRNA/1000 cells, three times more after induction with a phorbol ester an d ionomycin, ACH-2 expressed about 400- (basal) or 10- (induced) fold less CD95L mRNA than the parental cell line A301; U937 and U1 were below the lim it of detection. In cells of lymphoid origin (ACH-2) chronic HIV infection inhibits the expression of CD95L, the phenomenon occurring at the transcrip tional level. In cells of monocytic origin (U1) the infection decreases the plasma membrane expression of CD95. This suggests that HIV could trigger d ifferent anti-apoptotic strategies which likely depend upon the cell line w hich is infected. In monocytic cells which act as a viral reservoir, the ex pression of the molecule whose binding triggers apoptosis decreases, while in lymphoid cells, capable of exerting cytotoxicity, the expression of a mo lecule which induces apoptosis is reduced. (C) 1999 Federation of European Biochemical Societies.