INTERACTION OF HIV GP120 AND ANTI-CD4 ANTIBODIES WITH THE CD4 MOLECULE ON HUMAN CD4(-CELLS INHIBITS THE BINDING-ACTIVITY OF NF-AT, NF-CHI-BAND AP1, 3 NUCLEAR FACTORS REGULATING INTERLEUKIN-2 GENE ENHANCER ACTIVITY() T)

The membrane glycoprotein CD4 is required for optimal antigen-mediated activation of CD4(+) T cells restricted by class II molecules of the major histocompatibility complex (MHC). CD4 cross-linking by anti-CD4 antibodies or binding by human immunodeficiency virus (HIV) gp120 has been shown to inhibit antigen-dependent and -independent T cell activa tion, abrogating T cell proliferation, IL-2 synthesis and the increase in the intracellular calcium concentration. The molecular basis of th ese opposing phenomena is ill-defined. To characterize further the inh ibitory role of the CD4 molecule,we investigated the effects of CD4 li gands on the transcription factors regulating the IL-2 gene enhancer a nd IL-2 synthesis. We first confirmed that pre-treatment of peripheral human CD4(+) T lymphocytes by CD4 ligands, HIV gp120 or anti-CD4 mono clonal antibodies inhibited IL-2 production and cell proliferation, wh ich was normally induced by an anti-CD3 antibody (UCHT1) plus a protei n kinase C activator (PMA). Moreover, these CD4 ligands inhibited the proliferation and synthesis of IL-2 induced by activators bypassing me mbrane events, i.e. PMA and calcium ionophore, pointing to an active s ignaling pathway triggered by the CD4 molecule. Gp120 and anti-CD4 ant ibodies induced a specific, significant decrease in the binding activi ty of NF-AT, NF-kappa B and AP-1, three transcription factors regulati ng IL-2 gene enhancer activity, as demonstrated by electrophoretic mob ility shift assays. Inhibition was similarly observed following cell a ctivation by activators involving membrane events and those bypassing them. These results strongly suggest that the inhibition mediated by c ross-linking of the CD4 molecule is at least partly due to a negative signal down-regulating the availability of nuclear factors necessary f or the regulation of IL-2 gene transcription.