Ligand passing by the p75 tumour necrosis factor receptor enhances HIV-1 activation

Recently, a HIV-dependent upmodulation of the p75 tumour necrosis factor receptor (TNFr75) was observed using latently-infected OM-10.1 promyelocytes; although the participation of TNFr75 in HIV-1 activation remained undefined. Here, using receptor cross-linking by agonistic antibodies, no direct HIV-1 activation via TNFr75 was observed. Signalling via the p55 tumour necrosis factor receptor (TNFr55) accounted for the full extent of HIV-1 activation in OM-10.1 cultures. However, in tumour necrosis factor alpha (TNF-alpha) dose titration experiments, antibody blockade of TNFr75 decreased the dose response markedly, indicating a ligand passing function. TNFr75 blockade did not alter the dose response to agonistic TNFr55 antibody induction; verifying that the effect on the TNF-alpha dose response was not due to negative signalling or cytolysis. These results demonstrate that, although not directly involved in signal transduction resulting in HIV-1 activation, TNFr75 can serve a critical ligand passing function and permit continued HIV-1 expression during limited TNF-alpha availability.