Natural killer cells, dendritic cells, and the alarmin high-mobility group box 1 protein: a dangerous trio in HIV-1 infection?

PURPOSE OF REVIEW: Natural killer (NK) cells promote antiviral immunity by producing proinflammatory cytokines and by lysing infected cells. In addition, NK cells can modulate dendritic cell functions. NK-dendritic cell crosstalk results in activation of both cell types, with dendritic cells promoting NK-cell activity and NK cells inducing further maturation of dendritic cells. Here we review the recent evidence suggesting that NK-dendritic cell crosstalk is disrupted during HIV-1 infection and we discuss the consequences on HIV persistence in dendritic cells. RECENT FINDINGS: NK cell-mediated dendritic cell editing is compromised during HIV-1 infection, and NK cells from viremic individuals show a decreased ability to kill immature dendritic cells. The defect is associated with impaired NKp30 function. Moreover, the resistance of HIV-1-infected dendritic cells to NK-mediated lysis is associated with the upregulation of apoptosis inhibitors, thus protecting infected dendritic cells from TRAIL-dependent apoptosis. These inhibitors are upregulated by the high-mobility group box 1 protein (HMGB1), an alarmin produced at NK-dendritic cell synapse that is essential for NK-dependent dendritic cell maturation, but also promotes viral replication in infected dendritic cells. SUMMARY: HIV-1-induced impairment of NK-dendritic cell crosstalk may significantly alter both innate and adaptive immunity. It may also contribute to HIV persistence in dendritic cells through an HMGB1-dependent mechanism.