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Objective: Autologous HIV-1-infected CD4 primary T cells (aHIVCD4) have been shown to be largely resistant to natural killer (NK)-cell-mediated lysis because of viral strategies of immune evasion. We have previously shown that a preactivation of NK cells with plasmacytoid dendritic cells can significantly augment lysis of aHIVCD4 through a mechanism dependent on interferon-alpha (IFN-α)., Design: The goal of the present study is to identify the specific NK-activating receptors involved in NK lysis of aHIVCD4 following IFN-α activation., Methods: Peripheral blood mononuclear cells (PBMC) were incubated with aHIVCD4 to induce the secretion of endogenous levels of IFN-α and drive NK activation. We then utilized a standard chromium lysis assay to assess the degree of IFN-α-activated lysis of aHIVCD4 in the presence or absence of masking antibodies to a panel of NK-activating receptors and co-receptors., Results: Direct recognition of HIV-1-infected, but not uninfected, autologous CD4 primary T cells by PBMC induced the secretion IFN-α (median 2280 pg/ml, P < 0.001, n = 9) that, in turn, activated NK cells (P < 0.001, n = 12) and significantly increased their cytolytic potential against aHIVCD4 (P < 0.01, n = 12). The masking of NKp46 (P < 0.01, n = 8) and NKG2D (P < 0.05, n = 8), but not 2B4, NTBA, NKp30 or NKp44, significantly reduced IFN-α-activated lysis of aHIVCD4., Conclusions: Taken together, these results demonstrate that endogenous levels of IFN-α secreted by plasmacytoid dendritic cells induce NK cells to lyse aHIVCD4 via the engagement of NKp46 and NKG2D.

Background: The HIV-1-induced expansion of highly dysfunctional natural killer (NK) cell subsets represents a strategy to evade NK cell antiviral functions. In this context, the loss of NKG2A NK cells in chronic viremic HIV-1-infected individuals has also been associated with a dramatic expansion of NKG2C NK cells. The viral trigger associated with high frequencies of NK cell subsets expressing NKG2C is still being debated., Objective: To confirm that human cytomegalovirus (HCMV) infection is necessary for the expansion of NKG2C NK cells and to assess whether this phenomenon affects NKG2A/NKG2C ratio on NK cells in patients coinfected with HIV-1 and HCMV., Design: We measured the expression of NKG2A and NKG2C on NK cells from 70 healthy donors, 21 early, 96 chronic and 27 long-term nonprogressor's (LTNPs) HIV-1-infected patients using a multicolor flow cytometric approach. HCMV infection was detected by titrating the serum levels of specific circulating antibodies., Results: A significant expansion of NKG2C NK cells could be detected only in HCMV-infected patients. This phenotypic feature, together with the HIV-1-mediated downmodulation of NKG2A, pathologically reverses the ratio of NKG2A/NKG2C uniquely on NK cells from chronic viremic HIV-1-infected patients with a concomitant HCMV infection. The normalization of NKG2A/NKG2C ratio to values more than one occurred only after 24 months of suppression of HIV-1 replication following antiretroviral therapy., Conclusion: The inversion of NKG2A/NKG2C ratio characterizes advanced stages of HIV-1 disease in patients showing a concomitant HCMV infection. This NK cell immune parameter renders this cohort of patients distinguishable from LTNPs and early HIV-1-infected individuals.

We investigated whether a different pattern of HLA-specific inhibitory natural killer receptor (iNKR) expression on peripheral blood mononuclear cells (PBMC) of long-term non-progressor (LTNP) patients explained their benign course of HIV-1 infection. The surface expression of p70, p140 and CD94/NKG2A in their CD3+CD8+ PBMC was comparable to that of uninfected donors. The lack of iNKR-mediated functional inhibition of HIV-1-specific cytotoxic T lymphocytes in vitro could provide an additional mechanism for the efficient control of virus spread in LTNP patients.

Background: Highly active antiretroviral therapy (HAART) is associated with a decrease in viral replication to undetectable levels and with an increase in CD4 T lymphocytes. Residual HIV-1 replication occurs together with incomplete recovery of cytotoxic CD8 T lymphocyte (CTL) numbers and function. We sought to determine whether expression of HLA class I-specific inhibitory natural killer receptors (iNKR) on the CTL of patients who had been treated successfully with HAART for 24 months could be involved, at least in part, in residual CTL functional inhibition., Methods: Two-colour cytofluorometry was used to analyse the expression of six different iNKR including p58.1, p58.2, p70, p140, CD94/NKG2A and LIR1/ILT2 on the CD3, CD8 lymphocytes of eight patients with successful long-term suppression of viral replication before and after 3, 6 and 24 months of HAART. Healthy subjects were analysed as controls. HIV-1-specific cytotoxic activity was determined after 24 months of HAART in the presence and absence of iNKR-masking., Results: No significant reduction of iNKR expression on CD8 T cells was observed by 6 months. Expression of p70 and p140 was inversely correlated with the increasing CD4 numbers. After 24 months CD8 T-lymphocytes expressing p58.1, p58.2, p70, p140 and CD94/NKG2A returned to levels indistinguishable from those of the healthy controls. A significantly increased proportion of CD8 CTL still expressed LIR1/ILT2, a receptor with broad HLA-class I specificity. Functional analysis of freshly separated cells revealed that the disruption of the interaction between LIR1/ILT2 and HLA-class I could partly restore HIV-1-specific lysis., Conclusions: A decrease in CD3CD8iNKR cells is observed beyond 6 months of HAART. In some patients functional impairment due to LIR1/ILT2 expression may persist even after 24 months of successful HAART.