IL-10 induces aberrant deletion of dendritic cells by natural killer cells in the context of HIV infection

Abstract

Persistent levels of IL-10 play a central role in progressive immune dysfunction associated with chronic viral infections such as HIV, but the underlying mechanisms are poorly understood. Because IL-10 affects the phenotypic and functional properties of DCs, which are responsible for initiating adaptive immune responses, we investigated whether IL-10 induces changes in DC phenotype and function in the context of HIV infection. Here, we show that IL-10 treatment of immature and mature human DCs in culture induced contrasting phenotypic changes in these populations: immature DCs exhibited aberrant resistance to NK cell-mediated elimination, whereas mature DCs exhibited increased susceptibility to NKG2D-dependent NK elimination. Treatment of immature and mature DCs with HIV resulted in potent IL-10 secretion and the same phenotypic and functional changes observed in the IL-10-treated cells. Consistent with these in vitro data, LNs isolated from individuals infected with HIV exhibited aberrant accumulation of a partially "immature" DC population. Together, these data suggest that the progressive immune dysfunction observed in chronic viral infections might be caused in part by IL-10-induced reversal of DC susceptibility to NK cell-mediated elimination, resulting in the accumulation of poorly immunogenic DCs in LNs, the sites of adaptive immune response induction.

Figure 1. Accumulation of aberrant DC populations in the LNs of HIV-infected individuals.

Shown are mean ± SEM of (A) HLA-DR and HLA-I (i.e., HLA-A, -B, or -C) and (B) costimulatory molecules CD40, CD83, CD80, and CD86 on the surface of CD3^–CD14^–CD56^–CD11c⁺ DCs in PBMCs and LNs from HIV-infected and HIV-negative donors. *P < 0.05.

Figure 2. IL-10 reverses DC subset susceptibility to NK cell–mediated lysis via altered MHC-I expression levels.

(A) Changes in MHC-I (i.e., MHC-A, -B, or -C) expression on the surface of immature and mature monocyte-derived DCs in the presence of medium alone or IL-10. (B) Box and whisker plot denotes median and range of MHC-I expression on immature and mature DCs in the presence or absence of IL-10 (n = 6 per group). (C) Mean ± SEM percent lysis of immature or mature DCs at 1:10, 1:20, and 1:50 effector/target ratios with NK cells after coculture with medium alone or with IL-10 (using 6 independent donors).

Figure 3. IL-10 treatment of immature and mature DCs results in a more tolerogenic DC phenotype.

(A) Expression pattern of a range of phenotypic markers on the surface of immature and mature monocyte-derived DCs in the presence of medium alone or IL-10. (B) Mean ± SEM of the phenotypic markers for all 5 experiments. *P < 0.05.

Figure 4. NK cells eliminate IL-10–treated mature DCs in an NKG2D-dependent manner, which is blocked by IL-10R blockade.

(A) Binding capacity of an NKG2D-fusion construct and expression of MIC-A/B on immature and mature DCs in the presence of medium alone or IL-10. (B) Coexpression levels of MIC-A/B and MHC-I on the surface of immature or mature DCs in the presence and absence of IL-10. (C) Mean ± SEM capacity of NK cells to lyse IL-10–treated mature DCs in the absence or presence of an NKG2D-blocking antibody (n = 5). (D) Mean ± SEM percent lysis of mature DCs by autologous NK cells after maturation in the presence of medium alone, IL-10 alone, and IL-10 plus IL-10R–blocking antibody — either during maturation in vitro (culture) or during the NK cell/DC killing assay (killing). *P < 0.05; **P < 0.01.

Figure 5. Coculture of DCs with HIV results in IL-10 secretion and an altered DC phenotype.

(A) Expression patterns of phenotypic markers on the surface of immature and mature monocyte-derived DCs in the presence of medium alone or HIV JRCSF. (B) Range of IL-10 secretion measured by ELISA in the supernatant of immature and mature DCs cocultured in the presence of or absence of HIV JRCSF (n = 5). (C) Mean ± SEM percent lysis of immature and mature DCs at 1:10, 1:20, and 1:50 effector/target ratios with NK cells after coculture with HIV (using 5 independent donors).