Reciprocal activating interaction between natural killer cells and dendritic cells

Abstract

We analyzed the interaction between human peripheral blood natural killer (NK) cells and monocyte-derived immature dendritic cells (DC). Fresh NK cells were activated, as indicated by the induced expression of the CD69 antigen, and their cytolytic activity was strongly augmented by contact with lipopolysaccharide (LPS)-treated mature DC, or with immature DC in the presence of the maturation stimuli LPS, Mycobacterium tuberculosis or interferon (IFN)-alpha. Reciprocally, fresh NK cells cultured with immature DC in the presence of the maturation stimuli strongly enhanced DC maturation and interleukin (IL)-12 production. IL-2--activated NK cells directly induced maturation of DC and enhanced their ability to stimulate allogeneic naive CD4(+) T cells. The effects of NK cells were cell contact dependent, although the secretion of IFN-gamma and TNF also contributed to DC maturation. Within peripheral blood lymphocytes the reciprocal activating interaction with DC was restricted to NK cells, because the other lymphocyte subsets were neither induced to express CD69, nor induced to mature in contact with DC. These data demonstrated for the first time a bidirectional cross talk between NK cells and DC, in which NK cells activated by IL-2 or by mature DC induce DC maturation.

Figure 1.

Activation and generation of cytotoxic activity in NK cells cultured with DC. (A) Purified NK cells and DC were cultured for 18 h separately or together in medium, or in the presence of killed M. tuberculosis (M. t.), IFN-α, LPS, IL-2, or latex particles. (B) DC were cultured for 18 h in medium, or with LPS or IFN-α, and washed before 18-h coculture with fresh NK cells. Cytolytic activity (A and B) was evaluated against the Daudi cell line. (C) DC were cultured for 18 h in medium or with LPS and washed before a 18-h coculture with PBL; CD69 expression was evaluated on CD56⁺, CD16⁺, or on CD3⁺ PBL by double immunofluorescence.

Figure 1.

Activation and generation of cytotoxic activity in NK cells cultured with DC. (A) Purified NK cells and DC were cultured for 18 h separately or together in medium, or in the presence of killed M. tuberculosis (M. t.), IFN-α, LPS, IL-2, or latex particles. (B) DC were cultured for 18 h in medium, or with LPS or IFN-α, and washed before 18-h coculture with fresh NK cells. Cytolytic activity (A and B) was evaluated against the Daudi cell line. (C) DC were cultured for 18 h in medium or with LPS and washed before a 18-h coculture with PBL; CD69 expression was evaluated on CD56⁺, CD16⁺, or on CD3⁺ PBL by double immunofluorescence.

Figure 2.

Cytokine production and CD86 expression on DC in mixed culture of NK cells and DC. Fresh NK cells and DC were cultured separately or together in the absence of any stimulus (medium), or in the presence of IFN-α, killed M. tuberculosis (M. t.), or LPS. (A) IL-12 p70, p40, and IFN-γ were measured in culture supernatants. Two or one asterisks indicate P < 0.005 or P < 0.05, respectively, by Student's t test, using two-tailed distribution of paired samples, comparing cytokine production by cells cultured separately or together. (B) CD86 expression was determined on DC.

Figure 3.

IL-2–activated NK cells induce DC maturation. (A and B) DC were cultured for 18 h in medium only or in the presence of LPS, IL-2–activated [NK(IL-2)] or untreated [NK(medium)] NK cells. (A) Cells were washed and DC expression of CD86, CD83, CD80, HLA-DR, and CCR7 was analyzed by immunofluorescence. (B) DC, depleted of NK cells and irradiated, were cultured for 5 d with allogeneic naive CD4⁺ PBL, and ³H-TdR uptake was determined. (C) CD86 expression was determined on DC after an 18-h culture in the absence of any stimulus, or with PBL, or NK-depleted PBL (PBL–NK), either IL-2–activated or untreated.

Figure 4.

Contact between IL-2–activated NK cells and immature DC is required for induction of CD86 on DC. CD86 was evaluated on DC cultured for 18 h in the same well (A and B) with IL-2–activated [NK(IL-2)] or untreated [NK(medium)] NK cells, or across a porous membrane (C and D) from IL-2–activated NK cells and DC, untreated NK cells and DC, or IL-2–activated NK cells (C) in the absence (A and C) or in the presence (B and D) of neutralizing anti–IFN-γ plus anti-TNF mAb. CD86 expression in DC cultured in the absence of NK cells (medium) is indicated by dotted lines. Numbers in brackets indicate percent recovery of DC after culture with IL-2–activated NK cells in comparison to DC cultured alone.